Yearling Hampshire sows, 15 pregnant and 8 nonbred, were used to compare hormone relationships during the estrous cycle and the first 26 to 28 days of pregnancy. Blood and urine were collected on day 16 preceding and during the third post-weaning estrus. Subsequent collections were made from 12 of the sows on day 2 and the remainder on day 4, and at 4 day intervals thereafter through days 26 or 28. Urine was analyzed for 4 metabolites of progesterone using enzyme and solvolysis procedures for hydrolysis during extraction, and gas-liquid chromatography for quantification of the compounds as the acetate derivatives. Luteinizing hormone (LH) was determined by radioimmunoassay. Progesterone concentration in peripheral blood plasma was similar, except at periods around estrus, whether determined by double isotope derivative or competitive protein binding assays (n=86; r=0.75; P<.01). Days when samples were collected in relation to estrus or breeding were significantly related to the substances measured. The data for pregnant sows differed significantly as compared to nonpregnant sows in levels of progesterone and LH in peripheral blood plasma and rate of excretion of two metabolites of progesterone in urine, namely 5β-pregnan-3α-ol-20-one and 5β-pregnan-3α,6α-diol-20-one. Compared to nonpregnant sows, changes in excretion of metabolites may be detected as early as the fourth to eighth day after breeding as indicated by increased excretion of 5β-pregnan-3α-ol-20-one and 5β-pregnan-3α,6α-diol-20-one. The four metabolites of progesterone were correlated with each other and with total metabolites at different stages of the estrous cycle and the first 28 days of pregnancy. It appears that measurement of 5β-pregnan-3α-ol-20-one in urine would provide reasonable estimates of luteal function and total metabolites of progesterone in urine.
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Tillson et al. (1970) studied this question.