Production response, nutrient digestibility, and energy partitioning of post-peak dairy cows when palmitic acid-enriched supplements are included in diets: a meta-analysis and meta-regression

Abstract Text:

This analysis was performed to evaluate the effects of palmitic acid-enriched supplements (PA; >80% C16:0) on production response, nutrient digestibility, and energy partitioning of post-peak dairy cows. The database was formed with 1056 individual observations from 215 dairy cows in 12 studies. Diet mean nutrient content (% DM) was 30% NDF (range 24 to 37%), 17% CP (range 16.7 to 17.8%), 27% starch (range 22 to 32%), and 3.95% fatty acids (FA; range 2.1 to 5.6%). PA was fed on average at 1.8% of diet DM (range from 0.75 to 2.25%) replacing either soyhulls or ground corn in diets. The effects of PA were compared to non-fat supplemented diets used as controls (CON). The meta-analysis was performed to calculate the mean difference in least square means between CON and PA treatments using a model considering the random effects of study and cow. The meta-regression evaluated the effect of C16:0 intake using a random regression model. PA compared with CON did not affect DMI (P=0.32), milk yield (P=0.37), BW (P=0.70), or BCS (P=0.75), but increased milk fat content (3.81 vs. 3.58%; P<0.01), milk fat yield (1.59 vs. 1.49 kg/d; P<0.01), 3.5% FCM (44.8 vs. 43.0 kg/d; P<0.01), and feed efficiency (3.5% FCM/DMI; 1.60 vs. 1.53; P<0.01). PA increased 16-carbon milk FA yield (590 vs. 475 g/d; P<0.01) compared with CON but did not affect de novo (P=0.23) or preformed (P=0.76) milk FA yields. PA increased NDF digestibility (44.3 vs. 41.5%; P=0.02), 18-carbon FA digestibility (80.3 vs. 78.4%; P=0.02) and DM digestibility (68.2 vs. 66.7%; P=0.01), but reduced 16-carbon FA digestibility (68.4 vs. 74.3%; P<0.01), and total FA digestibility (71.5 vs. 75.8%; P<0.01) compared with CON. PA increased net energy intake (47.4 vs. 46.0 Mcal/d; P=0.04), milk energy output (31.1 vs. 29.9 Mcal/d; P=0.01) and partitioned more dietary energy to milk (66.6 vs. 65.0%, P=0.03) compared with CON. Using the random regression model we observed positive linear relationships between C16:0 intake and milk fat yield (P<0.01; R²=0.57), 3.5% FCM (P<0.01; R²=0.53), and 16-carbon milk FA (P<0.01; R²=0.87), as well as NDF digestibility (P=0.01; R²=0.55) and energy partitioned towards milk (P=0.01; R²=0.47), but a negative linear relationship for total FA digestibility (P=0.01; R²=0.64). In conclusion, supplementation of palmitic acid-enriched supplements increased yields of milk fat and 3.5% FCM, feed efficiency, and NDF digestibility with no reduction in DMI or loss of BW or BCS.

Keywords: fat supplementation,  meta-analysis,  production response