Dry Cow Nutrition

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Dairy Nutrition Management

Dry Cow Nutrition The Key to Improving Fresh Cow Performance

Robert J. Van Saun, DVM, MS, PhD *

Management by neglect. Unfortunately, this statement best typifies the dry cow program on many dairy farms. Marginal quality feeds, unbalanced rations, and inadequate housing all characterize poor dry cow management practices. Deficient dry cow care can result in decreased milk yield, increased incidence of periparturient health disorders, and impaired fertility. The end result is reduced overall productive efficiency (pounds milk per unit cost) and decreased profits. A reorientation of our perception of the nonlactating cow is needed. Characterizing the dry period as a resting phase between lactations and emphasizing it as a period of lowest nutritional requirements for the cow has given producers the wrong impression of the critical role of the dry cow. Low nu trient requ iremen ts sh ould not b e equ ated with poor qu ality feed s and management. In actuality, the dry cow is not resting at all. Many essential dynamic physiologic processes that set the stage for the next lactation are being engaged. Therefore, the dry period should be viewed as a lactation-preparation period, thus emphasizing the dry cow's critical role on subsequent lactational performance. This article presents a brief review of the physiologic changes associated with the nonlactating period in an effort to better understand dry cow nutritional requirements and management practices necessary to optimize lactational, health, and reproductive performance in the subsequent lactation. PHYSIOLOGIC DYNAMICS OF THE DRY PERIOD Mammary Gland Involution and Development Cessation of milking marks the start of the dry period and initiates reabsorption of nonsecreted milk along with rapid loss of mammary secretory epithelial cells, a process termed involution. 106 Involution is usually completed within a 14-day period, one which is associated with the highest susceptibility to new intramamrnary infections. 1 6 , 8 4 Once the udder reaches a stable nonsecretory state, natural defense mechanisms are enhanced, thus greatly reducing *Diplomate, American College of Theriogenology and American College of Veterinary Nutrition; Practitioner/Nutritional Consultant, Friesen Veterinary Service, P.C., Carson City, Michigan Veterinary Clinics of North America: Food Animal Practice—Vol. 7, No. 2, July 1991

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susceptibility to new infections. 8 5 However, prior to calving, as the udder begins to produce secretions in preparation for lactation, susceptibility to new infections again increases, with this higher susceptibility continuing into the early postpartum period.16,84,85 Initiation of lactatio n occu rs ju st prior to parturition, stimulated by changes in absolute amounts of estrogen and progesterone and their ratio during late gestation. 3 0 Alterations of these steroids induce changes in other lactogenic regulatory hormones (e.g., prolactin, insulin, glucocorticoids), initiating the cascade of events preparing the mammary gland for copious secretory activity. Milk yield is dependent upon secretory cell number. 61,106 Following parturition, existing secretory cells rapidly proliferate, accounting for the rise in milk production to peak. Dry period length influences this proliferation process by some unknown mechanism without affecting existing cell number. 1 0 6 Short dry periods (< 40 days) significantly reduce subsequent milk yield. 14,20,40,98 Excessive days dry (> 70 days) also have shown reduced milk yields or insufficient increases to economically compensate for more days dry. 14,20,40,98 Optimum length of the dry period is influenced by factors such as age, milk yield, and days open. 20,40 On the basis of optimum milk yield, a range of 50 to 69 days seems to be an adequate dry period.14,20,40,98 Another important process dependent upon an adequate dry period is colostrogenesis. Colostrum is a milk-like fluid secreted by the mammary gland at the onset of lactation. Colostrum composition differs from milk by greater concentrations of minerals (except potassium), protein, fat, and fat-soluble vitamins. 83 More importantly, colostrum contains high concentrations of maternal immunoglobulins essential for passive transfer of immunity to the neonate. 83 Ingesting colostrum containing these elevated concentrations of trace minerals augments prenatal reserves of these essential nutrients and may play a substantial role in modulating postnatal immune competency. Inadequate days dry or poor quality dry cow nutrition may adversely affect colostrum quality and quantity. Conceptus Development The products of conception include fetus, placenta, and fetal fluids (i.e., conceptus). Additionally, there is development of maternal tissues (e.g., uterus, mammary gland) for nutritional support of the conceptus pre- and postnatally. Bovine fetal growth is not linear by gestational age, but exponentia1, 24 ' 33 ' 93 with more than 60% of total fetal weight being accrued during the final 2 months of gestation (Fig. 1). Maximal rates of fetal and placental gain occur 6 to 8 and 9 to 11 weeks prepartum, respectively. 93 This fetal growth pattern places the greatest nutritional burden of pregnancy on the dry cow. Even though requirements for pregnancy are minor compared to lactation, inadequate dry cow nutrition can result in a substantial drain of maternal nutrient reserves to sustain the developing conceptus. Maternal reserve depletion prepartum may have detrimental repercussions on subsequent lactation performance and calf viability. Presence of a second fetus increases pregnancy requirements, placing a relatively large nutritional burden on the dam and her reserves, which may account for the increased incidence of health disorders associated with twin pregnancies.62 Maternal Metabolic Alterations Metabolically, the dry period is one of transition, a period where the dairy cow must alter her metabolic priorities for available nutrients from net tissue deposition (e.g., midgestation) to reserve tissue mobilization (e.g., early lactation).2 Homeorrhetic regulation allows the dairy cow to metabolically accom-

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WEEK OF GESTATION Figure 1. Accumulative weights for fetus, placenta, fetal fluids, and uterus by week of gestation for a cow delivering a 42-kg calf. (Data from Prior RL, Laster DB: Development of the bovine fetus. J Anim Sci 48:1546, 1979; and Fox DG, Sniffen CJ, O'Connor JD, et al: The Cornell Net Carbohydrate and Protein System for Evaluating Cattle Diets: Search:Agriculture. Ithaca, NY, Cornell University Agriculture Experimental Station Number 34, 1990.)

