SEASONAL-VARIATION IN OVARIAN AND ESTROUS ACTIVITY OF TROPICAL MENZ SHEEP AS AFFECTED BY PLANE OF NUTRITION

Forty-eight mature Ethiopian Menz ewes were used to investigate the ef fect of nutrition on oestrous and ovarian activity in tropical sheep. A control group was fed on hay alone and a high nutrition group receiv ed an additional 400 g per ewe per d of a concentrate feed providing 2 63 g crude protein/kg dry matter and 10.5 MJ metabolisable energy/kg d ry matter. Half the ewes in each group interacted with harnessed vasec tomized rams to detect oestrus, which was also verified by weekly plas ma progesterone assays. Ram presence did not depress feed intake or li veweight gain (P > 0.05). The mean percentage of ewes showing oestrus at [east once a month was very high (95%) and there was a marked reduc tion in sexual activity from June to September, the wet season. Only 7 9% of ewes cycled in August and the number of heats per ewe per month dropped to 1.3 during this wet season in contrast to 1.9 the rest of y ear. Ewes came into oestrus 21 times (range 18-23) a year with no sign ificant effect of level of nutrition. Mean cycle duration was 17.9 +/- 8.7 d; 22% of cycles were short (less than or equal to 13 d), 56% nor mal (14-19 d), 11% long (20-26 d), 8% silent or missed (27-40 d) and 3 % represented anoestrus (greater than or equal to 40 d) with no major difference due to nutrition lever. Individual animal progesterone prof iles revealed that ewes failing to show oestrus had experienced increa sed silent ovulations. Forty percent of undetected heats were from the same animals. We concluded that, although Menz ewes are year-round br eeders, they experience an apparent reduction in sexual activity from June to September, which appears to be independent of the level of nut rition, but might influence their breeding activity and flock producti on.