Abstract:
Proc. Aust. Soc. Anim. Prod. (1978) 12: 196 BETWEEN-BREED VARIATION- IN OVULATION RATE IN DORSET HORN, MERINO AND CORRIEDALE EWES AND THEIR CROSSES B.M. BINDON*, L.R. PIPER* and T.S. CH'ANG** Ovulation rate is a major determinant of sheep reproductive rate and measurement of this character is useful for assessing the reproductive . potential of sheep breeds and their crosses. In this study in April 1977 at Armidale ovulation rate was measured by laparoscopy in the nine genotypes generated by reciprocal matings of Dorset Horn (D.H.), South Australian Merino (Mer.) and Corriedale (Corr.) breeds. There were 161 ewes aged two years and 190 aged six years, with sub class numbers ranging from eight to 34 for the nine genotypes. Mean ovulation rates are shown in Table I, adjusted for body weight in the case of two year old ewes where the regression of ovulation rate on body weight was significant ([3 = +O.Ol8 ovulations kg; P < 0.05). The S.E. terms associated with the means ranged from 0.09 - 0.16 for two year old ewes and 0.11 T 0.25 for those aged six years. There were no significant maternal breed effects on ovulation rate in either age group. The paternal breed effect was significant (P < 0.05) in ewes aged six years and the overall age effect on ovulatizn rate was highly significant. The results also provide the estimates of heterosis shown in Table II. None of the estimates is significant and the trends are inconsistent for the two age groups. This is in agreement with overseas work involving crosses between low and high fecundity sheep breeds (Land et al., 1973; G. Ricordeau, -m pers. cog.), but contrasts with the local value of +45% heterosis for ovulation rate in Border Leicester x Merino cross ewes (B.J. McGuirk, unpublished). LAND t R-B.1 PELLETIERr J- r THIMONIER J. Endocr., 58:303. --P - , J. and MAULEON, P- (1973). * CSIRO, Division of Animal Production;Armidale, N.S.W. 2350. ** CSIF0, Division of Animal Production, Epping, N.S.W. 2121. 196.
