Feed intake and activity level of two broiler genotypes foraging different types of vegetation in the finishing period G. F. d. Almeida,*1 L. K. Hinrichsen,† K. Horsted,* S. M. Thamsborg,‡ and J. E. Hermansen* *Department of Agroecology, and †Department of Animal Science, Faculty of Science and Technology, Aarhus University, Blichers Allé 20, Research Centre Foulum, PO Box 50, DK-8830 Tjele, Denmark; and ‡Danish Centre for Experimental Parasitology, University of Copenhagen, Dyrlaegevej 100, DK-1870 Frederiksberg C, Denmark ABSTRACT A study was performed with 2 broiler genotypes (slow and medium growth) restricted in supplementary feed and foraging 2 different mixed vegetations (grass/clover or chicory) to identify possible benefits of herbage on nutrition during the finishing period (80 to 113 d of age). Three hundred birds were included in a 2 × 2 factorial design with groups of 25 birds replicated 3 times. The use of outdoor areas, performance, and forage intake were investigated. To identify possible differences in foraging activity, the use of the range was monitored one day per week at 4 different times of the day. Feed intake from foraging was estimated by killing 4 birds per plot (2 males and 2 females) in the morning and in the evening on 3 d during the experiment and measuring crop content. Vegetation type did not influence broiler use of the free-range area, feed intake, or performance. Differences in the use of
the range area, activity level, and feed content in the crops were observed in relation to genotype, sex, age of broilers, and also the time of day. Foraging activity was positively correlated with age. Medium-growth broilers spent more time inside and closer to the broiler houses during the day with increased foraging activity during evenings, in contrast to the slow-growing broilers that showed a more uniform activity during the day. Based on the measurement of crop content it was estimated that the slow-growing genotype had a daily intake of 5 to 8 g of forage per day, whereas the medium-growing genotype had an intake of 9 g for females and 20 g for males. In conclusion, limitation of supplemented protein feed in the finishing period may be acceptable for broilers that have access to highly nutritious vegetation.
Key words: broiler, crop content, forage, free-range, organic system 2012 Poultry Science 91:2105–2113 http://dx.doi.org/10.3382/ps.2012-02187
INTRODUCTION In organic production systems, broilers must have access to an outside area during part of the rearing period (EU, 2007). This is in addition to the high standards of animal welfare, avoidance of water and soil pollution, and increased agroecological biodiversity/resilience set out in the organic ideals (IFOAM, 2005) that guide worldwide certification procedures for livestock production in organic systems. In Europe, legislation for organic systems (EU, 1991) specifies that the outside areas available to broilers must be mainly covered with vegetation. However, the nature and type of the vegetation is not specified, and in practice most free-range land is just identified as grass or plants (Walker and Gordon, 2003). Little attention has been given to make outdoor runs attractive and nutritious to broilers as ©2012 Poultry Science Association Inc. Received January 25, 2012. Accepted May 2, 2012. 1 Corresponding author:
[email protected] or
[email protected]
part of agroecosystem management (Van de Weerd et al., 2009). In older traditional systems (Prothero, 1936), chickens were normally left to roam more naturally, seeking essential parts of their nutritional needs on or below the soil surface and consuming not only oil seed crops and cereals supplied by humans but also vegetation, seeds, fruits, soil particles, microorganisms, different stages of insects, and other arthropods and earthworms (Lomu et al., 2004; Gordon et al., 2006). Thus, Robinson (1961) estimated that feed savings could be up to 10% when fresh grass was available to hens in free-range systems. In a more recent investigation by Horsted and Hermansen (2007), laying hens managed on different types of vegetation were able to meet a considerable part of their nutritional requirements through foraging. Other recent studies have suggested that plots cultivated with chicory (Cichorium intybus cv. Grassland Puna) were attractive to laying hens and reported a high intake of this plant (Horsted et al., 2006, 2007). A natural extension of this hypothesis is that similar benefits might be achieved for broilers.
