Genetic and nutritional effects on lactational performance of gilts selected for components of efficient lean growth

Abstract

AbstractLactational performance was measured in Large White gilts from lines that had been divergently selected over seven generations for daily food intake (DFI), lean food conversion ratio (LFC), lean growth rate with ad-libitum (LGA) or restricted (LGS) feeding during performance test. Control line gilts were included in the study. During the lactation period of 21 days, gilts were given to appetite five isoenergetic diets differing in ileal digestible lysine: energy (0·40, 0·58, 0·76, 0·94 and 1·12 g/MJ digestible energy). The study consisted of 223 gilts with a similar number of animals in each selection line.Live-weight loss was greater in the low LFC and LGA lines than in the high lines and food intake was significantly lower in the low LGA line than in the high line. Litter-weight gain of the low LFC and high LGA lines were greater than in the complementary selection lines. Prediction equations for nutrient utilization were used to express the effect of diet and selection line in terms of energy and protein inputs and outputs. Selection on DFI or LGS resulted in gilts that did not mobilize lipid during lactation as sufficient energy for milk and maintenance was provided by dietary intake. In contrast, there was insufficient dietary energy with selection on LFC or on low LGA so lipid mobilization was required to achieve energy balance. The energy required to excrete excess protein and energy from lipid mobilization increased as the dietary lysine energy ratio increased, but there were no other dietary effects on energy and protein utilization. Genotype with nutrition interactions were detected for energy intake and lipid mobilization, which were due to the lines selected for low DFI and LGA. The general absence of genotype with nutrition interactions for lactational performance in gilts selected for components of efficient lean growth and the lack of significant dietary effects on energy utilization indicated that the consequences of changing nutritional inputs will be broadly similar for genotypes within the set of genotypes studied. Selection strategies which result in reduced food intake during lactation should be avoided if lipid mobilization is then required to attain energy balance and there are resultant negative effects on subsequent reproductive performance.