modate to the increased demands of a given physiologic state (i.e., pregnancy, lactation, growth). 2 , 2 6 Although this metabolic transition is associated with parturition, it does not occur as abruptly, but gradually over a 1- to 3-week period prepartum. Alterations in adipose tissue metabolism best demonstrate the p rincip les of ho meorrh esis, although many other tissues are also so regulated. In midgestation there is a net deposition (lipogenesis) of adipose tissue (i.e., energy reserves) in contrast to late gestation/early lactation when lipolytic activity increases. 2,26,68,111 Increasing concentrations of nonesterified fatty acids and fl-hydroxybutyrate beginning 2 to 3 weeks prepartum and continuing through early lactation are indicative of increasing lipolytic activity. 44,111 These metabolic changes are concurrently associated with a decline in insulin (i.e., lipogenic hormone) activity 4 4 , 1 1 1 and increased adipose tissue sensitivity to fl-adrenergic agonists (i.e., lipolytic hormone) such as epinephrine. 53,111 Lactation dramatically increases lipolytic activity, 2 , 2 6 , 6 8 , 1 1 1 with the degree of postpartum lipolysis (i.e., body condition loss) dependent upon genetic potential for milk production and severity of negative energy balance.69 For these metabolic changes to be effective in providing the necessary nutrients, they must be coordinated with the given physiologic state (e.g., pregnancy, lactation). Homeorrhetic regulation of maternal metabolism during

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gestation and lactation needs to be aligned with fetal growth and milk production, respectively. In ruminants, placental lactogen secreted by the conceptus has been postulated to regulate maternal metabolism during pregnancy while growth hormone controls nutrient partitioning during lactation. 2 These homeorrhetic hormones reset the homeostatic controls of tissue metabolism to redirect available nutrients to the particular productive function. Inability to adequately coordinate metabolism to meet production demands results in increased incidence of clinical or subclinical metabolic disorders. NUTRIENT REQUIREMENTS OF THE DRY DAIRY COW Nutritional requirements of the pregnant nonlactating dairy cow are only slightly higher than maintenance, approximately equivalent to the energy and protein required to produce 4 to 7 kg of 4% milk/day. 8 0 However, providing suf f icient quantities of essential nutrients is just as critical for the dry cow as the lactating cow to maintain optimum performance. Given the lower nutrient requirements of dry cows and the quality of forages on most farms today, fulfilling dry cow nutrient requirements is relatively simple compared to lactating cows. Many nutritional problems associated with dry cows result from overfeeding particular nutrients, especially energy and calcium. Dry cow feeding programs with nutrient deficiencies, most notably selenium, vitamin E, and magnesium, also have been associated with increased health disorders in the periparturient period. The National Research Council (NRC) has established dry cow dietary recommendations for energy, protein, fiber, 14 minerals, and three vitamins (Table 1). 8 0 Nutrient requirements determined by the NRC have been developed using a factorial methodology. Mathematical models estimating a nutrient requirement for a given physiologic function (i.e., maintenance, growth, pregnancy, lactation, reserve deposition) are summed over all appropriate states for a particular animal to determine the total nutrient requirement. For example, the energy requirement (Mcal NE 1 /day) for a mature, nonlactating pregnant cow would equal the sum of her maintenance (0.08 X BW kg 0.75 ) and pregnancy (0.024 X BWkg0.75) requirements.80 If this animal was pregnant for the first t i me , a n a d d i t i o n a l g r o w t h ( 0 . 0 9 1 2 X B W k g 0 . 7 5 X G a i n k g / d 1 . 1 1 9 ) c o mp o n e n t would also be included in the total energy requirement. All equations used to estimate requirements for all classes of dairy cattle are available in the most recent NRC report.80 Requirements for pregnancy represent nutrient amounts necessary to support both growth rate and maintenance of fetus, placenta, uterus, and mammary gland. Conceptus maintenance expenditure is a substantial portion of the total pregnancy requirement as evidenced by the low ef f iciencies of utilization for metabolizable energy (12.5%) 7 2 and protein (50%). 3 3 Requirements for conceptus nutrient accretion (e.g., energy, protein, minerals) depend upon birth weight, fetal numbers, rate of growth, and compositional analysis. Unfortunately, data describing fetal growth and chemical composition throughout gestation for Holstein cows are very limited. However, data 2 4 , 3 3 , 9 3 on fetal growth in beef and beef–dairy crossbreeds are available and can be extrapolated to improve recommendations for Holstein cows.37 Required Nutrients Water. Clean, high-quality water should always be available to the dry cow. Water is an essential nutrient required in the greatest amounts, but is often the most neglected. Water is required for a vast array of physiologic and metabolic functions, including pregnancy. Significant amounts of water are


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Table 1. Recommended Dietary Nutrient Concentrations (Dry Matter Basis) Suggested for Pregnant Nonlactating Dairy Cattle

*Early dry period is defined as 4-6 weeks after dry off with suggested nutrient densities based on a dry matter intake of 1.9-2.1% of body weight. †Close-up dry period is defined as 2-4 weeks prior to calving with suggested nutrient densities based on a dry matter intake of 1.6-1.8% of body weight. ‡Minimum recommended dietary fiber levels. §Increases dietary concentrations to 0.3-0.35% when potassium levels exceed 1.2-1.5%, respectively. ║Maximum intake allowed by the Food and Drug Administration. Adapted from National Research Council: Nutrient Requirements of Dairy Cattle, ed 6. Washington DC, National Academy Press, 1989, assuming a thermoneutral environment and 10% activity allowance. sequestered in the gravid uterus as fetal fluids. Pregnancy increases daily maintenance water intake by 57 to 35% for cows ranging in body weight from 35 to 725kg, respectively. 1 1 5 Daily water intake by pregnant cows can be estimated from their dry matter intake. For each kg of dry matter, cows will consume (linearly within ranges) 3.1, 3.1 to 5.2, and 5.2 to 15.6 kg of water per day over ambient temperature ranges of —12 to 4.4, 4.4 to 26.7, and 26.7 to 37.8°C, respectively.115 Water quality for dry cows should be evaluated for color, taste, odor, pH, contaminants, and dissolved substances. Of practical importance for dry cows is additional consumption of dissolved minerals and their potential effect on mineral status. Of concern might be the effect of calcium intake from water on potential incidence of parturient paresis (PP). A dry cow drinking 75 kg of water containing 350 ppm calcium would ingest an additional 26 g (75 kg X

