Body composition and other physical parameters as determinants of age at sexual maturity and performance efficiency in dwarf hens divergently selected for body weight

Glucose Tolerance and Plasma Non-Esterified Fatty Acid Levels in Chickens Selected for Low Body Weight, Red Junglefowl, and their Reciprocal Cross

Responses of an individual to food deprivation, such as a 16-h fast, are complex, and are influenced by environmental and genetic factors. Domestication is an ongoing process during which adaptations to changing environments occur over generations. Food deprivation by their caretakers is less for domestic chickens than for their junglefowl ancestors. Unlike domestic chicken, the junglefowl adapted over generations to periods of food deprivation, which may be reflected in differences in metabolic responses to brief periods without food. Here, we compared the blood glucose and plasma levels of non-esterified fatty acids (NEFA) among four populations when deprived of feed for 16 h. The four populations included a domestic White Rock experimental line (LWS) maintained for generations under ad libitum feeding, adult red junglefowl (RJF), and a reciprocal cross of the lines. Although there were significant differences in adult (31-week) body weight between the RJF (683 g) and LWS (1282 g), with the weight of F₁ crosses being intermediate, the amount of abdominal fat relative to body weight was similar for all populations. Patterns for blood glucose responses to a glucose bolus after a 16-h fast were similar for the initial and final points in the parental and cross populations. However, RJF reached their peak faster than LWS, with the reciprocal cross intermediate to the parental populations. Plasma NEFA concentrations were higher after the 16-h fast than in fed states, with no population differences for the fasting state. However, in the fed state, NEFA levels were lesser for LWS than for others, which was reflected further in percentage change from fed to fasted. This larger change in LWS suggests differences in mobilization of energy substrates and implies that during domestication or development of the LWS line, thresholds for responses to acute stressors may have increased.

Examination of the physical characteristics in a diverse group of dwarf White Leghorn pullets before and after first oviposition

The purpose of the present experiment was to measure changes in physical variables with sexual maturity (SM), the oviposition of first egg, in sex-linked dwarf pullets when SM was delayed by the photoschedule. Offspring were produced from matings of dwarf Single Comb White Leghorn chickens divergently selected for high (H) or low (L) 20-wk BW. At 15 wk of age, pullets from half-sibling sets were randomly assigned to a diet either of low energy (LE: 2,500 kcal/kg of ME, 15% CP) or high energy (HE: 3,000 kcal/kg of ME, 15% CP) and were placed in cages. When a pullet reached SM, the mature (M) pullet and an immature (I, absence of oviposition), half-sibling pullet on the same diet were sampled for BW as well as for the weights of abdominal fat, liver, ovary, oviduct, whole egg (M pullets), yolk, and shell and for the number of rapidly developing follicles. Proximate measurements (wet weight) were made for defeathered carcasses and livers as well as for ovaries and oviducts. There were significant (P less than or equal to .01) line effects for BW at SM (H greater than L); age at SM (L greater than H); weights for the liver, abdominal fat, egg, albumen, shell (H greater than L), and yolk (L greater than H); number of developing follicles (H greater than L); percentage of carcass protein (L greater than H) and of fat (H greater than L); as well as for liver protein (L greater than H), fat (H greater than L), and ash (L greater than H). There were significant (P less than .01) diet effects for abdominal fat (HE greater than LE) and shell weight (LE greater than HE). There was a line-by-diet interaction for total feed intake and for total energy intake from 15 wk to oviposition of the first egg. There were significant (P less than .01) SM effects (M greater than I) for BW at SM, number of developing follicles, oviduct weight, and fat content of the reproductive organs; also, reproductive organ weights accounted for differences in BW at SM. There was an interaction for line by maturity state; the L pullets showed a greater increase in ovarian weight with oviposition of the first egg than did the H pullets. The results of this study indicated that the threshold requirements for BW, composition, or both, for SM may have been exceeded in Leghorn-type chickens when photoscheduling was used to delay the onset of SM.

Egg production efficiency in dwarf lines selected for high and low body weight as influenced by feed restriction

Hens from dwarf Single Comb White Leghorn lines selected for four generations for high (H) and low (L) body weight (BW) plus randombred controls (C), sixty birds per line, were placed in cages at 18 wk of age and randomly assigned to either a full-fed (FF) or restricted-fed (R) (10 percent less than FF group) treatment. Birds received a layer ration having 16% protein and 2,816 kcal/kg metabolizable energy. Water was provided ad libitum. Individual BW and egg weights (EW) were obtained, and daily feed intake (DFI), egg production (EP), performance efficiency (PE) [egg mass (EM) per BW], and feed efficiency (FE) [EM/DFI] were calculated for 28-day periods from 18 to 41 wk of age. There were significant line, treatment, and age effects and line by age interactions for BW, EW, EM, DFI, and PE; FE was significantly influenced by age. There were significant treatment by age interactions for BW, DFI, and FE. Feed intake, BW, and EW were greatest for FFH hens and increased in all lines with age. Maximum EM occurred during 30 to 33 wk for RH and RL hens, during 34 to 37 wk for FFH, and during 38 to 41 wk for FFL. Maximum PE occurred during peak EP. Maximum FE for FFH and FFL occurred during 26 to 29 wk and during 30 to 33 wk for RH and RL. Data for C hens were intermediate to the other lines. Feed efficiency was improved by restriction for L hens from 26 to 33 wk and for H hens from 26 to 33 wk and for H hens from 26 to 41 wk of age.

Selection for body weight at eight weeks of age. 19. Influences of heterozygosity and dwarfism on early egg production and associated traits

Body weight, body components, and reproductive traits were compared during the first 60 days after onset of lay in pullets from lines of White Plymouth Rocks selected for high or low juvenile body weight, their reciprocal F1 crosses, an F2 cross, and dwarfs from the parental lines. Absolute and relative body weight gains were less for dwarf than for nondwarf pullets in the high weight line. In the low weight line, there were differences in absolute but not relative weight gains. Among nondwarfs, both relative and absolute changes in body weight during the first 60 days of lay were similar for crosses and the high weight parental line, and considerably less for the low weight parental line. Numbers of ovulation were the same for the crosses and the high weight parental line, however, more normal eggs were produced by F1 crosses than either parental line. Rate of production was influenced mainly by variation in body weight at onset of lay in the high weight nondwarfs and low weight dwarfs, and by age at first egg in low weight nondwarf pullets. None of the independent variables had a significant association with normal egg production in crosses and high weight dwarf populations.