Performance and metabolic measures of lactating dairy cows fed diets supplemented with mostly saturated or more unsaturated fatty acids

A 10-wk lactation trial was conducted using 45 late lactation cows (199.7 ± 66.3 DIM and 32.0 ± 5.2 kg milk/d) to determine the effect of feeding supplemental fatty acids that were mostly (85%) saturated (SAT) or more (50%) unsaturated (UNS) on performance and select metabolic measures. The first 2 wk of the trial served as a standardization period, and all cows were then fed the control diet, which contained only whole cottonseed as a supplement. At the end of wk 2, cows were blocked by parity and randomly assigned to 1 of 3 treatments within each block for 8 wk. The 3 treatment diets were the control, the equivalent of 0.40 kg/d of SAT, and the equivalent of 0.46 kg/d of UNS. Dry matter intake, milk yield, milk fat percent, and milk protein percent were similar among treatments and averaged 23.8 kg/d, 32.5 kg/d, 3.47%, and 3.23%, respectively. Body weight gain and change in BCS were similar throughout the trial. Concentrations of total cholesterol, high-density lipoproteins, and low-density lipoproteins in the blood were higher for cows fed diets supplemented with UNS compared with control or SAT. Triglyceride and BUN concentrations were similar among treatments. Concentrations of nonesterified fatty acids were greater for UNS, whereas insulin concentrations were greater for SAT than either control or UNS. No differences in internal body temperature were observed among treatments, but there was an interaction of treatment and time during wk 4. Cows fed UNS had greater body temperatures from 0500 through 0530 h and from 0930 through 1030 h compared with control and SAT. These results indicate that supplemental SAT or UNS did not affect intake or performance of late lactation cows; however, feeding UNS did increase cholesterol and NEFA concentrations along with reduced insulin.