Evolution of maternal feed restriction practices over 60 years of selection for broiler productivity.

The effect of commercial selection by poultry breeders on the growth, efficiency, and sexual maturity of broiler breeders was studied using 2 University of Alberta Meat Control strains unselected since 1957 and 1978 (AMC-1957 and AMC-1978, respectively) and 2 strains originating from the University of Arkansas; 1995 Random-bred (1995RB) and 2015 Random-bred (2015RB). A study with a 4 × 2 factorial arrangement was conducted with the 4 strains fed at either ad libitum, or restricted levels to achieve a current commercial breeder target BW profile. Growth rate, feed intake, feed efficiency, age at sexual maturity, carcass components, and body conformation were measured. To assess reproductive development, birds were assigned to 2 fates: dissected at photostimulation or dissected after the second oviposition. At 22.4 wk of age, the restricted-fed AMC-1957, AMC-1978, 1995RB, and 2015RB reached 100, 61, 46, and 38% of their ad libitum-fed counterparts' BW, respectively. During the rearing phase, the amount of feed needed to maintain restricted-fed birds on the target BW was 99.4, 57, 29.5, and 24.9% of their ad libitum-fed counterparts for AMC-1957, AMC-1978, 1995RB, and 2015RB, respectively. Feed restricted birds in the 2015RB had lower heat production relative to the AMC-1957 and AMC-1978, which shows that modern strains utilized feed more efficiently compared to the antique strains. This might be related to the increasing severity of feed restriction of broiler breeders over the past 60 years. Relative to AMC-1957 and AMC-1978 strains, the 1995RB and 2015RB strains had heavier breast muscle and lower fat pad weight. Although the pubertal threshold for age and BW have increased over the last 6 decades, changes in selection programs for feed efficiency have resulted in broiler breeders that prioritize nutrient allocation to growth and breast development rather than adipose storage. As a result, feed restricted modern broiler breeders may have marginally sufficient fat resources to support reproduction.

Broiler growth and efficiency in response to relaxed maternal feed restriction.

Broiler growth performance can be influenced by maternal BW, maternal age, and sex. The present study evaluated broiler growth and efficiency in response to increased maternal BW (relaxed level of maternal feed restriction). It was hypothesized that BW and fatness would increase, and efficiency would be reduced as maternal BW increased. Ten BW trajectories were applied to precision-fed Ross 708 female broiler breeders (n = 30) from 2 to 42 wk of age. Trajectories varied in prepubertal and pubertal growth phases from 2.5 to 22.5% above the recommended BW target. Additional unrestricted breeders (n = 6) were not limited to a maximum BW (fed ad libitum). Two 35 d experiments were conducted with precision-fed broilers from these breeders at 35 and 42 wk of age. Two analyses (full and restricted analysis scopes) were performed to evaluate broiler BW, feed conversion ratio (FCR) and carcass traits with maternal BW at photostimulation (22 wk of age) as a continuous effect, and maternal age and sex as discrete effects. The full scope included broilers from all hens (feed restricted and unrestricted). The restricted scope excluded broilers from unrestricted hens. Differences were reported at P ≤ 0.05. For every kilogram increase in maternal BW, cumulative FCR increased by 0.235 and 0.471 g:g for broilers from all and feed restricted hens, respectively. Proportional gut weight of broilers from feed restricted hens decreased by 0.8244% per kilogram increase in maternal BW. Males were heavier than females on day 28 and 35, and broilers from 42-wk-old breeders were heavier than broilers from 35-wk-old breeders on day 0 and 35. Males from all hens were more feed efficient (1.318 g:g) than females (1.335 g:g) from day 29 to 35. Females from all and feed restricted hens had a greater proportional fat pad and breast muscle weight than males, and proportional breast muscle yield of broilers from 42-wk-old breeders was on average 1.04 times greater than that of broilers from 35-wk-old breeders. Maternal BW did not affect offspring BW, reduced cumulative FCR, and reduced gut weight in the restricted analysis scope.

Feeding, feed-seeking behavior, and reproductive performance of broiler breeders under conditions of relaxed feed restriction.

