Response of broiler breeder females to feed restriction below recommended levels. 3. Characterizing the onset of sexual maturity

Energy partitioning by broiler breeder hens in conventional daily-restricted feeding and precision feeding systems

An empirical linear mixed model was derived to describe metabolizable energy (ME) partitioning in broiler breeder hens. Its coefficients described ME used for total heat production (HP), growth (ADG), and egg mass (EM). A total of 480 Ross 308 hens were randomly and equally assigned to 2 treatments: precision feeding (PF) and conventional daily-restricted feeding (CON) from 23 to 34 wk of age. The PF system allowed birds to enter feeding stations voluntarily at any time, weighed them, and provided access to feed for 60 s if their BW was less than the breeder-recommended target BW. The CON birds were fed daily each morning. Energetic efficiency of hens was evaluated using residual feed intake (RFI), defined as the difference between observed and predicted ME intake (MEI). The energy partitioning model predicted (P < 0.05): MEI = A × BW0.67 + 1.75 × ADG + 0.75 × EM + ϵ. The coefficient A, a vector of age-specific HP, was 142 kcal/kg0.67/d; the energy requirement for growth and EM was 1.75 and 0.75 kcal/g, respectively. For the CON and the PF hens, respectively, MEI was 366 and 354 kcal/d (P = 0.006); RFI was -5.9 and 6.7 kcal/d (P = 0.009); HP% was 85.5 and 87.7 (P < 0.001); hen-day egg production (HDEP) was 65.5 and 55.2% (P < 0.001). Although the CON hens had higher MEI, the model predicted lower HP%; thus, CON hens had more nutrients available for egg production, increased egg production, and were more energetically efficient than the PF hens. The decreased egg production by the PF hens was likely due to these hens receiving production-related feed increases after an egg was laid. However, feed allocation increases for the CON hens resulted in increasing MEI for all CON hens at the same time. Therefore, the PF hens had lower MEI and lower HDEP than the CON hens.

Genome-Wide Association Studies for Comb Traits in Chickens

The comb, as a secondary sexual character, is an important trait in chicken. Indicators of comb length (CL), comb height (CH), and comb weight (CW) are often selected in production. DNA-based marker-assisted selection could help chicken breeders to accelerate genetic improvement for comb or related economic characters by early selection. Although a number of quantitative trait loci (QTL) and candidate genes have been identified with advances in molecular genetics, candidate genes underlying comb traits are limited. The aim of the study was to use genome-wide association (GWA) studies by 600 K Affymetrix chicken SNP arrays to detect genes that are related to comb, using an F2 resource population. For all comb characters, comb exhibited high SNP-based heritability estimates (0.61-0.69). Chromosome 1 explained 20.80% genetic variance, while chromosome 4 explained 6.89%. Independent univariate genome-wide screens for each character identified 127, 197, and 268 novel significant SNPs with CL, CH, and CW, respectively. Three candidate genes, VPS36, AR, and WNT11B, were determined to have a plausible function in all comb characters. These genes are important to the initiation of follicle development, gonadal growth, and dermal development, respectively. The current study provides the first GWA analysis for comb traits. Identification of the genetic basis as well as promising candidate genes will help us understand the underlying genetic architecture of comb development and has practical significance in breeding programs for the selection of comb as an index for sexual maturity or reproduction.

Reproductive Efficiency and Metabolism of Female Broiler Breeders as Affected by Genotype, Feed Allocation, and Age at Photostimulation. 2. Sexual Maturation

A 3 x 4 x 2 factorial design trial was conducted to determine the effect of 3 broiler breeder strains, 4 target BW profiles, and 2 photostimulation ages on sexual maturation traits. A total of 560 pullets from each strain (Hubbard Hi-Y, Ross 508, and Ross 708) were housed in 24 pens. The BW profiles diverged at 4 wk and subsequently converged at 32 wk of age as follows: standard (approximate mean target BW profile of the 3 strains), low (12-wk BW target = 25% lower than standard followed by rapid gain to 32 wk), moderate (12-wk BW target = 150% of standard followed by lower rate of gain to 32 wk), and high (12-wk BW target = 200% of standard followed by minimal growth to 32 wk). Birds were photostimulated at 18 (18WK) or 22 (22WK) wk. Eight birds per interaction (n = 192) were killed and dissected at sexual maturity (first oviposition). Body weight profile affected timing of sexual maturity with the 18WK but not the 22WK treatment. There was no effect of BW profile on initial egg weight. Mean BW at sexual maturity was 3.40, 3.21, 3.01, and 2.84 kg for high, moderate, standard, and low birds, respectively. This affected shank and keel length, indicating differences in frame size. Ovary weight at sexual maturity was 6 g heavier in the low treatment (55 g) compared with other BW profiles. This was related to recent feeding level, which was highest at sexual maturity in the low treatment. Arrangement of ovarian large yellow follicles (LYF) changed with photostimulation age. Birds that were photostimulated at 18WK had 1.33 LYF hierarchies, compared with 1.22 in 22WK birds. The 18WK-high birds had increased excess LYF production (55% paired) compared with other BW profiles, whereas both small yellow follicle number and atresia were increased. Feeding profiles affected growth and conformational traits, with little effect on reproductive morphology at sexual maturity.

