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Causes and Estimation of Environmental Changes in a Dairy Herd¹

Dairy Cattle Research Branch, USDA, Beltsville, Maryland

R. F. Davis

Dairy Department, University of Maryland, College Park

ABSTRACT

Environmental studies for 230 cows over 462 lactations were made for 7 yr. Statistical estimates of general environmental changes and the specific changes resulting from the influences of feeding and management factors were computed and compared. These estimates were based on 462 lactations of 230 cows made over a 7-yr. period in the Beltsville Holstein herd.

Studies with 293, 2 x 305 hand records indicated that the therms of estimated net energy consumed was the most important factor influencing changes in production. The length of previous dry period, season of calving, and herd size appeared to influence production, but their effects were not significant. Days carried calf was not an important effect.

General environmental changes were estimated by (a) maximum likelihood method of Henderson (6) and (b) the differences between first records of paternal half-sibs in different years, using M.E. records and M.E. records adjusted for the regression of daughter on dam. Comparisons of the methods indicated close accord between estimated changes, but adjustment of first records of paternal half-sibs for the regression of daughter on dam appeared to improve estimates of environmental changes.

Estimation of environmental fluctuations and trends by changes in factors known to influence production gave estimates agreeing closely with maximum likelihood estimates.

The data indicated that factors other than opportunity to feed, feed quality, weather, and palatabilty of the ration might have an important effect on the amount of feed consumed.

¹ These data are taken from a thesis submitted by the senior author to the Graduate School, University of Maryland, as part of the requirements for the degree of Master of Science.

² Present address: 105 Polk Hall, North Carolina State College, Raleigh, North Carolina.