Association between PrP genotypes and performance traits in a Welsh Mountain flock

The National Scrapie Plan (NSP) was launched in Great Britain in 2001, with the aim of eventually eradicating scrapie, a small ruminant transmissible spongiform encephalopathy, from the national sheep flock. Specifically, a selective breeding programme, the Ram Genotyping Scheme, was devised enabling pedigree ram breeders to reduce the number of scrapie-susceptible genotypes from their flocks. The effect of large-scale manipulation of PrP genotypes on commercially important traits within the sheep industry is, however, unknown. We have therefore examined production traits in a total of 43 968 lambs from 32 pedigree breeders across three British hill breeds, comprising 8163 North Country Cheviot (Hill), 21 366 Scottish Blackface and 14 439 Welsh Mountain lambs. Traits examined included: weights at birth, 8 and 20 weeks; ultrasonic fat and muscle depth, and average daily weight gain from 8 to 20 weeks. Linear mixed models were fitted for each trait, including animal (direct) genetic effects and up to three maternal effects. Potential associations with the PrP gene were assessed by fitting either PrP genotype or number of copies of individual alleles as fixed effects. A number of breed-specific significant associations between production traits and the PrP gene were found, but no consistent significant effects were detected across the three breeds. Breed-specific effects were as follows: (i) 0.37 kg higher birth weights (BWTs) in AHQ homozygous North Country Cheviot (Hill) lambs ( P , 0.01); (ii) 0.16 kg higher BWTs in ARR homozygous Scottish Blackface lambs ( P , 0.05); (iii) 0.5 kg higher 8-week weights in VRQ heterozygous Scottish Blackface lambs ( P , 0.01); (iv) a 0.72 kg decrease in scan weight associated with homozygous ARR Welsh Mountain lambs ( P , 0.01); (v) 0.51 mm higher ultrasonic muscle depths in AHQ homozygous Welsh Mountain lambs ( P , 0.01); (vi) 0.48 mm lower ultrasonic muscle depths in Welsh Mountain lambs carrying one or more copies of the ARR allele ( P , 0.05) and (vii) 0.2 mm higher ultrasonic fat depths in heterozygous VRQ Welsh Mountain lambs ( P , 0.05). The use of a Bonferroni correction to define appropriate significance thresholds across the three datasets, which account for the large number of independent comparisons made, resulted in breed-specific comparisons, with P , 0.01 becoming significant at P , 0.05, and the remaining breed-specific comparisons no longer being significant. The absence of a common effect across the three breeds suggests that any true association found may be due to breed-specific alleles of neighbouring genes in linkage disequilibrium with the PrP locus.

Section: Discussionsupporting

confidence: 86%

“…Alternatively, they have been performed on experimental rather than on commercial sheep populations (Man et al, 2006;Sawalha et al, 2007). Only the study of Pritchard et al (2008) has focused on commercial lamb performance data in a numerically important breed, the Welsh Mountain.…”

Section: Introductionmentioning

confidence: 99%

Associations of PrP genotype with lamb production traits in three commercial breeds of British hill sheep

Moore

Boulton

Bishop

2009

“…A study on three UK hill breeds by Moore et al (2009), showed that only the Welsh Mountain breed had any associations with ultrasonic traits in which the ARR and AHQ alleles were associated with lower muscle depths, while VRQ carriers were associated with more fat than other genotypes. In the same breed, Pritchard et al (2008) observed a contrasting result in which ARR homozygous lambs had significantly greater muscle depth than ARR heterozygous lambs. Extensive studies failed to show any significance of PrP genotype in determining the depth of muscle or fat in many other European sheep breeds (Roden and Haresign, 2001;Prokopova et al, 2002;de Vries et al, 2004;Vitezica et al, 2005;Isler et al, 2006;Man et al, 2006;Sawalha et al, 2007a;Sweeney and Hanrahan, 2008).…”

Section: Discussionmentioning

confidence: 93%

“…This led to the initiation of a research project in which potential associations between PrP genotype and performance and survival traits were investigated in a variety of sheep breeds from all sectors of the sheep industry in Great Britain. Results for hill breeds have now been reported (Man et al, 2006;Sawalha et al, 2007a;Pritchard et al, 2008;Moore et al, 2009), with the general conclusion being that although significant associations between PrP genotype and lamb performance are occasionally seen, these are generally small in magnitude and not consistent across breeds. However, the majority of British slaughter lambs are sired by terminal sire (i.e.…”

