Endocrine Response of the Cow to PMSG and Subsequent Multiple Corpora Lutea Regression by Prostaglandin F2α2

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Abstract
The effect of pregnant mare serum gonadotropin (PMSG) on progesterone, 20β-dihydroprogesterone, luteinizing hormone (LH) and total estrogen concentrations were measured in plasma of 15 parous Angus cows in which estrus was synchronized with prostaglandin F2α-tromethamine salt (PGF2α). Cows were grouped according to number of corpora lutea (CL): 0 to 1 - group 1; 2 to 3 - group 2; and greater than 3 - group 3. Hormone changes with time were similar in all groups following PMSG treatment, although progesterone and estrogen concentrations were higher in cows with a larger number of corpora lutea. Coefficients of correlation between number of CL and plasma progesterone and estrogen were .62 and .54 (P<.01), respectively. Efficacy of utilizing PGF2α to regress multiple CL of superovulated cows was tested by giving a single injection of 40 mg PGF2α tromethamine salt approximately 10 days post-insemination to cows with more than 3 corpora lutea. PGF2α caused a reduction (P<.01) in plasma progesterone which reached a nadir of 1.8 ± .8 ng/ml within 5 days followed by a low but steady increase to 2.7 ± 1.6 ng/ml 7 days after PGF2α. Unexpectedly, pregnancy continued to parturition in four of five animals in group 3. Progesterone from multiple CL apparently was adequate to maintain pregnancy, even though values reached levels as low as .5 ng/ml in three of five cows. Maintenance of pregnancy raised the possibility that the conceptus may have protected the CL from complete regression. Alternatively, the dose of PGF2α may have been inadequate for the increased mass of corpora lutea. Copyright © 1979. American Society of Animal Science . Copyright 1979 by American Society of Animal Science.

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