RESPONSE OF MATERNAL-LINE SOWS TO DIETARY-PROTEIN CONCENTRATION DURING LACTATION

One hundred eighty-one maternal-line (Yorkshire x Landrace x Chester White or purebred Landrace) sows were used to determine effects of dietary protein concentration during lactation on voluntary feed intake of sows and sow and litter performance. Throughout gestation, sows received 1.8 kg/d of a 14% CP corn-soybean meal diet. Sows were assigned to dietary treatments based on parity (range = 1 to 9) and expected farrowing date. Treatments were corn-soybean meal diets that contained 13.6 (Low, L), 15.5 (Medium, M), 17.5 (High, H), or 19.2 (Very High, VH) % CP. Calculated lysine content of diets was .62 (L), .76 (M), .90 (H), and 1.05 (VH) %. Sows had ad libitum access to their assigned diets from the day of parturition until weaning (24.6 +/- .46 d postpartum). Pigs were cross-fostered irrespective of dietary treatment until d 3 postpartum. Diet had a cubic effect (P < .05) on the lactational weight change of sows (L, -9.1; M, -2.1; H, -4.6; VH, .8 kg; SE = 1.57) but had no effect on change in backfat depth during lactation or on voluntary feed intake of lactating sows (xBAR = 6.0 kg/d). Litter size at weaning (9.6 +/- .17 pigs) was similar across dietary treatments; however, diet linearly affected (P < .05) daily litter weight gain (L, 2.01; M, 2.12; H, 2.18; VH, 2.14 kg; SE = .05). Postweaning interval to estrus averaged 5.2 +/- .25 d and was unaffected by dietary treatments. Our data suggest that dietary protein concentrations between 13.6 and 19.2% do not influence voluntary feed intake of lactating sows or weaning-to-estrus interval. Furthermore, maternal-line sows with high genetic potential for milk production and that consumed approximately 6 kg of feed daily require 1,070 g/d of CP (55 g/d of lysine) to maximize litter gain.