Effect of Sire and System of Mating on Estimated Embryonic Loss

Embryonic death has in recent years been recognized as a major cause of lowered fertility in dairy cattle.The predisposing factors for embryonic mortality and their relative importance are as yet largely unknown.The purpose of this study was to determine the possible effects of sire and system of mating on embryonic mortality by 5 months of gestation. )IATERIALS AND METHODSData for this report were collected from the Holstein-Friesian herd at the Emmons Blaine, Jr., Experimental Farm, Lake Mills, Wisconsin.The data include the results of all services in the herd between January 1, 1950, and July 31, 1953, as well as the lengths of all estrual cycles during the same period.The herd is composed of six lines of breeding, with the following mating systems being followed in each line: outbred dams mated to outbred sires of another line to produce line-cross outbred calves (0-O matings), outbred dams mated to related sires to produce inbred calves (O-I matings), inbred dams mated to related sires to produce inbred calves (I-I matings), and inbred dams mated to inbred sires of another line to produce outbred offspring (I-O matings).In addition, outbred control animals for the herd are obtained by mating line-cross outbred dams to nonproject sires in various artificial breeding studs.The inbred dams (59 in number) had a total of 91 service periods.Their coefficients of inbreeding ranged from 0.125 to 0.375; the mean was 0.233, with 41 of 59 coefficients between 0.20 and 0.30.The variation in inbreeding coefficients of the dams mated to a particular bull was not sufficient to permit classification within sire by degree of inbreeding.Eighteen herd sires were used ill the project during the period covered by this report.Only four of these project sires were considered to be used a sufficient number of times to justify classification of the results of their services by sire and system of mating; consequently, the services of all other project sires and nonproject sires were grouped together to allow classification by system