WINTER DECLINE IN SOLIDS-NOT-FAT CONTENT OF HERD BULK-MILK SUPPLIES

(1) A survey of the composition of the milk of individual cows in 4 commercial herds in the West Riding of Yorkshire was undertaken from October 1967 to May 1968. (2) In 3 of the 4 herds there was a decline in solids-not-fat (SNF) content throughout the winter feeding period. Milk protein content was at a minimum in January–February but in all 3 herds lactose content also declined and in 2 of the herds this was the major cause of the fall in SNF content. (3) The decline in lactose content was the result partly of the characteristic effect of an advance in lactation, partly of an increase in the incidence of mastitis throughout the winter period. In all herds there was a significant inverse relationship between lactose content and cell count in the bulked milk of individual cows. (4) In 3 of the herds autumn-calving (October–December) animals showed a pronounced fall in milk protein content in the early months of lactation which was not observed in summer-calving (July–September) animals. There was no response in SNF or protein content to supplementary concentrates offered towards the end of the winter-feeding period, whereas with the commencement of grazing in the spring there was an immediate increase in both protein and SNF contents. © 1969, Proprietors of Journal of Dairy Research. All rights reserved.