ADIPOSE-TISSUE PROGESTERONE CONCENTRATIONS IN DAIRY-COWS DURING LATE PREGNANCY AND EARLY LACTATION

The objectives of the study were to measure progesterone (P-4) concent rations in subcutaneous adipose tissue from the tailhead of dairy cows in various reproductive states, and to examine the effect of epinephr ine-induced fat mobilization on P-4 release from adipose tissue in vit ro, Blood samples and adipose tissue biopsies were taken from 12 cows twice during late pregnancy and three times during early lactation. Co ncentrations of P-4 in adipose tissue were higher (P < 0.005) during p regnancy than at any of the non-pregnant stages examined and, in gener al, the relative changes with reproductive state reflected changes in plasma P, concentration and body condition score. Plasma and adipose t issue P-4 concentrations were positively correlated (P < 0.001) at est rus and during the luteal phase of the estrous cycle. When adipose tis sue samples from eight cows were incubated as explants in vitro and ch allenged with epinephrine, non-esterified fatty acid (NEFA) and P-4 co ncentrations increased (P < 0.05) with increasing concentrations of ep inephrine. These results demonstrate that substantial quantities of P- 4 are sequestered in adipose tissue, depending on the reproductive sta te, and indicate that lypolysis may result in the release of P-4 from this tissue, thereby influencing plasma P-4 concentrations.