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350 mg/kg± 1000 mg/g) of calcium above that received from the diet. This could negate expected responses of diets specially formulated for low calcium intake. Energy. Energy required to support the pregnant cow is derived from endproducts of dietary carbohydrate fermentation in the rumen (see the articles by Hoover and Allen elsewhere in this issue.) In order to meet desired dry cow dietary energy density (see Table 1) and maintain maximum dry matter intake, a balance needs to be struck between amounts of structural and nonstructural carbohydrates. Structural carbohydrates (i.e., cell wall fiber) physically restrain dry matter intake as a result of their bulky nature, although this can be modified by reducing particle size. Neutral detergent fiber (NDF), a measure of total cell wall content, is negatively associated with dry matter intake. 70 Acid detergent fiber (ADF) represents the indigestible fiber material and is associated with feed digestibility and not feed intake. Nonstructural carbohydrates (i.e., sugars, starches) are concentrated forms of energy with low bulk and if fed in amounts exceeding desired ration energy levels, will reduce intake and alter rumen conditions to suppress fiber fermentation. Dietary nonstructural carbohydrate levels, from grain or corn silage, need to be managed appropriately in an effort to obtain optimum body condition of the dry cow and prevent overconditioning, which adversely affects performance. 15,103 An optimum balance of carbohydrates can be obtained when sufficient amounts of fiber are included to maximize intake potential. Table 2 presents suggested NDF intakes (% of body weight basis), which should allow for optimum rumen fill and appropriate energy density. Reduction in NDF intake capacity in late pregnancy is anticipated as a result of the gravid uterus expanding into the abdomen. Moe and Tyrrell 7 2 evaluated metabolizable energy requirement throughout pregnancy and found it to be an exponential function of days pregnant, similar to the fetal growth curve. At term, the pregnant cow requires 175% of the energy required by an equal weight, nonpregnant cow. 7 2 The NRC pregnancy energy recommendation 80 is an average energy value required to be fed daily throughout the dry period to equal the cumulative energy required for pregnancy as determined by Moe and Tyrrell. This recommendation results in cows being overfed energy in the early dry period, but more importantly, underfed energy in the last 5 to 6 weeks of gestation in comparison to actual requirements (Fig. 2). Increased energy above NRC recommendations during late pregnancy were associated with decreased metabolic and reproductive disorders. 1 9 A better approach to managing dry cow energy requirements is a two-tier system: A low-energy density diet fed in the early dry period followed by a higher energy density diet, thus better addressing animal needs within reasonable management capabilities. Protein. Our understanding of protein nutrition in ruminants has been expanded well beyond the concept of crude protein. Dietary protein is partitioned in relation to its rumen degradability and solubility. 78 (See the article by Chalupa and Sniffen elsewhere in this issue.) Conceptually, soluble and rumenTable 2. Suggested Neutral Detergent Fiber Intake Guidelines for Pregnant

Nonlactating Dairy Cattle as a Percent of Body Weight HEIFERS

Early Dry Close-up Dry

MATURE

% of Body Weight

PERIOD

0.95-1.1 0.80-0.90

1.1-1.3 0.95-1.05


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WEEK OF GESTATION Figure 2. Comparison of models estimating metabolizable energy requirement for gestation. Estimated requirements are based on a 620-kg cow delivering a 42-kg calf. The energy balance data are derived from Moe et a1,71 the composition model data are from Fox et al37 and Prior and Laster;93 and the NRC 1984 and 1989 data are from The National Research CounciI.77,80

degradable protein support microbial protein production, which in addition to rumenundegradable protein, supply the amino acids that support the animal's productive functions. This approach allows for a more efficient feeding of protein. Data describing rumen fermentation dynamics in the dry cow are negligible compared to lactating cows. However, concepts of this protein system are applicable to the dry cow. With the large amounts of structural carbohydrates to be fermented in typical dry cow diets, a greater percent (40% – 50%) of the dietary protein should be in the form of soluble protein or nonprotein nitrogen sources compared with lactating cows (30%-35%). These protein sources are rapidly converted to ammonia, an essential nutrient of cellulolytic bacteria.'" Some rumen-degradable protein is also necessary to provide essential branch chain volatile fatty acids for these same organisms. The amount of rumen-undegradable protein needed to supplement microbial protein production to satisfy maintenance and pregnancy protein requirements is less well defined at the present time. Additional undegradable protein fed during late gestation has improved body condition at calving and subsequent lactational performance in first-lactation heifers. 5 2 , 1 0 9 Recent studies by the author, feeding additional undegradable protein prepartum to mature cows, resulted in fewer health disorders and improved reproductive performance. One study feeding higher levels of protein (15%), all from rumen-degradable sources, reported a 66% incidence of downer cow syndrome compared to a lower protein (8%) diet.58 Protein requirements for pregnancy are even less well defined than those

