Calcium Metabolism of Hens Secreting Heavy or Light ...

Calcium Metabolism of Hens Secreting Heavy or Light Egg Shells1 SHMUEL HURWITZ AND ARIE BAR

Division of Poultry Science, The Volcani Institute of Agricultural Research, Rehovot, Israel (Received for publication April 11, 1967)

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A previous study (Hurwitz, 196S) had indicated that it was difficult to apply the usual kinetic models to study the calcium parameters of the laying hen, and we are still in search of a suitable model. However, incorporation of radioactive calcium into various bone segments and appearance of calcium-45 in blood plasma, under conditions of continuous calcium-45 feeding, 1

Contribution from The National and University Institute of Agriculture, Rehovot, Israel. 1967 series, No. 1149 E. This research has been financed in part by the U. S. Department of Agriculture under P.L. 480.

could serve as an index of bone turnover, at least on a comparative basis (Hurwitz, 1965). This method was, therefore, used to compare the calcium turnover of various bone segments, in hens producing heavy or light shells. In addition, calcium balances were conducted in order to detect any differences in calcium retention and balance between those two groups of birds. METHODS AND RESULTS

General Procedure: Birds: Single Comb White Leghorn laying hens, 10 months of age, were used in this study. Except when in metabolism cages, they were kept in individual laying cages situated in an open shed. Prior to the start of the experiment they were fed a commercial laying ration containing 3.5% calcium and 0.64% phosphorus. Individual egg production records were kept for several months prior to the start of the experiment. Only birds laying above 70% were considered for this study. The groups of experimental birds were selected out of a flock about three times as large. Three eggs were collected from each bird; the eggs were weighed, their contents emptied, and their shells thoroughly washed. Shell weight was determined after an overnight drying at 105°C. From those measurements, two groups were selected: those with shells weighing above 5.5 g. were taken as the heavy-shell producers (HSP), and those with shells weighing below 5 g. were taken as light-shell producers (LSP). Out of these groups, hens with extreme body or egg weights were removed. This selection resulted in two groups with similar egg production, body and egg

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ESPITE the extensive studies on egg shells there is little information on the calcium metabolism parameters of birds producing heavy shells versus those producing light shells. Such information is available on plasma alkaline phosphatase (Gutowska et al., 1943), and limited data on the calcium balance (Tyler, 1957). The blood calcium may be considered as at least part of a calcium pool with entries and exits out of this pool and mixing within the pool. The entries into the pool are absorbed calcium, and bone resorption. The exits out of the pool are shell deposition, bone formation, urinary calcium and endogenous fecal calcium. Decreased entries into the pool, such as decreased calcium absorption, Va, may lead to reduced shell deposition, (Hurwitz and Bar, 1966). Similarly, decreased shell deposition may be caused by reduced bone resorption. This would mean that the bone turnover rate may be important in determining the rate of shell deposition.

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BONE TURNOVER AND CA BALANCE

weights, but with markedly different shell weights. Diets: Practical rations were used (Table 1). The diets contained 3.72% and 3.99% Ca, in trials 1 and 2, respectively. The diets were intended to supply more than the minimum calcium requirement of 3 g./day in order to eliminate any confounding effects of calcium restriction. Calcium-45 was mixed into the diets as previously described (Hurwitz, 1965).

TABLE 1.—Composition of experimental diets Ingredients Soybean meal (50% protein) Wheat bran Yellow corn Milo Fish meal Alfalfa meal Mineral mixture 1 Vitamin mixture 1 Soybean oil, refined DL Methionine Calcium carbonate, precipitated Calcium phosphate, dibasic A.R.

Trial 1

Trial 2

23.00

22.00 5.00 25.00 29.15 3.00 2.00 0.30 0.25 4.00

— —

62.65

— —

0.30 0.25 4.00 0.10

—

8.00

8.00

1.70

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3.72 3.99 Analytical procedures: Blood was obtained Calcium content, assayed, % 1 by heart puncture, using heparin as an anFor composition of mineral and vitamin mixticoagulant. After killing the birds, their tures, see Hurwitz and Bornstein (1963). femurs, and in trial 2 also the sternum, were removed. The femurs were then di- dissolution of these materials. The dried vided into ends, cortical and medullary seg- samples were then re-dissolved in 0.5N hyments as described previously (Hurwitz, drochloric acid, and aliquots were placed in 1964). scintillation flasks. After scintillation liquid Fecal samples, shells and bones were (Bray solution) had been added, the samdried and ashed. The resulting ash was dis- ples were counted in a Tri Carb liquid scinsolved in appropriate amounts of hydro- tillator previously calibrated for minimum chloric acid. Calcium was determined in variation due to acid quenching. Standards blood plasma and in shells by direct EDTA taken from ashed feed were treated similartitration using calcein and hydroxy naph- iy. thol blue, respectively, as indicators. In bone and feces, calcium was titrated with Balance techniques: The hens used for calEDTA, following oxalate precipitation and cium balance were placed in metabolism H 2 0 2 oxidation (Hurwitz and Griminger, cages 10 days before the trial. These cages 1960), using hydroxy naphthol blue as in- had a double wall so that the collection trays extended beyond the sides of each dicator. cage, in order to avoid the loss of excreta Calcium-45 was determined in a planfrom dripping down the wall and out of the chet counter in trial 1 and by liquid scintiltray. Water was supplied from a low-preslation in trial 2. For the planchet counting, sure drip system, the founts being activated calcium was precipitated as oxalate, calciby the beak of the bird. Feed was given in um was precipitated as oxalate, filtered on feeders enclosed on three sides by high filter-paper disks and mounted on planwalls, to avoid any loss of feed. chets. Stable calcium was added to the samples in order to obtain a uniform thickExcreta were collected from the stainless ness. The planchets were counted in a steel tray and placed in the jar of a Waring Baird Atomic gas-flow detector. For liquid Blender. They were then homogenized; scintillation, aliquots of bone and egg shell foam was avoided by using silicon antisolutions were oven-dried to remove any foam. After homogenization, the total fecal excess of hydrochloric acid needed for the collection was transferred into a volumetric

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S. HURWITZ AND A. BAR

TABLE 2.—Body weight, egg production, and calcium in egg shells, blood plasma and femur of groups of hens selected on the basis of shell weight Parameter

Heavy shells1

Light shells

Body weight, g. Shell Ca, g./shell Egg production, eggs/8 days Plasma Ca, mg./100 ml.3 Femur Ca, mg./segment ends cortical medullary

1,682±922 2.16±0.08 6.5 + 0 . 5 26.1 ± 2 . 8

1,594+178 1.77 + 0.07** 6.3 + 0 . 7 26.0 ± 6 . 1

406 ±69 332 ±56 129 ±44

344+49 321 + 58 97±29

1

Heavy shells =group of hens selected for high shell deposition (over 5.5 g./shell). Light shells =group of hens selected for poor shell deposition (less than 5.0 g./shell). 2 Mean± standard deviation. *=significant (P