Parturition body size and body protein loss during lactation influence performance during lactation and ovarian function at weaning in first-parity sows.

We investigated the effect of body protein mass at parturition and different degrees of body protein loss in lactation on sow performance. In a 2 x 2 factorial arrangement, 77 Genex gilts were fed to achieve either a standard or high body mass at parturition and to lose either a moderate (MPL) or high (HPL) amount of protein in lactation. Pregnant gilts were fed either 24.4 MJ of ME, 266 g of CP, and 11 g of lysine/d or 34.0 MJ of ME, 436 g of CP, and 20 g of lysine/d resulting in divergent (P < 0.01) live weights (165 vs. 193 kg) and calculated protein masses (24.3 vs. 30.0 kg) and slightly different backfat depths (20.0 vs. 22.8 mm; P < 0.05) at parturition. Diets fed during lactation were formulated to deliver 731 g of CP and 37 g of lysine/d or 416 g of CP and 22 g of lysine/d to induce differential body protein mobilization. Sows were slaughtered at weaning (d 26), and the weight of the organs and the lean, fat, and bone in five primal cuts was measured. The external diameter of the eight largest follicles on each ovary was recorded, and the follicular fluid from these follicles was collected, weighed, and analyzed for estradiol. Losses in lactational live weight (26 vs. 20 kg; P < 0.01) and calculated protein mass (17.8 vs. 10.7%; P < 0.001) were greater, and the carcass lean mass at weaning was 10% lighter (P < 0.05) in HPL sows. Backfat (5.1 +/- 0.8 mm; P = 0.29) and calculated fat mass (25.8 +/- 1.5%; P = 0.84) losses did not differ between treatments. Both sow body mass (P < 0.05) and lactation protein loss (P < 0.01) affected litter growth rate. Litter growth rate decreased (P < 0.05) at the end of lactation in HPL sows once these sows had lost 10 to 12% of their calculated protein mass. Ovarian follicular development was most advanced in high body mass sows that lost the least protein; these sows had the heaviest (P < 0.05) uterine weight and highest (P < 0.05) follicular fluid estradiol concentration. Follicular development was least advanced in standard body mass sows that lost the most protein. These sows had the lowest (P < 0.05) muscle:bone ratio at weaning and likely lost the largest proportion of their muscle mass compared with the other treatments. In conclusion, ovarian function at weaning and litter performance was higher in high body mass sows and in sows that lost the least protein in lactation, suggesting that a larger lean mass may delay the onset of a decrease in performance in sows that lose protein in lactation.

Selective protein loss in lactating sows is associated with reduced litter growth and ovarian function.

This study was designed to test the degree of protein loss that may be sustained by lactating sows before milk biosynthesis and ovarian function will be impaired. First-parity Camborough x Canabrid sows were allocated to receive isocaloric diets (61 +/- 2.0 MJ of ME/d) and one of three levels of protein intake in lactation: 1) 878 g of CP and 50 g of lysine/d (n = 8), 2) 647 g of CP and 35 g of lysine/d (n = 7), or 3) 491 g of CP and 24 g of lysine/d (n = 10). Every 5 d during a 23-d lactation, sow live weight, backfat depth, and litter weight were recorded, and a preprandial blood sample was collected. Milk samples were collected on d 10 and 20 of lactation. Sows were slaughtered on the day of weaning, and liver and ovarian variables were measured. Lower dietary protein intakes elicited progressively larger live weight losses during lactation (-13, -17, and -28 +/- 2.3 kg; P < 0.001), but similar and minimal backfat losses (-1.3 +/- 0.29 mm). Approximately 7, 9, and 16% of the calculated body protein mass at parturition was mobilized by d 23. Lactation performance did not differ among treatments until d 20, at which time approximately 5, 6, and 12% of the calculated protein mass at parturition had been lost. The milk protein concentration on d 20 of lactation reflected the amount of body protein lost, and was lowest (P < 0.05) in sows that lost the most protein. After d 20, piglet growth rate decreased (P < 0.05) in a manner related to the amount of body protein lost. At weaning, ovarian function was suppressed in sows that had mobilized the most body protein; they had fewer medium-sized follicles (> 4 mm; P < 0.05), their follicles contained less (P < 0.01) follicular fluid, and had lower estradiol (P < 0.05) and IGF-I (P < 0.10) contents. Culture media containing 10% pooled follicular fluid (vol/vol) from high-protein-loss sows were less able to support nuclear and cytoplasmic maturation of oocytes in vitro, evidenced by more oocytes arrested at metaphase I (P < 0.05) and showing limited cumulus cell expansion (P < 0.06). Plasma insulin and IGF-I concentrations did not seem to be related to the observed differences in animal performance. Our data suggest that no decline in lactational performance or ovarian function when a sow loses approximately 9 to 12% of its parturition protein mass. However, progressively larger decreases in animal performance are associated with a loss of larger amounts of body protein mass at parturition.

