Effect of an artificial photoperiod on the resumption of postpartum ovarian activity in Pelibuey ewes in Mexico

Abstract

THE EFFECT OF AN INVERSE ARTIFICIAL PHOTOPERIOD ON THE RESUMPTION OF OVARIAN ACTIVITY WAS STUDIED. SIXTEEN PREGNANT PELIBUEY EWES FROM MARTINEZ DE LA TORRE, IN THE STATE OF VERACRUZ, MEXICO WERE USED. ANIMALS WERE RANDOMLY DIVIDED INTO THREE GROUPS. ONE GROUP (REFERENCE GROUP, N = 8) REMAINED IN MARTINEZ DE LA TORRE, WHERE IT WAS KEPT UNDER NORMAL FORAGING CONDITIONS. THE OTHER TWO GROUPS WERE MOVED TO TOPILEJO, CLOSE TO MEXICO CITY, WHERE ONE OF THE GROUPS (TREATED GROUP, N = 4) WAS EXPOSED TO AN INVERSED ARTIFICIAL PHOTOPERIOD USING A PHOTOPERIODIC CHAMBER THAT GRADUALLY ALLOWED TO ADJUST THE DURATION OF THE PHOTOPERIOD IN A WAY THAT EACH CALENDAR DAY SIMULATED THE PHOTOPERIOD AT THE SAME LATITUDE DURING THE OPPOSITE DAY OF THE YEAR. THE OTHER GROUP (CONTROL GROUP, N = 4) WAS KEPT UNDER A NATURAL PHOTOPERIOD. IN ALL GROUPS LAMBING DATE OCCURRED BETWEEN APRIL 24TH AND APRIL 27 TH, 1997, WHICH IS NORMALLY A TIME OF REDUCED OVARIAN ACTIVITY IN PELIBUEY SHEEP. BLOOD SAMPLES WERE OBTAINED FROM ALL THE ANIMALS TWICE A WEEK DURING 130 DAYS POSTPARTUM. PROGESTERONE DETERMINATIONS WERE CARRIED OUT BY RADIOIMMUNOASSAY. THE INTERVAL BETWEEN LAMBING AND THE RESUMPTION OF OVULATION WAS SIGNIFICANTLY SHORTER (P < 0.01) FOR THE ANIMALS KEPT IN AN INVERSED PHOTOPERIOD (73.2 ± 4.6 DAYS) THAN FOR THE CONTROL (101 ± 6.9 DAYS) OR REFERENCE ONES (104 ± 2.8 DAYS). IT IS CONCLUDED THAT EXPOSURE OF SPRING-LAMBING PELIBUEY EWES TO A PHOTOPERIOD CHARACTERISTIC OF THE FALL RESULTS IN AN ADVANCE OF THE RESUMPTION OF POSTPARTUM OVARIAN ACTIVITY.