241 EFFECT OF INTRODUCTION OF THE INVERDALE FECUNDITY (FecX^I) GENE INTO A TEXEL × SCOTTISH HILL EWE (CHEVIOT) FLOCK ON LITTER SIZE, BIRTHWEIGHT, AND LAMB SURVIVAL

Abstract

The naturally occurring Inverdale fecundity gene (FecX^I), first identified in a Romney flock in New Zealand is located on the X-chromosome and is a point mutation of the bone morphogenetic protein-15 (BMP-15) gene. Although homozygous carriers are infertile due to abnormal development (hypoplasia) of the ovaries, heterozygotes exhibit an increase in ovulation rate and numbers of lambs born, thus making the gene a candidate for improving prolificacy of crossbred hill ewes in a stratified hill and lowground sheep industry. Heterozygous Inverdale gene-carrying crossbred (Texel × Cheviot) ewes (n = 76) and noncarrier controls (n = 18) were mated by non-carrier Texel rams at approximately 18 months of age. Ultrasound pregnancy scanning took place at approximately 70 days of gestation. Lambing records comprised litter size and birthweight data and all losses, including mummified fetuses. Regression analysis tested effects of ewe genotype, pre-mating liveweight, and body condition score on litter size. ANOVA and Kruskal-Wallis tests were used to compare genotype and litter size category effects on dam and offspring data. Mean (± SEM) litter size was 2.6 ± 0.10 and 1.9 ± 0.11 for FecX^I carrier and noncarrier ewes (P < 0.001). Although carrier ewes had lower pre-mating liveweights (60 ± 5.2 vs. 63 ± 3.8 kg; P < 0.05) and body condition scores (3.1 ± 0.29 vs. 3.3 ± 0.24; P < 0.01) than noncarrier ewes, litter size was not affected by either factor. Ultrasound scanning was a good predictor (r² = 0.86; P < 0.001) of the eventual lamb crop. Incidences of singletons, twins, triplets and higher multiples were 8, 38, 42 and 12%, respectively, among FecX^I carrier dams. Corresponding incidences among noncarriers were 17, 78, 5, and 0%. Peri- and neonatal losses increased with litter size. Of lambs from single, twin or triplet births, losses were 20% and 6% for FecX^I carrier and noncarrier ewe groups, respectively (P = 0.049). Of 32 quadruplets (mean live weight = 2.65 kg), 9 did not survive; the sole set of quintuplets (mean = 1.52 kg) also succumbed. Birth weights of lambs influenced survival (P < 0.001); among quadruplets, for example, survivors were 0.5 kg heavier than counterparts that died. Surviving triplets from FecX^I carrier dams were 0.8 kg heavier than non-survivors (3.66 kg vs. 2.86 kg). Overall, in this study mortality was four times greater among lambs below 3 kg live weight than among their heavier counterparts. Consequently, further studies are needed to investigate how Inverdale gene-carrying ewes can be managed during the peri-conception period to optimize litter size, placental function, and prenatal growth for maximum lamb survival.

This work was funded by HIE, ANM Group, Britbreed, Ltd., and Harbro Ltd.; F. M. A. is a Genesis Faraday Associate and is sponsored by the SAC Trust, Harbro, Ltd., and Innovis.