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More information on the feeding habits of broilers managed in free-range systems is needed to reassure farmers of the value of different types of vegetation as a means of nutrient supplementation. In a previous investigation on the foraging habits of different broiler genotypes, slow-growing broilers were found to spend considerably more time outside than fast-growing broilers, and this might influence foraging behavior (Nielsen et al., 2003). The economic benefit of foraging, however, also depends on how it affects the feed conversion rate (FCR; feed used per kg of BW gain). Feed is used partly for maintenance and partly for tissue growth (Leeson and Summer 1997), where the former is a function of BW. Thus, FCR is generally impaired with increasing BW because of the proportionally higher feed requirement for maintenance compared with growth. Similarly, FCR is generally impaired in slow-growing birds because of proportionally higher demands for maintenance compared with growth. Organic production is typically based on a substantially higher slaughter weight and use of moderate- to slow-growing genotypes—aspects that are expected to impair feed conversion. If a part of this additional feed requirement can be supplied with herbage, this may improve the profitability of the production and reduce the load of nutrients at the outdoor area. Also, stimulating to foraging may be a means to counteract the higher cost of supplementary feed used for slow-growing broilers. In addition, supplementing low-protein, low-energy diets, sometimes in a commercial strategy to reduce costs for industrial broiler systems, may lead birds to consume more of the available feed and thus increase feed intake (Leeson and Summers, 1997). This suggests that for free-range systems, restriction in commercial diet may stimulate broilers to increase feed intake of herbage available in the range. On this background we investigated foraging activity, performance attributes (weight gain, feed intake, and FCR) of 2 broiler genotypes—a slow-growing (pure breed) and a moderate-growing (hybrid) genotype— raised with access to different types of vegetation in the finishing phase of their growing period in a system closely resembling common farming practices to explore the contribution of foraging to the nutritional needs of the broilers.
MATERIALS AND METHODS Study Site and Study Design The experiment was performed at Research Centre Foulum, Faculty of Sciences and Technology, Aarhus University, Denmark (56°48′ N, 9°58′ E) in the summer and autumn of 2010. The experiment used a 2 × 2 factorial design of 2 genotypes of broilers with access to 2 different types of mixed vegetation: grass (Lolium perenne) and clover (Trifolium repens) versus a mix of chicory (Cichorium intybus cv. Grassland Puna) and
spontaneous weeds (Lolium perenne, Trifolium repens, Artemisia vulgaris, Senecio sp., and Tripleurospermum sp.). The experimental treatments were replicated 3 times, thus including 12 flocks, each with 25 broilers of mixed sex, for a total of 300 broilers. Each group of 74-d-old birds was allocated a specific plot of 105 m2 (12 × 8.75 m) separated from each other by nylon net fences, yielding a stocking rate of 4.2 m2 of outdoor area per animal and a mobile hut (4.6 m2) with cover and perches in compliance with the European regulation for organic broilers (EU, 1999). The experiment began when the broilers were aged 80 d and terminated when they were 113 d old.
Experimental Birds and Housing The 2 genotypes in question were White Bresse line L40 (L40) from the Research Centre Foulum, a pure breed with slow-growing characteristics, and Kosmos 8 Red (K8R), a hybrid genotype with medium-growing characteristics purchased from an Italian breeding company (http://www.olandia.it). The study was subdivided into 3 different periods as suggested by Pedersen et al. (2003) for the production of organic broilers in Denmark: inside (1 to 29 d of age), transition to the range areas during which coccidial infections in broilers of both genotypes were monitored (29 to 74 d of age), and the finishing period (from 74 to 113 d of age). In the latter period, the use of range area, activity level, feed intake, and performance attributes of broilers were all investigated. Day-old chicks were grown in a clean and disinfected chicken house until the age of 29 d. Figure 1 illustrates the timeline of our study. In the transition period, the chicks were randomly selected and allocated to plots (n = 12) cultivated with grass/clover so they could adapt to the outdoor range and where subclinical coccidial infections were monitored until they were subdued when broilers were aged 74 d. Between d 45 and 74, 10 birds per group were monitored individually for coccidia oocyst excretion twice weekly as described in a previous study (Almeida et al., 2012). Prior to the experimental period in the present study, the broilers were randomly redistributed in the 12 flocks within genotype. In addition, to avoid any effects or bias from intestinal nematode infections, all birds were treated (from 74 to 80 d of age) with flubendazole (Flubenol, Janssen Animal Health Ltd., Beerse, Belgium) via drinking water at recommended doses. During the experimental period (from 80 to 113 d of age), animals of both genotypes were fed a typical organic feed for broilers in a restriction scheme (50 g/ bird) to stimulate birds to forage especially for protein and whole wheat and water supplied ad libitum. Two feeders with supplementary feed (wheat and concentrate) were located inside the broiler houses, and a 25-L water tank was located outside. The experimental protocols involving broilers conformed to Danish legislation regarding animal care and health.