Feeding lactating primiparous sows to establish three divergent metabolic states: I. Associated endocrine changes and postweaning reproductive performance.

We investigated effects of different metabolic states on reproductive performance in lactating, primiparous sows. Sows were fed ad libitum (AL; n = 12), alimentated via a gastric cannula to 125% of AL feed intake (SA; n = 8), or restricted (R; n = 9) to 50% of AL from d 1 to 28 of lactation. At weaning, all sows were fed 2.5x maintenance energy requirements until standing heat and then fed twice maintenance energy requirement until slaughter. Sow weight, backfat, and litter weights were recorded weekly. After weaning, sows were tested twice daily for the onset of estrus and inseminated twice using pooled semen. At d 28 of gestation, sows were slaughtered, and the reproductive tracts were recovered to determine ovulation rate and embryo survival. Intensive blood sampling was performed before and after weaning for 12-h periods to characterize changes in plasma LH, insulin, and IGF-I. After weaning, additional samples were taken to monitor changes in LH and progesterone. Insulin and IGF-I were determined at standing heat. During lactation, AL and R sows lost, whereas SA sows gained, body weight and backfat (P < .001). Litter growth rates did not differ among treatments. Although plasma insulin was not different among treatments, plasma IGF-I concentration was lower (P < .001) in R sows. Mean LH and pulse frequency before (P < .03 and P < .06, respectively) and after (P < .001; for both) weaning were lower in R than in AL or SA sows. After weaning, SA sows lost more weight (P < .01) and backfat (P < .01) and ate less feed (P < .001) than AL or R sows. At standing heat, no differences in plasma IGF-I or insulin were observed, although energy balance for SA sows was lower (P < .01) than for AL or R sows. Weaning-to-estrus interval was extended (P < .02) in R sows. We observed no treatment difference in ovulation rate or embryo survival. Our results demonstrate that making sows anabolic during lactation did not ameliorate the negative impact of the suckling stimulus or improve fertility after weaning.

Feeding lactating primiparous sows to establish three divergent metabolic states: III. Milk production and pig growth.

First-litter sows fitted with stomach cannulas were used to test the hypothesis that making gilts anabolic during lactation by providing them with extra nutrition would increase milk production and pig growth. Gilts were allocated to one of three dietary treatments after farrowing: 1) restricted, sows were fed 50% of their estimated ad libitum intake; 2) ad libitum, sows were encouraged to eat as much feed as possible; and 3) superalimented, sows were infused seven times daily through their cannula to achieve a 25 to 30% increase in energy intake in excess of that achieved by sows fed on an ad libitum basis. Milk production was estimated in mid- (d 10 to 15) and late (d 21 to 25) lactation by a modification of the isotope dilution technique. Milk production was similar between treatments in mid- and late lactation (P > .05), and this was reflected in a similarity in weaning litter weight (P = .238). Milk composition was similar also (P > .05) between dietary treatments. Superalimentation provided gilts with 38% more energy (P < .001) than gilts fed on an ad libitum basis, and they accrued live weight (5.1 kg) and backfat (1.8 mm) during lactation (P < .001). These data provide evidence that, unlike multiparous sows that show an increase in milk yield when made anabolic during lactation, primiparous sows seem to partition extra energy into body growth rather than into milk production.

