Genetic and environmental aspects of udder infections.

Information on the presence or absence of bacterial infections and abnormal secretions in each quarter of cows in their initial survey on the New York State Veterinary College Mastitis Program was used to obtain several criteria of udder infection. Year-season and stage of lactation effects were statistically significant for several criteria of infection in first, second, and later lactation groups but did not explain much of the variation in any infection criterion. Age within first and second lactation group also accounted for little of the variation in infection although age within later lactations accounted for up to 5% of the variation in some criteria. Heritabilities from sire components of variance were all low for first, second, and later lactation cows. Heritabilities from daughter-dam regression were low for first and second lactation cows but moderately high for later lactation cows. Regression of second lactation infections on first lactation infections, later lactation infections on first lactation infections, and later lactation infections on second lactation infections were moderately high. t teritabitities from sire components of variance were not increased by using two surveys per cow, by using only herds with high incidence of infections, or by using only sires with large nmnbers of daughters. Phenotypic relationships between milk yield and infections were all low. Some of the overall measurements of infection on later lactation cows had genetic correlations of" approxinmtely .3 with first lactation milk production. Introduction The continuing problem of economic losses in the d a i ~ industry due to udder infections Received for publication January 26, 1971. 3 Present address: Department of Animal Science, University of Guelph, Guelph, Ontario. Financial assistance Eastern Artificial Insemination Cooperative, Ithaca, I~ew York, for key punch support is gratefully acknowledged. dictates that all methods of reducing infections be examined. The possibility of selection to reduce infection rates has been raised by indications of genetic resistance to udder infections (1, 6, 8, 12). Other work, however, has found either no genetic resistance (10) or varying estimates depending on the criterion of infection (11). Precision in estimation of genetic parameters, as well as in control programs and control and production studies, can be increased by information on the influence of various environmental factors on udder infections. The purpose of this paper is to provide further information on the effects of yearseason, stage of lactation, and age on udder infections and on genetic resistance to udder infections as measured by several different criteria in three lactation groups of cattle. Materials and Methods Data on udder infections were from the New York State Veterinary College Mastitis Program from January ], 1959 to December 31, 1965 for 638 herds. Information on the presence or absence of Streptococcus agalactiae~ other streptococci and hemolytic Staphylococcus as well as other bacterial organisms and on the presence or absence of abnormal secretions were obtained for each quarter of each cow in the herds on the program. An overall clinical rating was assigned if there was any evidence of abnormal secretions from any quarter or of unusual hardness or swelling of the udder. Varying numbers of surveys were made in each herd. Data on the first survey i n a cow's lactation were used, except where noted otherwise, to avoid the complication of treatment effects following the initial survey. Infection was measured by percentage of cows with a clinical rating or with some kind of infection, by number of quarters per cow with abnormal secretion or with some kind of infection, by number of kinds of infection per cow, and by number of infections of all kinds per cow. Milk yield and pedigree information were from the Cornell University Dairy Records Processing Laboratory. The three lactation groups were cows calving at less than 36 183