Abstract :
A total of 74 Farafra adult eweswere used to estimate the effects of lambing season [SE; end
of winter (February) vs. onset of summer (June)], parity (PA; primi- vs. multiparous), litter
size (LS; singletons vs. twins), dam body weight (DBW; heavier or lighter than 38 kg), total
milk yield (TMY; above or less than 40 kg), and their interactions on the time interval to complete
uterine involution and onset of postpartum luteal activity. The maximum diameter
of the uterine horns was recorded and the ovarian structures identified by using transrectal
ultrasonography at twice-weekly intervals—beginning 3 d after lambing for a period of
73 d postpartum. Jugular blood samples were also collected twice weekly between day 14
and day 73 postpartum for serum progesterone analyses. Results showed that the mean
interval for complete uterine involution to be shorter (P < 0.05) for ewes lambing in February,
compared to those lambing in June (29.4±1.2 d vs. 33.9±1.1 d). The other parameters
investigated and the interactions had no effect on the uterine involution. The proportion of
ewes that demonstrated luteal activity within 35 d, >35–42 d, and >42 d postpartum were
12.1%, 24.2%, and 63.7% following the February lambing; and 53.7%, 36.6%, and 9.7% following
the June lambing, respectively (P < 0.01). Ewes that lambed in June recorded a serum P4
concentration of more than 1 ngml−1 earlier (P < 0.01) than for those lambing in February
(39.0±1.2 d vs. 69.3±1.2 d). A high-milk production delayed the onset of the postpartum
luteal function (P < 0.01). There was no effect of parity, litter size, dam body weight or their
interactions on the postpartum luteal function.No meaningful correlationwas also recorded
between the time for completion of uterine involution and the onset of luteal function. The
results obtained demonstrated that for Farafra sheep lambing in the subtropics lambing
season and milk yield are important factors that determine the onset of postpartum luteal
function, while the macroscopic uterine involution is affected only by lambing season as
such
