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A total of 191 crossbred sows were used to determine the effect of energy intake during one lactation on (1) sow and pig performance and (2) the percentage of sows in estrus by 7, 14, 21 and 70 d postweaning. Sows received 8 (Lo) or 16 (Hi) Mcal of metabolizable energy (ME)/d (Exp. 1 and 2) and 8 (Lo), 12 (Md) or 16 (Hi) Mcal of Me/d (Exp. 3) during a 28-d lactation period. All sows were fed an equal amount of crude protein, vitamins and minerals that met or exceeded the recommendations of the National Research Council. Each day after weaning, sows were fed 1.8 kg of a 14% crude protein diet and checked for estrus using boars. Serum samples were obtained weekly from sows not detected in estrus by 15 d postweaning for progesterone analysis. In Exp. 1 sows fed Lo lost more (P less than .01) weight and backfat, and weaned lighter weight (P less than .01) pigs than sows fed Hi. Fewer sows fed Lo exhibited estrus (P less than .01) by 7, 14, 12 and 70 d postweaning than sows fed Hi. In Exp. 2, sows fed Lo lost more (P less than .01) weight and backfat than sows fed Hi, but pig weaning weights did not differ. Fewer sows fed Lo expressed estrus by 7 d (P less than .01) postweaning than those fed Hi. In Exp. 3 sow weight and backfat loss decreased (P less than .01) linearly as energy intake increased. Pig weaning weights were not affected by energy intake. Fewer sows fed Lo expressed estrus (P less than or equal to .05) by 7, 14, 21 and 70 d postweaning than those fed Md and Hi. There was no difference in the percentage of sows fed Md or Hi that exhibited estrus by these time periods. Blood samples collected on d 110 of gestation and d 14 and 26 of lactation, indicated that energy intake did not influence hematocrit values, total serum protein or albumin concentrations. A significant energy intake by time interaction was observed for serum blood urea N. Three of the 25 sows bled for progesterone analysis had luteal tissue activity suggesting ovulation had occurred even in the absence of a detected behavioral estrus.

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SummaryFour trials were conducted with a total of 188 crossbred sows to determine the effect of feeding diets supplemented with tallow (0 or 8%) and choline chloride (220 or 770 mg/kg diet) prior to parturition and during lactation on preweaning pig performance. On d 100 of gestation, sows were allotted to four factorially arranged dietary treatments: 0% tallow-220 mg/kg choline chloride, 0% tallow-770 mg/kg choline chloride, 8% tallow-220 mg/kg choline chloride, 8% tallow-770 mg/kg choline chloride. Diets without tallow were fed at the rate of 1.82 kg/d with an additional .18 kg/d of cornstarch, whereas sows receiving diets supplemented with tallow were fed 1.82 kg/d. Daily metabolizable energy intake was constant for all diets (approximately 6,240 kcal). Following parturition, the diets were fed ad libiturn for a 21-d lactation period. Pig survival to 21 d, in relation to the number of pigs born alive/litter, did not differ significantly between litters from sows receiving tallow (94.0%) and litters from sows receiving the control diet (92.5%). Although not significantly different, there was a trend toward slightly heavier pigs (6.35 vs 6.11 kg) and litters (53.97 vs 51.94 kg) after the 21-d lactation period in the groups nursing sows receiving tallow-supplemented diets. Litter performance was not improved by