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Figure 1. Study timeline and description of activities in relation to age of broilers. Broilers were randomized and allocated to the experimental plots at 74 d of age.
The consumption of whole wheat was recorded twice a week before refilling the feeders. Fifty grams per bird of commercial diet was filled into the feeders daily at 1100 h. All broilers under study were weighed individually when 84 and 113 d old. From this strategy, it was possible to estimate the daily and accumulated gain, total weight gain, and FCR for both genotypes.
Assessment of the Use of Outdoor Areas and Broiler Activity Level The number of broilers found outside and their activity were assessed by the same observer twice a week during the experiment. In the transition, preexperimental period (29 to 74 d), the observer was trained in using the instrument of data collection and at the same time the broilers became used to the presence of the observer. Observations were performed when broilers were 80, 87, 94, 101, and 108 d of age from 0830 to 1000 h and again 1130 to 1300 h (Wednesdays) and from 1530 to 1700 h and 1830 to 2000 h (Thursdays). Weather conditions were found to be approximately similar for the 2 consecutive observation days in each week, so they were combined to give only 1 day of observation per week. To evaluate broiler behavior, the paddocks were visually subdivided into 5 main areas by inserting marking sticks in each corner of the subplots (Figure 2). The decision on which plot to start observations for each period of the day was made randomly by using a 12-sided die, each side representing one of the plots. After the initial plot had been determined, the remaining plots followed in numerical order. Observation of broiler behavior started after the observer had stood for 1 min at a specified point outside the plot (marked 1 in Figure 2) to get the chickens used to the presence and snapshots were then taken as suggested previously by Martin and Bateson (2007). From the snapshots, the number of broilers found outdoors in each subdivision was noted. The broilers categorized as being outdoors were those found in subplots 2 to 5, whereas broilers found either in subplot 1, drinking water, not visually found, or close to the houses were considered to be inside. The type of outdoor activity broilers were engaged in was
Figure 2. Plot spatial subdivision (areas 1 to 5) during behavioral studies, and point 1 outside the plots is the position of the observer when taking measurements and recordings.
also recorded in 2 main categories: either resting with the body in contact with the soil/dust bathing or moving around/searching for food (foraging) in the range. Data were systematized and grouped for each plot according to treatment (type of vegetation) and genotype. Results are presented as the mean percentage of broilers found outdoors for each period of the day and also as the percentage of broilers for the specific activities based on the number of broilers found outdoors.
