Effect of exogenous bovine somatotropin on mammary lipid metabolism and milk yield in lactating dairy cows.
Eight lactating Holstein cows were used to study the effect of bovine somatotropin on mammary lipid metabolism, milk production, and milk composition. Eight cows were injected with either excipient (n = 4) or 50 IU somatotropin/d (n = 4). A 2-wk adjustment period preceded a 10-d period when treatments were administered. On d 9, serial blood samples were collected from 2 to 5 h post-injection to determine concentrations of somatotropin and metabolites in plasma. Mammary tissue biopsies were obtained 2 to 3 h after a.m. milking on d 10 to determine lipoprotein lipase activity and in vitro rates of acetate incorporation into fatty acids and acetate oxidation by mammary tissue slices. Activity of lipoprotein lipase in milk and mammary tissue and rate of acetate metabolism by mammary tissue were not affected by treatment. The following means for placebo and somatotropin, respectively, were: milk production (21.5 and 24.8 kg/d), milk fat (3.8 and 4.0%), and 4% FCM (20.7 and 25.1 kg/d). Plasma concentrations of somatotropin (3.0 and 43.4 ng/ml) and free fatty acids (105.6 and 219.5 mu eq/L) were significantly elevated with somatotropin. The injection of somatotropin into lactating dairy cows did not affect the mechanisms of fatty acid synthesis or metabolism evaluated in this study.
Lough
D S
DS
Department of Dairy and Animal Science, Pennsylvania State University, University Park 16802.
Muller
L D
LD
Kensinger
R S
RS
Griel
L C
LC
Azzara
C D
CD
D000818:Animals; D002417:Cattle / Q000378:metabolism*; D004435:Eating; D005227:Fatty Acids / Q000096:biosynthesis* / Q000097:blood / Q000378:metabolism; D005260:Female; D013006:Growth Hormone / Q000097:blood / Q000494:pharmacology*; D007774:Lactation; D050356:Lipid Metabolism; D008055:Lipids / Q000032:analysis / Q000097:blood; D008071:Lipoprotein Lipase / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D008892:Milk / Q000032:analysis / Q000201:enzymology; D008894:Milk Proteins / Q000032:analysis; D011247:Pregnancy; D013997:Time Factors
D005227:Fatty Acids; D008055:Lipids; D008894:Milk Proteins; D013006:Growth Hormone; D008071:Lipoprotein Lipase