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EFFECTS OF PALMITIC ACID ON MILK PRODUCTION AND INSULIN SENSITIVITY IN MID-LACTATION DAIRY COWS. Alice Mathews This masters of science research evaluates the effects of palmitic acid (C16:0) supplementation on milk production and insulin sensitivity in mid-lactation dairy cows. The ability of saturated fatty acids (SFA) to enhance milk yield in dairy cows may be due to shifts in glucose utilization caused by reduced insulin sensitivity in adipose tissue. Our objective was to evaluate the effects of palmitic acid (C16:0) on milk production and insulin sensitivity in cows. Twenty multiparous mid-lactation Holstein cows were enrolled in a study consisting of a 5 d covariate, 49 d treatment, and 14 d post-treatment period. All cows received a common sorghum silage-based diet and were randomly assigned to a diet containing no supplemental fat (control; n = 10; 138 ± 45 DIM) or C16:0 at 4% of ration DM (PALM; 98% C16:0; n = 10; 136 ± 44 DIM). Blood and milk were collected at routine intervals. Intravenous glucose tolerance tests (300 mg/kg of body weight (BW); GTT) were performed at d -1, 21, and 49 relative to start of treatment. Data were analyzed as repeated measures using a mixed model with fixed effects of treatment and time, and milk yield served as a covariate. PALM increased milk yield, energycorrected milk (ECM), and milk fat yield at wk 3, responses that were maintained at wk 7. Furthermore, PALM increased protein yield at wk 7. Changes in milk production occurred in parallel with enhanced energy intake and improved feed efficiency (ECM/dry matter intake). Enhanced milk fat yield during PALM treatment was due to increased C16:0 and C16:1 incorporation. Supplementation of PALM had no effect on concentration of milk components, BW, or body condition score. Two weeks post-treatment, ECM and milk fat yield remained elevated in PALM-fed cows while yields of milk were similar between treatments. The concentration of non-esterified fatty acids (NEFA) in plasma increased by d 4, 6, and 8 of PALM treatment, a response not observed thereafter. Although PALM supplementation did not modify insulin, glucose, or triacylglycerol levels in plasma, total cholesterol in plasma was elevated by wk 3. Estimated insulin sensitivity was lower during the first week of PALM treatment; however, glucose disposal following GTT was not modified. In contrast, PALM feeding reduced glucose-stimulated NEFA disappearance by wk 7. Results demonstrate that increasing dietary energy from C16:0 for a 7 wk duration improves milk yield and milk composition without modifying systemic glucose tolerance. Reduced glucose-stimulated NEFA disappearance with PALM supplementation and elevated circulating NEFA may reflect changes in adipose tissue insulin sensitivity.

Effects of palmitic acid on milk production and insulin sensitivity in mid-lactation dairy cows