Crop Content, Sward Harvesting, and Estimation of Forage Degradation Three times during the experiment, 4 broilers from each plot were necropsied to estimate the food habits at ages 84, 100, and 112 d. Two broilers (one male and one female), randomly selected from each plot, were killed (cervical dislocation) in the morning (between 0800 and 0900 h) and 2 broilers (one male and one female) in the evening (between 1800 and 1945 h). The entire crop was removed immediately afterward as suggested by Horsted et al. (2007), stored in plastic bags, identified with the bird ID and plot number, and stored in the freezer for future analysis. As originally suggested by Jensen and Korschgen (1947), individual crops were thawed in the laboratory and the content separated by forceps into different fractions: commercial broiler feed; wheat; grass; clover; chicory; other plant material; seeds; insects; earthworms, larvae, and pupae; grit stones; and soil. All fractions were dried in a forced air-drying oven at 60°C for approximately 24 h, and calculation of crop content was based on air-dried fractions (Antell and Ciszuk, 2006; Horsted et al., 2007). Because of the very small amount of seeds, insects, earthworms, larvae, pupae, grit stones, and soil found in the crops, these were
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Almeida et al. Table 1. Nutritional contents of different feed ingredients1 used in the study (% DM) Type of vegetation2
Supplementary feed Item Total DM (%) Percent of DM CP (N × 6.25) Crude fat Ash Starch Sugar Cellulose ME (MJ/kg of DM) Amino acids (g/kg of DM) Lysine Methionine Threonine Cysteine
Commercial broiler feed
Whole wheat
Grass+ clover
Chicory+ weeds
88.4 19.7 6.3 6.3 46.0 3.8 5.8 13.4 10.5 3.0 7.4 3.5
86.5 11.6 2.0 1.5 67.9 2.3 2.1 14.1 3.5 1.8 3.5 2.8
15.1 15.9 2.6 9.9 4.0 6.6 29.8 4.2 9.5 3.2 9.0 1.5
16.1 11.2 2.4 12.4 3.7 6.2 28.6 3.6 8.5 1.6 7.7 1.4
1Two samples from each supplementary feed were analyzed with the mean values reported. Six samples from each type of vegetation were submitted for analyses, and the mean values are presented. 2Forage sampled before the introduction of broilers to the plots.
omitted from the analysis and we based our analysis on the contents of supplementary feed (commercial broiler feed and wheat) and herbage found in the crops. In our results we categorized the vegetative ingredients as grass, clover, chicory, and other plants. We estimated the total plant intake by summing the total herbage material found in the crops to evaluate the vegetative food intake and consequently the food habits during the experiment and from different periods of the day (morning and evening). Before the experiment began, samples of vegetation were harvested from two 0.25-m2 patches from each plot. The location of the patches for sampling was decided beforehand, and the same locations were used for all 12 plots. The vegetation was cut approximately 2 cm above ground, and the harvested biomass from the 2 patches was pooled for each plot and stored in the freezer for further analysis. To identify degradation of vegetation with time, 6 visual assessments (one per week) were performed from when the broilers were first introduced to the experimental plots. Vegetation degradation was estimated by 4 different visual measures in a 1-m2 area in each plot with the same location used for the 12 plots. The percentages of the main components of grass, clover, chicory, weeds, bare soil, and decomposed vegetation were estimated for each plot to a sum of 100%. The change in relative cover of the different components was compared to represent the degradation of herbage with time, and results were averaged according to treatment combinations.
Statistical Methods Effects of treatments on the use of the range, crop content, and performance attributes were subjected to ANOVA by linear models in SAS (SAS Institute, 2000). Data on the use of the range were based on
plot observations (plot as the experimental unit) and were found to be not normally distributed. Logarithmic transformation was performed to obtain normality and homogeneity of variance (Quinn and Keough, 2002). All main factors and their possible interactions were first included using a full model. No significant 3-way interactions existed, and these were therefore excluded from the final model. For the crop content analysis, individual observations were available, thus including the sex of the broilers. The data were checked and found not normally distributed. The test was then performed with the natural log-transformed value to obtain normality and homogeneity of variance with plots considered as the error term. Weight gain, feed intake, and FCR (feed intake/weight gain) were analyzed with plot as the experimental unit, and data were checked and found to be normally distributed. Where transformation was used, results are presented with back-transformed values. Feed conversion rate was estimated by the total amount of food supplemented (mean) divided by the averaged weight gain (mean). In addition to the above tests, behavior information was subjected to analysis of covariance to identify possible correlations between broilers found outdoors, their activity, and age. The P-values less than or equal to 0.05 were considered statistically significant.
