Co-Authors:
Wolfenson, D., Department of Animal Science, Faculty of Agricultural, Food and Environmental Quality Sciences, Hebrew University of Jerusalem, Rehovot 76100, Israel
Sonego, H.H., Department of Animal Science, Faculty of Agricultural, Food and Environmental Quality Sciences, Hebrew University of Jerusalem, Rehovot 76100, Israel
Bloch, A., Department of Animal Science, Faculty of Agricultural, Food and Environmental Quality Sciences, Hebrew University of Jerusalem, Rehovot 76100, Israel
Shaham-Albalancy, A., Department of Animal Science, Faculty of Agricultural, Food and Environmental Quality Sciences, Hebrew University of Jerusalem, Rehovot 76100, Israel
Kaim, M., Institute of Animal Science, Agricultural Research Organization, Bet Dagan 50250, Israel
Folman, Y., Institute of Animal Science, Agricultural Research Organization, Bet Dagan 50250, Israel
Meidan, R., Department of Animal Science, Faculty of Agricultural, Food and Environmental Quality Sciences, Hebrew University of Jerusalem, Rehovot 76100, Israel
Abstract:
This study examined seasonal differences in progesterone (P4) production by granulosa cells (GC) and thecal cells (TC) that were luteinized in vitro during the winter or the summer; it also compared plasma P4 concentrations of lactating dairy cows in the two seasons. First-wave dominant follicles obtained from Holstein cows were dissected on day 6 of the cycle, GC and TC were separated, enzymatically dispersed, and cultured for 9 days in media containing 1% fetal calf serum, forskolin (10 μmol/mL) and insulin (2 μg/mL), to induce cell luteinization. All experimental procedures were identical and characteristics of the follicles were similar in the two seasons. During 9 days of culture, P4 production by luteinized GC was higher in winter than in summer, but the difference only tended to be significant. In contrast, luteinized TC produced three times as much P4 in winter as in summer (324 versus 100 ng/105 cells). In the in vivo experiment, P4 concentrations in plasma collected during entire estrous cycles in winter and summer were compared. The cows were, on average, at 70 days postpartum and yielded similar amounts of milk. Concentrations of progesterone in plasma were significantly higher in winter than in summer; during the mid-luteal phase the difference between the two seasons was 1.5 ng/mL. These results indicate that chronic effects of heat-stress are possibly carried over from an impaired follicle to an impaired corpus luteum (CL), and that luteinized TC are more susceptible to heat-stress than luteinized GC. © 2002 Elsevier Science Inc. All rights reserved.
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