Effect of feeding level on ovarian and oestrous characteristics of local (Rahmani) ewe lambs at pre- and post-pubertal ages [electronic resource].

Includes references.

A total of 36 weaned Rahmani ewe lambs (82.25+1.04 days and 14.42+0.4 kg LBW) was used to study the effect of feeding level on ovarian and oestrous characteristics pre- and post-pubertal ages. The experimental animals were fed 60% concentrate feed mixture and 40% berseem hay and divided into two comparable groups, 18 animals in each. Ewe lambs in 1st group (G1) received 100% of the recommended feed allowance by the NRC (1985) and those in 2nd group (G2) were fed orally 85%. During the experimental period (from weaning up to conception), LBW and age were recorded at puberty (1st oestrus), 1st mating and conception. A laparoscopy technique was individually employed to visualize and examine ovarian characteristics in each group at 7 months of age and about 5 days after mating. Weekly progesterone concentration in blood plasma at 5 weeks pre-puberty and every two days from puberty (1st oestrus) up to 2nd oestrus incidence was determined. The results show that LBW at puberty was heavier (P<0.05) in G1 than in G2 (38.3 vs. 40.5 kg). Numbers of small (SF) and large follicles (LF) as well as numbers of corpora lutea (CLs) and corpus albicans (CA) examined at 7 months of age were greater on ovarian surface of ewe lambs in G1 than in G2 (7.46, 1.53, 0.13 and 0.06 vs. 8.6, 1.93, 0.2 and 0.2/ovary), but the differences were not significant. After mating, number of SF and LF was insignificantly greater in G2 (6.6 and 1.93/ovary) than in G1 (4.9 and 1.53/ovary), respectively, while number of CLs was greater (P<0.05) in G1 than in G2 (1.06 vs. 1.46/ovary).and number of CA was the same in both groups (0.20/ovary). Lambing rate and litter size after the 1st mating was higher in G1 than in G2 (50% and 1.0 vs. 66.6% and 1.08/ewe). More pronounced finding was continuously and higher increase in P4 concentration in plasma during three weeks prior to puberty in G1 than in G2. Nearly similar pattern of change in P4 level during oestrous cycle was observed in both groups. Data divided on the base of precocious and late puberty showed that LBW at puberty was heavier (38.2 vs. 39.9 kg, P<0.05), average age at puberty and 1st mating was earlier (314.2 vs. 344.4 days, P<0.05), duration of the 1st oestrus was shorter (15.6 vs. 22.9 h, P<0.05) and number of CA/ovary was greater (0.06 vs. 0.2/ovary, P<0.05) were higher in precocious than in late puberty group. Lambing rate and litter size after the 1st mating was higher in precocious than in late group (47.6 and 1.0 vs. 60.0% and 1.11). Progesterone level was higher in precocious than in late puberty group in particular during three weeks prior to puberty. Nearly similar pattern of change in both groups was observed during oestrous cycle, but ewes in late group showed slightly higher P4 level during luteal phase (8-14 day) than that in precocious group. The onset of puberty in local sheep (Rahmani ewe lambs) is affected by several factors, such as age, body weight, ovarian characteristics and progesterone profile preincidence of puberty. Advancing the pubertal age through genetic selection has been successful, but the use of high nutritional level (100% of NRC, 1985) is important to be environmental option that producers may exploit to advance pubertal age.

Summary in Arabic.

1