Fetal development in cattle with multiple ovulations.

Treatment of lactating and nonlactating parous cows (n = 379) with 12 mg of FSH-P to evaluate development of multiple bovine fetuses resulted in ovulation rates ranging from 1 to 27 corpora lutea (CL). Fertilization rate (i.e., ova fertilized at 6 to 8 d postmating, 80.0%) was not affected by ovulation rate. The percentage of fetuses developing normally at 51 to 53 d postmating decreased (P less than .01) as ovulation rate increased; 1 CL, 100.0%; 2 CL, 100.0%; 3 CL, 66.7%; 4 CL, 45.8%; 5 CL, 33.3%; 6 to 10 CL, 13.6%; and greater than 10 CL, 8.9%. Of the 86 cows permitted to calve, 47 produced singles, 22 twins, 9 triplets, 7 quadruplets, and 1 quintuplets. Calf birth weight and gestational length decreased (P less than .01) as the number of calves born increased from one to two to three. Smaller decreases (P less than .05) in birth weight occurred among triplets, quadruplets, and quintuplets, whereas gestational length did not differ (P greater than .1) among these groups. Systemic progesterone concentrations in the dam were proportional (P less than .01) to the number of fetuses in utero between d 126 and 266 for dams gestating one, two, or three or more fetuses; estrone sulfate was lower (P less than .01) in dams with one than in those with two or more fetuses. Placental weight (i.e., cotyledons plus intercotyledonary membranes) per fetus at 52 +/- 1 d of gestation and at term decreased as the number of fetuses increased. The chorioallantoic membranes were often fused among multiple fetuses and contained either all viable or all dead fetuses, but not both, within the same anastomosed placental unit. These results suggest that ovulation rate is the first limiting factor to increasing cow productivity for beef cattle because some bovine females had the capacity to gestate up to three fetuses per uterine horn, or a total of five fetuses, above which pregnancy was terminated.