Effect of number of conceptuses on maternal mammary development during pregnancy in the pig

An experiment was conducted to determine if manipulation of conceptus number could alter estrogen, progesterone or prolactin concentrations in gilts and thereby influence mammary development. Estradiol-valerate injections, oviduct ligation or no treatment were utilized to form three groups of gilts with zero (n=5), 4 to 7 (n=4), or 8 to 11 (n=4) conceptuses, respectively. Blood samples were taken throughout pregnancy, and at day 110 of gestation all gilts were slaughtered and total mastectomies were performed. Mammary glands were analyzed for wet weights, dry weights, RNA and DNA contents. Results indicated conceptuses stimulated mammary development since mammary glands from pseudopregnant gilts had only 22% as much DNA as mammae from pregnant gilts. However, mammary DNA was not different between gilts with 4 to 7 or 8 to 11 conceptuses. The relationship between conceptus number and mammary gland DNA in gilts was best described by the quadratic equation y = 577 + 583x − 38x², where y = total mammary DNA (mg) and x = conceptus number. Significant positive among-animal and within-group correlations between estrogen-sulfate or estrone concentrations in blood and maternal mammary DNA content suggest that estrogens may be the primary conceptus-derived mammogenic hormone in gilts.