Broiler breeders are feed restricted to optimize reproductive performance. A randomized controlled study was conducted to investigate the effect of increasing female broiler breeder BW on feeding, feed-seeking behavior, and reproductive performance. It was hypothesized that a greater BW would decrease feeding and feed-seeking behavior, and reduce reproductive performance. Ross 708 female broiler breeders (n = 36) were fed using a precision feeding system from 2 to 42 wk of age. Ten BW trajectories were created from a multiphasic Gompertz growth model that increased growth from 0 to 22.5% in the prepubertal and pubertal phases of growth, in 2.5% increments. Six unrestricted birds were not limited to a maximum BW. Body weight was evaluated as a 2-way ANOVA. Two linear regression analyses were conducted, one which included all birds and one which excluded the unrestricted birds. For the regression analyses, BW at photostimulation (22 wk of age) was used as the continuous independent variable to represent the degree of variation between trajectories. Differences were reported at P ≤ 0.05. Body weight increased as trajectory-specific BW targets increased from 6 to 28 wk of age. Differences of BW between BW trajectories decreased during the laying period, which was a result of individual bird variation within BW trajectories. Station visit frequency decreased per kilogram increase in BW for all birds during rearing and lay, and within feed-restricted birds during lay only. The number of meals and ADFI increased with age, which reflected nutrient intake to support maintenance, growth, and reproductive requirements. Mean egg weight (EW) of all birds increased by 0.72 g per kilogram increase in BW from 22 to 41 wk of age. From 22 to 29 wk of age, mean EW of feed-restricted birds increased by 2.78 g per kilogram increase in BW. For every kilogram increase in BW, age at first egg comparing all birds decreased by 10.83 d. Two unrestricted birds came into lay before photostimulation. In contrast with the hypotheses, BW increased up to 22.5% above the recommended target did not reduce feeding and feed seeking behavior, or negatively impact reproductive performance.

A model of pre-pubertal broiler breeder estradiol-17ß levels predicts advanced sexual maturation for birds with high body weight or short juvenile day-length exposure.

As broiler breeders face increased reproductive challenges specifically related to overfeeding, a clear understanding of the physiological effects of BW and rearing photoperiod on reproductive development is needed. The objective was to use mathematical models to compare plasma estradiol-17ß (E2) concentration to characterize the effect of BW and rearing photoperiod on E2 levels. A 2 × 3 factorial arrangement of treatments was used. Hens (n = 180) were fed with a precision feeding system to allocate feed individually to achieve the breeder-recommended BW curve (Standard) or to a BW curve reaching the 21 wk target at 18 wk (High). Hens were on 8L:16D, 10L:14D, or 12L:12D photoschedules during rearing and were photostimulated at 21 wk. Age at first egg (AFE) was recorded. Plasma E2 levels were determined weekly between week 20 and 28. Two modified Gompertz models described E2 level as a function of (a) chronological or (b) physiological (relative to AFE) age. Timing of E2-inflection point was compared between models and treatments. Differences were reported as significant at P ≤ 0.05. The chronological age model inferred that High BW reduced the duration between the E2-inflection point and AFE, whereas the physiological age model inferred that High BW only reduced the duration between photostimulation and the E2-inflection point. Hens on the Standard BW treatment had a longer period between photostimulation and the E2-inflection point compared to hens on the High-BW treatment (11.03 vs. 1.50 wk, respectively, based on physiological age). Hens on the 12L:12D photoschedule had a longer period between photostimulation and the E2-inflection point compared to hens on the 8L:16D or 10L:14D photoschedule, both in the Standard and High BW (28.91 vs. 1.78 and 2.40 wk, 2.65 vs. 0.93 and 0.94 wk, respectively, based on physiological age). The described methodology and results provide quantitative insight into E2 dynamics and serves as a model for future endocrinological studies in poultry reproduction.

Early photostimulation at the recommended body weight reduced broiler breeder performance.

