Composition and Flavor of Milk Produced by Cows Injected with Recombinant Bovine Somatotropin

Milk from 10 Holstein cows injected with 30.9 mg/head per d recombinant bovine somatotropin and 11 control cows was analyzed for composition and flavor. Experimental treatments started wk 15 postpartum and continued to the end of lactation. Milk samples were analyzed at wk 14 postpartum (pretreatment for covariant adjustment) and wk 2, Adjusted means for total protein (3.48, 3.49%), true protein (3.28, 3.28%), casein (2.63, 2.58%), NPN (.03, .03%), fat (3.47, 3.52%), freezing point (-.547, -.545"H), titratable acidity (.16, .16%), pH (6.60, 6.64), initial acid degree value (.58, .59), and acid degree value of milk with induced hydrolytic rancidity (3.41, 3.56) were similar for control and somatotropin milk, respectively, whereas serum protein (.65, .71%) and lactose (4.71, 4.80%) were higher and casein as a percent of true protein (80.2, 78.8%) was lower with the somatotropin treatment. Proportions of short-chain (11.6, 10.5%) and medium-chain (58.5, 56.0%) fatty acids were reduced and long-chain fatty acids (26.9, 30.4%) increased for control and somatotropin milks, respectively. In-