The objective of this research was to evaluate effects of female broiler breeder dietary ME and CP during rearing and dietary ME during early lay on broiler offspring performance and carcass yield dynamics. A factorial arrangement of treatments, with 2 ME levels, and 2 balanced protein levels from 3 to 24 wk, followed by 2 ME levels in the lay diets, and in the broilers, 2 sexes. A total of 1,635 broilers were housed in 32 pens, with 8 replicate pens according to maternal laying diet and sex. Maternal pullet diets were nested within pen (n = 9 to 14, depending on hatch rate). The broilers originated from 384 Ross 708 hens, which had been fed diets containing high (2,736 kcal/kg, HEREAR) or low ME (2,528 kcal/kg, LEREAR) combined with either high (15.3%, HPREAR) or low balanced protein (13.7% CP, LPREAR). Equal numbers of hens from each pullet treatment were then fed either a high (2,900 kcal/kg, HELAY) or low ME diet (2,800 kcal/kg, LELAY) containing 15% CP. Broilers were hatched from eggs collected at 28 wk of age, and fed identical diets. Broilers were individually weighed weekly. Serial dissections were conducted to evaluate yield breast muscle and abdominal fatpad dynamics. At 39 d, 180 broilers were processed to measure carcass yield. Female progeny of hens with the lowest CP intake during rearing (HEREAR × LPREAR) were lighter from 22 to 36 d of age than female offspring from hens that consumed more CP as pullets. We predicted the heaviest female progeny would result from an ME:CP ratio of 18.25 kcal/g in maternal pullet diets (P = 0.0063). Broiler breast yield increased when maternal EM:CP ratio increased after switching from pullet to laying diets. Hens fed HEREAR were fatter and had fatter progeny than LEREAR. Maternal diet, even during the pullet phase, influenced progeny growth and yield.
With increasing disparity between broiler breeder target weights and broiler growth potential, maintenance energy requirements have become a larger proportion of total broiler breeder energy intake. Because energy is partitioned to growth and egg production at a lower priority than maintenance, accurate prediction of maintenance energy requirements is important for practical broiler breeder feed allocation decisions. Environmental temperature affects the maintenance energy requirement by changing rate of heat loss to the environment. In the ME system, heat production (energy lost) is part of the maintenance requirement (ME). In the current study, a nonlinear mixed model was derived to predict ME partitioning of broiler breeder hens under varied temperature conditions. At 21 wk of age, 192 Ross 708 hens were individually caged within 6 controlled environmental chambers. From 25 to 41 wk, 4 temperature treatments (15°C, 19°C, 23°C, and 27°C) were randomly assigned to the chambers for 2-week periods. Half of the birds in each chamber were fed a high-energy (HE; 2,912 kcal/kg) diet, and half were fed a low-energy (LE; 2,790 kcal/kg) diet. The nonlinear mixed regression model included a normally distributed random term representing individual hen maintenance, a quadratic response to environmental temperature, and linear ADG and egg mass (EM) coefficients. The model assumed that energy requirements for BW gain and egg production were not influenced by environmental temperature because hens were homeothermic, and the cellular processes for associated biochemical processes occurred within a controlled narrow core body temperature range. Residual feed intake (RFI) and residual ME (RME) were used to estimate efficiency. A quadratic effect of environmental temperature on broiler breeder MEm was predicted ( < 0.0001), with a minimum energy expenditure at 24.3°C. Predicted ME at 21°C was 92.5 kcal/kg; requirements for gain and EM were 2.126 and 1.789 kcal/g, respectively ( < 0.0001). Birds fed the HE diet were more efficient, with a lower RME than birds on the LE diet (-0.63 vs. 0.63 kcal/kg), translating to ME of 135.2 and 136.5 kcal/kg, respectively. In the current experiment, optimal biological efficiency was predicted at 24.3°C in feed-restricted broiler breeders fed the HE diet.