To synchronize the onset of sexual maturity in the face of high BW variation, the age at photostimulation has been increasing in the broiler breeder industry. This experiment studied the effects of increased BW and earlier photostimulation on broiler breeder reproductive performance where within-treatment BW uniformity was very high. The experiment tested BW and age at photostimulation treatments in a 2 × 2 factorial arrangement. Hens (n = 120) were fed with a precision feeding system to allocate feed individually following the breeder-recommended target BW (Standard) or to a 22% heavier target BW curve reaching the Standard 21 wk BW at 18 wk (High). Hens were photostimulated at either 18 wk (18WK) or 21 wk (21WK) with a 16L:8D photoschedule. Age at first egg (AFE) and individual egg production to 55 wk were recorded. Differences were reported as significant if P ≤ 0.05. The AFE was decreased and maturation interval between photostimulation and AFE was shorter for hens on the High BW treatment compared to the Standard BW treatment (178.1 vs. 194.7 d and 41.8 vs. 58.2 d, respectively). Hens on the 21WK treatment had a decreased AFE compared to the 18WK treatment (177.0 d vs. 195.9 d) and their maturation interval was shorter (30.0 d vs. 69.9 d). The CV for AFE was higher in the 18WK treatment compared to the 21WK treatment (28.2% vs. 11.2%). Total egg production was higher for hens on the High BW treatment compared to the Standard BW treatment (129.4 vs. 92.8, respectively). Total egg production was higher for hens on the 21WK treatment compared to the 18WK treatment (138.4 vs. 83.8, respectively). Egg weight of Standard BW × 18WK hens was lower compared to High BW × 18WK hens. Current recommended breeder BW may be too low for optimal sexual maturation after photostimulation. It is concluded that even when BW variation is minimized, photostimulation at 18 wk of age is not recommended.

Effects of broiler breeder management on pullet body weight and carcass uniformity.

An experiment was conducted to study the effect of broiler breeder feeding management practices on pullet performance, BW uniformity, and carcass traits during rearing (to 22 wk of age). At 3 wk of age, 1,200 Ross 308 breeder pullets were assigned to one of 5 treatments: 1) control: standard mash diet, fed daily; 2) high fiber: mash diet containing 25% lower nutrient density, fed daily; 3) scatter: standard diet in pellet form scattered on litter, fed daily; 4) skip-a-day: standard mash diet, fed on alternate days; or 5) grading: standard mash diet, fed daily (birds sorted into low, average, and high BW groups every 4 wk). Birds on the high fiber treatment consumed more feed (P<0.0001) and had the highest feed conversion ratio (FCR; P<0.004) but the lowest ME to gain and CP to gain ratios (P≤0.002). Skip-a-day treatment pullets consumed more ME and CP than birds in any other treatment (P<0.001). Grading yielded the highest BW uniformity at 22 wk of age (CV=6.2%), while control and high fiber treatment groups were least uniform (CV>15%; P<0.0001). Skip-a-day feed restriction produced birds with the significantly lowest breast muscle and highest liver weight compared to all other treatments (P<0.05). Variation in shank length, chest width, and breast muscle was lowest in the grading treatment, whereas the CV for fat pad and liver was lowest in the skip-a-day treatment. In this trial, broiler breeder target BW profiles were achieved using combinations of quantitative and qualitative feed restriction, or preemptive management practices. Qualitative diet dilution and skip-a-day management did little to increase flock uniformity relative to the control during the most intense period of feed restriction (7 to 19 wk). Scatter feeding increased flock uniformity to a small degree, whereas grading yielded the highest increase in BW and carcass trait uniformity.

Growth, efficiency, and yield of commercial broilers from 1957, 1978, and 2005.

