Sexual behaviour and reproductive performance of ewe lambs at and after puberty

Abstract

SUMMARYObservations were made on mating behaviour and reproductive performance during the puberal period in 61 well-grown Perendale (Cheviot × Romney) ewe lambs. In four animals, the first oestrus (as indicated by raddle marks) was not accompanied by ovulation, and three other lambs, though marked by the rams, were not inseminated.The behavioural responses to a ram, of ewe lambs experiencing oestrus for the first and second times, showed many signs of inadequacy by comparison with those of mature ewes. Individual ewe lambs and mature ewes in oestrus were exposed to a ram in a pen for 3 h, and their responses were ranked on a scale of 1 (full adult response) to 5 (weak response). Of mature ewes 95% scored 1, compared with only 27% of ewe lambs. Across the lambs 59% scored 3 or more, indicating failure of some aspects of the courtship sequences which are required to sustain and reinforce the ram's interest. In a paddock-mating system many lambs showed a strong tendency to disassociate themselves from the rams after each courtship and mating sequence. Consequently there was little evidence of harem formation. Fifty-six per cent of services came in the first 2 h of oestrus, only 14% after the 6th hour and none after the 11th hour.Duration of the first oestrus in lambs was 18·4 h compared with 29·3 h in mature ewes. Mating the 61 ewe lambs over the first three cycles after puberty resulted in 38 of them being pregnant with 46 foetuses at autopsy in mid to late pregnancy. The success rate did not differ between cycles.