One cycle of high-intensity selection on BW was conducted to study correlated effects on performance under high ambient temperature (AT). From a large flock of a commercial sire-line, 3 males and 15 females with the highest BW at 35 d of age were mated and produced a group of 120 BW-selected chicks. Three average-BW males and 15 average-BW females from the same flock were mated to produce a control group of 120 chicks. On Day 17, the two groups were equally divided between two temperature-controlled chambers and housed in individual cages. One chamber was set to a normal AT (NAT; constant 22 C) and the second chamber to high AT (HAT; constant 32 C). Under NAT, the relative advantage of the selected broilers over the controls did not change from 17 to 42 d of age, averaging about 15% for BW gain and 9.7% for feed consumption. These differences were halved under HAT from Days 17 to 28 and were reversed from 28 to 42 d of age, when the selected broilers consumed significantly less feed and gained less BW than the controls. Water-to-feed ratio was measured in each AT treatment. From 28 to 42 d of age, averaged over the two groups, birds under HAT consumed 2.5 g water/g of feed compared to only 1.5 g water/g feed under NAT. The diminished superiority of the selected broilers under HAT led to a substantial genotype-by-environment interaction involving high AT and within-stock genetic differences in growth rate. It appears that broilers selected for rapid growth under optimal conditions do not achieve their genetic potential under high AT. Thus, specific indicators of adaptation to heat, possibly water consumption or body temperature, should be added to commercial selection for rapid growth to improve broiler performance in hot climates.

In the present study, we examined the composition, amount, and uptake of yolk nutrients [fat, protein, water, and carbohydrates (COH)] during incubation of eggs from 30- and 50-wk-old broiler breeder hens. Eggs were sampled at embryonic d 0 (fresh eggs), 13, 15, 17, 19, and 21 (hatch). Egg, embryo, yolk content, and yolk sac membrane were weighed, and the yolk sac (YS; i.e., yolk content + yolk sac membrane) composition was analyzed. From 30 to 50 wk of age, the albumen weight increased by 13.3%, whereas the yolk increased by more than 40%. The proportion of fat in the fresh yolk of the 30-wk-old group was 23.8% compared with 27.4% in the 50-wk-old group, whereas the proportion of protein was 17.9% compared with 15.6%, respectively. During incubation, results indicated that water and protein infiltrated from other egg compartments to the YS. Accordingly, the calculated change in the content of water and protein between fresh yolk and sampled YS does not represent the true uptake of these components from the YS to the embryo, and only fat uptake from the YS can be accurately estimated. By embryonic d 15, fat uptake relative to embryo weight was lower in the 30-wk-old group than in the 50-wk-old group. However, by embryonic d 21, embryos of both groups reached similar relative fat uptake, suggesting that to hatch, embryos must attain a certain amount of fat as a source of energy for the hatching process. The amount of COH in the YS increased similarly during incubation in eggs from hens of both ages, reaching a peak at embryonic d 19, suggesting COH synthesis in the YS. At hatch, the amount of protein, water, and COH in the residual YS, relative to the weight of the yolk-free chick, was similar in eggs from young and old hens. However, chicks from the younger hens had less fat in the YS for their immediate posthatch nutrition compared with those from the older hens.

Male and female broiler chicks from five different broiler crosses (WI, LF, and HF = Israeli chicks selected for high body weight gain, and low and high abdominal fat, respectively; FC and WN = Dutch chicks selected for favorable feed conversion and high body weight gain, respectively) were raised at a high ambient temperature (32 to 33 C). Weight gain, protein and fat content in the carcass and feed, and protein efficiency were determined at 4, 6, and 8 wk of age. The effect of the high temperature was evaluated by comparing these data with those of similar chicks raised at a normal temperature (20 to 33 C) up to 6 wk of age. The reductions in body weight, protein gain, and feed and protein efficiency due to the high temperature increased with age and were much larger in males than in females. This trend was more pronounced in WI and WN chicks than in LF, HF, and FC chicks. Females of WI and WN crosses were as heavy as males at 6 wk and heavier at 8 wk. In LF, HF, and FC crosses, both sexes had similar weights at 8 wk. Growth reduction due to the high temperature was largest in the groups with the highest growth rate at the normal temperature (WI and WN males). Chicks with a lower growth rate and a higher capacity for energy storage in fat depots (all females, HF chicks), or a higher capacity for heat loss (FC chicks), were less affected by the high temperature. The results suggest that females should be preferred over males for broiler production in hot facilities or locations. Broiler genotypes selected for feed efficiency at the expense of fast growth may allow for a more profitable broiler production in high-temperature regions.