The effect of commercial selection on the growth, efficiency, and yield of broilers was studied using 2 University of Alberta Meat Control strains unselected since 1957 and 1978, and a commercial Ross 308 strain (2005). Mixed-sex chicks (n = 180 per strain) were placed into 4 replicate pens per strain, and grown on a current nutritional program to 56 d of age. Weekly front and side profile photographs of 8 birds per strain were collected. Growth rate, feed intake, and measures of feed efficiency including feed conversion ratio, residual feed intake, and residual maintenance energy requirements were characterized. A nonlinear mixed Gompertz growth model was used to predict BW and BW variation, useful for subsequent stochastic growth simulation. Dissections were conducted on 8 birds per strain semiweekly from 21 to 56 d of age to characterize allometric growth of pectoralis muscles, leg meat, abdominal fat pad, liver, gut, and heart. A novel nonlinear analysis of covariance was used to test the hypothesis that allometric growth patterns have changed as a result of commercial selection pressure. From 1957 to 2005, broiler growth increased by over 400%, with a concurrent 50% reduction in feed conversion ratio, corresponding to a compound annual rate of increase in 42 d live BW of 3.30%. Forty-two-day FCR decreased by 2.55% each year over the same 48-yr period. Pectoralis major growth potential increased, whereas abdominal fat decreased due to genetic selection pressure over the same time period. From 1957 to 2005, pectoralis minor yield at 42 d of age was 30% higher in males and 37% higher in females; pectoralis major yield increased by 79% in males and 85% in females. Over almost 50 yr of commercial quantitative genetic selection pressure, intended beneficial changes have been achieved. Unintended changes such as enhanced sexual dimorphism are likely inconsequential, though musculoskeletal, immune function, and parent stock management challenges may require additional attention in future selection programs.

Effects of maternal energy efficiency on broiler chicken growth, feed conversion, residual feed intake, and residual maintenance metabolizable energy requirements.

This study investigated the effect of maternal energy efficiency on broiler chicken growth and energy efficiency from 7 to 40 d of age. Residual feed intake (RFI) and residual maintenance ME requirement (RME) were used to measure energetic efficiency. Residual feed intake was defined as the difference between observed and predicted ME intake, and RME(m) as the difference between observed and predicted maintenance ME requirements. A total of 144 Ross-708 broiler breeder pullets were placed in individual laying cages at 16 wk of age. Hens with the greatest RFI (n = 32) and lowest RFI (n = 32) values from 20 to 56 wk of age were selected (maternal RFI; RFI(mat)). Selected hens were retrospectively assigned to a high- or low-RME(m) category (maternal RME(m); RME(mmat)). At 59 wk, eggs were collected for 8 d and pedigree hatched. A total of 338 broilers grouped by dam and sex were raised in 128 cages where feed intake, BW, and temperature were recorded from 7 to 40 d to calculate broiler feed conversion ratios, RFI, and RME(m). The design was a 2 × 2 × 2 factorial with 2 levels of RFI(mat), 2 levels of RME(mmat), and 2 sexes. Neither the RFI(mat) nor RME(mmat) category affected broiler offpring BW or total conversion ratio. The high-RFI(mat) × low-RME(mmat) broilers had decreased growth to 40 d. Low-RFI(mat) × low-RME(mmat) broilers had a lower RME(m) (-5.93 kcal of ME/kg(0.60) per day) and RFI (-0.86 kcal of ME/d) than high-RFI(mat) × low-RME(mmat) broilers (RME(m) = 1.70 kcal of ME/kg(0.60) per day; RFI = 0.38 kcal of ME/d). Overall, hens with low maintenance requirements (low RME(m)) produced more efficient broilers when other efficiency related traits, represented in a lower RFI, were present. Exclusion of high-RFI × low-RME(m) hens from selection programs may improve energy efficiency at the broiler level. The RME(m) methodology is a viable alternative to evaluate energy efficiency in broilers because it avoids confounding environmental effects and allows measurement standardization.

A data envelope analysis to assess factors affecting technical and economic efficiency of individual broiler breeder hens.

