Enzymic Changes in Bovine Adipose and Mammary Tissue, Serum and Mammary Tissue Hormonal Changes with Initiation of Lactation

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Abstract
Yrimiparous Holstein heifers 180 or 260 days pregnant were studied for changes in serum and mammary tissue hormones and enzymatic changes in adi- pose and mammary tissue with induced lactation. Mammary and adipose tissue were collected on the day of caesarean section (3 and 14 wk prepartum) and while lactating (2 wk postsurgery). Mammary lipoprotein lipase (pmoles/hr/ mg protein) increased from .5 to 46.9 while adipose lipase decreased (12 to 8) with onset of lactation. Similarly, glycer- ide synthesis increased 8-fold in mam- mary tissue and decreased 6-fold in adi- pose tissue. Mammary dehydrogenase ac- tivity for isocitrate, glucose-6-phosphate, and 6-phosphogluconate increased 44, 18, and 40-fold with onset of lactation. Ex- tractable protein for mammary tissues collected at surgery and 2 wk later were 130 and 62 mg/g tissue. Corresponding adipose tissues were 8 and 7. Serum pro- )actin and growth hormone measured 3 consecutive days before surgery were not different from postsurgical values (days 2 to 14 during lactation). Serum proges- fins dropped from 15.5 ng/ml presurgery to .85 ng/ml by day 1 postsurgery and remained low for the rest of the test period. Serum corticoids appeared to peak day 1 postsurgery, afterwards de- clining to presurgery amounts. Corfisol and progesterone in mammary tissue de- creased with induction of lactation while corticosterone remained constant.