Milk and Fat Yield Differences for Grade Cows Sired by Artificial and Natural Insemination

Abstract

Available lactations of grade cows calving between 1954 and 1969 and coded as one of five dairy breeds with identified, registered sires were screened. All herd-years having grade progeny sired by bulls in active artificial insemination service and progeny of sires not in active artificial insemination service were used. There were 819 Ayrshire, 6,834 Guernsey, 60,190 Holstein, 5,294 Jersey, and 898 Brown Swiss herd-years. Three subsets were formed for comparisons at the same age (2 yr, 3 and 4 yr, 5 yr and older) in a herd-year. Cows sired by bulls in artificial insemination service had higher yields in almost all breed-age-year subclasses, but most values, except Holsteins, were not significant. Such superiority was generally greatest in cows calving as 2-yr-olds, usually declining with age. Average milk superiorities in kilograms over all ages for 1966 to 1969 were: Ayrshire, 84; Guernsey, 71; Holstein, 57; Jersey, 53; and Brown Swiss, 65. Fat superiorities were: Ayrshire, 3.2; Guernsey, 2.5; Holstein, 2.9; Jersey, 2.7; and Brown Swiss, 3.3.Regression showed this superiority for milk increasing in only 4 of 20 subclasses; superiority increased at a declining rate in another. Superiority for fat increased in only 7 of the 20 subclasses, with superiority in 2 subclasses increasing at a declining rate. Bulls in artificial insemination studs siring grade cows were little better than bulls siring grade cows by natural service during the period.