Evidence for paternal imprinting of the Beta-3 adrenergic receptor gene and a variant association with reduced twinning rate in New Zealand merino sheep (Ovis aries L.)

Abstract

Reproduction efficiency is key for the productivity and performance of New Zealand sheep farms. Thus improving reproduction efficiency and lamb survival is crucial for improving farm efficiency and profitability. Merino sheep are known to have lower scanning-rates than other sheep breeds within New Zealand. The development of the Lincoln University Cold Tolerance Gene Marker (LUGMCTT) based on variants of the ovine beta-3 adrenergic receptor (β3-AR) gene has allowed sheep farmers to select for better cold tolerance and therefore improving lamb survival. Of the variants tested by the LUGMCTT, the D allele is only found in Merino sheep and is thought to have altered ligand binding. This is thought to impair receptor function due to amino acid changes in a highly conserved region of the gene. Recent research indicates the receptor may have a role in physiological functions during pregnancy in other tissues which indicates that the D allele may have adverse effects on scanning-rate. Thus the aim of this study is to identify whether the D allele of the ovine β3-AR gene is being selected against in New Zealand Merino populations and to identify whether the allele’s presence has any effect on Merino scanning-rate. Chi squared goodness of fit tests were performed to determine if the β3-AR genotypes of the sheep tested by the commercial LUGMCTT fit the Hardy-Weinberg equilibrium. Merino sheep were genotyped for the variants of the ovine β3-AR gene intron using the PCR-SSCP method of the Lincoln University Gene Marker Test Laboratory. 440 Merino ewes were mated to 9 rams, 5 of which were carrying the D allele of the β3-AR gene. Associations between dry rate and twinning rate at scanning and the presence of 0, 1 or 2 D alleles of the ewe and 0 or 1 D allele of the ram were accessed using Pearson Chi squared tests. A conditional forward stepwise logistic regression was used to determine if there was an interaction between sire and presence of D allele. There were significant differences between observed and expected genotypes of theβ3-AR gene alleles in all populations except one population. There was no association of the presence of ewe D allele on twinning rate. There was no association of presence of D allele from either the ewe or the ram on dry rate. Both sire (P = 0.054) and the presence of D allele (P = 0.000) had an effect on twinning rate. Sires with the D allele produced a reduced twinning rate (P = 0.003) of a large range of 7.10%-29.30%. This study provides evidence that the D allele of the β3-AR gene reduces Merino scanning-rate, however the effect is complex with evidence of paternal imprinting and the presence of a sire effect. These results indicate that farmers could improve Merino scanning-rate by selecting rams that do not carry the D allele. Additionally selecting the rams without the D allele would be doubly beneficial for an increased scanning-rate due to paternal imprinting.