Effect of the FecXR polymorphism in the bone morphogenetic protein 15 gene on natural or equine chorionic gonadotropin-induced ovulation rate and litter size in Rasa Aragonesa ewes and implications for on-farm application1

Abstract

A new mutation in the bone morphogenetic protein 15 (BMP15) gene (FecX(R) allele) causing increased prolificacy in heterozygous (R+) and sterility in homozygous ewes has been recently described in Rasa Aragonesa, a low-prolificacy Mediterranean breed. The current study determined, first, the effect of this polymorphism on natural and eCG-induced ovulation rate (OR) and the effect of eCG dose on reproductive performance; and second, its effect on prolificacy and its interaction with progestagen + eCG treatment on farms, which have not been reported to date. The FecX(R) allele increased OR by 0.44 and 0.63 ovulations in young (n = 91) and adult (n = 84) R+ ewes, respectively (both, P < 0.01), increments less than reported in prolific breeds carrying other mutations in BMP15. When the standard dose of eCG used on farms (480 IU) was applied to R+ ewes (n = 36), an extremely high OR (3.95) was recorded, which was accompanied by greater partial failure of multiple ovulations (PFMO). On the contrary, OR using 240 IU in R+ ewes (2.90; n = 35) was similar to 480 IU in wildtype (++) ewes (2.82; n = 48; both P < 0.01 when compared with 480 IU in R+ ewes). No differences were found in the birth weight of the offspring between R+ and ++ eCG-stimulated ewes within the same litter size. To validate the genealogy identification on farms, PCR genotyping was carried out in 1,667 ewes from 4 elite flocks, resulting in a negligible misclassification of R+ ewes, which demonstrated that identification by genealogy is a reliable tool to identify FecX(R) ewes within the breeding program. In recorded farms, the natural litter size of ++ ewes (1.34, n = 599,160 lambing records) was increased due to the FecX(R) allele by 0.35 lambs (P < 0.0001, n = 6,593 lambing records). A similar increase (0.30) was observed when comparing ++ and R+ ewes treated with 480 IU of eCG (P < 0.0001, n = 62,055 and n = 866, respectively). When applying 480 IU of eCG to R+ ewes, the increase in prolificacy was only due to increased percentages of triplets (P < 0.001) and quadruplets (P < 0.0001), but not of twin births. In conclusion, the favorable reproductive performance of R+ ewes, with 0.63 extra ovulations and 0.35 extra lambs per lambing ewe, is responsible for the increased interest in the use of this polymorphism. Nevertheless, care must be taken in the application of eCG to R+ ewes, with the current results showing that the standard dose increases prolificacy by only increasing triple and higher-order births.

Genes con efecto mayor sobre la fertilidad de ovejas. Revisión

“…Por otra parte, ya se han iniciado estudios para evaluar las ventajas potenciales que ofrece el uso estratégico de ovejas con estas mutaciones en la producción de corderos, asociado a estrategias de manejo reproductivo y nutricionales (42,43) , las cuales ofrecen beneficios potenciales en la producción de corderos.…”

“…Recientemente se han reportan alelos del gen BMP-15 en las raza Aragonesa en España, las denominadas cola grasa de Malasia (razas Afshari, Baluchi, Makui y Mehraban) y en las razas Banpalas y del valle de Kashmir en la India, asociados a mayor prolificidad en las ovejas heterocigotas (39,(42)(43)(44)(45)(46) .…”

“…On the other hand, studies are starting to evaluate potential advantages that offer strategic use of ewes with these mutations in the production of lambs, associated with reproductive management and nutritional strategies (42,43) , which offer potential benefits in lamb production.…”

Analysis of major fecundity genes in autochthonous Laticauda and Bagnolese sheep breeds

“…This gene maps to the X chromosome (Galloway et al, 2000) and it is constituted by two exons, separated by an intron. Several studies revealed the presence of SNPs (Galloway et al, 2000;Hanrahan et al, 2004;Bodin et al, 2007;Lahoz et al, 2011;Polley et al, 2010) and deletions (Martinez-Royo et al, 2008;Monteagudo et al, 2009) in BMP15 exon 2 associated with increased ovulation rate in heterozygous carriers and with sterility in homozygous carriers (Table 1).…”

Using sheep lines with mutations in single genes to better understand ovarian function

“…At least six different mutations have been identified in the BMP15 gene (Galloway et al 2000, Bodin et al 2007, Martinez-Royo et al 2008, Monteagudo et al 2009, Lahoz et al 2011 wherein ewes heterozygous for the mutations have increased ovulation rates and those homozygous for the mutations are infertile. While all the mutations have similar general effects on fertility, there are subtle differences, as the increases in ovulation rate observed in the heterozygous animals (Table 1) vary from 35 to 100% (McNatty et al 2004).…”