Expression of insulin-like growth factor-I in cows at different stages of lactation and in late lactation cows treated with somatotropin.
Relative amounts of IGF-I mRNA were measured in livers of Holstein cows at different stages of lactation (6 early, 6 mid, 6 late lactation, 6 dry) and 6 late lactation cows treated with bST for 1 wk. Milk yield was greater for early lactation cows than for mid and late lactation controls. All cows except those in early lactation were in positive energy balance. Serum IGF-I increased as lactation progressed and was greatest during the dry period. Liver IGF-I mRNA was less in cows in early than in late lactation but greater in lactating than in dry cows. Treatment with bST increased milk yield and concentrations of serum IGF-I, hepatic IGF-I mRNA, and serum IGF-binding protein-3, decreased concentration of serum IGF-binding protein-2, and did not alter abundance of mammary IGF-I mRNA. These parallel changes in serum IGF-I and hepatic IGF-I mRNA suggest that exogenous bST increases IGF-I synthesis in liver of cows during late lactation and that IGF-I synthesis is depressed during early lactation when cows are in negative energy balance. We conclude that IGF-I may play an endocrine role in mediating galactopoietic effects of exogenous bST during late lactation. However, the role of IGF-I during early lactation remains unclear.
Sharma
B K
BK
Department of Animal Science, Michigan State University, East Lansing 48824.
Vandehaar
M J
MJ
Ames
N K
NK
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D002417:Cattle / Q000378:metabolism*; D004734:Energy Metabolism; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D015870:Gene Expression / Q000187:drug effects*; D013006:Growth Hormone / Q000494:pharmacology*; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000235:genetics* / Q000378:metabolism; D007774:Lactation / Q000187:drug effects / Q000502:physiology*; D008099:Liver / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism
D002352:Carrier Proteins; D005230:Fatty Acids, Nonesterified; D018969:Insulin-Like Growth Factor Binding Proteins; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone