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Live Weight of Cow at Various Stages of Lactation in Relation to Milk-Energy Yield

Illinois Agricultural Experiment Station, Urbana, Illinois

ABSTRACT

Eleven records of Holstein cows are fitted with the equation, FCM = aW^b, in which W is live weight measured successively at monthly intervals during the lactation period, and FCM is milk-energy yield for the first 8-months of the lactation period. There is a vast difference in the resulting value of b (.28 to 1.49), according to the stage of lactation at which live weight is measured. FCM and W are most closely related where live weight is measured in the first month of lactation (r = .70).

The above records and other experimental evidence indicate that, within a dairy breed and within a herd (comparable environment) FCM is proportional to the 1.07 power of live weight, where live weight is measured in the first month of lactation. Both practical and biological considerations indicate the desirability of estimating live weight of the cow in the first month of each lactation in D.H.I.A. and similar milk-recording work. Measuring live weight in this way, it appears sound to measure lactation performance of the cow at each lactation in terms of FCM/W, that is, milk-energy yield for the 8-months partial lactation per unit live weight in the first month of the lactation.