Abstract :
Reproductive performance of 165 contemporary non-prolific Sardi (S), prolific D’man (D)
and ¼-D, ½-D and ¾-D crossbred ewes mated to Ile-de-France (IF) and Mérinos Précoce
(MP) rams, and growth and survival of their 209 lambs were analysed in order to assess
the performance in a terminal crossbreeding system. Breed group of ewe had a significant
effect on the litter size and ovulation rate, but not on embryo survival. The lowest litter size
and ovulation rate were recorded for Sardi ewes, the highest for D’man and ¾-D ewes, and
the other breed groups were intermediate, with an increase tendency as the proportion of
D’man genes increased in the ewe genotype. Moreover, litter weight at birth and litter size
at 60 days were affected by breed group of ewe, but conception rate and litter weight at 60
days were not influenced. Litter weight at birth of purebred and crossbred D’man ewes was
the heaviest and that of Sardi breed was the lowest. Litter size at 60 days was the lowest
for Sardi ewes, the highest for purebred D’man ewes and intermediate for crossbred D’man
ewes. Sardi ewes weaned 0.49, 0.53, 0.88 and 1.05 lambs less than ¼-D, ½-D, ¾-D and
purebred D’man ewes, respectively. Except conception rate on which service ram breed
had a significant effect, the other reproductive traits were unaffected. Conception rate of
ewes sired to MP rams was 19% lower than that of ewes mated to IF rams.
Breed group of dam influenced significantly lamb weight at birth, at 30 days and at 60
days, but not lamb survival prior to weaning. Lambs born to Sardi and ¼-D crossbred dams
had the highest weights, those from D’man and ¾-D dams had the lowest weight, and
those from ½-D ewes were intermediate. Extreme differences between weights of lambs
from different breed groups of dams were 0.78 kg at birth, 1.72 kg at 30 days, and 2.00 kg at
60 days. Breed of sire had a significant effect on lamb weight at 30 days only. Lambs sired
by IF rams were 0.62 kg heavier at 30 days than those sired by MP rams. It was concluded
that in a terminal sire production, using ¼-D, ½-D and ¾-D crossbred ewes would be better
than the use of non-prolific purebred ewes, since this system takes advantage of increased
reproductive capacity in the ewe with sensible increase in lamb performance
