Effect of saturated fatty acid supplementation on production and metabolism indices in heat-stressed mid-lactation dairy cows.

Experimental objectives were to determine the effects of supplemental saturated fatty acids on production, body temperature indices, and some aspects of metabolism in mid-lactation dairy cows experiencing heat stress. Forty-eight heat-stressed Holstein cows were allocated into 3 groups (n=16/group) according to a completely randomized block design. Three treatment diets consisted of supplemental saturated fatty acids (SFA) at 0 (SFA0), 1.5 (SFA1.5), or 3.0% (SFA3) of dry matter (DM) for 10 wk. Diets were isonitrogenous (crude protein=16.8%) and contained 1.42, 1.46, and 1.49 Mcal of net energy for lactation/kg of DM for the SFA0, SFA1.5 and SFA3 diets, respectively. The average temperature-humidity index at 0700, 1400 and 2200 h was 72.2, 84.3, and 76.6, respectively. Rectal temperatures at 1400 h were decreased with fat supplementation. Treatment did not affect dry matter intake (20.1+/-0.02 kg/d), body condition score (2.72+/-0.04), body weight (627+/-16.1 kg), or calculated energy balance (1.32+/-0.83 Mcal/d). Saturated fatty acid supplementation increased milk yield, milk fat content, and total milk solids. Increasing fat supplementation decreased plasma nonesterified fatty acids (8%) but had no effect on other energetic metabolites or hormones. In summary, supplemental SFA improved milk yield and milk fat content and yield and reduced peak rectal temperatures in mid-lactation heat-stressed dairy cows. This demonstrates the remarkable amount of metabolic heat that is "saved" by energetically replacing fermentable carbohydrates with supplemental SFA. Copyright (c) 2010 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.