1. Heterozygous (Na/na) naked neck chickens and their normally feathered (na/na) sibs, were exposed to constant ambient temperatures (Ta) ranging between 15 and 35 degrees C and 12h: 12h diurnal high:low temperatures of 15 degrees C:35 degrees C. 2. No significant effect of genotype was obtained in weight gain and food intake. However, the naked neck birds tended to gain somewhat more weight at high Ta and consume more food at low Ta. 3. At 35 degrees C Na birds showed better regulation of body temperature (Tb) and demonstrated considerably higher radiation from the neck. 4. The greater food intake of the naked neck chickens at 15 degrees C was associated with significantly higher packed cell volume, haemoglobin concentration, heart and liver size. These appear to involve both higher heat production and haemodynamic changes to accommodate the higher oxygen demands of the naked neck chickens at low Ta. 5. The results indicate the ability of the naked neck chickens, on the one hand to thermoregulate at low Tas and, on the other their slightly better capacity to maintain Tb at high Tas. However, no genotype advantage was obtained under diurnal cyclic temperature conditions.

BackgroundScaleless (sc/sc) chickens carry a single recessive mutation that causes a lack of almost all body feathers, as well as foot scales and spurs, due to a failure of skin patterning during embryogenesis. This spontaneous mutant line, first described in the 1950s, has been used extensively to explore the tissue interactions involved in ectodermal appendage formation in embryonic skin. Moreover, the trait is potentially useful in tropical agriculture due to the ability of featherless chickens to tolerate heat, which is at present a major constraint to efficient poultry meat production in hot climates. In the interests of enhancing our understanding of feather placode development, and to provide the poultry industry with a strategy to breed heat-tolerant meat-type chickens (broilers), we mapped and identified the sc mutation.ResultsThrough a cost-effective and labour-efficient SNP array mapping approach using DNA from sc/sc and sc/+ blood sample pools, we map the sc trait to chromosome 4 and show that a nonsense mutation in FGF20 is completely associated with the sc/sc phenotype. This mutation, common to all sc/sc individuals and absent from wild type, is predicted to lead to loss of a highly conserved region of the FGF20 protein important for FGF signalling. In situ hybridisation and quantitative RT-PCR studies reveal that FGF20 is epidermally expressed during the early stages of feather placode patterning. In addition, we describe a dCAPS genotyping assay based on the mutation, developed to facilitate discrimination between wild type and sc alleles.ConclusionsThis work represents the first loss of function genetic evidence supporting a role for FGF ligand signalling in feather development, and suggests FGF20 as a novel central player in the development of vertebrate skin appendages, including hair follicles and exocrine glands. In addition, this is to our knowledge the first report describing the use of the chicken SNP array to map genes based on genotyping of DNA samples from pooled whole blood. The identification of the sc mutation has important implications for the future breeding of this potentially useful trait for the poultry industry, and our genotyping assay can facilitate its rapid introgression into production lines.

High ambient temperatures (AT) decrease the growth of broilers because of difficulty in dissipating heat through the feather coverage. Broilers selected for higher growth rate eat more and generate more heat per unit of time; hence, they may become more sensitive to high AT. Reduced feather coverage, either by decreased number or by modified shape, may help birds to dissipate internal heat more efficiently. Two broiler stocks were studied; each was segregated for four genotypes with regard to the genes for naked neck (Na) and frizzled feathers (F): heterozygous naked neck (Na/na f/f), heterozygous frizzle (na/na F/f), double heterozygous (Na/na F/f), and normally feathered (na/na f/f). One stock had a high growth rate (GR) similar to current commercial broilers, whereas the second stock had a lower GR. Birds of each stock, genotype, and sex were reared under constant standard AT (24 C) or high AT (32 C). Body weight at 4 and 7 wk, weight gain (WG) from 4 to 7 wk, breast meat yield, and feather weight were recorded. Reduction in WG from 4 to 7 wk because of high AT was greater in high-GR birds than in low-GR birds, but, in both stocks, the high AT effect was greater on normally feathered birds than on the other three genotypes. AT 32 C, in low- and high-GR stocks, the F allele increased WG from 4 to 7 wk and increased the BW at 7 wk of fully feathered (na/na) broilers but had no effect on meat yield. The effects of the Na allele were similar to or greater than those of the F allele. The Na allele did not affect breast meat yield of low-GR broilers but increased it significantly in high-GR broilers. Combining the two allles resulted in an additive effect, which was more pronounced in the high-GR stock.

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Two lines of White Plymouth Rock chickens that have been divergently selected for 8-week body weight for 31 generations were compared for patterns of DNA fingerprints (DFP). Digestion of DNA with HinfI and hybridization to Jeffreys' minisatellite probe 33.6 resulted in DFPs that were relatively similar within lines (bandsharing = 0.50) and less similar between lines (bandsharing = 0.22). Analyses of scorable DFP bands produced by mixing DNA from individuals within lines indicated that 48% were line-specific. Causes for the differences in DFP patterns between lines and for occurrence of line-specific bands for the two lines divergently selected for body weight are discussed.