The food production system needs to be sustainable including poultry sector to feed the increasing global population. An accepted economical and environmental approach of broiler production is to produce larger broilers faster while using less feed. Broiler production is aimed at producing consumable meat and meat products. The global broiler meat market has evolved over the years with increasing selection pressure shifted toward attaining yield characteristics for increased cut-up parts such as breast and thighs. There is a shift toward a big bird market in the U.S. with approximately 70% of the broiler meat produced from large birds (>2.72 kg). Genetic selection of broilers for quantitative traits such as growth rate and lean muscle mass without increasing the fat mass has altered broiler physiological homeostasis to adapt toward the larger rates of muscle protein turnover. Physiological stresses created due to selection pressures in broilers have produced several muscle myopathies including an emerging one called woody breast myopathy. The sustainable broiler production practice may require humane consideration of raising broilers in less stressful grow-out regimes that will have minimal impact on broiler metabolic health. Another sustainability approach of broiler production toward feed efficiency lies on understanding dietary formulation approach of amino acids and energy that promote optimal nutrient utilization and minimal nutrient output to environment while also fulfilling the growth demands and body composition changes associated with increased protein gain in current meat broilers brought by the genetic progress.

Developmental hormonal changes in Cobb 500 chick embryos and hatched chicks were determined by measuring plasma insulin, glucagon, insulin-like growth factor (IGF)-I, IGF-II, triiodothyronine, thyroxine, and glucose concentrations at different ages of embryogenesis and posthatch development. Plasma samples were obtained daily from 10 d of embryogenesis (10E) through 13 d posthatch and also at 17 and 21 d posthatch. A significant increase in plasma insulin was observed with increasing age from 10E to hatch. Plasma glucagon levels remained low until 17E, and then significantly increased approximately 3-fold at hatch, which corresponded with increasing plasma glucose levels during late embryo development. The plasma insulin to glucagon molar ratio of incubation from 14E to 17E ranged from 2 to 4, and was significantly higher than at any other time during incubation. These results indicate that insulin may be an important promoter of chick embryonic growth by the anabolic drive to promote protein deposition. Insulin and glucagon increased after hatch, which may be due to increased feed consumption and increased utilization of carbohydrates as the key energy source, compared with nutrients obtained through lipolysis and proteolysis in the embryos. Plasma triiodothyronine increased 4-fold from 18E to 20E, and thyroxine increased 3-fold from 16E to 19E. Insulin-like growth factor-I and IGF-II peaked at 14E. Insulin-like growth factor-I steadily increased above embryonic levels during the 3 wk of the posthatch period, whereas IGF-II levels steadily declined. These results suggest that IGF-II may be a more important functionary for chick embryonic development than IGF-I, and that IGF-I may be more important than IGF-II after hatch. The profile of metabolic hormones in the present study may help support an understanding of significant changes that occur in embryonic development and posthatch growth in chicks.

Background: In recent years, there has been a growing body of evidence indicating that replacing cholecalciferol (vitamin D3) with 25-hydroxycholecalc

Three hundred twenty Cobb 500 broiler breeder pullets at 21 wk of age were selected from a flock fed according to Cobb Breeder Management Guide specifications. One hundred sixty pullets at 21 wk of age were switched to ad libitum feeding, and the remaining 160 pullets continued to be control-fed. The pullets were photostimulated at 22 wk and maintained until 36.5 wk. Plasma samples were obtained, BW was determined, and hens were killed for determination of body composition at the following periods: 24 h prior to photostimulation, 2.5 wk after photostimulation, 24 h after first egg, and 36.5 wk following peak egg production. Compared with ad libitum-fed breeders, the restricted breeders had a higher percentage carcass protein and lower percentage carcass fat at all sampling periods. Total egg numbers were greater, and abnormal eggs were less for the restricted pullets compared with the ad libitum-fed pullets at 36.5 wk. Carcass percentage fat of ad libitum-fed pullets was positively related to plasma glucagon, insulin-like growth factor-II (IGF-II), and 17β-estradiol but negatively related to plasma insulin, insulin/glucagon M ratio, insulin-like growth factor-I (IGF-I), thyroxine (T₄), and triiodothyronine (T₃). Carcass percentage fat of feed-restricted pullets was negatively related to IGF-I, IGF-II, and T₄. The T₄ was the most important hormone for predicting the percentage carcass fat in ad libitum-fed pullets, and IGF-I was the most important hormone for predicting the percentage carcass fat in feed-restricted pullets. The percentage carcass protein for ad libitum-fed breeders was positively correlated to IGF-I, T₄, T₃, insulin/glucagon M ratio, and insulin. Carcass percentage protein for feed-restricted breeders was positively correlated to IGF-I, IGF-II, T₄, and glucagon. Stepwise regressions for predicting percentage carcass protein for breeders fed by both systems shows that T³ and IGF-I concentrations were the most important for ad libitum-fed breeders, whereas IGF-II and T₄ were best for feed-restricted breeders. The hormone status of breeders may be a key indicator to help predict the body composition and thus support management decisions for maintaining optimum production.

Two experiments were conducted to determine the effect of feed restriction programs on breeder reproductive performance. In experiment 1, every day (ED), skip-a-day (SK), 4-3, and 5-2 programs were compared. Diets did not differ, and feed intake was identical in all groups. Four hundred twenty pullets were reared on each program. At 21 wk, 80 breeders from each program were individually housed to record performance parameters. Body weight and frame size were larger in ED pullets than SK, 4-3, or 5-2 despite equal intakes. Hens fed ED reached sexual maturity at a younger age than other groups. Hens fed ED also produced more total and settable eggs than SK hens. Egg weight was heavier in 5-2 hens than in ED with 4-3 and SK intermediate. Efficiency of feed utilization was best in ED hens. In experiment 2 the same programs were tested, but pullets were reared to reach equal BW. One hundred seventy-five pullets were reared on each program, of which 60 were housed. Feed intake was greater for SK, 4-3, and 5-2 than ED pullets to reach the same BW. Frame size did not differ, indicating that BW was the cause of differences in experiment 1. In experiment 2, differences in performance were attenuated but not eliminated by feeding to reach equal BW, suggesting that metabolic factors aside from BW are altered by feeding programs. The 5-2 produced larger eggs than ED with the trend among programs being identical to that in experiment 1. These results suggest that metabolic changes such as increased lipogenesis or alterations in body composition may result in larger eggs in feeding programs that include off-feed days. Mortality, fertility, and hatchability were not affected by feeding programs in either experiment. Body composition analysis indicated the importance of total lean protein mass as a threshold for the onset of sexual maturity. Programs like SK are less efficient than ED and may result in reduced performance.

Digestibility coefficients of nutrients, metabolizable energy (ME), net energy (NE) and the ratio of NE to ME (NE/ME) of 20 diets were measured in br