Reproductive performance of semi-intensively kept Döhne Merino ewes fed with different protein supplements
A trial was conducted to determine the possible effects of an easily digestible nitrogen source in the form of urea compared to an undegradable protein supplement, age and birth status on the reproductive performance (ovulation rate and rate of twinning) of ewes. The weight, age and birth status of Döhne Merino ewes were recorded. A total of 144 Döhne Merino ewes were randomly allocated in two dietary treatment groups (either urea-based or undegradable protein group) synchronised, mated and the ovulation rate (estimated from the number of corpora lutea on the ovaries), foetuses observed on day 55 of gestation, lambs born per ewe and mass of the ewe after lambing were recorded. Dietary protein supplement had no significant effect on ovulation rate, pregnancy status, the number of lambs born per ewe or ewe weight after lambing. The number of lambs born per ewe of the one-year-old (0.99 ± 0.316), two-year-old (1.23 ± 0.134) and seven year old (0.92 ± 0.305) ewes were lower than that of four (1.69 ± 0.222) and six-year-old ewes (1.897 ± 0.248). Ewe age did not influence the ovulation rate of ewes, but the highest number of foetuses counted on day 55 of gestation was observed in 3-year-old ewes (1.68 ± 0.196). The number of lambs born per ewe of single born ewes (1.23 ± 0.104) was lower than that of twin born ewes (1.62 ± 0.106). It was concluded that dietary protein supplementation had no significant effect on ovulation rate or the number of lambs born per ewe mated, while age and birth status influenced the reproductive rate of Döhne Merino ewes.
Keywords: Urea, undegradable protein, ovulation rate, lambing status, reproductive rate