Animal Production Research Institute, Dokki-Giza Department of Theriogenology, Faculty of Veterinary Medicine, Assiut University Factors affecting the postpartum uterine involution and luteal function of sheep in the subtropics M. Hayder, A. Ali Small Ruminant Research 73 (2007) 277–282 Impact factor: 1.193

Introduction The postpartum fertility in sheep depends on two main factors, the involution of the uterus the onset of postpartum ovarian cyclicity. Farafra sheep at the Mallawi farm is managed in an accelerated lambing system. In such an accelerated mating and lambing system, ewes would lamb three times in 2 years, which necessitates the postpartum period being as short as possible.

Aim Investigate the relative importance and impact of certain environmental factors on the time for completion of uterine involution in sheep and the resumption of the luteal function in the Farafra breed in such an accelerated lambing system.

Materials and methods Animals 74 adult Farafra ewes lambed in: February (SE; end of winter; n = 33) June (SE; onset of summer; n=41) The ewes were categorized according to: parity (PA; primiparous n = 26; multiparous n = 48) litter size (LS; singletons n = 63, twins n = 11), dam body weight (DBW;≤38 kg, n = 35; >38 kg, n = 39) total milk yield (TMY; ≤40 kg, n = 34; >40 kg, n = 40).

Materials and methods Management The experiment was performed at Mallawi Animal Production Research Station of the Animal Production Research Institute.

Materials and methods Estimation of milk production Lamb suckling weight differential technique (Economides, 1987). Lambs were separated from the dams at 17:00 in the evening preceding the milk recording. On the following morning at 7:00, lambs were weighted and allowed to suckle their dams for a 15-min period. The body weight of the lambs was then recorded and lambs separated again until 17:00, thereafter the procedure was repeated. After the last suckling, ewes were hand milked to remove any surplus milk. The difference in the weight of the lambs before and after suckling presented the amount of milk suckled by the lambs. The milk suckled plus the amount of surplus milk was considered to be the total daily milk production of the ewe. After the eighth week postpartum lambs were weaned and the milk yield estimated by hand milking twice daily at 7.00 and 17:00.

Materials and methods Ultrasonic examinations of the postpartum uterus and ovaries Ultrasonographic examinations were performed on all ewes twice weekly—starting 3 d after parturition. The maximum diameter of the previous gravid horn was recorded. Uterine involution was considered to be complete when no further reduction in the uterine diameter for three successive examinations was recorded.

Materials and methods Ultrasonic examinations of the postpartum ovaries The ovaries were examined to record the first newly formed corpus luteum after parturition. The postpartum luteal activity was considered to have started following the detection of a corpus luteum larger than 9mmin diameter, for three successive examinations.

Materials and methods Blood sampling and progesterone determination Jugular blood samples were collected twice weekly. Sampling was initiated on day 14 and continued until day 73 postpartum. Progesterone concentrations were determined using the RIA kits.

Results Ovine postpartum uterine involution The overall interval for complete uterine involution averaged 31.9±1.2 d. The time for uterine involution was shorter (P < 0.05) for ewes that lambed in February (end of winter) than for those lambing in June (onset of summer; 29.4±1.2 d vs. 33.9±1.1 d). The other recorded factors and the possible interactions had no significant effect on the mean interval to complete uterine involution.

Results Ovine postpartum uterine involution

Results Postpartum luteal activity The proportion of ewes that recorded luteal activity within 35 d, >35–42 d, and >42 d postpartum were 12.1%, 24.2%, and 63.7% for the February lambing; and 53.7%, 36.6%, and 9.7% following the June lambing, respectively(P < 0.01).

Results Postpartum luteal activity The percentage of ewes that showed luteal activity within the same previous periods were 47.1%, 38.2%. 14.7% for those with total milk yield (TMY) ≤40 kg; and 17.5%, 32.5%, and 50% for those with a TMY >40 kg (P < 0.01). No effect was recorded regarding the parity (PA), the litter size (LS), and dam body weight (DBW) at parturition, or their interactions on the interval to the onset of the postpartum luteal activity.

Results Serum progesterone profiles Ewes that lambed in June (summer) recorded a serum progesterone concentration of more than 1 ngml−1 earlier (P < 0.01) than for those that lambed in February (winter; 39.0±1.2 d vs. 69.3±1.2 d, respectively. Moreover, following the June lambing three of the five ewes exhibited a complete estrous cycle (17–18 d in length), and two of the five ewes displayed a short estrous cycle (7–9 d in length) within the observation period.

Results Serum progesterone profiles In contrast, following the February lambing season, none of the ewes exhibited a complete estrous cycle (0/6), and only one ewe(1/6) showed a short cycle (11 d in length) within the same period. No relationship was recorded between the onset of the luteal function and the interval to complete uterine involution (r = 0.001).

Progesterone profiles Results Postpartum Progesterone profiles

Conclusion Farafra breed in the subtropics is satisfactorily effective to be utilized in an accelerated lambing programs. Some environmental factors could modulate the efficiency of the accelerated lambing programs. Lambing season and milk production are important factors affecting the onset of the postpartum luteal phase. Macroscopic uterine involution is affected only by the lambing season. No correlation was recorded between the time of uterine involution and the onset of postpartum luteal function.

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