Search

Four experiments were conducted to investigate feed and water intake, feed efficiency, and abdominal fat levels of six lines of chickens developed from two randombred control populations following selection for high 8-wk BW under high (1.6%), low (.2%), and normal (.4%) dietary salt selection environments. The Athens-Canadian Randombreds (AC) and Athens Randombreds (ARB) served as base populations for development of the six lines. Progeny from these lines were evaluated in the first, fifth, sixth, and seventh generations in Experiments 1, 2, 3, and 4, respectively. In Experiment 1, abdominal fat levels were shown to be inversely related to dietary salt level. The lowest abdominal fat level was observed in birds fed the 1.6% salt diet and the highest abdominal fat level in birds fed the .2% salt diet. Birds receiving the normal (.4%) salt diet had intermediate abdominal fat levels. In Experiments 2, 3, and 4, selected lines were exposed to different dietary salt levels to measure both line and dietary salt response patterns. Significant (P < .05) differences were observed between genotypes (AC vs ARB) and between dietary salt treatments for BW, feed and water intake, and water to feed ratio. However, there was no evidence of genetic change between lines in abdominal fat level as a result of selection under different salt environments.

Growth patterns of quail lines divergently selected for 4-wk BW under split and complete nutrition environments were investigated utilizing a diallel mating scheme. The design, involving 16 mating combinations, allowed investigation of heterotic effects, reciprocal cross effects, and combining ability. Progeny from Generation 27 breeders were evaluated in two hatches under both selection diets. Heterosis for hatch weight was essentially zero; however, percentage heterosis from High x High crosses and Low x Low crosses ranged from 5 to 18% after 1 wk of age. Quail progeny from Low x High crosses were consistently larger than quail from reciprocal High x Low crosses under both selection diets. Reciprocal differences were greatest immediately posthatch and declined with age. However, in crosses involving males from High and Low split diet lines mated to females from High and Low complete diet lines, large reciprocal differences in BW remained at 8 wk. Mean heterosis values for BW across ages from crossing High and Low lines both within and across selection environments were negative in six of eight comparisons. Mean values ranged from +3 to -11% and indicated that greater selection responses may have been made in divergent selection for low 4-wk BW than for high BW. General combining ability of lines was greater when transmitted via females as opposed to males, and was similar under the two diets (split and complete). There was evidence that high-BW lines exhibited greater general combining ability under both dietary environments than did low-BW lines.

Selection for feed conversion substantially influenced growth and gross feed efficiency of mice. Realized heritabilities and genic correlation for increased gain on fixed feed intake (FF) and decreased feed intake on a constant gain (FG) were estimated to be .56, .73 and -.93, respectively. The genic correlations between FF and 56-day weight and between FG and 56-day weight were estimated to be .67 and -.95, respectively. The relative efficiency in changing FF or FG by selecting directly for 56-day weight was found to be .7 in either case. When efficiency was defined as the incorporation of biomass independent of maintenance, no difference was found between selection treatments. Differences in mature weight and feed intake approached significance with selected lines having higher means than controls. The absence of a correlated response in the ability to use energy for growth indicates that selection for feed to gain ratio changes maintenance requirements but not requirements for growth.