High Fat Rations for Dairy Cows. Effects on Feed Intake, Milk and Fat Production, and Plasma Metabolites

Abstract

High fat diets (2.9 to 10.8% ether extract in total diet dry matter) for cows in early lactation were compared in two 4×4 Latin squares. In Trial I, grain concentrate was 42% of the ration dry matter. Total diets and their ether extract (percent) were: 1) control, 3.2; 2) ground raw soybeans, 5.9; 3) hydrolyzed fat, 5.7; and 4) hydrolyzed fat, 10.8. While dry matter intake of Holsteins was lowest with Diet 2 and highest with Diet 3, milk production, fat, and protein were not different. Jerseys produced the most fat-corrected milk per unit metabolic body size on Diet 4.In Trial II, two concentrations of total diet ether extract and crude protein were arranged factorially in isoenergetic diets. Ether extract (percent) and crude protein (percent) were, respectively: 1) 3.3, 13.6; 2) 2.9, 15.9; 3) 5.9, 13.5; and 4) 6.8, 16.3. In Diets 1 and 2, grain was 50% of dry matter fed; in Diets 3 and 4, grain was 33% of dry matter fed. Dry matter intake and milk production were not different among diets. Mean milk fat (percent) of low and high fat diets was 2.7 and 3.4. Consequently, 4% fat-corrected milk was higher with high fat diets.In 32 digestion trials, high fat diets increased digestibility of ether extract and did not reduce digestibility of any other nutrient. In some instances fat increased digestibility of crude protein but not nitrogen balance. Digestibility of acid detergent fiber was increased nonsignificantly.In Trial I, Diet 2 decreased rumen acetate to propionate ratio; in Trial II, the high grain (low fat) rations decreased acetate to propionate ratio and milk fat percent and increased body weight gain.Fat increased total lipid of plasma in Trial II but not in Trial I. Triglycerides and nonesterified fatty acids were increased by fat in both trials. Glucose was not affected by fat in either trial. Rumen ammonia and plasma urea-nitrogen were increased but amino acids of plasma were unchanged by high protein diets in Trial II.Seven to eight percent fat can be included in lactation total diets to 1) increase diet energy density or 2) increase the forage to concentrate ratio to maintain milk fat percent, without negative effects on digestibility.