Fatty acid digestibility and lactation performance by dairy cows fed fats varying in degree of saturation.

Holstein cows fed fats varying in degree of saturation were used to evaluate lactation performance (35 multiparous and 15 primiparous cows) and fatty acid digestibility (5 cows). Data from wk 2 and 3 of lactation were used for covariable adjustment of data from wk 4 through 19. Diets were a basal diet (control) with no added fat and four diets with 5% added fat from tallow, tallow plus partially hydrogenated tallow in proportions of 2:1 or 1:2, or partially hydrogenated tallow; iodine values were 45, 35, 26, and 16 for the diets with added fat, respectively. Digestibilities of OM, NDF, and N were not affected by fat supplementation (mean of four fat treatments vs. control) or by degree of fat saturation. Fatty acid digestibility was lower for cows fed fat than for those fed the control diet and decreased linearly with increased fat saturation. In both trials, DMI increased linearly as fat saturation increased. In the digestion trial, cows fed fat tended to have lower DMI than those fed the control diet, primarily because of the unsaturated fat. In the production trial, DMI was similar for cows fed the control diet (22.3 kg/d) or the diet with added fat from tallow (22.1 kg/d) and tended to be higher for cows fed the diet containing partially hydrogenated tallow (23.9 kg/d). Milk production was higher for cows fed fat than for cows fed the control diet, but 4% FCM was unaffected. Milk fat and protein percentages were not affected by fat supplementation but increased linearly with increased fat saturation. Mean body condition score of cows increased as fat saturation increased. The lower digestibility of the diet with added fat from partially hydrogenated tallow was offset by higher DMI and percentages of milk fat and protein as fat became more saturated.