The effect of thermal stress on superovulatory response and embryo production in Bharat Merino ewes

This experiment was conducted to observe the effect of thermal stress during estrous cycle on superovulatory response and subsequent embryo production in Bharat Merino ewes (fine wool crossbred developed for the tropical environment). Fourteen cycling, multiparous ewes were randomly allocated to two groups (n = 7/group). The animals in Group-I were maintained in a shed from 10.00 to 16.00 h while animals in Group-II were exposed to the elevated temperature for a period of 6 h (10.00–16.00 h) for 4 weeks. Animals grazed on natural pasture of Cenchrus ciliaris during the morning (7.00–10.00 h) and evening hours (16.30–19.30 h), and drinking water was offered once daily at 16.30 h. Daily meteorological observations were recorded during the trial. Superovulation was induced in all the ewes using FSH (ovagen 5.4 mg in eight injections) and PMSG (200 IU). Estrus in the ewes was synchronized with 2 doses of PGF2 (10 mg) 10 days apart. Ewes demonstrating estrus were hand mated with the aid of Bharat Merino rams. Ovarian examination and embryo/ova recovery were performed using laparoscopy on days 3–5 following mating. All the ewes exhibited estrus within 48 h after the second PGF2 injection. Ewes in Group-I exhibited estrus earlier (25.5 ± 1.1 h) and the estrus period was longer (37.7 ± 1.6 h) than ewes exposed to thermal stress, i.e. 30.6±1.2 and 31.7±3.6 h, respectively. No significant difference were observed for the two groups with respect to the superovulatory response and embryo/ova recovery rate. The ewes exposed to thermal stress yielded relatively poor quality embryos. The results indicate that thermal stress could adversely affected the quality of the embryos in Bharat Merino sheep during the preovulatory period. © 2004 Elsevier B.V. All rights reserved