Abstract
Beta-carotene (precursor of vitamin A) is required not only for maintaining vital tissues in the reproductive tract but also for keeping the body in good health. Although green forages are the major source of carotenoids including beta-carotene (BC), but they are not available throughout the year. Therefore, the aim of this study is to figure out the long-term effect of BC synthesized chemically on live body weight (LBW), age at puberty, estrous cycle (EC) length and progesterone (P4) and estradiol -17 β (E2) profiles during pre and post-puberty in Farafra ewe lambs. 48 ewe lambs with mean body weight 13.25 ± 0.43 kg were divided into two equal groups (24 per each), the first group was injected i.m. with arachis oil (peanut oil) and considered control for the other treated group, the second group was injected i.m. 0.1 mg/kg by BC loaded on arachis oil 2 times a week for 4 months starting from weaning period to age at puberty. Beside detection of estrus by a ram, P4 value was taken as a marker in determining age at puberty. All ewe lambs were fed maintenance ration and housed in semi-open pens under Upper-Egypt environment conditions, El-Minia Governorate. Blood samples (10 ml/animal) were withdrawn from 6 animals per each group (control and treatment) by jugular vein puncture into tubes without anticoagulant. After clotting blood samples were centrifuged at 3,000×g for 10 min to separate the sera, which were stored at −20°C until P4 and E2 assay. Statistical analysis showed that LBW was significantly higher in the treated animals than the controls. BC did not significantly affect age at puberty and level of P4 during post-puberty, but it influenced significantly on E2 concentration at puberty and post-puberty. All animals exhibited their first short EC (puberty) with average of 6.20 ± 1.74 days (treatment) and 7.40 ± 1.97 days (control). The percentage of short EC observed during 69 days post-puberty was significantly (p<0.05) higher in the treated animals than the controls (73.3 % vs. 20 %). While, percentages of normal and long EC in the treated animals were 6.7 % and 20 % compared with the controls (40 % and 40 %, respectively). Mean P4 value was < 1.0 ng/ml three times during 35 days post-puberty (days 14, 31 and 35) in the treated animals and days 17, 28 and 35 in the controls. From weaning to the day 53 pre-puberty, P4 was < 1.0 ng/ml in the two groups, then it reached 2.64 ± 1.38 ng/ml on day 45 pre-puberty in the treated animals vs. 0.88 ± 0.25 ng/ml in the control group. Furthermore, from the day 45 to the day 3 pre-puberty, P4 level was around 2.0 ng/ml in the two groups. At puberty, the mean P4 concentration in the two groups was between 1.0 and 1.1 ng/ml blood serum. The total mean P4 concentration did not differ in the two groups during pre and post-puberty. From weaning to the day 53 pre-puberty, E2 level was very low except one animal in the treated group and another in the controls, after that, the E2 level rose several times until the animals reached puberty in the two groups. The mean E2 level at puberty and post-puberty was significantly higher in the treated group than the controls. This means that BC may have a positive effect on development of ovarian follicle granulosa cells more than the luteal cells. In conclusion, BC had a positive effect on LBW. All animals displayed their first short EC almost 7 days of puberty, and the percentage of short cycles were significantly higher in the treated animals than the controls. P4 level during puberty and EC (estrous and met-estrous phases) was ≥ 1.0 ng/ml, < 1.0 ng/ml and > 1.0 ng/ml in the two groups. The long-term BC injections did not advance the age at puberty in Farafra ewes, and did not increase the levels of P4 pre or post-puberty. Otherwise, BC had a significant positive effect on E2 levels during puberty and post-puberty (a day 28) in Farafra ewe lambs. However, increasing E2 concentration by BC may open other study in investigating the role of BC on estrous induction out of breeding season.