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WEEK OF GESTATION

Figure 3. Comparison of models estimating net protein requirement for gestation. Estimated requirements are based on a 600-kg cow delivering a 42-kg calf. The composition model data are from Fox et a137 and Prior and Laster;93 and the NRC 1984, 1985, and 1989 data are from the National Research Council:77,80

for energy. Figure 3 presents current beef cattle, 77 dairy, 80 and exponential 78 models estimating net protein requirement in late gestation compared to a model extrapolated from actual conceptus composition analysis. 37,93 This figure suggests that the current models underestimate the actual gestational protein requirement throughout late gestation. This discrepancy may result in depletion of labile protein reserves' to support gestation rather than early lactation, possibly accounting for the positive responses postpartum to undegradable protein supplementation prepartum. Curtis et a1 49 showed feeding higher protein concentrations relative to the NRC requirement 3 weeks prepartum reduced metabolic and reproductive health disorders. Clearly, further investigation in this area is warranted. Macrominerals. Calcium (Ca), phosphorus (P), magnesium (Mg), potassium (K), sodium (Na), chloride (C1), and sulfur (S) are all essential for successful fetal development and delivery. Catheterization studies" 4 revealed greater fetal concentrations of macrominerals than maternal, suggesting active transport processes or independent fetal regulatory systems or both. Sufficient amounts of each macromineral without detrimental excesses need to be provided to meet dam and fetal requirements (see Table 1). Primary interest in macrominerals in the dry cow diet has revolved around their relationship to parturient disease processes. Certainly, Ca and P have received the most attention with respect to their association with PP. 6 , 8 , 5 6 , 6 0 , 8 8 , 9 6 Actual amounts of Ca and P ingested are more directly associated with PP incidence than the Ca:P ratio. Low Ca diets (< 20 g/d) are almost completely effective in preventing PP. 4 7 , 1 1 2 However, these


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diets are impractical to formulate with typical feeds and cannot be fed longer than 2 to 3 weeks as a result of their negative Ca balance effect on Ca reserves. A general recommendation is to limit dairy Ca and P intake to less than 90 and 4 0 g/d, respectively, and maintain an optimum Ca: P ratio of 1.5 to 2 . 0 : 1 . 45,56,60 Other mineral interactions may also have a bearing on PP incidence. Hypomagnesemia, in addition to producing clinical signs of tetany, reduces an animal's ability to maintain Ca homeostasis. 51 Excessive K intake, usually from overfertilized forages (K content > 3.0%), results in clinical signs of udder edema 9 5 and reduces dietary Mg availability. 67 Thus, associative mineral deficiencies may be present, impacting on the incidence of clinical symptoms. Sodium bicarbonate feeding to dry cows results in excessive Na intake and potential clinical signs of udder edema. 95,110 Recent studies have suggested an important role of dietary acidity in modulating PP incidence. Diets high in Na, K, or both (alkaline) have been associated with increased rates of PP compared to diets containing high levels of Cl, S, or both (acidic). 4,89,96 Diet acidity has been related to anion — cation balance, determined by the equation (Na + K) — (Cl + S) on a milliequivalent basis. Other equations incorporating Ca, P, or Mg in some manner have also been evaluated with respect to their ability to predict PP incidence. 96 Diets high in Cl and S are thought to induce metabolic acidosis and accentuate Ca intestinal absorption and bone resorption. Recommendations suggest incorporating 100 to 200 g ammonium salts of chloride, sulfate or some combination in dry cow diets 2 to 3 weeks prior to calving to prevent PP. 89,96 These salts are best used in a total mixed ration to prevent palatability problems. At high rates of intake (>200 g/d), these salts are also potentially toxic by inducing system acidosis. Microminerals. Similar to the macrominerals, the microminerals iron (Fe), copper (Cu), cobalt (Co), iodine (I), manganese (Mn), selenium (Se), and zinc (Zn) are essential for the successful completion of pregnancy. Also like the macrominerals, fetal micromineral concentrations, especially hepatic, exceed maternal values. 50,107 Concentrating trace minerals in fetal liver might suggest a labile reserve pool, available in periods of mineral deficiency, especially during postnatal life. Additional trace mineral reserves are realized from colostrum ingestion. Trace minerals are indirectly or directly associated with a tremendous variety of metabolic processes. Deficiency diseases affect almost every physiologic function and include immune dysfunction (Cu, Zn, Se); developmental abnormalities (Cu, Mn, I); retained placenta (Cu, Se, I); and metabolic disturbances (Co, Fe, Zn, 1). 5 , 8 0 Therefore, it is essential that trace minerals be adequately provided throughout pregnancy (see Table 1). Incorporating all mineral supplements into the ration is a much preferred method to ensure adequate intake over a free-choice mineral program. Vitamins. Supplementation of ruminant rations with B-vitamins is thought to be unnecessary because rumen microorganisms synthesize adequate amounts of these compounds. This may not be the case in extreme stress situations like early lactation or aberrant rumen fermentation conditions. Supplementing 6 to 12 g/d niacin starting 1 to 2 weeks prepartum through early lactation has been shown to minimize ketosis incidence 3 8 and increase milk production.54 Fat-soluble vitamins A, D, and E should be included in dry cow rations. Vitamin D is a component of the Ca regulatory system and has been used to prevent PP. 8,60,88,96 Near toxic doses of vitamin D administered within a narrow window of opportunity just prior to calving are required to prevent PP. As a result, routine use of vitamin D as a preventive agent is limited; however,

