Hereditary Variation in Conception Rate of Holstein-Friesian Cattle

Variation in conception rates (based on birth of a live calf from first insemination to a high-fertility service sire) of 1,406 Holstein females was studied at one or two service periods (1,824 records) in 41 artificially inseminated berets.:Fertility did not vary significantly between herds.Conception rates ranged from 43 to 94% in 27 paternal half-sib groups of heifers (P ~ 0.05 on an average of 23.4 heifers per half-sib group) and from 33 to 91% in 36 paternal half-sib groups of parous cows (P : 0.05 on an average of 22.7 parous cows per half-sib group).The heritability of conception rate was estimated from intrasire correlations of paternal half-sib groups to be approximately 8.5%.A comparison of the records of daughters at both service periods from 22 sires showed a trend toward an interaction between sire and parity of daughters (P ~-0.07).The value of selection in improving conception rate is discussed.Previous investigations have shown little evidence for genetic variability in conception rate in dairy cattle.Dunbar and Henderson (3) considered nonreturn to first service by 180 days as an indication of conception in production-tested Holstein cows.tIeritability estimated from the variance due to sires was near zero.At the Danish progeny testing stations, heritability estimates for conception rate at first and second services, in heifers of three breeds, bracketed zero (6).Among cows of an experimental Holstein herd, Mares et al. (4) found highly significant differences, depending on the ancestral sire-line to which the cows belonged, and also significant differences between the sire-lines in the effects of inbreeding and ]ine-erossing on conception rate at first service.Only sire-line differences in the effects of inbreeding and line-crossing on the embryo, as a factor in conception rate, were significant for heifers in the same herd.The following study of farm herds was undertaken to analyze the variation in conception rates of Holstein females from different sires, when bred artificially to high-fertility Holstein bulls.