EFFECT OF PROTEIN AND ENERGY INTAKE BY PRIMIPAROUS SOWS DURING LACTATION ON SOW REPRODUCTIVE PERFORMANCE AND BODY COMPOSITION, AND SOW AND LITTER PERFORMANCE (ESTRUS, UREA, THYROXINE)

Three experiments were conducted to investigate protein and energy intake during lactation on sow reproductive performance and body composition, and sow and litter performance. Dietary treatments consisted of two protein levels 380 (LP) and 760 (HP) g of crude protein.sow(\u27-1).d(\u27-1) and two energy levels 8 (LE) and 16 (HE) Mcal of metabolizable energy (ME).sow(\u27-1).d(\u27-1) in a 2 x 2 factorial arrangement. Treatments were LE-LP, HE-LP, LE-HP or HE-HP and were initiated at parturition and fed during a 28-d lactation. In Experiment 1, 34 sows were used to determine the effect of protein and energy intake on concentrations of sow serum T(,4) and urea. Concentrations of serum T(,4) were lower during lactation than gestation, and after weaning increased to the highest level on the second day of estrus. Neither protein nor energy intake affected T(,4) concentrations. However, an interaction (P = .083) occurred on d 14 and 28. Concentrations of serum urea were influenced by both protein (P = .001) and energy, (P = .001) and a significant (P = .005) interaction was observed. Sows from experiment 2 (221) fed LP or LE lost more weight (P = .001) than sows fed either HP or HE, and a significant interaction (P = .001) was observed. Backfat loss was greater (P = .001) from sows fed LE whereas sows fed HP lost more backfat (P = .016) than sows fed LP. Pig weights on d 28 were heavier (P \u3c .04) for sows fed either HP or HE. Litter size at d 14 and 28 was smaller (P \u3c .05) from sows fed HP than LP. A higher percentage of sows (P \u3c .06) fed HP exhibited estrus postweaning than sows fed LP. Thirty-two sows (Experiment 3) were used to investigate the dietary treatment effects on sow body composition after weaning. The data indicate that sows mobilized protein and(or) fat from internal organs and the carcass to support lactation. However, the mobilization of protein from sows fed HE-LP, and their poor reproductive performance experienced in Exp. 2 indicates protein catabolism was more deleterious regarding return to estrus postweaning than was fat catabolism