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alternative vitamin D analogs are being investigated. 60,96 A minimal amount of vitamin D should be provided to the dry cow (see Table 1) with precautions taken to prevent excess intake, thus predisposing the cow to PP.96 Compared to B-vitamins, fat-soluble vitamins cross the placenta in limited amounts. 65,108 Thus ingestion of colostrum, rich in fat-soluble vitamins, is critical to maintaining sufficient vitamin status in the neonate. Adequate vitamin A and E supplementation (see Table 1) to the dry cow is essential to prevent deficiency diseases and produce quality colostrum. Retained placenta has been associated with both vitamin A 80 and E 57 deficiencies. Supplemental vitamin E also has been associated with reduced incidence and duration of mastitis symptoms.100 Nutrient Prioritization Available nutrients need to be partitioned to all tissues supporting a given productive function. It is suggested that there is a prioritization of physiologic functions for available nutrients and not an equal distribution process, a result of homeorrhetic metabolic regulation. A proposed order of prioritization of physiologic functions for available nutrients from highest to lowest is: maintenance, pregnancy, growth, lactation, reserve deposition, and reproductive cyclicity.37,90,99 This is not an absolute system where, for example, all the maintenance energy requirement is met before energy is available to support pregnancy. Rather, when a nutrient is inadequately supplied, productive functions having lower priority will bear a greater burden of the nutrient deficiency than those having higher priority. 3 7 A good example of this phenomenon is the young heifer that becomes pregnant too early. Most producers are inclined to reduce feed to this animal in an effort to produce a smaller sized calf and thereby reduce the possibility of a dystocia. 3 In contrast, given the prioritization of productive functions, this heifer's growth rate (i.e., frame size) will be more adversely affected by induced nutrient deficiency than fetal growth rate. 7 5 Thus the potential for a maternal–fetal disproportion dystocia may actually be accentuated through this practice as a result of reducing maternal growth rate (e.g., pelvic size) at the expense of maintaining a fairly normal fetal growth rate. Bellows and Short 3 found no difference in dystocia rates in heifers fed low- and high-energy diets, even though calf birth weight was reduced. However, one should not interpret this to suggest overfeeding nutrients to growing, pregnant heifers. Overnutrition of pregnant heifers results in excess condition, potentially predisposing the animal to increased dystocia rate as a result of fat accumulation in the birth canal. Factors Influencing Nutrient Requirements A veritable plethora of factors can influence an animal's requirement for a particular nutrient. Intrinsic factors defining the animal, such as breed, age, sex, body weight and condition, productive function, and rate of production, comprise the basis by which nutrient requirements are determined. However, extrinsic factors, such as animal activity 36,80 and environment, 36,76 can dramatically modify nutrient needs. Under typical dry cow management practices, activity allowances and environmental stresses should be considered if nutrient needs are to be appropriately addressed. Current dairy cattle NRC mainten an ce en ergy requ iremen ts in corporate a 10 % activ ity allo wan ce. 8 0 This should be a sufficient energy allotment to account for animal activity when housed in stanchions with limited exercise or free-stall facilities. Many dry cow programs, however, include extensive pasture usage. Additional increases in maintenance energy requirement of 10 to 20% for grazing quality or sparse pastures, respectively, are recommended.80


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Nutrient recommendations by the NRC are based on the animal being exposed to a stress-free, thermoneutral environment." In other words, the animal does not need to expend any additional metabolic energy to maintain homeothermy. 7 6 Climatic factors (e.g., ambient temperature, humidity, air movement, precipitation) and animal factors (e.g., behavior/postural responses, hide thickness, flesh condition, hair length) all interplay to modify the range of thermoneutrality for an animal under the given environmental conditions. 36,76 Depending on geography, dry cows are exposed to a wide variety of environmental conditions placing them outside of their thermoneutral zone (i.e., cold or heat stress), requiring adjustments to their energy requirement. Collier et al 11 found heat stress during pregnancy reduced calf birth weight by 7 kg and altered placental and maternal hormonal concentrations. Cows exposed to heat stress and shade during the dry period produced more milk in the subsequent lactation compared to cows without shade." Although this difference in milk yield was not statistically different, these researchers concluded that heat stress during pregnancy may indirectly affect milk yield through alterations in endocrine profiles and reduced calf birth weight. Ambient temperatures below the lower critical temperature (i.e., cold stress) result in increased maintenance energy to maintain body temperature. 1 1 6 Increased dry matter intake usually compensates for this increased ene rgy nee d in ma rgi n al cold st re ss s itu ati ons. 7 6 A c o m p u t e r s i m u l a t i o n model 3 7 that accounts for a variety of climatic and animal factors affecting energy requirement was used to determine representative increases in maintenance energy requirement of dry cows under varying environmental conditions. For a pregnant Holstein cow in moderate condition, maintenance energy requirement was increased 27% and 52% at ambient temperatures of 1°C and — 12°C, respectively, for cows that are wet or mud-covered compared to dry and clean. 37 However, if air movement is increased from 1.6 to 16 kph, these same wet or mud-covered cows would have energy increases of 42% and 73%, respectively. These simulation data suggest that environmental conditions need to be accounted for in dry cow diet formulations. Otherwise, extreme body condition loss will occur under conditions of severe cold stress without dietary adjustment, which will have a seriou s detrimental impact on subsequent performance. DIETARY MANAGEMENT OF THE DRY COW Dry Matter Intake Nutrient recommendations are usually presented as a percentage or parts per million (ppm) basis for ease of reference. However, cows do not eat percents or ppm of nutrients. Cows require specific nutrient amounts (i.e., lb, oz, g, mg) to meet their metabolic needs. Dry matter intake is the most critical factor in evaluating nutritional adequacy of a diet. Unfortunately, accurate assessment of a cow's dry matter intake is difficult at best, especially for dry cow group feeding situations. Factors that contribute to the inability of accurately determining dry cow intake include feeding pregnant heifers with dry cows; separate availability of dry hay from a bunk mix; feeding leftover lactating cow rations; and not cleaning out unconsumed feed from the bunk. Dietary nutrient densities for dry cows, based on NRC requirements, are determined on an assumed average dry matter intake of 1.6 to 2.0% of body weight (i.e., 9.6 - 12.0 kg/d for a 600-kg cow). 8 0 If a cow consumes less dry matter than expected of diets containing these suggested nutrient densities, she will ingest inadequate nutrient amounts to meet her defined requirements.

