Estimates of early embryonic loss in ewes mated to rams selected for high and low prolificacy

Fertilizing ability of semen from rams of high- and low-prolificacy flocks

“…A positive relationship between prolificacy of female relatives and litter size produced by the ram has been shown previously by Vakil et al (1968) who found an increase of 0-12 lambs born per ewe lambing to twin-born rams compared with single-born rams. Burfening, Friedrick & Van Horn (1977) have reported that rams selected for high prolificacy (on the basis of their dams' lambing records) produced more lambs born per randomly selected ewe mated than did rams selected for low prolificacy. This effect was not reflected in any differences in fertilization rates or in embryo deaths but these results may not conflict with our findings because Burfening et al (1977) did not consider multiple-and single-ovulating ewes separately.…”

Theoretical aspects of selection for reproductive performance, with sheep as an example1

“…The findings of KNIGHT et al and those of SMITH (1977) mentioned earlier are to be regarded as examples of genetic variances in an offspring reproductive component. Much information about the existence of non-maternal effects on reproductive traits could be gained from investigations such as that of BURFENING et al (1977). The authors described the effects of selection ram lambs on the basis of their dams' lambing records.…”

The number of spermatozoa, the number of ovulations per ewe, and immunization against androstenedione affect fertility and prolificacy of sheep

“…Variations in semen quality (Hulet et al, 1965;Dun & Hamelton, 1965), ram:ewe ratio (Fowler, 1982) and genotype of the ram (Burfening et al, 1977) have all been associated with variation in the number of lambs born per ewe lambing (prolificacy).…”