What is the difference between polled and horned

An added complication when breeding for polling is the issue of scurring which can occur. Scurs are small growths of material very similar to horns that can develop in polled cattle.

Traditionally it has been believed that scurs are sex-influenced due to the fact that they have been shown to be more common in bulls than cows. An example of this is that when Aberdeen Angus cattle are crossed with Brown Swiss the result is scurred bulls and smooth polled non-scurred cows. Similarly to polling there are two forms of the gene that control whether an animal has scurs.

Again these are inherited from the parents with the offspring receiving one copy from the Sire and one from the Dam. The two forms are:. SC — This form causes scurring and the capitalisation indicates that it is dominant over the other form.

However there is an added complication because the genes controlling scurs are also affected by the presence of the genes for polling. For a bull to develop scurs they must have a copy of the recessive form of the polling gene p and one copy of the dominant form of the scurring gene SC.

Heifers however must have two copies of the dominant form of the SC gene to have scurs along with a copy of the recessive form of the polling gene p. The outcomes of the different genotypes in the different sexes are outlined in the table below scurred cattle are highlighted :. In all of these cattle the genes for polling appear to be dominant so the cattle appear smooth polled.

The presence of two copies of the SC gene and a copy of the p gene causes scurs in both bulls and cows. The single copy of the SC and p genes lead to scurs in the bulls but not in the cows where a further scurring gene would be needed.

Both bulls and cows appear smoothly polled as only the recessive forms of the scurring genes are present. The selection for the polled trait is made complicated however by the inability to visually distinguish between a polled animal carrying two copies of the gene and an individual with only one copy. We had access to the performance records of Charolais bulls horned and polled and 1, Hereford bulls 1, horned and polled. As shown in Table 1, we found very little difference between the horned and polled bulls in the traits that were measured.

The polled Charolais bulls did carry significantly more backfat than their horned counterparts, but they were not different in average daily gain, adjusted yearling weight or in scrotal circumference. The polled Hereford bulls in Saskatchewan had a significantly higher average daily gain compared to the horned bulls and tended to be larger yearlings.

Polled Hereford bulls in Alberta also tended to have a greater average daily gain, but the difference was not considered significant. Our findings were similar to other studies. Research by Lange in found no difference between polled and horned German Simmental cattle in growth, carcass yield, carcass composition, health and reproductive performance. Work reported by Frisch and coworkers from Australia in - comparing various beef breeds - showed no difference between horned and polled crossbred lines in live weight, fertility and mortality rates.

Another encouraging finding was that the ratio of polled bulls at each Canadian test station over the time period had gradually increased as the number of horned bulls decreased. In other words, good polled bulls are becoming more readily available.

Historically, polled beef bulls may have been inferior, but there is no evidence that overall differences still exist today. Dehorning beef cattle via genetics is a welfare friendly practice that everyone in the industry should embrace and support. Contact him at [email protected]. Because the polled condition is a dominant trait, some polled bulls can be heterozygous and carry one copy of the polled gene and one copy of the horned gene. In the literature, different modes of inheritance have been discussed for the polled phenotype in sheep.

Differences in the effects of horned and polled alleles for males and females were already suggested by Wood in the s [ 30 ] and Dolling in the s specifically for Merino sheep [ 31 , 32 , 33 ].

Johnston et al. Dominik et al. Inconsistent results with the insertion are observed mainly for sheep breeds with sex-dependent or variable horn status.

In Merino sheep, horn status is sex-dependent, and the occurrence of scurs and knobs is observed especially in females. Figure 2 shows the predicted phenotype given its genotype class by including dominance or assuming additivity only.

Our findings confirm the importance of dominance in both males and females, but do not confirm any maternal imprinted effect results not shown. This is the first study to show statistical evidence for sex-dependent differences in the additive and dominance effects for horned and polled phenotypes.

In this section, we discuss three different observations from our study. First, we discuss the importance of a model that explicitly includes SNPs with large effects on the trait, then the genetic architecture of the polled and horned phenotype and the influence of genes outside the RXFP2 region, and finally the importance of identifying the 1. The four methods used to predict polled and horned phenotypes were evaluated based on the correlation between phenotype and predicted phenotype from a fivefold validation.

Similar results were described by Lee et al. Similar results were also observed in dairy cattle for the DGAT1 gene that has a large effect on milk fat percentage. Also a study in pigs in which a large QTL for number of teats in pigs was explicitly fitted, resulted in increased accuracy of prediction [ 38 ].

For the prediction of both horned and polled phenotypes, including a polygenic effect in the model achieved better prediction accuracies compared to using only a single SNP, with little difference between modeling the polygenic covariance structure via pedigree-based relationships versus genomic relationships.

