| Summary: | Abstract:: We determined the effect of feeding diets similar in neutral detergent fiber (NDF), starch, and crude protein (CP) with different amounts of forage on the yields of milk and milk components of mid-lactation dairy cows. Thirty-two Holstein cows (132 ± 68 d in milk) were used in a crossover design with 2 consecutive 28-d periods, with sample and data collection during the final 5 d of each period. Treatment diets were (1) control diet (CON) containing high forage (55.5% diet dry matter [DM]; forage NDF 19.2% diet DM) and no supplemental fatty acids or AA; and (2) low-forage (LF) diet containing low forage (36.6% diet DM; forage NDF 12.7% diet DM), including supplemental fat (1.43% diet DM; 82% C16:0-enriched supplement) and rumen-protected methionine and lysine. Diets were balanced for similar NDF (∼30.2% diet DM), starch (∼26.7% diet DM), and CP (∼16.2% diet DM). There was no effect of treatment on milk yield, milk fat content, or body weight. Compared with CON, LF increased DM intake (30.8 vs. 31.8 kg/d), milk fat yield (1.78 vs. 1.84 kg/d), milk protein yield (1.47 vs. 1.56 kg/d), milk protein content (3.24% vs. 3.41%), energy-corrected milk (48.3 vs. 50.2 kg/d), and body condition score (3.2 vs. 3.3). Our results demonstrate that feeding a low-forage diet supplemented with a C16:0-enriched fatty acid supplement and AA increased DM intake and the yields of milk fat and protein, without changes in body weight. The effect of a low-forage diet without supplemental fatty acids and AA was not tested.
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