Relationship Between the mRNA Expression Level of TGF-β Receptor Genes in Tissues and Ovulation Rate in Hu Sheep

Eight ewes of Hu sheep which bred multi-lamb were used as the high-fecundity group and the other eight ewes of Hu sheep which bred single lamb were used as the control group to investigate the relationship between the mRNA expression level of TGF-β receptor genes in tissues and ovulation rate in Hu sheep. Cloprostenol sodium was injected to make the synchronization of estrus treatment, then all ewes were slaughtered within 24-36 h after empathema and the ovaries were collected. Furthermore, the number of ovulation points was counted to determine ovulation rate for each sheep. Tissue expression analysis was conducted by RT-PCR for one ewe form the high-fecundity group and the relationship between the mRNA expression of genes encoding TGF-β receptors and ovulation rate was detected by real-time fluorescent quantitative PCR. The results showed that the relative expression level of TGF-flR I gene in the reproductive organ was significantly higher than in the lung and muscle （P 〈 0.01）, while relative expression level of TGF-βR H in reproductive organ was significantly higher than that of other tissues （P 〈 0.01）, indicating that these are highly expressed genes in the ovary. In addition, mRNA expression level of TGF-βR I and TGF-flRH in the ovaries of the high-fecundity group were significantly higher （P〈 0.01） and obviously higher （P= 0.011） than the control group, respectively. The mRNA expression level of TGF-βR I and TGF-βR H had a positive correlation with ovulation rate and the correlation coefficients were 0.562 （P〉 0.05） and 0.711 （P〈 0.05）, respectively. It is suggested that TGF-β receptors have close relationship with highfecundity in Hu sheep.

Artificial Induction of Twinning by an Active Immunization of Beef Cows Against Inhibin Partially Purified from Porcine Seminal Plasma

Two hundred and seventy multiparous Chinese Yellow cattle (beef) were selected at 1 to 3 months postpartum and divided into three groups (90 cows for each). Animals were given both a primary and booster immunizations with a total dose of 3 mg (Group Th) or 1.5 mg (Group Tl) of seminal preparation containing inhibin activity, emulsified with Freund's complete adjuvant and incomplete adjuvant (for booster) , at 3 or 4-week intervals. Other cows were treated with the same volume of seminal preparation without inhibin activity as procedures mentioned above to serve as a control (Group C). Artificial inseminations were given twice at 8 - 12 h intervals when the cow was in heat. Jugular venous blood samples were collected from each cow and used to assay the presence of antibody against seminal preparation by double-diffusion in agar precipitation test and to detect the titer of inhibin antibody by an ELISA method. Data from 247 cows showed that 83.9% (73/87) of cows were in estrus and ovulated 89 ova altogether, of which 19 cows ovulated twin ova and 15 cows produced twins in Group Th (n = 87). However, only 61.1% (44/72) of cows in Group TI (n = 72) and 62.5% (55/88) of cows in Group C were in estrus and ovulated 46 and 52 ova altogether respectively. The ovulation rate (1.27 ± 0.03), calving rate (126.3%) and twinning rate (26.3%) in Group Th were greater than those in Groups Tl or C (P<0.01). Furthermore, the ovulation rate was associated with antibody titer in sera of immunized animals (r = 0.7507, P<0.01). These results indicate that active immunization of postpartum cows against inhibin purified from porcine seminal plasma may increase the ovulation rate and induce twinning, suggesting the potential to develop a method to improve fertility in cows.

Progress on major genes for high fecundity in ewes

The existence of major genes affecting fecundity in sheep flocks throughout the world has been demonstrated.Three major genes whose mutations can increase ovulation rate have been discovered,and all related to the transforming growth factorβ(TGF-β)superfamily.The mutant FecB of bone morphogenetic protein receptor 1B(BMPR1B)has an additive effect on ovulation rate.Six mutations(Fec^(XI),Fec^(XH),Fec^(XG),Fec^(XB),Fec^(XL),Fec^(XR))of bone morphogenetic protein 15(BMP15)related with fertility have been identified that share the same mechanism.All the mutants can increase ovulation rate in heterozygotes and cause complete sterility in homozygotes.Homozygous ewes with two new mutations(FecX^(Gr),FecX^(O))of BMP15 had increased ovulation rate without causing sterility.There are five mutations in growth differentiation factor 9(GDF9)associated with sheep prolificacy where FecG^(E) and FecG^(F) have additive an effect on ovulation rate and litter size.The newly identifiedβ-1,4-N-acetylgalactosaminyltransferase 2(B4GALNT2)gene of FecL is proposed as a new mechanism of ovulation rate regulation in sheep.Woodlands is an X-linked maternally imprinted gene which increases ovulation rate.In addition,several putative major genes need to be verified.This review is focused on the identification of the mutations and mechanisms whereby the major genes affecting ovulation rate.