Ewe and teaser breed effects on reproductive behaviour and performance

H.H. Meyer

Ruakura Animal Research Station, Hamilton

Proceedings of the New Zealand Society of Animal Production. 1979, 39: 68-76

Dorset, Finn x Romney and straightbred Romney vasectomized rams were joined 10 weeks prior to mating with ewes sired by nine breeds of rams. Dorset rams stimulated onset of seasonal oestrus about 3 weeks earlier than teasers of the other two breeds; however, the earlier onset of oestrus had no effect on either ovulation rate at the first oestrus after start of mating or conception rates to mating with entire rams. Dorset x Romney and Booroola x Romney F₁ ewes exhibited first seasonal oestrus about 1 week earlier than other breeds. There were no teaser x ewe breed interactions observed.

Ovulation rate at the first oestrus following the start of mating varied considerably over ewe breeds and ages. Finn F₁ ewes had a mean ovulation rate of 2.09, with little variation among the three ages present. Booroola F₁ ewes, represented by only 1½-year-olds, were very similar to Finn cross ewes of the same age but showed a markedly high proportion of single and triple ovulations (and hence fewer twin ovulations) than the Finn crosses. Straightbred Romney ewes had the lowest mean ovulation rate for all three age groups. Finn F₁ ewes had the highest conception to first mating (82%) and the lowest proportion barren (3%), while Romney ewes had poorest conception (62%) and most barren (15%). Twin-ovulating ewes had a 5% higher conception rate to first mating than did single ovulators. Among ewes conceiving to twin ovulations, the number of foetuses present shortly before parturition ranged from 1.71 per ewe for Romney to 1.93 for Finn F₁ ewes.

The cumulative effect of ovulation rates, conception rates and litter size produced proportions of foetuses to ewes ranging from 97% for Romney ewes to 192% for Finn F₁ ewes. There was a high proportion of barren ewes among the Booroola crosses, but the high litter size of pregnant ewes produced a mean "lambing" percentage of 153%, second only to the Finn cross.

Keywords: NZSAPAB;

Last Updated 12-09-1998