Feeding lactating primiparous sows to establish three divergent metabolic states: II. Effect on nitrogen partitioning and skeletal muscle composition.

We established an experimental model to study nitrogen (N) partitioning in lactating primiparous sows alimented to three levels of nutrient intake. Thirty-six sows fitted with a gastric cannula and fed a 15.4 MJ DE/kg and 18.6% CP diet were allocated to one of three treatments after farrowing: 1) ad libitum-fed; 2) restricted-fed to 55% of the ad libitum feed intake; and 3) superalimented to at least 125% of the ad libitum feed intake. These feed intakes were successfully achieved throughout lactation. Nitrogen balance was studied for three 5-d periods starting on d 2, 11, and 19 of lactation, and a triceps muscle biopsy was taken on d 26. For all treatments, N intake increased, milk N production increased, urinary N losses decreased, but fecal N losses increased as the 28-d lactation progressed. Restricted-fed sows had the lowest fecal N and urinary losses and mobilized the most maternal protein (-23.0 vs -7.4 +/- 6.5 g N/d for ad libitum-fed sows) during lactation. As a consequence of these economies, and extensive protein mobilization, restricted-fed sows were able to maintain milk N production similar to that of sows on the other treatments. Superalimented sows did not mobilize protein, had the poorest protein digestibility, directed the least digestible N toward milk (40.1 vs 78.3% in restricted-fed sows), and produced amounts of milk N similar to those produced by sows on the other treatments. The treatment differences in N retention measured by N balance were reflected in differences in skeletal muscle variables and urinary creatinine. Skeletal muscle cell size (protein:DNA ratio) and protein synthetic capacity (RNA:DNA ratio) increased in response to feed intake. The protein:DNA ratio increased (P < .01) linearly and the RNA:DNA ratio increased (P < .05) in a curvilinear manner. These data suggest that primiparous sows partition additional retained N toward their maternal reserves rather than milk N. They also suggest that sows fed inadequate N intakes maintain milk production by mobilizing maternal protein reserves. Such sows also conserve maternal N during lactation, possibly by reducing muscle protein synthesis.

Effect of delayed breeding on the endocrinology and fecundity of sows.

The effect of serving sows at first or second estrus after weaning was determined using 114 Camborough sows (Parities 1 to 8). Eighty sows were paired according to weaning-to-estrus interval and parity. One sow of each pair was bred at first and the other at second estrus after weaning. A further 27 sows were catheterized on d 3 after weaning or d 20 of the first estrous cycle and bred at first or second estrus, respectively. Blood samples were taken every 30 min from 0800 to 1330 on the day after catheterization, every 6 h from catheterization until 1 d after standing estrus, and every 12 h for a further 3 d. Of the 80 sows, litter size increased (P < .002) by breeding Parity 1 and 2 sows at second rather than at first estrus (10.4 vs 12.8 total pigs born). These increases in litter size were achieved in the absence of any significant changes in sow weight or backfat during lactation and between weaning and breeding, and predicted changes in fat and protein during lactation. Similar but nonsignificant results (P = .15) were observed for the 27 catheterized sows. Plasma progesterone concentrations measured 50 h after the preovulatory LH surge were higher in Parity 1 and 2 sows bred at second rather than at first estrus (5.4 +/- .7 vs 3.7 +/- .3 ng/mL, P < .04). Sows of Parity 1 and 2 bred at first rather than at second estrus had higher plasma IGF-I (P < .05) and glycerol (P < .001) concentrations and tended to have lower preprandial insulin concentrations (P = .09).(ABSTRACT TRUNCATED AT 250 WORDS)