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Effects of ß-carotene supplementation and age on the oxidative status, production and reproductive performance of grazing ewes

Osman Ahmed , Abubeker Hassen , Khoboso Lehloenya

Abstract

Context. There are some evidences that physiological stages such as breeding, pregnancy, parturition and lactation may trigger oxidative stress. It is also observed in several species, including sheep, that age affects their vulnerability to oxidative stress. Aim. This study investigated the effects of supplemental ß-carotene and age on the oxidative status of grazing ewes around breeding, pregnancy, parturition and early lactation as well as on their production and reproduction performance. Methods. Hundred and four ewes were divided into two broad age groups (young=1-3 years and old =4-6 years). Within age groups, ewes of similar age were randomly assigned to four treatment groups (A1, A2, A3, C) using a completely randomized block design. The young (n=13) and old sheep (n=13) in groups A1, A2 and A3 were daily drenched with 100 mg, 75 mg and 50 mg ß-carotene, respectively. Group C was unsupplemented (Control). Supplementation lasted 28 days before oestrus synchronization; 14 days during oestrus synchronization (CIDR) and hand-mating; 18 days post-hand-mating; 30 days before lambing and 15 days after lambing. All animals were grazed on Kikuyu grass (Pennisetum clandestinum). Six ewes from each group (total = 24) were sampled for blood to measure oxidative and hormonal status during the experiment. Key results. Supplemental ß-carotene ≥75 mg/day may act as a pro-oxidant in ruminants under oxidatively stressed conditions such as parturition. Age did not affect the ewes’ oxidative status. The supplemental ß-carotene did not affect bodyweight, oestrus parameters, corpus luteum size, conception rate and litter size. Except for a tendency of lambs from supplemented ewes to have heavier weight at 15 days old (P = 0.080), age group and supplemental β-carotene did not affect the lamb mortality rate or weight at birth or 15 days old. Older ewes showed earlier and longer duration of oestrus than younger ewes. Conclusions. Supplementation of grazing ewes with ß-carotene should not be ≥75 mg/day especially at parturition period as it may work as a pro-oxidant. The older ewes seem to have earlier oestrus with a longer duration than the younger ones. Implications: Caution is urged when administering high doses of β-carotene to ewes during the peri-parturient period.

AN23220  Accepted 01 June 2024

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