This study reports the effect of feeding formaldehyde-treated or untreated spray-dried casein–safflower oil (1:1, w/w) particles on the fatty-acid composition of milk and plasma lipids of cows.
When the formaldehyde-treated particles were given to Jersey, Sahiwal and Jersey × Sahiwal crossbred cows (1 kg per cow per day) the linoleic acid (18:2) present in the safflower oil was not hydrogenated by the rumen micro-organisms and was incorporated into milk fat.
When the untreated supplement was fed, however, the 18:2 fatty acid was hydrogenated in the rumen and there was an increased proportion of octadecenoic acid (18:1) in the milk fat.
The increased proportions of 18:2 (treated supplement) and 18:1 (untreated supplement) were associated with decreased proportions of palmitic (16:0) and myristic (14:0) acids in the milk fat. All 3 breeds showed similar responses.
The fatty-acid composition of plasma triglycerides, which are an important source of long-chain fatty acids for mammary-gland lipogenesis, was similarly affected. Furthermore, there were significant changes in the fatty-acid composition of other plasma lipids (e.g. phospholipids and cholesteryl esters). The interrelationships between dietary, plasma and milk fatty-acid compositions are discussed.