Metabolites of Progesterone and Estrogen in Domestic Sow Urine. III. Effect of Litter Size2

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Abstract
The relationships between litter size and rates of excretion of six urinary metabolites of estrogen and progesterone were evaluated at each of 14 stages of pregnancy (19 to 110 days). Litter size at farrowing for 44 gilts ranged from two to 16 piglets (avg 9.6±0.4). The metabolites measured were two estrogens, estradiol-17β and estrone, and four pregnanes, 5β-pregnan-3α-ol-20-one, 5α-pregnan-3β-ol-20-one, 5β-pregnan-3α,20α-diol and 5β-pregnan-3α,6α-diol-20-one. Excretion rates were expressed as ng/mg of urinary creatinine. Significant effects of litter size (linear and quadratic) were determined by regression analysis. Rate of excretion of total estrogen which was principally estrone increased significantly (P<.01) as litter size increased at 26 days of pregnancy but not at other weekly intervals. Total pregnane (sum of the four pregnane compounds) excretion rate was higher for larger litters at each weekly interval from 19 to 54 days of pregnancy (P<.01 at 33 and 40 days) and was generally lower from 61 to 96 days, except for day 75 (P<.05 at 68 days). Data for the individual pregnanes also were presented. Ratios of total pregnanes to total estrogen were lower (P<.01) at 33 days for litters of nine piglets than litters with a greater or lesser number. At 40 days (P<.05) and 75 days (P<.01) these ratios increased as litter size increased. Based on this and other studies it appears that embryos additively influence ovarian steroid metabolism (increase) from 19 to 54 days or, at least, from 26 to 40 days of pregnancy. Other factors appear to be more important or equally important after 54 days of pregnancy. Copyright © 1971. American Society of Animal Science. Copyright 1971 by American Society of Animal Science.

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