An Investigation of the Milk Yield of Dairy Cows: Being a Statistical Analysis of the Data of the Scottish Milk Records Association for the Years 1908, 1909, 1911, 1912, 1920 and 1923

Abstract

In 1911 the mean yield for a lactation period of 36.78 weeks was 634.82 gal.; in 1912 the yield for 37.41 weeks was 654.20 gal. Butterfat was 3.7% in both yrs. The distributions of milk yield, percentage of butter fat, weeks in milk, and yield of butter fat are fitted by Pearsonian Type IV curves. The coefficients of variation are 8.7-43.4. The correlation of milk yield and fat % is[long dash].16; the regressions are practically linear. The regressions of milk yield, fat %, and fat yield on age are non-linear. The maximum milk yield is at 13 yrs., the maximum fat yield at 10-11 yrs. The correlation of milk yield and length of lactation is about + .6, the regression of the former on the latter being practically linear. Mean fat yield for given age and length of lactation is shown. The correlations of milk yield and fat yield with age are not due to selection. Milk yield has increased over 4% from 1911 to 1920. Cows calving Aug.-Nov. have longer lactation period.