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Overconsumption of dry matter produces the opposite result—excess nutrient intake—which can be just as problematic. Dietary nutrient densities need to be tailored to determine dry matter intake to ensure adequate consumption of nutrients. Feed intake is affected by a wide array of physiologic, metabolic, and environmental factors,79 suggesting a need for continued monitoring. Mean dry matter intake of dry cows has been reported to range from 7 to 15 kg/d, equivalent to 1.3 to 2.1% of body weight. 1 2 , 4 9 , 6 6 , 7 4 , 1 0 1 , 1 0 9 , 1 1 7 Much of this variation can be accounted for by animal parity and dietary forage : concentrate ratio. Cows entering their first lactation consume less dry matter (mean, 7 to 12 kg/d) than older cows (mean, 10 to 15 kg/d). 66,109,117 Low forage diets are consumed in lesser amounts than high forage diets. 1 2 However, mean dry matter intake values may be misleading. Investigations tracking daily dry matter intake throughout the dry period all report a gradual decline in intake beginning 2 to 3 weeks prior to calving followed by a precipitous drop 48 to 72 hours before calving.12,49,66,109,117 Management goals for dry cows should focus on maximizing dry matter intake throughout the dry period in an effort to potentially allow a more rapid increase in intake postpartum. This may be accomplished by feeding ad libitum a total mixed ration appropriately formulated for energy and fiber levels. Expected ad libitum dry matter intake (% of body weight basis) for high forage (> 85%) diets, composed of corn silage and grass forage, would be 2.0% ± 0.3 and 1.7% ± 0.3 (mean ± SD) for mature cows in early (first 4 to 6 weeks) or close-up (last 2 to 4 weeks) dry periods, respectively (RJ Van Saun, unpublished data, 1990). Similar to slightly lower values can be expected in first lactation animals.109 These levels of intake guidelines indicate the need for two dry cow groups to adequately meet nutritional needs. For a 650-kg dry cow, her expected dry matter intake would be 13.0 and 11.1 kg/d for early and close-up dry periods, respectively. This dry matter intake difference of approximately 2 kg can dramatically alter the nutritional adequacy of the close-up ration. Nutrient densities need to be increased in the close-up ration (see Table 1) to accommodate for reduced dry matter consumption to maintain sufficient nutrient intake. Nutrient intake during this close-up period is crucial in preventing subsequent health disorders and optimizing production.18,19,29 Feed Ingredients Forages. Forages should constitute a major portion of the dry cow ration. High forage rations (> 85%) have been thought to maintain maximal rumen fill and volume, stimulate rumen motility, and allow healing of rumen wall lesions resulting from high-grain lactation rations. Maintaining maximal rumen fill and tone may be beneficial in promoting dry matter intake postpartum. A wide variety of forage and roughage ingredients can be fed to the dry cow when rations are appropriately formulated for energy, protein, fiber, and mineral concentrations. Trials in which dry cows were fed corn silage (limit fed), long hay, hay-crop silage, or combinations of these forages showed essentially no difference in subsequent production, health, or reproductive performance.55,86,87,117 Forage programs consisting of ad libitum corn silage or legumes are inappropriate and will predispose animals to a multitude of health disorders. 12,39,59,87 Legume forages typically contain excessive amounts of Ca for dry cows and should be limited to 30 to 50% of diet dry matter, depending upon Ca content. Corn silage intake should be limited to 30 to 40% of diet dry matter, otherwise the diet will contain excess energy as well as being deficient in protein. These forages can be combined with alternative roughages like


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stover, straw, or lower quality forages to dilute the excess nutrients. A quality grass forage is ideally suited for the dry cow. Feed analysis reports from all potential forage ingredients are absolutely essential to formulate a reasonable dry cow dietary program and appropriately balance mineral requirements with the forage program. In addition to nutrient content, particle size (i.e., effective fiber) of forages needs to be considered. Dry cows require long coarse fibrous material to stimulate rumination and saliva flow to promote maximal fiber fermentation. If the ensiled forages being fed are finely chopped, some long coarse dry hay should be incorporated into the ration. In an effort to make a smooth dietary transition to lactation, ensiled forages to be fed in lactation should be offered to close-up dry cows if they are currently being fed an all dry hay ration. An uneventful transition is best accomplished by feeding an appropriately formulated total mixed ration ad libitum, ensuring sufficient intake of all nutrients on a daily basis throughout the dry period. Such a feeding situation is in contrast to a set-up in which cows can choose between a bunk mix and available dry forage, rendering adequate nutrient intake uncertain. Concentrates. In most instances, energy requirements of the dry cow can be met exclusively by a quality forage program. Providing additional concentrates above the energy requirement is unnecessary and detrimental to animal performance. 25,39,41,59,73 Situations where concentrate feeding would be appropriate would include poor quality forages, cows in thin body condition, adverse environmental conditions (see previous discussion), or any combination of these factors. The close-up dry cow ration may also require some concentrates to increase energy density, compensating for reduced intake and increased energy requirement. This brings up the practice of "lead feeding," which is daily increasing concentrate intake in the immediate prepartum period up to 1.0 to 1.5% of body weight. Conceptually, this allows time for the rumen microorganisms to adapt to higher levels of nonstructural carbohydrates in preparation of the typical high-grain lactation rations. Unfortunately, this practice is often abused and difficult to implement in a group feeding situation. Incorporating some concentrate or increasing the amount of corn silage in the close-up ration will essentially accomplish the same goals, providing additional rapidly fermentable nonstructural carbohydrate and increasing available dietary energy. One needs to be aware of the concentrate being offered. Using current lactation concentrate mixes may be inappropriate since they usually contain high levels of Ca and other cations, possibly predisposing the cow to PP, udder edema, and other metabolic problems. Dietary Associations with Periparturient Disease Dry cow diet plays a critical role in modulating a cow's predisposition to periparturient health disorders. 18,19,29 Epidemiologic studies using path analysis have shown periparturient health disorders not to be totally independent events, but rather a complex of interrelated disorders. 17,19,27,28,29 Path analysis has shown that if a cow succumbs to PP she is four times more likely to also have a retained placenta. 19 Being afflicted with retained placenta increases the probability of ketosis incidence by 16.4 times. 1 9 These relationships further emphasize the importance of disease prevention as a goal for improving productive efficiency. Specific nutrient imbalances in the dry cow diet have been related to increased incidence of parturient hypocalcemia, 6,8,18,56,60,88,94,96 h y p o m a g n e s e mic tetany, 51 ,64 ,67 ,102 retained 23 ,57 ,105 placenta, downer cow syndrome,58,64 mastitis, 3 1 , 1 0 0 u d d e r 25,64,95,110 edema, ketosis,1,35,45,63,64 and displaced aboma-

