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Milk and Fat Differences for Registered Cows Sired by Artificial and Natural Insemination

Animal Physiology and Genetics Institute, ARS, USDA, Beltsville, Maryland 20705

ABSTRACT

About four million 305-day mature equivalent lactations of cows milked twice daily registered in the herdbooks of the five major dairy breeds were studied. These lactations were by cows sired by bulls in artificial insemination studs and by cows sired by natural service and calving between 1954 and 1969. All herd years in which were both types of registered progeny had 9,629 Ayrshire, 39,646 Guernsey, 190,131 Holstein, 26,200 Jersey, and 11,753 Brown Swiss comparisons. Subsets were also formed for comparisons at the same age (2 yr, 3 and 4 yr, 5 yr and older) in a herd-year. Artificially sired cattle had larger milk and fat yields in almost all breed-age-year subclasses. Their superiority was generally greatest in cows calving at 2 year and usually declined with advancing age. Average superiorities in kg over all ages for carvings in 1966 to 1969 were, for milk: Ayrshire, 191; Guernsey, 128; Holstein, 117; Jersey, 79; Brown Swiss, 34; and for fat: Ayrshire, 6.6; Guernsey, 4.5; Holstein, 4.4; Jersey, 4.1; Brown Swiss, 1.4. In 20 of the 40 milk and fat breed-age subclasses, artificially sired superiority increased linearly over time, and it increased at a declining rate in 10 of them. Bulls in artificial insemination sired higher yielding cattle between 1954 and 1969 than bulls used by the same dairymen for natural service.

¹ present address: Animal Science Department, North Carolina State University, Box 5127, Raleigh 27607

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