The Relation between the Month of Calving and Yearly Butterfat Production

Approximately 71 per cent of the dairy cows of Oregon are located west of the Cascade Mountains; and about two-thirds of these, or 46 per cent of the total, are found on farms in the ten Willamette Valley~ounties, a region with an average temperature of 52 ° F. and a monthly mean range from a high of 65 ° F. in July to 38 ° F. in December.The average rainfall of about 42 inches comes mostly during the winter months.Since the climate under these conditions is mild and does not show large seasonal variations in comparison with some other parts of the United States, it became of interest to study the effect of the month of calving on butterfat production.Differences in yearly milk production between cows freshening in the different months of the year, in various parts of the United States, have been found to exist (1,2,5,7,8).The season of the year in which the cow freshens also was reported to exert an effect on her butterfat production (1,4,8).In Connecticut, Frick et al. (2) found that the differences in milk production of cows calving in the different months of the year were highly significant statistically.PROCEDURE