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Milk yield and milk fat responses to increasing levels of stearic acid supplementation of dairy cows
Dose-dependent effects of a stearic acid-enriched fat supplement on feed intake, production responses, and the maximum amount of stearic acid that can be incorporated into milk fat were evaluated. Multiparous Holstein cows (n=32; 145 ± 66 DIM) with a wide range in milk yield (25 – 70 kg/d) were blocked by milk yield and assigned to replicated 4 x 4 Latin squares. Treatments were diets supplemented with a stearic acid-enriched fat (SA; 87% C18:0) at 0, 0.8, 1.6, or 2.4% of diet DM. Periods were 21 d with the final 5 d used for data and sample collection. The corn silage and alfalfa silage-based diets were formulated to contain 25.8% forage NDF and 17.0% CP. The statistical model included the random effect of cow and the fixed effects of treatment, period, and their interaction. Linear, quadratic, and cubic contrasts were used to determine the effects of increasing doses of SA. Intake of DM increased as SA supplementation increased (28.4, 29.0, 29.5, and 29.9 kg/d; linear, P=0.02). Milk fat concentration was 3.78, 3.73, 3.74, and 3.82% for increasing doses of SA (quadratic, P=0.10). Treatment had no effect on milk yield (38.2 kg/d, P=0.54), milk fat yield (1.41 kg/d, P=0.75), milk protein yield (1.32 kg/d, P=0.51), or milk protein concentration (3.49%, P=0.88). Feed efficiency (ECM/DMI) was 1.43, 1.39, 1.36, and 1.36 for increasing doses of SA (linear, P=0.0003). Supplementation of SA had no effect on BW or BCS (P>0.23). The yield of C18:0 plus cis-9 C18:1 in milk fat was increased by SA supplementation (linear, P=0.005); however, the increase from 0 to 2.4% SA was only 17 g/d resulting in no effect of SA supplementation on yield of total preformed milk FA (>16-carbons, P=0.69). The yield of de novo (<16-carbons) and 16-carbon FA in milk fat were also unaffected by SA supplementation (P=0.72 and P=0.33, respectively). In conclusion, although increasing SA supplementation increased DMI it had no effect on the yield of milk or milk components. While SA supplementation increased the yield of C18:0 plus cis-9 C18:1 in milk fat, it had no overall effect on the yield of de novo or preformed FA in milk.
Keywords: fat supplementation, milk fat, stearic acid