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sum. 1 2 , 1 3 The reader is referred to these references for a detailed discussion of the specific disease pathogenesis and preventive practices. A summary of dry cow dietary imbalances (nutrient deficiency or excess) and the potential resulting disorder is compiled in Table 3. A simplistic implication from this table is that if the nutrient imbalance is corrected, potentially the problem will be remedied; however, one must also recognize other confounding factors of age, environment, production level, and nutrient interactions and their impact on disease processes. Multiple marginal nutrient imbalances may produce health disorders equally as well as a single severe nutrient imbalance. A basic understanding of nutrition, animal requirements and physiology, and environment will go a long way in helping to treat and prevent a wide variety of clinical disorders negatively impacting productive performance. DRY COW MANAGEMENT TO OPTIMIZE PERFORMANCE Early Dry Period (First 4 to 6 Weeks After Dry Off)

Given the previous discussion of dry cow nutrient requirements and their differences in comparison to lactating cows, it is obvious that dry cows need to

Table 3. Prepartum Dietary Nutrient Imbalances (Deficiency or Excess) and Their Associated Predisposition to Periparturient Metabolic and Reproductive Disorders NUTRIENT STATUS* PO TE N TI AL D I S EA SE PROCESS

A S S OC I A TE D D e f i c i e n c y †

Dystocia Parturient paresis

Energy, protein Ca, Mg, protein

Hypomagnesemic tetany Downer cow syndrome Retained placenta Delayed uterine Involution/Metritis Mastitis Udder edema Ketosis Displaced abomasum

E x c e s s

DI SEASES

Mg

Energy Ca, P, Na, K, vit D, energy(?) K

PP, FCS DYST, RP, KET, MAST, LDA(?) PP(?)

P, K(?)

Protein

PP, FCS

Se, vit E, vit A Cu, I, protein Ca, Co, vit D

Energy

FCS, PP, KET

Energy

RP, FCS, LDA(?)

Se, vit E, vit A — Protein, energy

Na, K, energy(?) Energy(?)

Fiber (forage)

Energy (grain)

T

PP, LDA MAST(?) PP, RP, LDA, FCS MET, MAST, PP, KET T

Abbreviations: ? = signifies an uncertain association based on data from the literature; dystocia (DYST); parturient paresis (PP); retained placenta (RP); ketosis (KET); metritis (MET); mastitis (MAST); left displaced absomasum (LDA); and fat cow syndrome (FCS). *Relative to recommended NRC nutrient requirements (Table 1, reference 80). †Either an absolute or induced deficiency state. Induced deficiency results from excess levels of interfering nutrients reducing bioavailability of the nutrient of concern. ‡Concurrent or predisposing condition as compiled from data presented in references 17, 18, 19, 29, 73.


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be housed and fed separately from the lactating herd to best meet their requirements. Cessation of lactation needs to be accomplished successfully, that is with minimal induction of clinical mastitis. These clinical mastitis cases may persist throughout the dry period and are potentially responsible for clinical mastitis at parturition. 85 Cows with low milk yield at dry off can have lactation successfully terminated by either intermittent or abrupt-stop milking practices followed by an appropriate dry cow intramammary antibiotic treatment. 82,92 For high-producing cows (> 20 kg/d), reducing concentrate intake and feeding a lower quality forage in the week prior to dry off will greatly reduce milk yield and minimize mastitis incidence. Limiting access to water for 12 to 24 hours also is beneficial. Prevention of new intramammary infections and treatment of existing infections can be effectively accomplished through dry cow therapy, in which all four quarters are infused with an appropriate antibiotic agent, environmental pathogen exposure management, and possibly teat dipping. 81,85,91 Once dry-treated, the cow must be watched for any potential signs of clinical mastitis. Once the udder has reached a stable nonsecretory state, relatively resistant to new infections, other dry cow management practices can be initiated. The dry period is an appropriate time to address issues of foot care (therapeutic or prophylactic), [parasite control (internal and external)], and possibly vaccinations. Vaccines administered to induce colostral antibody production usually need to be given at specific time frames relative to calving. One must always be cognizant of any contraindications for therapeutic agents administered during the dry period relative to their effects on pregnancy. Soon after the cow has settled into her dry period, she should be evaluated for body condition (i.e., degree of body fatness). Body condition at parturition plays a pivotal role in determining subsequent health 39,73 and productive 42,43,97 and reproductive 21,22,48 performance. Moderate body condition is essential for support of milk production in early lactation, when milk energy output exceeds feed energy intake (i.e., negative energy balance), and to initiate reproductive cyclicity. Either extreme in body condition (emaciated or obese) results in reduced milk yield, 4 2 , 4 3 increased health disorders, 2 2 , 3 9 , 7 3 and impaired fertility. 10,48,73 Severity of body condition loss in lactation may be more critical in modulating postpartum reproductive fertility rather than body condition status per se. 1 0 , 4 8 Body condition scoring subjectively grades cows by amount of subcutaneous fat stores over the loin, pelvis, and tailhead into five categories covering physical states of emaciated (1), thin (2), average (3), fat (4), and obese (5). 9 ,32 ,113 Body condition scoring is an excellent cow monitor that is easily quantified for evaluation of nutritional programs. Cows should be evaluated for body condition at dry off, calving, early lactation, time of breeding, and late lactation. Body condition score goals (Fig. 4) for the gestation — lactation cycle are to have cows dry off at 3.5, maintain this condition to calving, loose less than 1 condition score in early lactation, then regain condition back to 3.5 during late lactation. 9,32 On a herd basis, condition loss in early lactation should average — 0.5 units or less.32 As defined by these goals, replenishment of body reserves to be utilized in early lactation actually begins in late lactation when the animal returns to positive energy balance. Efficiency of tissue repletion is suggested to be greater in late lactation (75%) compared to late gestation (60%), thus requiring fewer feed dollars for tissue restoration. 71 However, due to the critical nature of these reserves on early lactational performance, greater emphasis should be placed on ensuring that adequate reserves are present at calving and not on differences in metabolic efficiencies. Adequate tissue replacement in cows that experience severe condition loss may be limited by available time if recondi-