The effect of low-density diets on broiler breeder development and nutrient digestibility during the rearing period

Low-density diets might help to reduce hunger feeling in restricted-fed broiler breeders. Effects of low-density diets on nutrient digestibility and bird development were studied in Cobb 500 broiler breeder hens from 4 wk of age until the onset of the lay (wk 26). The experiment included 4 treatments. The control treatment was a normal density diet (ND; 2,600 kcal/kg). Treatments 2 and 3 had a 12 and 23% lower nutrient density than ND (LD12 and LD23, respectively) through inclusion of palm kernel meal, wheat bran, wheat gluten feed, and sunflower seed meal. Treatment 4 also had a 12% lower nutrient density than ND but included oats and sugar beet pulp (LD12(OP)). Total daily intake of energy, digestible lysine, calcium, retainable phosphorus, sodium, and linoleic acid was kept constant in the low-density dietary treatments. Animal performance and development of the intestinal tract and reproductive tract were determined in addition to digestibility and feed passage rate. The LD12(OP) provided a lower AME and nutrient digestibility than calculated and was related to lower live weights. Birds given LD23 and LD12(OP) showed a faster ovarian and oviduct development between wk 24 and 26 compared with ND. At 22 wk of age, LD23 and LD12(OP) diets resulted in higher empty jejunum and ileum weights. Low-density diets did not affect intestinal tract contents and decreased mean retention time of the contents. It was concluded that low-density diets can affect live weight and development of digestive and reproductive tracts.

The Effect of Low-Density Diets on Broiler Breeder Performance During the Laying Period and on Embryonic Development of their Offspring

The effect of low-density diets on bird performance, egg composition, and embryonic development was studied with 2,100 female and 210 male Cobb broiler breeders from 25 to 60 wk of age. The experiment included 5 treatments. These included a control group with a normal density diet (ND, 2,800 kcal of AME/kg). Treatments 2 (LD11) and 3 (LD21) had a 11 and 21% lower nutrient density. Treatment 4 (LD11(OP)) had a 11% less dense diet, which was obtained by inclusion of other feed ingredients. In these 4 treatments similar diets were given during the rearing and the laying period. Treatment 5 combined LD12 in the rearing period and ND diets during the laying period (LD12-ND). Egg composition and embryonic development were measured in eggs of ND and LD21 birds at 29 and 41 wk of age. During the laying period from wk 25 to 60, live weights did not differ among treatments, except that birds fed LD11(OP) had lower live weights. A significantly higher rate of lay was provided by LD11 compared with ND. Egg weights were significantly higher when low-density diets were fed, particularly in LD11(OP). Percentage of fertile eggs did not differ among treatments. Compared with the other treatments, LD11(OP) provided a significantly lower hatchability. We found that LD21 resulted in a better development of the area vitellina externa and heart and embryo weight at 29 wk of age. It was concluded that this was related to a higher egg weight and egg white proportion. This suggests that the amount of egg white in eggs of hens fed ND was limiting for embryonic development, particularly in eggs of young broiler breeders.

Age-dependent changes in plasma biochemistry of yellow-legged gulls (Larus cachinnans)

The study of avian plasma chemistry is providing useful reference values for the management of endangered and game species, supporting veterinarians in their diagnostics, and also bringing to light relevant physiological adaptations during periods of food-shortage. Age is an important source of variability for plasma chemistry. Here I report plasma chemistry of yellow-legged gulls Larus cachinnans from different ages, between post-independence and adulthood, a 5-year interval. Increase in plasma cholesterol concentration and decreases in uric acid, inorganic phosphorus and alkaline phosphatase values were seen. Body mass corrected by body size (i.e. body condition) increased with age, plasma cholesterol being positively correlated in females, but not in males. Moreover, cholesterol was also positively correlated to gonad size in both sexes. Long-term developmental changes in this species, such as gonad development and the acquisition of an optimal body mass for reproduction, could explain these findings. Finally, inorganic phosphorus and alkaline phosphatase, both traditionally related to osteogenesis, were not associated to deferred skull ossification, as originally was suggested in other species.

Effects of body weight and feed allocation during sexual maturation in broiler breeder hens. 1. Growth and carcass characteristics

The effects of broiler breeder BW and nutrient intake on carcass traits were examined at photostimulation (PS) (21 wk) and at sexual maturity (SM) in birds of standard (STD) BW or either 20% lighter (LOW), or heavier (HIGH) at PS and subsequently allowed restricted (RF) or ad libitum (AL) access to feed. Of the 30 Shaver Starbro pullets assigned to each BW group at PS, 10 birds of each size were processed immediately for carcass analysis and 10 birds assigned to each of the RF and AL feeding regimens. Remaining birds were processed for assessment of carcass traits following SM. The mean BW of LOW, STD, and HIGH birds processed at PS were 1,639, 1,995, and 2,394 g, respectively. The relative breast muscle weight, abdominal fat pad weight, and total carcass lipid content of LOW birds were significantly lower than those of STD or HIGH birds. Body weight at PS primarily affected lipid stores, with absolute carcass lipid content being 103, 180, and 241 g in LOW, STD, and HIGH birds, respectively. The mean AL BW increased by 85% between PS and SM compared to 46% for RF birds. Although LOW birds weighed less than HIGH birds at SM, abdominal fat pad weight and carcass lipid content did not differ. Mean carcass lipid weight was 740 g in AL birds compared to 370 g in RF birds at SM. The use of AL feeding accelerated the onset of lay (25 d from PS) compared to RF birds (39 d), and removed body size effects on the rate of sexual maturation. Initial BW affected timing of SM in RF birds, with LOW, STD, and HIGH birds reaching SM 51, 38, and 27 d after PS, respectively. As the carcass composition of these birds varied greatly at PS, improving BW and composition uniformity at PS would be beneficial for a more uniform onset of lay and reduced early production losses from small hens. Whereas thresholds for BW, carcass protein, or carcass lipid appeared to affect the onset of lay in RF birds, the rapid onset of production in their AL counterparts suggests that the actual internal signal for reproductive development is more likely a metabolic one.