The Fertility of Interbreed vs. Intrabreed Matings as Determined from Artificial Breeding Data

The reasons underlying the practice of crossbreeding dairy cattle may be attributed to a number of factors : (a) Desire to produce smaller calves by firstcalf heifers, (b) indifference as to the breed of sire, (c) attempts to increase the butterfat test or milk production, (d) desire to increase the value of progeny for veal purposes, (e) belief by some dairy farmers that conception is enhanced by crossing breeds.Many dairy farmers believe that interbreed matings improve fertility.The possibility of such matings, especially in commercial herds, has increased markedly as a result of the recent expansion of artificial breeding.Data by Christian, Dreher, and Casida, and published by Casida (2) suggested the possible influence of breed crossing on breeding failures.However, in a later study including 66 cows, each of which had been bred four or more times previously without apparent conception, Christian et al. (3) found no evidence that breed crossing is beneficial in increasing conception rate in repeatbreeder cows.The object of this investigation was to obtain further information on this problem by comparing the fertility of interbreed matings and intrabreed matings which have occurred in the practice of artificial breeding.:EXPERIMENTAL PROCEDURE University of Wisconsin artificial breeding records for the period from Oct. 1, 1948, to Oct. 1, ]950, were summarized in making the necessary comparisons.Of the 44,056 first-service inseminations made during this 2-yr.period, a total of 1,576 services by 22 Holstein-Friesian bulls, and 1,116 services by 14 Guernsey bulls was studied.Fertility was measured by 60-to 90-day non-returns and was based on first-services to Holstein-Friesian and Guernsey cows in Dane and Sauk County herds.The interbreed inseminations were compared with intrabreed inseminations made ou the same day, by the same technician and with semen from the same bull.No attempt was made to balance the frequency of the within-and between-breed matings of each bull.As in most artificial breeding data, the breed of the cows was established from reports submitted by the field technicians.Only cows reported as ttolstein-Friesian or Guernsey were included in the study.Three per cent of the 1,576 first-service Holstein-Friesian cows and three per cent of the ],116 first-service Guernsey cows employed in this trial were registered animals.Only one of