Mammary gland growth as influenced by litter size in lactating sows: Impact on lysine requirement

Twenty-eight primiparous sows were used to determine the effect of litter s ize on the growth of mammary glands and nursing pigs during lactation. Litt er size was set to 6, 7, 8, 9, 10, 11, or 12 pigs by cross-fostering immedi ately after birth. Four sows were allotted to each litter-size group. Sows were allowed to consume a daily maximum of 13.6 Meal ME and 46.3 g of lysin e during lactation. Sows were slaughtered on d 21 (20.6 +/- 1.1) of lactati on. Mammary glands were collected at slaughter and trimmed of skin and the extraneous fat pad. Each gland was separated, weighed, and ground for chemi cal analysis. Dry matter, dry fat-free tissue (DFFT), crude protein, ash, a nd DNA contents were measured. Only glands known to have been nursed were i ncluded in the data set. Wet and dry weights and the amounts of DFFT, prote in, DNA, ash, and fat in individual nursed mammary glands linearly decrease d (P < .05) as litter size increased. Percentages of DFFT, protein, and DNA were quadratically affected (P < .05) by Litter size on d 21 of lactation. Total mammary wet and dry weights and total DFFT, protein, DNA, fat, and a sh amount of all nursed mammary glands of each sow were increased as litter size increased (P < .05). Changing litter size from 6 to 12 pigs resulted in 2,098, 432, 253, 227, 4.4, 178, and 20 g increases in the amounts of tot al mammary wet weight, dry weight, DFFT, protein, DNA, fat, and ash, respec tively, on d 21 of lactation. Litter weight gain was 18.1 kg greater in sow s with 12 pigs than in sows with 6 pigs. Sows with a larger litter size had a greater increase in total mass of mammary gland tissue and litter weight but had lower growth of individual nursed mammary glands and individual pi gs than sows with the smaller litter size. The need for nutrients to suppor t additional mammary gland and litter growth as litter size increases shoul d be considered when estimating nutrient requirements for lactating sows. S ows need an additional .96 g lysine per day to account for mammary gland gr owth for each pig added to a litter.