The variance explained by models including a polygenic effect was larger than that explained by models without pedigree information. These results indicate that the single SNP does not explain all the genetic variance. Although selection against horns can be successful, other forms of horns will still exist such as knobs and scurs.

The potential influence of other genes outside the RXFP2 region was further investigated via within- and across-family validation. Polygenic traits such as milk production or growth tend to show a pattern in which across-family prediction is lower than within-family prediction.

Assuming that non-genetic effects e. In our study, differences between across- and within-family predictions were small Table 7 , which clearly shows that the effect of other genes, captured by the polygenic effect, was not strong for the polled and horned phenotypes [ 35 ].

In addition, we detected no other significant regions outside the RXFP2 region when sheep with knobs and scurs were tested against horned sheep in the GWAS see Additional file 2 : Figure S2 , which indicates that the trait is not polygenic and the majority of the variation is determined by the RXFP2 region.

In this study, imputation of the 1. The most likely reason for the lower prediction accuracy is that none of the animals in this study were sequenced and, thus the insertion was not detected directly on the animal itself but rather obtained through imputation.

The accuracy of imputation could have been a limiting factor for not reaching a better prediction accuracy. Even lower LD estimates of 0. Estimates of LD for polled or horned breeds were much higher 0. Incomplete penetrance, allelic heterogeneity or other environmental interactions could cause variability in the horn status within genotype. However, prediction of horn status based on predictive single SNPs provides close to maximum accuracy and can be used succesfully in sheep breeding programs to reduce the frequency of horned phenotypes.

An important factor for a successful breeding program is to ensure accurate phenotype recording. Although the trait seems simple, classifying between horns, scurs, knobs or polled is still a challenge especially with the interference due to castration of males.

Clear guidelines for such recording are necessary to improve the overall prediction of horned and polled phenotypes. Currently, the number of phenotypes and genotypes is not sufficient to evaluate the accuracy of prediction based on these SNPs, although the expectation is that these SNPs could increase the prediction accuracy even more.

The mode of inheritance for polled and horned phenotypes is sex-dependent. Horned vs. Prediction of horned females is difficult since this phenotype is rare and no genetic model is clearly favourable, while polled vs. Addition of pedigree information via a numerator relationship matrix or a GRM to a single SNP model did result in an increased accuracy, but only in a slight one. However, interaction with or effects of genes outside the RFXP2 region were not detected.

Asdell SA. The genetic sex on intersexual goats and a probable linkage with the gene for hornlessness. Castle WE. Genetics of horns in sheep. J Hered. Article Google Scholar. Microsatellite mapping of a gene affecting horn development in Bos taurus.

Nat Genet. Independent polled mutations leading to complex gene expression differences in cattle. PLoS One. Bovine polledness—an autosomal dominant trait with allelic heterogeneity. A, Genome-wide association mapping identifies the genetic basis of discrete and quantitative variation in sexual weaponry in a wild sheep population. Mol Ecol. Article PubMed Google Scholar. Anim Genet. The 1. Genet Sel Evol. Inheritance of horns in sheep: triple alleles in a Dorset-Rambouillet cross.

Marshall FH, Hammond J. On the effects of complete and incomplete castration upon horn growth in Herdwick sheep. J Physiol. A single nucleotide polymorphism on chromosome 10 is highly predictive for the polled phenotype in Australian Merino sheep. Design and role of an information nucleus in sheep breeding programs. Anim Prod Sci. Browning BL, Yu Z. Simultaneous genotype calling and haplotype phasing improves genotype accuracy and reduces false-positive associations for genome-wide association studies.

Am J Hum Genet. A new approach for efficient genotype imputation using information from relatives. BMC Genomics. Genomic prediction from observed and imputed high-density ovine genotypes. Accuracy of genotype imputation based on random and selected reference sets in purebred and crossbred sheep populations and its effect on accuracy of genomic prediction. ASReml user guide release 41 structural specification. Google Scholar. Fast and accurate long-range phasing in a UK Biobank cohort.

Common SNPs explain a large proportion of the heritability for human height. Dominance genetic variation contributes little to the missing heritability for human complex traits. GCTA: a tool for genome-wide complex trait analysis. MTG2: an efficient algorithm for multivariate linear mixed model analysis based on genomic information. Pindel: a pattern growth approach to detect break points of large deletions and medium sized insertions from paired-end short reads.

BreakDancer: an algorithm for high-resolution mapping of genomic structural variation. Nat Methods. Next-generation genotype imputation service and methods. Akaike H.