This study evaluated the effect of feed allocation and energetic efficiency on technical and economic efficiency of broiler breeder hens using the data envelope analysis methodology and quantified the effect of variables affecting technical efficiency. A total of 288 Ross 708 pullets were placed in individual cages at 16 wk of age and assigned to 1 of 4 feed allocation groups. Three of them had feed allocated on a group basis with divergent BW targets: standard, high (standard x 1.1), and low (standard x 0.9). The fourth group had feed allocated on an individual bird basis following the standard BW target. Birds were classified in 3 energetic efficiency categories: low, average, and high, based on estimated maintenance requirements. Technical efficiency considered saleable chicks as output and cumulative ME intake and time as inputs. Economic efficiency of feed allocation treatments was analyzed under different cost scenarios. Birds with low feed allocation exhibited a lower technical efficiency (69.4%) than standard (72.1%), which reflected a reduced egg production rate. Feed allocation of the high treatment could have been reduced by 10% with the same chick production as the standard treatment. The low treatment exhibited reduced economic efficiency at greater capital costs, whereas high had reduced economic efficiency at greater feed costs. The average energetic efficiency hens had a lower technical efficiency in the low compared with the standard feed allocation. A 1% increment in estimated maintenance requirement changed technical efficiency by -0.23%, whereas a 1% increment in ME intake had a -0.47% effect. The negative relationship between technical efficiency and ME intake was counterbalanced by a positive correlation of ME intake and egg production. The negative relationship of technical efficiency and maintenance requirements was synergized by a negative correlation of hen maintenance and egg production. Economic efficiency methodologies are effective tools to assess the economic effect of selection and flock management programs because biological, allocative, and economic factors can be independently analyzed.

Nonlinear mixed models to study metabolizable energy utilization in broiler breeder hens.

This study developed mathematical models to overcome limitations of linear models of energy partitioning in hens. The fit of 1 linear and 2 nonlinear models of ME intake (MEI) were compared, using empirical data of 288 caged broiler breeder hens from 20 to 60 wk of age. Pullets were individually caged at 16 wk and assigned to 1 of 4 feed allocation groups. Three groups had feed allocated on a group basis with divergent target BW: standard (STD), HIGH (STD x 1.1), and LOW (STD x 0.9). The fourth group had individual-based feed allocation (IND) and followed the STD BW target. The linear model expressed MEI as a function of BW(0.75), ADG, egg mass (EM), and temperature. Nonlinear mixed models employed a normally distributed term associated with hen metabolic BW, and exponential terms of ADG and EM, or Cobb-Douglas form interactions between terms. Fit was evaluated with the Bayesian information criterion and systematic bias was analyzed through linear regressions of observed versus expected values. The linear model estimated energy partitioned to maintenance and retention in the range of reported values in the literature. However, this model had the poorest fit (R(2) = 0.64) and exhibited a slope bias of 0.91 (i.e., MEI was overestimated at low values and underestimated at high values). The first nonlinear mixed model indicated that MEI partitioned to ADG was a factor of ADG(1.15), whereas the ME partitioned to EM was a factor of EM(1.12). This model had improved fit (R(2) = 0.71) relative to the linear model. The second nonlinear mixed model indicated that the energy requirement for ADG increased by 0.60% and the EM energy requirement decreased by 2.07% for each 1% increment in BW. This model further improved fit (R(2) = 0.75). Nonlinear mixed models reduced estimation bias by accounting for individual variation in maintenance energy expenditure. These nonlinear mixed models may be used to analyze energy partitioning in animals, to develop prediction equations of MEI, to evaluate individual efficiency for maintenance, and to assess diets regarding the slope of bias in coefficients of maintenance energy requirements.

Characterization of energetic efficiency in adult broiler breeder hens.

This trial characterized residual feed intake (RFI) and residual maintenance requirement (RME(m)) as measures of energetic efficiency in broiler breeder hens. The RFI was defined as the difference between observed and expected ME intake and RME(m) as the difference between observed and expected maintenance requirements. A total of 600 Ross 708 1-d-old pullets were placed in floor pens. At 16 wk, 144 hens were caged and randomly assigned to 1 of 2 feed allocation treatments (72 birds each). The control treatment had feed allocated on a group basis (GRP) following the standard BW target. A second treatment had feed allocated on an individual-bird basis (IND) and followed the same BW target as GRP. Sexual maturity age, egg and chick production, and several feed conversion ratios were correlated to standardized efficiency indices of RFI (SRFI) and RME(m) (SRME(m)) in each treatment. Greater SRFI and SRME(m) values described a greater energetic efficiency. Residual feed intake was more variable in IND than GRP hens (P < 0.001). The variability of RME(m) did not differ between treatments (P = 0.14). The SRFI was positively correlated to egg production in the GRP hens (r = 0.31), but negatively correlated in IND hens (r = -0.40) and was correlated to feed conversion per chick only in the GRP-based feed allocation (r = -0.44). The SRME(m) correlated strongly to egg production (r = 0.64), chick production (r = 0.64), and feed conversion per chick (r = -0.59) in both feed allocation treatments. Feed intake confounded the RFI calculation, which limits the value of RFI as a selection criterion in meat-producing animals. The independence of RME(m) from feed intake is desirable for energetic efficiency assessment in selection programs because consistent values can be obtained across different management schemes. Hens with lower maintenance requirements (greater RME(m) efficiency) partitioned more energy toward reproduction than did high-maintenance hens. The RME(m) methodology provided an unbiased estimate of energetic efficiency by adjusting the maintenance requirement for the effect of dietary thermogenesis.