RESULTS AND DISCUSSION During the entire experimental period (aged 80 to 113 d), birds showed excellent health (no signs of footpad burns and good plumage state). Mortality was restricted to 2 of the K8R and 1 of the L40 genotypes. Causes of death were either unknown or culled because of injuries. There were no reports of predation because the 12 experimental plots were electrically fenced to keep out foxes and were covered with nylon nets to avoid avian predation.
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TWO BROILER GENOTYPES FORAGING DIFFERENT VEGETATION Table 2. Mean supplementary feed consumption (kg per bird), daily intake, initial BW, weight gain, and feed conversion rate (FCR, supplementary feed divided by weight gain) in the finishing period (80 to 113 d of age) by genotype Genotype Item Consumption of whole wheat (kg/bird) Consumption of commercial broiler feed (kg/bird) Total feed consumption (kg/bird) Daily intake of supplementary feed (g/bird) Mean initial BW (g) Mean weight gain (g) FCR (total feed/weight gain)
Nutritional Content of Supplementary Food and Broiler Performance Table 1 describes the nutritional content of food ingredients supplemented to the broilers during the experimental period. Both types of vegetation contained high levels of the essential amino acid lysine, and the grass/clover mixture had a content of methionine comparable with the commercial broiler feed. Consumption of supplemented feed, initial BW, and mean weight gain during the experimental period of both genotypes are presented in Table 2. Total intake of supplemented feed was higher for the hybrid K8R (+27.5%) compared with the pure L40 because of their higher consumption of whole wheat. Even with higher cereal consumption, the superior growing rate achieved by the K8R hybrid resulted in a more efficient FCR compared with the slower-growing genotype (Table 2).
Use of Range Area by Broilers In agreement with our hypothesis, the slow-growing genotype (L40) was found more outdoors and was more
L40
K8R
SEM
P-value
2.59 1.65 4.24 128 1,906 728 5.82
4.20 1.65 5.85 177 2,698 1,111 5.28
0.11 0.01 0.11 3 38 14 0.13
0.001 1.00 0.001 0.001 0.001 0.001 0.013
active than the hybrid genotype (K8R; Table 3). A positive correlation between activity and age of broilers was found for both genotypes (Table 3). Thus, more birds (from both genotypes) were found in activity as they grew older (4.6% increase in the number of broilers observed outdoors and 7% increase in activity per week of observation), which is in agreement with Keeling et al. (1988) in a study with layers and with Mirabito and Lubac (2001) in a study with broilers. The expected increase in feed consumption as broilers grew older associated with a higher confidence in exploring the range areas over time may have contributed to the increased presence outdoors and activity of broilers reported in our study. In addition, the proportions outdoors in this experiment were considerably larger than in the studies by Dawkins et al. (2003), Hegelund et al. (2005), and Jones et al. (2007) with large commercial flocks. However, the flock size in the present study was small compared with commercial flocks, and it is well known that the size of the flock (Bubier and Bradshaw, 1998) and the genetic background of the chicks influence broiler activity (Nielsen et al., 2003). Another explanation for the
Table 3. Proportion of the flock that was outdoors and the proportion of those found active, percentage, and P values1 Item
% of flock outdoors
% of flock active
Genotype Kosmos 8 Red White Bresse L40 P-value Kosmos 8 Red Time of day (h) 0830 to 1000 1130 to 1300 1530 to 1700 1830 to 2000 White Bresse L40 Time of day (h) 0830 to 1000 1130 to 1300 1530 to 1700 1830 to 2000 P-value (time of the day) P-value (genotype × time of the day) Regression coefficient for % per week P-value (age in days) P-value (genotype × age)
39.9 (2.8) 68.6 (2.4) 0.001 34.7 (5.4) 17.6 (4.1) 36.9 (4.8) 70.4 (3.5) 76.6 (4.0) 57.3 (4.6) 61.7 (5.3) 78.7 (3.9) 0.001 0.001 4.6 0.001 0.65
33.3 (2.7) 46.1 (2.5) 0.001 30.1 (5.1) 13.2 (3.4) 26.8 (4.4) 62.9 (3.7) 52.2 (5.3) 40.5 (4.4) 35.3 (4.4) 56.2 (4.9) 0.001 0.001 7.3 0.001 0.14
1Standard
error of the mean in parentheses.