Genetic selection programs in broiler stocks have contributed to changes in the responsiveness of the broiler breeder female to nutritional factors. A study was conducted to investigate the effect of photostimulation (PS) age on sexual maturity traits in current broiler breeder pullets. Seven hundred twenty Ross 308 pullets with full access to feed to 1 or 3 wk of age were divided among 8 environmental rooms to 16 wk of age. At this time, 128 pullets (64 per initial feeding treatment) were randomly assigned to individual cages in 8 rooms with 16 pullets per room. Pullets were PS at 17 (PS17), 19 (PS19), 21 (PS21), or 23 (PS23) wk of age by increasing the day length from 8L:16D to 16L:8D (multiple steps). Each hen was dissected on the morning after first oviposition (sexual maturity). Data were analyzed by 2-way ANOVA with additional analysis of covariance analysis done using sexual maturity on BW as a covariate. Sexual maturation occurred later with later PS ages. Rate of sexual maturation was accelerated at later PS ages, although age at PS did not affect variation in age at sexual maturity. Despite a 42 d difference in PS age between the PS17 and PS23 groups, only a 25 d difference existed in mean age at sexual maturity among these groups. Initial egg weight, breast muscle weight, frame size, and abdominal fat pad weight at sexual maturity increased in birds with later PS ages. Covariate analysis indicated that these effects were influenced primarily by increased age and BW at sexual maturity in later PS birds. Pullets PS at 17 wk of age had 11.0 large white ovarian follicles, compared with 14.9 in PS23 birds. Comparison to previous studies demonstrates that the years of genetic selection for growth traits have not changed the interval between PS and sexual maturation. Previous research published on this theme likely had a confounding effect of mean BW on estimates of variation at various PS ages. Photostimulating later presented advantages with regard to development of the reproductive tract; these effects were BW dependent.
Broiler breeder pullets are fully fed for several weeks to give chicks a vigorous start, to establish an adequate frame size, and to build increased flock BW uniformity. This study was designed to determine whether reducing the length of the initial ad libitum feeding period of pullets would be detrimental to subsequent fleshing, skeletal development, and BW variation. A total of 720 Ross 308 pullets were placed in 8 pens on the day of hatch and provided ad libitum access to feed at 1 wk (1WK) or 3 wk (3WK) of age, at which time a 5:2 restriction program began. Individual BW and external fleshing scores, and flock BW variation (CV and uniformity) were monitored. At 4, 8, 12, and 16 wk, 60 randomly selected birds per treatment were dissected for assessment of breast muscle, fatness, and reproductive development. At 3 wk of age, BW of the 3WK pullets (471 g) was greater than that of the 1WK pullets (312 g), and the daily rate of gain was double. Although feed allocation was decreased markedly at 3 wk in 3WK birds, by 4 wk they weighed 30% more, and had a greater frame size and proportion of breast muscle than the 1WK birds. At 8 wk of age, the 3WK birds were still heavier (973 g for 3WK vs. 899 g for 1WK). Most carcass measures were similar between treatments at 12 wk of age, by which time BW profiles were similar. At 16 wk of age, frame size and proportion of breast muscle were not different between groups. The BW variation did not differ through the initial 12 wk, but was superior at 14 and 16 wk of age in 1WK birds, possibly because of greater feed allocation between 8 to 16 wk, which is the most intense feed restriction period. The reduced feed intake of 3WK birds at the onset of feed restriction reduced their ME requirement for maintenance, likely contributing to this result. Increasing the length of the ad libitum feed access period after hatch altered growth and conformation traits to 8 wk of age and did not affect frame size or proportion of breast muscle, but increased BW variability late in the rearing period.
The objective of the current research was to evaluate transgenerational effects of maternal dietary energy and protein on growth, efficiency, and yield of broiler offspring. A factorial arrangement of treatments consisting of high and low ME and CP levels fed during the rearing and laying phases was used. The study was a final 2 × 2 × 2 × 2 factorial arrangement of treatments, including broiler sex. Ross 708 broiler breeder pullets (n = 933) were fed diets containing 2,736 (HE REAR ) or 2,528 kcal/kg ME (LE REAR ) with either 15.3% (HP REAR ) or 13.7% CP (LP REAR ). From 25 wk, dams were fed a 15% CP laying diet containing 2,900 (HE LAY ) or 2,800 kcal/kg ME (LE LAY ). Following artificial insemination of the dams at 35 wk, eggs were collected for 1 wk, incubated, and pedigree hatched to preserve maternal identity. Broiler offspring were placed sex-separately into 32 pens, according to laying phase maternal treatments, with rearing maternal treatments nested within pens. Individual BW and pen level feed intake were recorded weekly. Broilers were processed at 40 d of age to evaluate yield. Maternal diet effects on offspring BW were sex dependent and transient. Female LP REAR × LE LAY broilers had lower pectoralis major and carcass yield than HP REAR × LE LAY females. Male HP REAR × HE LAY broilers had increased breast yield (19.8%) compared with 18.4% in HP REAR × LE LAY broilers. Carcass yield was lower in LE REAR × HP REAR broilers (63.7%) compared with HE REAR × HP REAR broilers (64.9%). LE REAR × HP REAR dams had the lowest ME to CP ratio (E: P) diets and highest rearing phase CP intake. Maternal diet did not influence offspring FCR. The most consistent contributor to increased BW was higher maternal dietary CP and ME during rearing. Low ME maternal laying phase diets increased BW of male offspring more consistently than of female offspring. Maternal nutrition also influenced broiler yield, and is thus economically important. Energy and protein dilution in broiler breeder pullet diets may have detrimental effects on offspring performance.
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