Five experiments were conducted to investigate the effects of early feed restriction on body weights, feed conversion, organ weights, fat deposition, carcass and muscle composition, plasma lipids, lipogenesis, lipolysis, and muscle tissue DNA and RNA in broiler chickens. In Experiments 1 and 2, broiler chicks were reared in litter pens for 49 days, while Experiments 3,4, and 5 were conducted in battery cages for 28 days. Feed restriction in all experiments was induced by providing male broiler chicks with 40 kcal/bird/day for 7 (Experiments 1 and 2) or 6 (Experiments 3, 4, and 5) days, starting at 4 days of age. Feed restriction (40 kcal/bird/day) for broiler females in Experiment 1 was imposed from 4 to 9 days of age. Ad libitum feeding was resumed after the restriction periods and continued to the conclusion of each experiment. Broilers fed ad libitum for the entire experimental period were used as controls in each study. Broilers under early feed restriction had significantly (P s .05) lower mean body weights than ad libitum fed controls, for all ages measured. However, feed to gain ratios for restricted birds were Significantly lower at 28 (Experiments 1 through 4) and 49 (Experiments 1 and 2) days of age than for birds fed ad libitum. Total pen body weights for restricted and ad libitum fed groups were similar at 49 days of age in Experiments 1 and 2 which, reflected a significant reduction in the rate of mortality observed in the early restricted groups. Significantly higher levels of lipogenic activity, plasma triglycerides and lipoproteins (VLDL + LDL), and significantly larger abdominal fat pads were observed in restricted broilers than in ad libitum fed controls at 28 days of age (Experiment 4). No significant differences were found in organ weights, carcass composition, lipolysis, and muscle tissue DNA/RNA levels, and muscle composition between early restricted and unrestricted broilers. Results from these studies indicate that restricted broilers were not able to attain body weights comparable to ad libitum fed birds at 49 days of age. In contrast, early feed restriction resulted in consistently better feed efficiency in restricted birds when compared to controls. Furthermore, it appears that early feed restriction altered lipid metabolism early in life; however, organ weights, fat deposition, muscle composition, and carcass composition were only minimally affected by this procedure. / Ph. D.

The association between selection for body weight and immune responsiveness was studied in Japanese quail and White Plymouth Rock chicken populations. Quail populations consisted of a randombred control (C) line and a line selected for high (HW) 28-day body weight. The chicken populations used were lines selected for high (HW) and low (LW) 56-day body weight, reciprocal Fi crosses (HL and LH), and F2 crosses of the Fi (HLHL and LHLH). Kinetics of primary and secondary antibody response to SRBC antigen was examined in Line C quail (Experiment 1). At most times post-primary inoculation (PPI), antibody titers were highest for antigen concentration 2.5%. The presence of MER antibodies was very low PPI, but increased following reinjection. Primary antibody response was then compared between C line and HW line of quail (Experiment 2). Antigen concentration 2.5% once again resulted in the highest titers. Line HW quail were less able to maintain high antibody titer levels to SRBC antigen than the randombred control line from which they originated. Mode of inheritance for immune responsiveness in selected populations of chickens and crosses between them was examined (Experiment 3). Additive genetic variation was important in the inheritance of both primary and secondary responses to this antigen. Reciprocal differences and heterosis of the F₁ crosses were also factors in the inheritance of secondary response. Kinetics of primary and secondary responses were evaluated in the parental weight lines and in lines of White Leghorn chickens divergently selected for antibody response to SRBC antigen. At all times PPI, line HA chickens had the highest antibody titers, while those from line LA consistently had the lowest titers. Lines HW and LW reacted similarly to line LA early in response, but showed higher peak levels later on. In both primary and secondary responses, the weight lines peaked at similar levels. Thereafter, line LW maintained a high antibody titer level to SRBC antigen than line HW. / Master of Science