Milk composition of Holstein, Jersey, and Brown Swiss cows in response to increasing levels of dietary fat

Milk composition is influenced by many factors that include nutrition, parity, stage of lactation and breed. The objective of this study was to determine the effect of increasing the level of dietary fat on the composition of milk from primiparous Holstein (H), Jersey (J) and Brown Swiss (S) cows. Twelve lactating cows, four from each breed, were utilized in a 4×4 Latin square design with 14-day experimental periods. All cows received a basal total mixed ration consisting of 490 g/kg chopped alfalfa hay and 510 g/kg concentrate. Dietary fat in the form of yellow grease was added at 0, 15, 30 and 45 g/kg of diet as-fed, replacing a portion of rolled barley grain. Milk yield was higher for H versus J and S, and there was a linear increase in 40 g/kg fat corrected milk yield with increasing level of supplemental fat in the diet. Diet did not affect dry matter intake, but intake was highest for H and lowest for J. Total milk N and casein N proportions in milk did not differ by breed, but both decreased linearly with increased supplemental fat. There were no differences in milk content of Ca, K, Mg and P by breed, but the concentration of Mg linearly increased, and P decreased, with increasing supplemental fat. J milk fat had higher proportions of short-chain and medium-chain FA versus H and S milk fat, while S milk had the highest long-chain FA and J the lowest. For short-chain FA, J milk fat was highest in C4:0, C6:0 and C8:0. Milk fat content of C18:1 cis 9 & cis 10 was highest for S and lowest for J with H intermediate. C18:1 cis 9 & cis 10 increased linearly with increasing supplemental fat. Breed had no effect on C18:0, C18:2 and C18:3 concentrations, but C18:0 increased and C18:2 and C18:3 decreased with increasing supplemental fat. C18:2 cis 9 & trans 11 did not differ by breed, but increased linearly with increased supplemental fat. The ratio of C18:1 cis to C18:0 was highest for S and lowest for J, suggesting possible differences in mammary desaturase activity. Finally, J milk fat had larger fat globules than those of H and S, and fat globules also tended to increase in size with increasing level of supplemental fat. Results indicate that nutrition and breed can be used as practical means to modify the composition of milk fat.