Researchers at the University of Guelph, Ontario, Canada, suggest a successful early weaning program can improve sow productivity by increasing the number of litters per sow per year.

An experiment was conducted to evaluate the effects of early weaning on the subsequent reproductive performance of first parity sows. Roger Hacker, University of Guelph animal scientist, says early weaning (at less than 14 days old) of litters often results in reproductive problems in sows. Problems can range from irregular heat cycles, an increase in weaning-to-estrous interval, reduced conception rates, development of cystic ovaries and small, subsequent litter sizes.

Conflicting results are present in existing literature on the topic of early weaning. The uterus has not completely recovered (involuted) until day 17 to 20 after farrowing in sows nursing litters, and the sow usually ovulates more eggs than the uterus can accommodate. Vernon Osborne, University of Guelph animal scientist, says high serum cortisol levels, which can indicate stress situations, have been positively correlated to reduced sow fertility. All these variables result in early embryonic loss and lost profitability.

This experiment was designed to determine the effects of weaning sows at day 7 and day 14 vs. day 28 post partum on the degree of stress (cortisol), ovarian function (cystic ovaries, ovulations), farrowing to fertile estrous interval, and subsequent litter size of first parity sows.

Eighteen first parity, purebred Yorkshire sows were randomly assigned to an experimental group. The sows were weaned at 7, 14 or 28 days of lactation.

Sows received the same diet and management practices throughout the trial period. Blood samples were collected for plasma cortisol analysis in the morning and afternoon on specified days during lactation and around weaning.

Sows were moved to a group pen after weaning and were mated naturally on the first day of standing estrous. Sows were sacrificed at approximately 50 days into gestation. The entire reproductive tract was excised for autopsy analysis. Reproductive tract analysis included counting the number of viable and poor fetuses, number of corpus luteum, mean diameter of corpus luteum and the incidence of ovarian cysts.

Table 1 shows the variables collected. Four sows on the 14-day weaning period were culled due to various reasons, resulting in missing information. The statistical analysis was adjusted for the missing data.

There was no effect of pigs weaned from the initial litter on the subsequent reproductive performance of all sows. The number of days from weaning to estrus was not significantly different across weaning times.

The ratio of ovulations (number of corpus luteum) to viable fetuses (percent of embryo to corpus luteum) was not significant across weaning times, but there was a substantial range in all weaning times (Table 1). Serum cortisol levels were not different and stress did not appear to be a factor in reproductive performance.

Optimum reproductive success includes ovulation, fertilization and implantation. Osborne says early weaning does not appear to affect ovulation. The reasons for embryo losses in early gestation are still not well understood. A lower number of embryos may be a consequence of incomplete uterine involution and not of early weaning. "The data in Table 1 illustrates that the reproductive response is unique for each sow and controlling the variance among animals is an ongoing challenge in the industry," Hacker says.

Researchers: Vernon R. Osborne, Robert M. Liptrap, and Roger R. Hacker, University of Guelph. Phone Roger Hacker at (519) 824-4120.