Some factors affecting milk yield

Abstract

(1) The variation of the total yields according to the month of calving is given, and causes for this variation are suggested from the mean lactation curves of cows calving in each month.(2) A curve showing the effect of pregnancy on the lactation yield has been prepared and corrections are given for different lengths of service periods after calving—“100 days” being chosen as a standard, as that was found to be the average of all service periods obtained, and as it gives a calf at about the same time in the following year.(3) The variation in yield as the cow gets older has been studied and corrections are given. The maximum yield appears to be reached at the fifth calf; it was found that service periods varied in a definite way with age.(4) The effect of the dry period before calving on the subsequent yield is shown; “85 days” has been taken as a standard and corrections given accordingly; the standard was the mean of all dry periods obtained, but is probably above the average throughout the country.(5) By applying these corrections, the variation of individual totals is reduced by approximately 20 per cent, and the number of lactations showing less than 5 per cent, variation is increased by 27·3 per cent.(6) A brief review of other literature on the subject is given, and the results obtained in this paper are compared with those of other investigators.The thanks of the authors are due to the members of the Penrith Milk Recording Society for the loan of their registers, which made this investigation possible, and to Mr Garnet, the Live Stock Officer of the district, and the Live Stock Branch, of the Ministry of Agriculture and Fisheries for the collection of the data; the authors are also greatly indebted to Mr G. Udny Yule, M.A., F.R.S., for much assistance in the purely statistical part of the work, and to Dr F. H. A. Marshall, F.R.S., for his advice during the course of the investigation.