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present result might be the restriction of protein-rich commercial diet, which may have stimulated the birds to explore the forage area. In our experiment broilers showed a diurnal rhythm that differed between the 2 genotypes in the study. The hybrid K8R was found much more inside and closer to the broiler houses during the day but with increased activity observed during evenings. In contrast, the slowgrowing genotype (L40) showed a more uniform activity pattern during the day. This confirms what other studies have found, namely that foraging behavior varies according to genotype (Kjaer and Mench, 2003), and most important for farm management, that there are preferences for specific times of the day. According to our results and in agreement with Dawkins et al. (2003), during the periods close to noon (from 1100 to 1500 h) there was limited foraging activity by broilers of both genotypes (Table 3), but especially the K8R broilers. Restriction of the commercial diet to a daily feed at 1100 h may have influenced and even increased the need for exploring the range, especially of hybrid K8R broilers in the evening periods.
0.25 0.28 0.14 0.41 0.38 0.0015 0.29 0.30 0.13 0.0374 0.35 0.0036
0.0130 0.75 0.0340 0.14 0.24 0.55
Sex × harvesting time Sex × harvesting date
Harvesting time × harvesting date
0.68 0.0102 0.0003 0.78 0.45 0.12 0.19 0.0217 0.0089 0.83 0.95 0.27
0.47 0.18 0.0019 0.26 0.86 0.58
Vegetation type × sex Vegetation type × genotype
Vegetation type × harvesting date
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1Total
plant: the total amount of grass, clover, and chicory accounted in the broiler crop.
0.58 0.96 0.50 0.44 0.0397 0.0001 0.74 0.0125 0.0162 0.0014 0.25 0.0212 0.12 0.94 0.22 0.78 0.0437 0.30 0.44 0.0163 0.08 0.89 0.38 0.67 Grass Clover Chicory Total plant1 Wheat Commercial broiler feed
Genotype × harvesting time Genotype × harvesting date Genotype × sex Vegetation type × harvesting time
0.0010 0.0033 0.0088 0.0001 0.0076 0.0001 0.0001 0.0031 0.0003 0.14 0.0114 0.0089 0.0002 0.0001 0.0063 0.0001 0.0001 0.0002 0.63 0.0058 0.0022 0.0001 0.0225 0.98 0.91 0.0001 0.0001 0.12 0.73 0.97 Grass Clover Chicory Total plant1 Wheat Commercial broiler feed
Harvesting time Harvesting date Sex Genotype Vegetation type Food type
Table 4. Significance (P values) of factors affecting the crop content of broilers of both genotypes
Feed Intake Based on Crop Content Table 4 gives the level of significance of factors affecting the content of grass, clover, chicory, wheat, and commercial broiler feed in the crops of the broilers. In particular, genotype, sex, and slaughter date—reflecting the age of the broilers—as well as time of the day influenced crop content of broilers. These effects are shown in Table 5, which for each genotype gives the amounts of total plant material, wheat, and commercial broiler feed found in the broiler crops for the morning and evening periods and for the 3 different harvesting dates in the experiment. Amount of plant material (total plants) in the crop was much higher in the afternoon than in the morning. The hybrid genotype K8R had higher amounts of plant material in the crops than the L40 genotype and males had a higher content than females. The effect of genotype and sex, however, interacted with harvesting date in that total plant material decreased over time in K8R broilers (most pronounced for males), whereas this pattern was not seen in L40 birds. This is probably a reflection of a reduction in plant availability at the end of the experiment (Figure 3). Looking at the grass and chicory separately, the amount of grass found in the crops increased linearly over time in contrast to the amount of clover and chicory, which linearly decreased over time (data not shown). This shows the reduction in availability of the highly nutritious clover and chicory (especially in chicory plots) during the period even at a low stocking rate (>4.2 m2/head outdoor area), as also illustrated in Figure 3. The amount of whole wheat in the crops was highest in the afternoon and highest for the K8R genotype (Table 5), highest for males compared with females, and the differences between sexes were most pronounced for
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Genotype did not appear to influence the content of concentrate in the crops. However, a difference was observed for sex (males having higher content than females) probably reflecting the competitiveness of the males in the situation with the restriction in supplemented commercial broiler feed. As already explained, all food items found in the crops were influenced by the time of the day in agreement with results of Horsted et al. (2007), with more items found in the crops for the evening than for the morning period.
