The effect of nutrition prior to and during mating on ovulation rate, reproductive wastage, and lambing rate in three sheep breeds

The effects of moderate (M) and high (H) levels of nutrition prior to and during mating were evaluated according to the reproductive performance of 46 Queue Fine de 1'Ouest (QFO), 45 D'Man and 40 D'Man x QFO ewes. For 6 weeks prior to synchronised mating and 3 weeks thereafter, ewes in M treatment were given a diet providing, proportionately, 1.0 for QFO and D'Man x QFO and 1.5 for the D'Man of the estimated metabolizable energy (ME) requirements for maintenance. Ewes in H treatment were fed a daily diet providing 1.6 for the QFO and D'Man x QFO ewes and 2.2 for D'Man ewes of the ME requirements for maintenance. Live-weight change was recorded and reproductive performance measured from the cyclic ovarian activity (COA) and corpora lutea (CL) counts at the induced oestrus as well as the incidence of lambing and the number of lambs born. Neither breed nor the nutritional level significantly influenced the magnitude of live-weight changes between the start of the experimental nutritional treatments and the start of the mating period, a time at which 94-100% of ewes in all treatment groups were found to be cycling. At the induced oestrus, ovulation rate (OR) averaged 1.57 per ewe and a positive response of OR to improved nutrition was recorded in the prolific D'Man breed (2.26 in H ewes versus 1.78 in M ewes; P < 0.05). When conception occurred at the induced oestrus, breed of sheep x level of nutrition interaction significantly influenced litter size (LS). Ewes from the H group of the low prolific QFO breed produced less lambs than M ewes (1.00 versus 1.25), and in terms of LS distribution, a higher proportion of M than H ewes produced twins (P < 0.01). Conversely, H ewes of the prolific D'Man breed yielded more lambs than did M ewes (1.94 versus 1.52; P < 0.05). In the three studied breeds, reproductive losses increased with OR. They tended to be higher in H than M ewes of both the QFO and D'Man ewes. Results demonstrated important interactions between sheep breeds with different inherent twinning rates and levels of nutrition around the time of mating, (C) 2003 Elsevier B.V. All rights reserved.