Effects of nutrient density and age at photostimulation on carcass traits and reproductive efficiency in fast- and slow-feathering turkey hens.

This study was conducted to compare BW gain, carcass composition, and reproductive fitness in fast- and slow-feathering turkey females between 29 and 56 wk of age. A total of 452 Hybrid standard fast-feathering (FF) and experimental slow-feathering (SF) hens (226/group) were fed either a control or a high-energy, high-protein diet. Birds were photostimulated at 29 or 31 wk. Data on BW and carcass characteristics (keel and shank, keel, breast muscle, fatpad, liver, ovary, and oviduct weight) and egg production were assessed. At photostimulation, FF birds had an increased shank length (2.6%) compared with SF birds. After photostimulation, FF birds were heavier than SF birds by 7.8%. Fast-feathering hens had greater ovary weight (49%), oviduct weight (52%), keel length (2.8%), and had one more large yellow follicle at the end of lay. The number of large yellow follicles was greater in birds photostimulated at 31 wk (8.3) compared with birds photostimulated 2 wk earlier (7.8). Absolute ovary weight and oviduct weight were increased by 21 and 18%, respectively, in birds photostimulated at 31 wk compared with 29 wk. These effects of delayed photo-stimulation were greater in SF birds. Ultimately, FF hens had a greater total hen-housed egg production (55 vs. 33%), peak egg production (76 vs. 68%), and laying sequence length (5.7 vs. 3.3 d). Although delaying photostimulation did not affect total egg production, it did reduce the number of double-yolked eggs. Nutrient density had minimal effects on production in this trial. These data indicate that despite having similar BW, fleshing, and conformation traits to FF birds, the SF strain had inferior reproductive efficiency traits. This problem will need to be remedied before an SF turkey strain can become commercially viable.

Reproductive efficiency and metabolism of female broiler breeders as affected by genotype, feed allocation, and age at photostimulation. 1. Pullet growth and development.

A 3 x 4 x 2 factorial design was carried out to determine the effect of 3 broiler breeder strains, 4 target BW profiles, and 2 photostimulation ages on pullet growth and development. A total of 560 pullets from each strain (Hubbard Hi-Y, Ross 508, and Ross 708) were reared on BW profiles that separated at 4 wk and converged at 32 wk of age as follows: standard (mean target BW profile of the 3 strains used), 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 wk (22WK). During the prephotostimulation phase (2 to 18 wk of age), 4 birds were killed for each of the 12 interactions at 14-d intervals to characterize changes in carcass traits. After 18 wk (wk 20, 22, and 24), 4 birds from each of the 24 interactions were killed and dissected (n = 768). Growth rate restricted frame size (e.g., 18-wk shank length: low = 101.8; standard = 105.6; moderate = 109.5; and high = 112.3 mm). At 24 wk of age, the 22WK birds had similar amounts of breast muscle compared with 18WK birds, whereas the later photostimulated hens had heavier abdominal fat pads. Early photo-stimulation resulted in increased 24-wk liver weights in all strains, but the difference was greatest in Ross 708 birds. The 22-wk ovary weight was influenced by age at photostimulation in high (18WK = 17.3; 22WK = 1.6 g) and moderate (18WK = 14.1; 22WK = 1.1 g) birds. The more extensive feed restriction of LOW birds before 12 wk of age appeared to limit breast muscle and fat pad growth and slow reproductive tract development following photostimulation. Pullets on heavier BW profiles respond to early PS by developing the reproductive system at the expense of breast muscle and fat pad growth. Genetic strain modulates some of the effect of very different target BW profiles.

