Concentrations of Progesterone, Follistatin, and Follicle-Stimulating Hormone in Peripheral Plasma Across the Estrous Cycle and Pregnancy in Merino Ewes That Are Homozygous or Noncarriers of the Booroola Gene

The circulating concentrations of progesterone, FSH, and follistatinacross the estrous cycle and gestation were compared inAustralian merino sheep that were homozygous for the Booroolagene, FecB, or were noncarriers. The Booroola phenotype is dueto a point mutation in the bone morphogenetic protein receptor1B. Progesterone concentrations began to rise earlier and werehigher in the Booroola ewes than in the noncarriers on mostdays of the luteal phase but not during the follicular phase ofthe cycle. Follistatin concentrations remained unchanged acrossthe estrous cycle in both groups of ewes, with no differencesbetween genotypes. FSH concentrations were higher in Booroolaewes than in noncarrier ewes on most days of the estrouscycle, with a significantly higher and broader peak of FSHaround the time of estrus. Progesterone concentrations were significantlyhigher in early and midgestation in Booroola ewes butwere lower toward the end of gestation than those in noncarriers.FSH declined in both groups across gestation, with lowerconcentrations of FSH in Booroola ewes during midgestation.Follistatin remained unchanged across gestation in Booroolaewes and noncarrier ewes with a twin pregnancy but declinedacross gestation in noncarrier ewes with a singleton pregnancy.These results suggest that follistatin concentration is not regulatedby the FecB gene during the estrous cycle and pregnancybut is influenced by the number of fetuses. However, the FecBgene appears to positively affect both progesterone and FSHduring the estrous cycle and across pregnancy, which suggeststhat bone morphogenetic proteins play an important role in theregulation of both hormones.