672. Variations in the solids-not-fat content of milk. Investigations into the nature of the solids-not-fat problems in the west Midlands

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Abstract
1. During the period September 1954—August 1956 monthly samples of milk were obtained from individual cows in herds selected because of known history of low solids-not-fat. Records were kept of general feeding and management. Milk was analysed for total solids, butter fat and s.n.f. (by difference). Crude protein and lactose were also estimated at three-monthly intervals.2. Mean lactation averages were calculated for s.n.f. These showed a normal distribution around a mean of approximately 8·5%.3. Throughout the period a high proportion of samples failed to reach 8·5%. The seasonal effect is at its worst in March and April when 70% of the samples were below 8·5%.4. Effect of advancing lactation (uncorrected for the effect of season) agreed broadly with previously published work but marked differences in the shape of the lactation curve were found between different herds. Variations in s.n.f. are largely a reflexion of variations in crude protein.5. Age distribution of the cows agreed favourably with published figures for the national herd, and a mean regression of s.n.f. with age gave 0·11% per year.6. Supervision of the feeding of the herds in the investigation gave no measurable improvement in s.n.f. and no significant response was obtained from short-term trials where extra s.e. was fed.7. There was no undue incidence of disease of the udder, either clinical or subclinical.8. Little information could be obtained on breeding, but it is concluded that the major cause of the problem is the genetically poor potentialities of the cows as judged from the average composition of the milk they produce.