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.

Reproductive efficiency and metabolism of female broiler breeders as affected by genotype, feed allocation, and age at photostimulation. 3. Reproductive efficiency.

A 3 x 4 x 2 factorial trial was performed to test the effect of 3 broiler breeder strains, 4 target BW profiles, and 2 photostimulation ages on egg and chick production. Hubbard Hi-Y, Ross 508, and Ross 708 pullets were reared on BW profiles that separated at 4 wk and converged at 32 wk: standard (approximate mean target BW profile of the 3 strains used), 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 wk (22WK). Twelve birds per interaction (n = 288) were individually caged at 17 wk and monitored for egg and chick production to 58 wk of age. The low BW profile delayed onset of lay, particularly in 18WK hens. Low and standard birds had a greater initial egg weight than moderate birds. The 18WK photostimulation age resulted in production of 31 small eggs (<52 g) compared with 15 in 22-wk birds. A settable (52 g) egg weight was reached earliest by standard birds (187 d of age). Average prime sequence length was reduced by 7.0 eggs in moderate and high birds compared with other profiles. The 18WK hens laid 9 more eggs (174) than 22WK birds, with no effect on unsettable eggs. The 22WK birds laid 7 more settable eggs due to increased early egg size. Total egg output was similar among BW profile treatments, although Ross 708-high hens under-performed compared with the other 708 profiles. The Ross 508-high birds laid the same number of eggs as Ross 508-standard birds (mean = 178.7). Feeding profiles affected egg production traits differently among strains. Feed intake had more effect on egg size and early production traits than BW profile or BW.

Relationships among egg characteristics, chick measurements, and early growth traits in ten broiler breeder strains.

This study evaluated egg traits, yolk utilization, chick conformation, and early growth rate in 10 broiler breeder strains. The strains included pure-, specialized- and commercial-line products. The 210 eggs/strain were weighed and randomly designated to 1 of 3 experimental determinations: 8 eggs for measurement of eggshell conductance, 52 eggs for determination of egg characteristics, and 150 eggs for incubation and chick traits. Egg characteristics included egg weight, specific gravity, yolk weight, albumen weight, albumen height, eggshell weight, and eggshell thickness. Chick traits included navel condition, hock color, chick length, shank length, and abdomen score by manual palpation. At hatch, half the birds per strain were dissected to assess the weight of the yolk sac, heart, liver, and breast muscle. The remaining chicks were randomly distributed into 4 rearing pens for a 14-d assessment of growth rate. There was a 3-g range in egg weight among the strains. Eggs from a pure line had the greatest amount of yolk (22.6 g), with yolk weight ranging to a low of 20.9 g in 2 other strains. The male line strain and 2 female line strains had the highest hatching weights (46.3, 46.5, and 45.4 g, respectively), whereas a commercial strain had the lowest hatching weight (43.1 g). Egg size affected chick weight more than did yolk size. The residual yolk mass at hatch ranged from 5.50 g (in the male line) to 3.70 g in the commercial strains. Residual yolk mass accounted for approximately 10 to 14% of chick BW at hatch. The abdominal palpation score correlated with actual hatch residual yolk weight (r = 0.50; P < 0.0001). At hatch, differences in breast muscle and internal organ weight were present. Shank length at hatch correlated more strongly with 14-d BW (r = 0.39; P < 0.0001) than did hatch weight and 14-d BW (r = 0.35; P < 0.0001). The results of this trial demonstrated significant strain variation in internal organ weight, residual yolk sac mass, and chick carcass reserves, which, when added together, resulted in observable differences in chick weights across strains.

Relationship between chick conformation and quality measures with early growth traits in males of eight selected pure or commercial broiler breeder strains.

