Effect of Lactation Length and Steroid Hormone Treatment on Embryonic Survival and Peripheral Steroid Concentrations in Multiparous Sows

Purdue University 1999 Swine Research Report. The increasing use of early weaning technology in the U.S. has led to the progressive reduction of average lactation length (weaning age). An estimated 25% of U.S. producers utilized an average lactation length 16.2 days in a recent records database summary, and the average lactation length for all 612 farms was 18.9 days (PigCHAMP, 1999). In addition to improving piglet health and growth rate, the short lactation lengths ( 17 days) necessary to derive pigs free of certain pathogens have the potential to increase sow productivity by decreasing the farrowing-to-farrowing interval and increasing the number of litters per sow per year (Dial et al., 1995; King et al., 1998). Unfortunately, these potential benefits are sometimes nullified by a reduction in the subsequent reproductive performance of the sow (Xue et al., 1993). Short lactation lengths are associated with an increase in the length and variability of the weaning-to-estrus interval (WEI), an increased incidence of follicular cysts and anestrus, and a reduced conception rate (CR) and subsequent litter size (SLS; Svajgr et al., 1974; Marsteller et al., 1997). The reduced SLS of early weaned (EW) sows is due to increased embryo mortality and not to a reduced number of ova shed (ovulation rate) or fertilized (Varley and Cole, 1976; Hays et al., 1978; Belstra et al., 1999). Incomplete uterine involution (repair) is generally accepted as a contributing factor to the reduced embryo survival of EW sows, although conclusive evidence is lacking. Another mechanism hypothesized to contribute to this phenomenon is based on evidence of aberrant postweaning estradiol-17b (E2) concentrations. Varley et al. (1981, 1984) reported abnormally elevated postweaning E2 concentrations in sows weaned after a 10-day versus a 42-day lactation, and a negative relationship between E2 concentrations and embryo survival. However, other studies have not confirmed these findings (Edwards and Foxcroft, 1983; Kirkwood et al., 1984). The conflicting evidence on the effect of short lactation lengths on postweaning steroid concentrations and the increasing number of U.S. producers practicing early weaning prompted our investigation. The primary objective of this experiment was to determine whether or not the increased embryonic mortality in EW sows is related to altered postweaning E2 or progesterone (P4) concentrations. The effect of an exogenous P4 and E2 treatment on embryo survival and endogenous concentrations of P4 and E2 was also evaluated.