Insulin-like growth factor (IGF)-I and -II and IGF binding proteins in serum and mammary secretions during the dry period and early lactation in dairy cows.
Concentrations of IGF-I and IGF-II, and IGF binding proteins (IGFBP) in serum and mammary gland secretions were surveyed during the dry period and early lactation of 30 Holstein cows. Although there was a threefold drop in the concentration of IGF-I in serum from the last week of the dry period to parturition (81 +/- 7 to 24 +/- 3 ng/ml, P less than .01), there was no significant change in serum IGF-II concentration during this period (150 +/- 17 vs 173 +/- 13 ng/ml, P greater than .05). Furthermore, a 57% increase in serum IGF-I was observed from the last week of lactation to the second week of drying off (100 +/- 5 to 157 +/- 8 ng/ml, P less than .05). Changes in serum IGF-II were not observed (126 +/- 11 vs 150 +/- 10 ng/ml, respectively; P greater than .05). Although IGF-I, IGF-II, and IGFBP concentrations in mammary secretions peaked 2 wk before parturition (2.95 +/- 1.1, 1.83 +/- .6, and 7.27 +/- .76 micrograms/ml, respectively), total output/quarter was highest in colostrum (394 +/- 119, 295 +/- 132, and 2,680 +/- 1,967 micrograms/quarter, respectively). Weekly milking of two individual quarters during the dry period did not affect (P greater than .05) IGF-I or IGF-II concentration (ng/ml) or total output (microgram/quarter) and milk yield in colostrum and milk (2 wk and 7 wk) compared with the ipsilateral quarter. The data support the hypothesis that IGF-I may be transported by the mammary gland epithelium. Furthermore, the secretion mechanisms of IGF-I, IGF-II, and IGFBP by the gland may be related to each other.
Vega
J R
JR
Dept. of Dairy and Anim. Sci., Pennsylvania State University, University Park 16802.
Gibson
C A
CA
Skaar
T C
TC
Hadsell
D L
DL
Baumrucker
C R
CR
D000818:Animals; D002352:Carrier Proteins / Q000032:analysis* / Q000097:blood; D002417:Cattle / Q000097:blood / Q000378:metabolism*; D002850:Chromatography, Gel; D003126:Colostrum / Q000737:chemistry / Q000378:metabolism; D005260:Female; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D007335:Insulin-Like Growth Factor II / Q000032:analysis*; D007774:Lactation / Q000097:blood / Q000378:metabolism*; D008321:Mammary Glands, Animal / Q000378:metabolism; D008892:Milk / Q000737:chemistry / Q000378:metabolism; D011863:Radioimmunoassay
D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II