Current commercial broiler products are derived from the crosses of various strains at the primary breeder level. This study investigated chick development, yolk utilization, and early growth rate of males from 8 broiler breeder strains. These strains were a combination of both specialized and commercial-line products. At hatch, 110 male chicks per strain were weighed and wing-banded, and chick quality was assessed. Traits included navel condition, hock color, chick length, shank length, and abdomen score by abdominal palpation (to evaluate residual yolk content on live chicks). At hatch, 50 chicks per strain were dissected to assess breast muscling and residual yolk weight. At 2 wk of age, 50 chicks per strain were dissected to characterize changes in weight, conformation, fleshing, and residual yolk content. Chick weight at hatch varied from 40.8 g in a heavily growth-selected line to a low of 36.9 g in a commercial strain. The mass of residual yolk at hatch ranged from 0.8 to 10.6 g across all chicks dissected at hatch. A heavily breast-selected pure-line strain had 5.8 g of residual yolk in contrast to the commercial strain that had only 3.0 g. Although there were no significant strain differences in abdomen score, this score correlated with dissected residual yolk weight (r = 0.50). Shank length and chick body length at hatch correlated more strongly with BW on d 14 than did hatch weight. This information stresses the importance of evaluating several characteristics at hatch to better quantify early chick quality.

Investigating the eggshell conductance and embryonic metabolism of modern and unselected domestic avian genetic strains at two flock ages.

The objective of this study was to determine if broiler strain and breeder flock age affect eggshell conductance, fertility, and hatchability parameters; heart and hepatic glycogen concentrations at hatch; and embryonic metabolism throughout incubation. The 3 broiler strains investigated were HBY, a modern commercial broiler strain selected for high breast yield; WBM, a modern commercial broiler strain selected for the whole bird market; and UN78, a female broiler parent strain unselected since 1978. Fertility and hatchability parameters for each of the 3 strains were determined when the flocks were 32, 34, 37, and 38 wk of age. Eggshell conductance was measured on separate eggs produced from flocks at 37, 45, and 53 wk of age. Concurrently, fertile hatching eggs from the 3 broiler strains at 2 flock ages (33 and 38 wk) were incubated in individual metabolic chambers. Total daily CO2 production of each embryo was measured. Strain and flock age did not influence any of the fertility or hatchability parameters. Strain had no effect on conductance, but eggs from the 37-wk-old flocks had higher conductance than eggs from the 45- or 53-wk-old flocks, which did not differ from one another. Strain had no significant effect on average total CO2 production over the entire 21.5 d of incubation. However, embryos from the 38-wk-old flock produced more total CO2 than did embryos from the 33-wk-old flocks. Also, there was an interaction between strain and flock age for total CO2 production; UN78 embryos from the 33-wk flocks had higher CO2 production than WBM embryos, and the CO2 production of HBY did not differ from either strain. When embryos from the 38-wk flocks were compared, WBM embryos had higher CO2 production than did UN78 embryos, and HBY embryos did not differ from either strain. The data showed that in the 3 strains examined in this study, genetic differences in embryonic metabolic rate were dependent upon breeder flock age.

Effects of nutrient density on growth and carcass traits in fast- and slow-feathering female turkeys.

Chickens have been sexed based on feather development at hatching for many years, but the slow-feathering gene has only recently been incorporated into a commercial line of turkeys. Female turkeys of a fast- and a slow-feathering strain were compared with regard to BW, gain, and carcass composition to 29 wk of age. A total of 432 fast-feathering (FF) and 432 slow-feathering (SF) poults were reared to 198 d on a control (CON) or a high-energy, high-protein (HIGH) diet. Data concerning BW and carcass characteristics (thoracic circumference and width, shank, keel, breast muscle, fat pad, and liver), feather scores, and breast muscle morphology were assessed over the course of the trial. Strain did not affect BW of the CON-fed birds until after 112 d, when FF birds were 3.1% heavier than SF birds. From 11 to 112 d, feeding the HIGH diet increased BW of SF birds significantly compared with birds fed the CON diet. From 170 to 198 d, FF birds were approximately 0.8 kg heavier than SF birds. At 42 and 84 d in FF birds, and at 84 d in SF birds, increased diet density increased measures of frame size and decreased liver weight. Breast muscle weight, area, and thickness were greater in SF than in FF birds at 42 and 84 d. Increased nutrient density increased feather score in SF birds at 32 (9.8%) and 56 d (7.1%).