Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/1998
Publication Date: N/A
Interpretive Summary: The production by the pig uterus of proteins which transport vitamins and minerals to the developing embryo likely influences the efficiency of embryo development; however, factors controlling protein production by the uterus are poorly understood. This experiment studied the influence of the pig embryo and of the ovarian hormone, progesterone, on the onset of uterine protein secretion which occurs around day 11 of the estrous cycle or pregnancy. Also, uterine protein secretion was compared between the Chinese Meishan, a highly prolific breed, and white crossbred composite breed. Results indicated that (1) the pig embryo has little or no effect on uterine protein secretion, (2) timing of the onset of uterine protein secretion is influenced by the timing of increased levels of progesterone and (3) Meishan pigs secrete less uterine protein than white crossbred pigs. The decreased uterine protein secretion in Meishan pigs may explain the increased fertility of this breed, by slowing conceptus development an limiting the interaction of embryos within the uterus. Interference with progesterone during early (day 2 to 3) pregnancy has the potential to duplicate this effect in white crossbred pigs, possibly increasing litter size in domestic breeds.
Technical Abstract: This experiment consisted of the following treatment-breed groups: (1) White crossbred gilts, (2) White crossbred gilts treated with progesterone (200 mg/d in corn oil given on d 2 and 3 after estrus), and (3) Chinese Meishan gilts. Pregnant and nonpregnant gilts (n = 3 to 6) from each treatment-breed combination were assigned to be slaughtered on d 10, 11, 12, 13 and 15. At slaughter each uterine horn was flushed with 20 mL minimal essential medium (MEM). Uterine flushings were assayed for total protein, acid phosphatase, uteroferrin, retinol binding protein, and oxytocin. Uterine flush total protein was increased by progesterone treatment, was unaffected by pregnancy status, and was less in Meishans. Similar patterns were found for retinol binding protein and uteroferrin, except that uteroferrin was greater in pregnant than in nonpregnant gilts. Oxytocin was greater in pregnant compared to nonpregnant gilts, was not influenced by progesterone treatment and was similar in Meishans and White crossbred gilts. These results indicate that the conceptus does not influence secretion of either total protein or retinol binding protein during pregnancy and that the onset of secretion of these uterine proteins may be controlled by progesterone. The presence of the conceptus is associated with increased uteroferrin and oxytocin production. The decreased secretion of uterine proteins in Meishan gilts may partially explain the slower embryonic development that has been reported for this breed.