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GESTATION-LACTATION CYCLE Figure 4. Goals, minimum, and maximum mean herd body condition scores for dairy cattle throughout the gestation—lactation cycle, based on a scoring system ranking cows from (emaciated) to 5 (obese). (Data from Braun RK, Donovan GA, Tran TQ, et al: Body condition scoring dairy cows as a herd management tool. Compend Contin Educ Pract Vet 8:F62, 1986; and Ferguson JD, Otto KA: Managing body condition in dairy cows. In Proceedings of the Cornell Nutrition Conference for Feed Manufacturers, Syracuse NY, 1988, p 75.)

tioning is confined exclusively to the dry period. Likewise, cows with excessively long dry periods are often predisposed to becoming overconditioned. Under intensive management conditions, fewer than 10% of the dry cows should have condition scores over 4.0 or under 2.5.9,32 Close-up Dry Period (2 to 4 Weeks Prior to Calving) As a cow approaches parturition, it is absolutely essential that she continues to receive her entire allotment of required nutrients to prevent any predisposition to metabolic disease around parturition. As already discussed, dry matter intake declines as a cow approaches calving, therefore, dietary nutrient density needs to be adjusted to compensate. This suggests that a single dry period diet may be inappropriate to sufficiently meet requirements throughout the dry period. Adding additional concentrate to a typical early dry cow diet will dilute all other nutrient intakes even further. A close-up dry cow group would be recommended, especially for herds experiencing increased incidence of health disorders around calving. This second dry cow group would also facilitate diligent monitoring of cows for impending parturition, particularly those with uncertain breeding dates, indications of dystocia, or other metabolic disorders. A stress-free and uncontaminated environment should be provided for the cow ready to calve. Maternity areas should be clean, well-ventilated, quiet, and


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provide secure footing. Potential pathogen exposure should be minimized by clean ing, sanitizing, and resting maternity areas between calvings. Wet, muddy, or manure-coated maternity areas increase exposure to pathogens responsible for retained placenta, metritis, mastitis, and calf septicemia. Clean, dry pastures can alleviate many problems associated with a contaminated calving area. When cases of severe udder edema or clinical mastitis arise prior to parturition, clinical symptoms may be ameliorated through initiation of prepartum milking. Greene et al 4 6 has shown no detrimental effects on cow health or performance or any increase in milk yield with prepartum milking. A pool of reserve quality colostrum, evaluated for immunoglobulin content, 34 should be available to feed newborn calves from cows milked prepartum. All colostrum should be evaluated for quality before being fed, as part of an overall calf management program, to ensure maximal potential for immunoglobulin absorption by the calf. Making a smooth transition from dry cow to early lactation diet is an important concern. Feeding lactating cow concentrates to the close-up cows or moving them into a low lactation group may increase the potential for metabolic disease as a result of their higher Ca and P concentrations. Potential declines in dry matter intake can result from subclinical hypocalcemia early postpartum. Never allowing the periparturient cow to go hungry or go off feed, thus inducing negative energy balance, will help to maintain adequate intake during the transition period. 1 5 Encourage intake by always having sufficient quality feed available. High quality lush hay may be beneficial to stimulate even the most reluctant eater. If both the close-up and early lactation rations are appropriately formulated for nutrient density and effective fiber to encourage ad libitum intake, cows should make a smooth transition from the dry cow ration directly to the high group milking ration. SUMMARY Evidence supports the concept of the dry period being a critical component to lactation preparation rather than an insignificant rest period between lactations. Required nutrient amounts for the dry cow are the sum of maintenance, pregnancy, and reserve replenishment needs with additional requirements for growth during the first two pregnancies. Maintenance energy requirements can be dramatically increased by level of activity and adverse environmental conditions. A wide variety of feed ingredients can be successfully fed to dry cows as long as rations are appropriately formulated to meet energy, protein, mineral, and vitamin requirements. A early and close-up dry program best matches increasing pregnancy requirements and declining intake capacity with management capabilities. The early dry cow ration is formulated for high fiber/low energy density while the close-up ration contains higher energy density with less fiber. Both rations contain sufficient other nutrients based on determined intake. This two-group system provides maximal flexibility in managing for optimum body condition at calving. Environmental stresses and dramatic dietary changes should be minimized during the transition period from late gestation to lactation. A sound dry cow program results from integration of quality nutrition and cow management practices as described. A dry cow program that enacts these guidelines should result in reduced incidence of clinical mastitis, successfully complete pregnancy with a viable calf, maximize genetic potential for milk production, minimize incidence of health disorders, and allows cows to breed back within an economically optimum time interval. Overall, a sound dry cow program is a critical key to improved fresh cow performance.

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