REPEATABILITY OF OVULATION RATE, NUMBER OF LAMBS BORN AND OVA LOSS IN SHEEP WITH DIFFERENT OVULATION RATES

Abstract

Ovulation and lambing records of 214 ewes from nine genetic groups varying in ovulation rate (OR) from 1.8 to 3.2 corpora lutea (CL) and number of lambs born (LB) from 1.2 to 2.1 were analyzed to study the relation between OR, LB, ova loss (OL) and their repeatabilities. The nine genetic groups were DLS, Finnsheep (F) and seven crosses from these two breeds ranging from 1/8 to 7/8 Finnsheep breeding. Intrayear repeatability of OR averaged 0.59 for all genetic groups combined. It ranged from −0.20 for DLS to 0.93 for 5/8 F. Interyear repeatability averaged 0.38 and ranged from 0 for DLS to 0.54 for 3/8 F. OR showed a linear increase (b = 0.22 ± 0.02) with increase in Finnsheep breeding whereas repeatabilities showed a significant quadratic relationship. Repeatability of OR was more associated with variability than with mean OR. Repeatability of OR for ewes which had 1, 2, 3 or 4 CL at first record and averaged 2.3 ± 0.5,2.5 ± 0.7,3.4 ± 1.0 and 3.4 ± 1.3 CL at the following two records was, −0.09, 0.33, 0.42 and 0.42, respectively. Lambs born increased with the increase in Finnsheep breeding from 1.2 for DLS to 2.1 for Finnsheep. Ova loss averaged 35% and was fairly constant in the different genetic groups. Repeatabilities for LB and OL for each genetic group were generally small and mostly nonsignificantly different from zero. For the genetic groups combined the estimates were 0.15 and 0.14 for LB and OL, respectively. The correlation between OR and LB (0.25) was lower than that between OR and OL (0.58) and LB and EM (−0.62). Key words: Ovulation rate, litter size, ova loss, repeatability, Finnsheep crosses, DLS sheep