Section: Introductionmentioning

confidence: 99%

Associations of PrP genotype with lamb production traits in three commercial breeds of British lowland sheep

Moore

Boulton

Bishop

2009

The Ram Genotyping Scheme was launched in Great Britain in 2001 as part of the National Scrapie Plan and was devised to reduce and eventually eradicate classical scrapie susceptible genotypes from the national pedigree flock. Anecdotal claims from breeders suggest that sheep with more resistant PrP genotypes may have inferior phenotypes. In this study, we test this possibility for lamb production traits in three breeds of lowland sheep: Charollais (22 752 lambs), Poll Dorset (22 589 lambs) and Texel (23 492 lambs). Data were received from 50 breeders and comprised weights at birth, 8 weeks and scanning (from which average daily weight gain was derived), and ultrasonic muscle and fat depths. Animal (direct) genetic effects and up to three maternal effects were fitted in linear mixed models for each trait. Fitting either PrP genotype or number of copies of individual alleles carried as fixed effects allowed potential associations with the PrP gene to be assessed. There were no significant associations seen in the Poll Dorset breed; however, significant associations were found with the number of allele copies carried in the other two breeds included in this study. Charollais lambs carrying one copy of the VRQ allele had significantly ( P , 0.01) greater ultrasonic muscle depth (0.58 mm) and fat depth (0.2 mm) than non-carriers. In the Texel breed, lambs with one ARR allele were significantly heavier than those with two or zero ARR alleles; heterozygous ARR lambs were 0.07 kg heavier at birth ( P , 0.05), 0.42 kg heavier at 8 weeks ( P , 0.01) and 0.17 kg heavier at scan weight ( P , 0.01), than non-carriers. After Bonferroni corrections to adjust significance thresholds to account for the large number of independent comparisons made, all significant results remained so at P , 0.05 or greater, except for the ARR allele effect on birth weight in the Texel breed, which was no longer significant. These results compare favourably with others from studies on many continental breeds of sheep, published in recent years, and add credence to the conclusion that selection on PrP genotype is unlikely to have any noticeable impact on the measured growth and carcass traits in sheep.

“…Several studies on sheep reported that no association exists between the PRNP and the most relevant economic traits in the sheep industry (reproductive and growth traits; meat traits and milk traits). Therefore, selection for scrapie resistance will not adversely affect progress in the traits (Vitezica et al, 2005(Vitezica et al, and 2013Pritchard et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

Review: A review on classical and atypical scrapie in caprine: Prion protein gene polymorphisms and their role in the disease

Curcio

Sebastiani

Lorenzo

et al. 2016

Scrapie is a naturally occurring transmissible spongiform encephalopathy in sheep and goat. It has been known for~250 years and is characterised by the accumulation of an abnormal isoform of a host-encoded prion protein that leads to progressive neurodegeneration and death. Scrapie is recognised in two forms, classical and atypical scrapie. The susceptibility to both types of scrapie is influenced by polymorphisms of the prion protein gene (PRNP). Sheep susceptibility or resistance to classical scrapie is strongly regulated by the polymorphisms at codons 136, 154 and 171 of the PRNP. The genetic role in atypical scrapie in sheep has been defined by polymorphisms at codons 141, 154 and 171, which are associated with different degrees of risk in the occurrence of the ovine disease. Progress has been achieved in the prevention of scrapie in sheep due to efficient genetic breeding programmes based on eradication and control of the disease. In Europe, the success of these programmes has been verified by applying eradication and genetic selection plans. In general terms, the ovine selection plans aim to eliminate and reduce the susceptible allele and to enrich the resistant allele ARR. During outbreaks all susceptible animals are slaughtered, only ARR/ARR resistant rams and sheep and semi-resistant females are preserved. In the occurrence of scrapie positive goats a complete cull of the flock (stamping out) is performed with great economic loss and severe risk of extinction for the endangered breeds. The ability to select scrapie-resistant animals allows to define new breeding strategies aimed to boost genetic progress while reducing costs during scrapie outbreaks. Allelic variants of PRNP can be protective for caprine scrapie, and the knowledge of their distribution in goats has become very important. Over the past few years, the integration of genetic information on goat populations could be used to make selection decisions, commonly referred to as genetic selection. The objective of this review was to summarise the main findings of polymorphisms of the caprine prion protein (PrP) gene and to discuss the possible application of goat breeding schemes integrating genetic selection, with their relative advantages and limitations.