EFFECTS OF SOURCE OF ENERGY AND ENERGY INTAKE DURING LACTATION ON REPRODUCTIVE PERFORMANCE AND SERUM HORMONE CONCENTRATIONS OF SOWS FOLLOWING WEANING

The influence of the energy source and energy intake during lactation on sow productivity and reproductive efficiency was studied in primiparous sows. In experiment 1, 90 crossbred sows were used to investigate the effects of restriction and source of energy intake during lactation on sow and litter performance. Either tallow (T) or cornstarch (CS) was added to the basal diet so that energy intake was equal to 8 Mcal of ME(.)sow(\u27-1)(.)d(\u27-1) during a 28-d lactation. Sows fed T lost more (P \u3c .05) weight and appeared to catabolize more protein (P \u3c .001) than sows fed CS. Energy digestibility of the diet with T was lower (P \u3c .01) than the diet with CS. Percentages of sows in estrus by d 7 and 14 postweaning were not different between treatments. In experiment 2, 146 crossbred sows were assigned to treatments consisting of three energy intakes; 10 (LE), 12 (IE) or 14 (HE) Mcal of ME(.)sow(\u27-1)(.)d(\u27-1) during lactation. Sow weight and backfat loss during lactation decreased (P \u3c .001) linearly as energy intake increased. Litter weaning weights improved linearly (P \u3c .05) as sow energy intake increased. In experiments 3 and 4, 31 crossbred sows were used to investigate the effect of energy intake on serum LH, estradiol (E(,2)), progesterone, triodothyronine and thyroxine at and after weaning. In experiment 3, 14 sows were randomly assigned to energy intakes of 8 (LE) or 16 (HE) Mcal of ME(.)sow(\u27-1)(.)d(\u27-1). Percentage of sows in estrus by 7 d after weaning was greater (P \u3c .05) for sows fed HE than LE. Following weaning, serum E(,2) and LH concentrations in HE sows were higher (P \u3c .05) than in LE sows. The sow fed LE that returned to estrus (LE-R) were slightly hyperthyroid on d 1 to 3 postweaning. Progesterone concentrations in HE sows were higher (P \u3c .001) on d 8, 11, 13 and 16 than in LE sows that did not return to estrus (LE-NR). In experiment 4, 17 sows were randomly assigned to the same dietary treatments as experiment 2. Mean serum E(,2) concentration was higher (P \u3c .05) on d 1 to 4 postweaning in IE or HE sows than those fed LE. Serum LH concentration was lower (P \u3c .05) on d 3 postweaning in LE-R sows than in HE or IE sows. The LE-NR sows were somewhat hypothyroid on d 5 and 6 postweaning