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Lactational responses to palmitic acid supplementation when substituted for soyhulls or corn grain
Effects of a palmitic acid-enriched fat supplement (PA; 87% C16:0) when replacing soyhulls or corn grain on feed intake and metabolic and production responses of dairy cows were evaluated. Twenty-four Holstein cows (185±70 DIM) were randomly assigned to treatment sequence in a 3×3 Latin square design. Treatments were a control diet (CON; no added PA), 1.5% added PA with soyhulls replaced (PA-SH), or 1.5% added PA with corn grain replaced (PA-CG). Treatment periods were 21 d with the final 5 d used for sample and data collection. The study was conducted from June through August 2013 when temperature-humidity index in the barn averaged 70.5 ± 5.7. The corn silage and alfalfa silage-based diets contained 20.0% forage NDF and 16.8% CP. The statistical model included the random effect of cow and fixed effects of period and treatment; preplanned contrasts evaluated the effect of PA treatments (CON vs. ½[PA-SH+PA-CG]) and the effect of PA-SH vs. PA-CG. The PA treatments increased milk fat concentration (3.55, 3.65, and 3.71%; P<0.01) and yield (1.38, 1.49, and 1.42 kg/d; P<0.05) for CON, PA-SH, and PA-CG, respectively. Compared with CON, there was no effect of PA treatments on DMI, milk yield, milk protein yield, or ECM (P>0.18). However, compared with PA-CG the PA-SH treatment increased DMI 1.35 kg/d, milk yield 2.38 kg/d, milk protein yield 0.08 kg/d, and ECM 2.26 kg/d (P<0.05). The PA treatments increased feed efficiency (ECM/DMI), 1.46, 1.51, and 1.50 for CON, PA-SH, and PA-CG, respectively (P<0.05). Compared with CON, PA treatments increased the yield of 16-carbon milk FA by 83 g/d (P<0.01) but did not affect the yield of de novo (P=0.38) or preformed (P=0.71) milk FA. There was a trend for increased yield of de novo (21 g/d; P=0.07) and preformed (27 g/d; P=0.10) milk FA for PA-SH vs. PA-CG. The PA treatments did not alter BW (P=0.42) or BCS (P=0.99), however PA-SH increased BW 9.5 kg vs. PA-CG (P<0.05). There was no effect of PA treatments on plasma concentrations of glucose (P=0.92) or insulin (P=0.57) whereas PA treatments increased NEFA (99.5, 110, and 109 uEq/L for CON, PA-SH, and PA-CG, respectively; P<0.01). Treatment had no effect on rectal temperature or respiration rate (P>0.46). Results demonstrate that a PA-enriched fat supplement increased milk fat concentration and yield and feed efficiency. Responses were greater when PA replaced soyhulls rather than corn grain.
Keywords: fat supplementation, milk fat, palmitic acid