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 ev aluate lactation performance (35 multiparous and 15 primiparous cows) and fatty acid digestibility (5 cows). Data from wk 2 and 3 of lactati on were used for covariable adjustment of data from wk 4 through 19. D iets were a basal diet (control) with no added fat and four diets with 5% added fat from tallow, tallow plus partially hydrogenated tallow i n 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, respectiv ely. Digestibilities of OM, NDF, and N were not affected by fat supple mentation (mean of four fat treatments vs. control) or by degree of fa t 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 saturati on increased. In the digestion trial, cows fed fat tended to have lowe r DMI than those fed the control diet, primarily because of the unsatu rated fat. In the production trial, DMI was similar for cows fed the c ontrol diet (22.3 kg/d) or the diet with added fat from tallow (22.1 k g/d) and tended to be higher for cows fed the diet containing partiall y 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 supplement ation but increased linearly with increased fat saturation. Mean body condition score of cows increased as fat saturation increased. The low er digestibility of the diet with added fat from partially hydrogenate d tallow was offset by higher DMI and percentages of milk fat and prot ein as fat became more saturated.