Abstract:
Proc. Aust. Soc. Anim. Prod. (1978) 12: 261 FECUNDITY OF THE FAT EWE I.A. CUMMING, D.J. RIZZOLI, J.D. CLARKE and S.R. McPHEE A survey of 400 Victorian sheep farmers conducted in 1974 by the Department of Agriculture, Victoria, indicated that many believed that highest reproduction rates are achieved when ewes are in 'forward store' condition and that as ewes become fatter reproduction rates fall. This paper reports a demonstration to show that at very high live weights reproductive rates do not fall. live weight of 59 kg range 50 to 70 kg). At this time the ewes were subjectively considered to be in forward-store to fat condition. All ewes were joined with rams for six weeks from mid-March. Ovulation rates were determined at laparoscopy by counting the corpora lutea. Group HH: Prior to joining the mean live weight of Group HH was increased to 63.5 kg (range 52 - 72 kg) at which time the ewes were assessed as fat. The mean live weight of this group was further increased in late pregnancy to 73.9 kg (range 64 to 83 kg) at lambing. Group HL: This group was managed as for Group HH until the end of the mating period. Mean live weight was then lowered to 58.5 kg (range 49 - 69 kg; assessed as forward-store) at 6 weeks prior to lambing and then raised to 62.0 kg (range 56 0.80 kg; assessed as fat) for the start of lambing. Group LL: The mean live weight and condition of these ewes were lowered to the start of mating (51.8 kg, range 44 to 62 kg; assessed as store to forward-store) and held until six weeks prior to mating when they were raised for the start of lambing (61.7 kg, range 50 to 77; assessed as fat). wercaliotted at rdndom to three groups, Groups HH, HL and LL (mean On 15 December, 1975, 149 mature Border Leicester x Merino ewes - The higher lambing percentages for Groups HH and HL (Table 1) reflected a higher percentage of ewes lambing and a greater number of multiple births. Fewer lambs died between birth and marking in Group LL but this saving was not sufficient to compensate for the smaller number of lambs born in this group. Lower,ing the live weight and condition of the ewes of Group HL during mid-pregnancy did not affect the number of lambs born nor lamb survival. This experiment demonstrates that increasing live weight before mating will increase fecundity even with ewes already in fat condition and at high live weights, Animal Research Institute, Dept. of Agriculture, Werribee. 3030. 261.