PLASMA GROWTH-HORMONE AND INSULIN CONCENTRATIONS IN, AND FREE FATTY-ACID RELEASE FROM ADIPOSE-TISSUE CULTURED INVITRO FROM HOLSTEIN COWS OF DIFFERING COW INDEX DURING EARLY AND LATE LACTATION

Early (EL) and late (LL) lactation Holstein cows were segregated into three Cow Index (CI) groups (high, HG; medium, MG; low, LG; n = 47). Feed intake by lactation group, individual milk yield data and blood samples, obtained by puncture of the coccygeal vein or artery at 12-hr intervals, were collected for 7 d. Cows were fed alfalfa hay top dressed with grain mixture. On day 7, 5 g of subcutaneous adipose tissue were removed from the tail-head region. Tissue was minced into 10-15 mg pieces in Krebs-Ringer bicarbonate buffer with 5 ng/ml insulin added (KRB). Triplicate 100-mg aliquots were incubated in KRB + 3% essentially fatty-acid-free bovine serum albumin with either 50 ng/ml growth hormone (G), 5-mu-g/ml epinephrine (EPI), both (G+E) or neither (CON) at 37 C for 2 hr. Early lactation cows averaged greater (P < .05) daily milk production (33.4 vs 22.1 kg), greater (P < .05) plasma growth hormone (GH) concentrations (3.9 vs 3.0 ng/ml) but lesser (P < .01) insulin (INS) concentrations (.49 vs .73 ng/ml) than LL cows. Adipose tissue FFA release in vitro was greater (P < .01) when media contained EPI (EPI: 8.10; G+E: 8.05-mu-E/l/g tissue) than when EPI was not present (CON: 1.33; G: 1.39-mu-E/l/g tissue), but was not affected by stage of lactation. Including hormonal data in the model as covariates indicated that increased plasma INS concentrations before biopsy reduced subsequent FFA release in vitro when tissue was incubated with added EPI, but not when incubation media lacked EPI. Increased GH concentrations had the opposite effect. Further, FFA release was greatest from HG cow adipose when incubated in media lacking EPI, but greatest from LG cow adipose when incubated in media containing EPI.