The milk from twelve individual cows in a mixed herd in Shropshire was sampled twice weekly over a period of 12 weeks, which covered the transition from winter to summer conditions of feeding. Detailed analytical results are tabulated, and certain figures presented in graphical form. In addition, bulk samples of both morning's and evening's milk were obtained and tested for fat and solids-not-fat.
On the whole the results show great individual consistency of composition, but an appreciable rise in the crude protein content of the milk from all cows took place in late April and in May, this effect being attributed to the change-over in feeding to an all-grass diet. From a consideration of the figures obtained, it is deduced that:
(1) The average composition of mid-lactation milk may differ markedly from cow to cow, but appears to be unchanged by minor alterations in the winter rations, provided these are reasonably satisfactory to begin with. There is, however, a marked increase in total protein resulting from the introduction of spring-grass feeding.
(2) The results show that a herd, although well-fed and efficiently managed, may produce milk in the late winter months, and even in the early spring, which is below the legal standard of 8·50% in s.n.f.