Forage Contribution to Broiler Nutrition Figure 3. Estimated forage availability and degradation during the occupation of the forage area (from 74 to 113 d of age).
L40. In addition, an interaction existed between genotype and harvesting date (age), where K8R had a higher increase in crop content with time than L40, probably reflecting the expected higher requirement for growth of the hybrid genotype when compared with the pure slow-growing breed. Apparently, due to a higher nutritional requirement, K8R broilers have compensated for a comparatively smaller availability of the commercial broiler feed by consuming more wheat compared with the slow-growing L40 genotype (daily allocation of concentrate was 50 g/bird, for both genotypes).
The analysis of broilers weight gain during the experiment shows that L40 broilers grew, on average, 22 g/d, which agrees with the findings by Hermansen et al. (2004) for L40 broilers slaughtered at 130 d. The K8R broilers grew 33.6 g/d, which is approximately 10% more than the growing rate advertised by the breeding company for the same growing period (30.3 g/d), indicating that growth rate was not substantially reduced by the restricted supply of commercial broiler feed. As expected and in agreement with Leeson et al. (1999), both genotypes in our study had a high feed consumption per kilogram of gain (Table 2) in the finishing period. However, the interpretation of these results is limited because we did not compare groups restricted with groups unrestricted in supplemented feed with appro-
Table 5. Amount of food items found in the crops based on genotype and sex of the broilers for each period of the day (morning and evening), for each of the 3 dates of harvesting and the estimated daily intake of herbage, by least squares means Genotype White Bresse L40 Item
Males plant1
Total (mg) Time of day: morning Time of day: afternoon Harvest age (average morning + evening) Age of broilers (d) 84 100 112 Wheat (g) Time of day: morning Time of day: afternoon Harvest age (average morning + evening) Age of broilers (d) 84 d 100 d 112 d Commercial broiler feed (g) Time of day: morning Time of day: afternoon Harvest age (average morning + evening) Age of broilers (d) 84 100 112 Intake of total plant2 (g DM/d) 1Total
Females
Kosmos 8 Ross Males
Females
SEM
627 933
192 560
1,343 2,797
423 1,171
120 284
711 802 827 7.3 10.4
350 219 560 3.2 7.4
2,394 3,117 701 12.1 13.1
744 1,140 507 11.6 10.4
162 425 87 0.8 0.9
8.6 8.4 9.4 2.1 15.7
3.4 6.0 6.5 1.4 7.2
9.7 14.1 13.7 0.2 18.7
7.7 17.3 12.0 0.2 13.5
0.7 1.2 1.1 0.2 1.2
8.5 11.6 6.4 7.7
2.5 4.9 5.3 5.1
6.6 12.6 9.0 20.7
5.0 3.0 12.5 9.4
1.1 1.6 1.5 3.2
plant: the total amount of grass, clover, and chicory in the crop. calculated by the regression equation y = 0.144x − 0.178 from Antell and Ciszuk (2006) where y is the total amount of plant in the crop on an air-dried based for the evening period and x is the estimated herbage intake per day, in grams of DM. 2Values
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priate replicates. Nevertheless, it remains unclear from our own measurements if the consumption of herbage affected FCR. As discussed earlier, the herbage available to the broilers (Table 1) showed a relatively high nutritional content of essential amino acids. However, we were not able to estimate the possible intake hereof based on crop content because soil-living organisms also have a high content of essential amino acids (Pokarzhevskii et al., 1997). The insignificant amounts of soil particles found in broiler crops suggest that the dietary restriction applied in our study was not sufficient to stimulate animals to seek their amino acids from elsewhere as reported by Horsted et al. (2007), who found larger amounts of soil in the crops of layers with no access to a commercial diet compared with layers with access. Nevertheless, to estimate the possible contributions of amino acids from the herbage found in the broiler crops in our study, we tried to contrast their typical requirements with the amount of these essential nutrients supplied in the feed (whole