The Effect of a Copper Supplement in the Diet on the Fat Content of Cow's Milk

Abstract

Eight cows with normal blood copper levels were used and the experiment was conducted over a series of periods each lasting for four weeks. During the second week of each four-week period the basal meal of each cow was supplemented by 1 g. or 2 g. of copper sulphate or 10 g. of sodium sulphate daily. The 1 g. copper sulphate/day level of feeding experiment extended over 24 four-weekly periods and the 2 g. copper sulphate/day level over 16 similar periods. The sodium sulphate trial also covered 16 four-weekly periods. The average results for the first, second and fourth weeks of the periods were compared. The yield dropped steadily in all trials with significant differences when copper sulphate was fed at the 1 g./day rate and when sodium sulphate was given. The fat percentage rose from the first to the second weeks and dropped from the second to the fourth weeks when copper sulphate was fed, the differences being significant at the 2 g./day level, but not at the 1 g./day level. Fat content showed a steady increase over the period when sodium sulphate was fed. Fat globule numbers increased significantly between the first and second weeks on copper sulphate at both levels, increased, but not significantly, on sodium sulphate, and fell, but not significantly, between the second and fourth weeks in all three trials. Fat globule diameters decreased significantly between the first and second weeks on the two levels of copper sulphate and decreased, but not significantly, on sodium sulphate, and rose between the second and fourth weeks in all three trials, the rise being significant at the 2 g. copper sulphate/day feeding level. The suggestion is made that when copper sulphate is fed to cows which are not suffering from a copper deficiency it causes a slight increase in the fat percentage of their milk. Because a similar change did not occur when sodium sulphate was fed it appeared that the effect was caused by the copper rather than the sulphate content. The possibility that the raised fat content was due to increased numbers of smaller fat globules which could pass more easily down the mammary ductules is mentioned.