Date of this Version
Normal diets and diets with 50 percent greater amounts of protein, vitamins and certain minerals were fed during the gilt development period through lactation to gilts of lines that differed in litter size. The lines had been developed with 10 generations of genetic selection that resulted in a difference between the prolific line and a randomly selected control line of 2.9 fully formed pigs at birth in first parity sows. However, the large litter size line also had greater numbers of stillborn pigs, smaller pigs at birth and greater pre-weaning mortality. The purpose of the experiment was to determine whether these losses in the prolific line could be reduced by feeding diets with greater density of all nutrients except energy during the period of gilt development through completion of the first lactation. The diet fed during gilt development and gestation did not affect total number of pigs born per litter or the number born alive. However, there was an increase of .9 pigs born alive (P=.07) in litters of the selected line when the high nutrient diet was provided. The increase in number born alive in the selected line was not significant at the .05 probability level customarily used for significance, but is close enough to indicate nutrient requirements for maximum productivity is greater for prolific gilts than for gilts with average litter sizes. The development/ gestation feeding regimen did not affect pig birth weights, so the greater number of live pigs in litters of prolific sows was not due to heavier pigs. Litter sizes were standardized at birth so variation in number born would not affect litter weaning traits. There was no difference in number weaned due to line, development/gestation diet or lactation diet. However, pig weaning weights were 95 pounds greater (P<.050) when the dam had received the high-nutrient diet during gestation. The carryover effect of the high-nutrient gestation diet was to significantly increase feed intake during lactation, which probably increased milk production and caused heavier pig weaning weights. In addition, weaning weights of pigs were .57 pounds greater (P<.05) when nursed by sows fed the high-nutrient diet during lactation, even though the sows did not consume more lactation feed than sows fed the normal diet. There were no interactions among lines and diets for traits measured at weaning. Genetic selection can increase litter size. Very prolific females may have greater nutrient requirements for maximum reproductive performance than sows with average litter sizes. Pig weaning weights can be increased by feeding more nutrient- dense diets from the gilt development period through the first lactation.