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Effects of diets differing in starch, fiber, and fatty acid concentrations on milk production and energy partitioning
Effects of feeding diets similar in energy composition, yet differing in starch, fiber, and fatty acid (FA) concentrations, on yield of milk and milk components and energy partitioning were evaluated in a crossover design experiment. Holstein cows (n=32; 102±22 DIM) were randomly assigned to treatment sequence. Treatments were a high starch diet containing 34% corn grain (mixture of dry ground and high moisture corn; HS) or a high FA diet containing 2.5% palmitic acid-enriched FA supplement (HF). Diets contained corn silage, alfalfa silage, and wheat straw as forage sources and contained 34 or 18% starch, 3.2 or 6.3% FA, and 26 or 34% NDF for HS and HF, respectively. Treatment periods were 28 d with the final 5 d used for data and sample collection. The statistical model included the random effect of cow and fixed effects of treatment and period. DMI was 27.4 and 26.9 kg/d for HS and HF, respectively (P=0.11). Compared with HF, HS increased milk yield (47.1 vs. 45.8 kg/d; P=0.02), milk protein concentration (3.07 vs. 2.93%; P<0.01), and milk protein yield (1.44 vs. 1.34 kg/d; P<0.01), did not alter ECM (P=0.47), but reduced milk fat concentration (3.58 vs. 3.95% kg/d; P<0.01), milk fat yield (1.68 vs. 1.81 kg/d; P<0.01), and milk to feed ratio (ECM/DMI, 1.73 vs. 1.78; P=0.03). HS increased the yield of de novo synthesized (<16-carbon) milk FA (58 g/d; P<0.01) and reduced the yield of 16-carbon milk FA (179 g/d; P<0.01). Yield of preformed (>16-carbon) milk FA was not affected (P=0.80). HS increased plasma concentration of insulin by 27% (P<0.01) but decreased triglycerides by 10% (P<0.01) and NEFA by 28% (P<0.01). Compared with HF, HS increased BW gain by 14 kg/28 d (P<0.01), change in BCS by 0.25 pt/28 d (P<0.01), and fat thickness over the rump by 0.79 mm/28 d and between the 12th and 13th rib by 0.23 mm/28 d (both P=0.04). Calculated body energy gain as a fraction of NEL use was greater for HS (10 vs. 3%; P<0.01), whereas milk energy as a fraction of NEL use was decreased for HS (68 vs. 74%; P<0.01). We conclude that the two diets resulted in similar NEL intake but the HS diet partitioned more energy toward body gain whereas the HF diet partitioned more energy toward milk. A high fiber and FA diet might diminish the incidence of over conditioning in mid-lactation cows.
Keywords: starch concentration, fatty acid concentration, energy partitioning