Date Full Report Received


Date Abstract Report Received



Primary Investigator:
Co-Investigators: Lídia Sbaraini Arend

The data on seasonal declines in fertility that result in reduced numbers of pigs available for market the following summer originates from estrus failures and delays in gilts and primiparous (P1) sows, reduced conception and farrowing rates. Research suggests that changing photoperiod determines the seasonality of reproduction by melatonin modulation of the function of hypothalamic-pituitary axis. The aim of this study was to determine if extending the duration of the nighttime increase in melatonin during summer and early fall would improve fertility similar to periods of higher fertility in winter and spring. Gilts and P1 sows were given oral melatonin once daily beginning in proestrus and extending into early gestation, coinciding with the periods of the follicular phase, corpus luteum formation, pregnancy recognition and embryo survival. The experiment (Expt.) was conducted at a 6,500 sow, breed to wean farm in 12 sequential replicates from Jun to Sep. In Expt. 1a, gilts (n=420) that had expressed a second heat-no-serve (HNS), were assigned by weight to receive either Melatonin (MEL, 3 mg once daily) or Control (CON) in a syrup solution at 1400 h for 3 wk starting 1 wk before insemination. In Expt. 1b, P1 sows (n=470) were assigned by lactation length and backfat to receive the 3 wk treatment starting approximately 1 wk before expected estrus after weaning. Season was classified in sequential 4 wk intervals as mid-summer, late summer, and early fall. In Expt. 1a there was no effect of treatment (P>0.10) on age at HNS (203 d) and cycle length (22.6 d). However, there was an effect of treatment (P=0.03) on number of follicles (MEL 14.6 and CON
13.1) and an effect of season (P< 0.005) for gilts expressing estrus within 23 d after HNS (mid-summer (61.3%), late summer (74.9%) and early fall (80.3%)). There was no effect of treatment or season (P>0.10) on farrowing rate (80.0%) or born alive (12.8). In Expt. 1b, MEL treatment did not affect number of follicles or wean to estrus interval (8.2 d), but MEL reduced estrus (P=0.03) within 7 d (73.5%) compared to CON (82.0%). Return to estrus was affected by season with rates greater in mid-summer (24.6%) than in late summer (11.6%) and early fall (7.5%). There was no effect of treatment on farrowing rate (83.0%), but an effect of season (P=0.001), with farrowing rate lower in mid-summer (73.6%) than late summer (85.9%) and early fall (89.5%). Total born was not affected (P>0.10) by treatment or season (13.0). In conclusion, season affected follicle development and estrus expression in gilts but surprisingly did not have any effect on farrowing rate or litter size. In P1 sows, season was associated with lower numbers of follicles and reduced 2 conception and farrowing rate, but without effect on estrus expression or litter size. Melatonin treatment in summer and fall increased numbers of follicles in gilts, but had no effect on expression of estrus, farrowing rate or litter size. In P1 sows, Melatonin treatment had no effect on number of follicles but did reduce expression of estrus, and did not affect farrowing rate or litter size. These results identify the complex effects of season on reproductive function and fertility in gilts and parity 1 sows. These two parity groups are critical as they comprise ~33% of the sows in the breeding herd and directly relates to measures of productivity, culling and longevity. The evidence in the present study supports previous literature indicating that exogenous Melatonin can affect pig reproduction and demonstrates effects on follicle development and estrus measures. However, positive or negative responses to Melatonin treatment depended upon the physiological stage of maturity and perhaps metabolic state since gilts and P1 responded differently. Further research should be performed to identify the underlying physiology behind seasonal infertility and the Melatonin effects as these impact reproductive physiology and fertility, but it is not clear how.