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

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Abstract
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, 4, 6, 8, 12, 16, 20, 24, and 28 of the treatment period. 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.degree.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. Individual and composited milk samples from control and somatotropin cows exhibited no off-flavors, and no differences between milks were observed. Milk from cows treated with somatotropin was no more susceptible to rancid or oxidized off-flavors than control milk.