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Effect of Added Dietary Fat and Bovine Somatotropin on the Performance and Metabolism of Lactating Dairy Cows¹

Department of Dairy and Animal Science, The Pennsylvania State University, University Park 16802

³ Reprint requests.

ABSTRACT

Four early lactation Holstein cows (44 to 105 d postpartum) were used in a 4 x 4 Latin square experiment in a 2 x 2 factorial arrangement of treatments to study effects of added dietary fat and/or bovine somatotropin on performance and metabolism. Treatments were: 1) control diet plus placebo injection; 2) 5% added dietary fat (hydrolyzed blend of animal and vegetable fat) + placebo injection; 3) control diet + 50 IU bovine somatotropin/d; and 4) 5% added dietary fat + 50 IU bovine somatotropin/d. Dietary fat reduced dry matter intake (21.6 vs. 22.7 kg/d) and elevated plasma triglycerides (34.7 vs. 29.2 mg/100 ml). Injection of somatotropin lowered blood urea nitrogen, increased plasma free fatty acids, and increased plasma somatotropin. Milk production, milk fat percent, and 4% FCM production were increased by the injection of somatotropin. Milk protein percent was decreased (3.30 vs. 3.44%) with added fat and tended to be lower with somatotropin. The percentage of short-chain fatty acids (C₆ to C₁₄) in milk fat decreased with added fat while the percentage of stearic and oleic acids in milk fat increased. Production responses for fat plus somatotropin and somatotropin treatments were similar. Under the conditions of this study, the addition of dietary fat with injection of somatotropin had little effect on production parameters compared with that found with somatotropin alone.

¹ Authorized for publication as Paper No. 7717 in the Journal Series of the Pennsylvania Agricultural Experiment Station.

² Dairy Science Department, University of Florida, Gainesville 32611.

⁴ Church & Dwight Co., Inc., 469 N. Harrison St., Princeton, NJ 08540.

⁵ Department of Veterinary Science.