GENETICS OF LAMENESS IN COWS ON TMR IN SOUTH AFRICA

Lameness due to claw lesions is a major hurdle for sustainable dairy production worldwide. The most frequent reason for lameness in dairy cattle is the occurrence of lesions on the animal’s claw(s). Novel phenotypes relating to these traits need to be included in breeding objectives and a large number of accurate phenotypic recordings are required for genetic evaluations and accurate selection. Hoof trimming is used as a preventative measure, and key to future improvement strategies, providing phenotypic records for genetic interventions. This has not really been pursued in the South African dairy industry. Therefore, the study cited aimed to evaluate hoof-trimming data in South African Holstein herds in total mixed ration (TMR) systems, to determine the prevalence of claw lesions, investigate the associated phenotypic and genetic parameters, and explore the use of genomic information to provide insight into the underlying genetic land scape of claw lesion traits.

Routine hoof-trimming events of five dairy herds in the central region of South Africa over a 10-year period, together with genotypes generated during the South African Dairy Genomic Programme provided the data for the study. Some 260 000 data points could be analysed.

More than 50% of cows showed a lesion on any one foot, with digital dermatitis (DD) as the most commonly recorded lesion, followed by the non-infectious lesions sole ulcer (SU), sole haemorrhage (SH), and white line (WL), most of which occurred in the rear feet. The relationships between housing systems, individual feet, and the different lesions were analysed using chi-square tests as well as correspondence analysis. SU and SH were strongly associated with each other, as were DD, interdigital phlegmon (IP), SH and WL. These associations between lesions could be used to inform a more simplified approach to lesion recording systems, and contribute to practical prevention strategies on-farm. Phenotypic correlations between individual lesions and groups (infectious, non-infectious, and total lesions) were investigated using Spearman correlation tests. Moderate to strong relationships were observed among the non-infectious lesions SH, SU, and WL (0.425–0.576), with the occurrence of SU and WL strongly positively associated with total non-infectious lesions (0.543–0.576). Similarly, the infectious lesion DD was positively correlated with the total infectious lesions (0.984). The estimated heritability of lesion categories was low, varying between 0.008 for total lesions to 0.05 for the total non-infectious lesions category. A genome-wide association study (GWAS) for non-infectious lesions was also performed using EMMAX. This resulted in the identification of one genome-wide significant single nucleotide polymorphism (SNP) and 15 genome-wide suggestive SNPs. Candidate genes associated with the significant SNP on chromosome 25 was related to abnormal skin morphology, immunity, and inflammation.

Comments and conclusions: From the literature, and this study, it is clear that claw lesions are highly polygenic. Differences among definitions and descriptions in the literature added to the complexity of the analyses. This study represents the first attempt to investigate claw lesions in South Africa using a combination of phenotypic and genetic data. The results confirmed the lack of adequate phenotypic data for genetic and genomic analyses, due to a lack of consistent farmer recording as well as a lack of coherence among data recording systems. Underlying genetic variability was confirmed and holds potential for further research but this requires consistent and complete phenotypic claw data. The prevalence of lameness is high and a simplified and standardised recording system will be a first step for applicable research to support the reduction of the incidence of this painful and costly disorder.