wheat + commercial broiler feed). The daily requirements for lysine and methionine were taken from Chwalibog (1993), who estimated these according to the genotype, growth rate, and age of broilers. Thus, L40 broilers required 340 mg of lysine and 275 mg of methionine, and K8R broilers 495 mg of lysine and 385 mg of methionine. By comparing the requirements presented by Chwalibog (1993) with the content available in the supplementary feed (whole wheat + commercial broiler feed) corrected for DM, both genotypes apparently received sufficient lysine but not methionine. Thus, a proximate deficit in methionine supplementation in the order of 10% for L40 and 15% for K8R hybrid broilers was found. To determine whether this shortfall would be met by its availability in herbage, we estimated the forage nutritional content by using a method first proposed by Antell and Ciszuk (2006) and later applied by Horsted et al. (2007), who investigated differences in herbage intake of layers foraging different types of vegetation. By applying the regression proposed by Antell and Ciszuk (2006), the herbage found in the crops for the evening periods reflects the daily herbage consumption in grams of DM per day (Table 5) for both genotypes and sexes. On the basis of the mean daily herbage intake from each genotype (Table 2) and the mean nutritional content of the herbages given in Table 1, the nutritional requirements seemed to be fulfilled considering those proximate calculations. We also tried to estimate the contribution of energy from the forage crops, although it was difficult to obtain good estimates for the energy requirements based on the genotypes and ages of broilers used in our study. We finally settled on a method proposed by Sakomura et al. (2003) for parent stock of fast-growing broilers combined with a method proposed by NRC (1994) for slow-growing layers, correcting for the requirements associated with egg production. By comparing the mean
values from both formulas with what was available from the supplemented feed, we propose that the supplemented feed was able to cover approximately 90% of the daily energy required for growth and maintenance of both genotypes. It is important to remember that neither method includes energy requirements for foraging activity. In conclusion, the slow-growing genotype (L40) was found to be more active in exploring the range compared with the hybrid genotype K8R, which confirms our hypothesis. Conversely, restricted access to a commercial diet may have encouraged broilers to explore the range areas, especially the hybrid K8R genotype, presumably because it had a higher deficit of the amino acid methionine. However, the supply of nutrients from forage to free-range broilers is more uncertain if large flocks are targeted, which limits the prospects of upscaling our findings. From a farm design point of view, it should be borne in mind that broilers can consume considerable amounts of forage as part of their nutritional needs and this is mainly influenced by genotype, age of the broilers and time of the day. Further studies are necessary to elucidate if a more restricted feeding of commercial broiler feed to large flocks, supplemented especially during morning periods, can stimulate foraging activity and increase the herbage intake during the evenings as part of a strategy to achieve 100% on-farm self-sufficiency in the nutrient supply to broilers in organic systems.
ACKNOWLEDGMENTS Aarhus University (Denmark) and SOAR (Research School for Organic Agriculture and Food Systems, Tjele, Denmark) are thanked for financing our study. The authors thank Orla Nielsen (Department of Agroecology, Research Center Foulum, Aarhus University) for his great technical support during the study. Thanks are also due to Margit Schacht (Aeces Flyter Ind, Agro Business Park, Tjele, Denmark) for her valuable help on the English revision of this manuscript. Finally, we wish to thank the two anonymous reviewers who constructively contributed to increasing the quality of the paper.
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