Genetics of trace-element deficiencies

Genetics of trace-element deficiencies in sheep in relation to productivity, fertility and health

The problem: Deficiencies in trace elements such as cobalt (i.e. vitamin B12), sulphur, selenium and zinc can impair animal productivity, fertility and health. Analyses of records from the VLA/SAC centres across Great Britain between 1999-2011 revealed an incidence of cobalt deficiency in sheep of around 7% between July and September each year. Given the known effects of cobalt deficiency on lamb growth this equates to a seasonal loss in sales of £5.3 million to the industry. Annual losses, considering lamb sales at other times of the year together with reduced ewe fertility, increased neonatal losses, and increased parasitic susceptibility, will be greater. Providing prophylactic trace-element supplementation for all ewes and lambs would cost the industry upward of £35-million annually and would be wasteful as not all animals would benefit. Furthermore, methods of trace-element supplementation (particularly short-term drenching) are intrusive and their frequency comprises welfare.

The premise: Deficiencies in the trace elements listed above disturb a specific series of metabolic pathways collectively referred to as one-carbon (1C) metabolism. Cobalt (B12), sulphur and zinc are central to these metabolic pathways; the effects of selenium are less direct. We also know that susceptibility of animals to deficiencies in these trace elements and their responses to supplementation are variable, and have good reason to believe that much of this variation is genetic in origin, with variants residing in components of 1C metabolism.

Objectives: Approximately 40 genes have been identified that encode enzymes, carrier proteins and transporter molecules central to 1C metabolism. It is proposed that mutations (i.e. single nucleotide polymorphisms or SNPs) in these genes account for much of the genetic variation in response to trace-element deficiencies and responses to supplementation. A series of experiments will be undertaken to (i) identify SNPs in these genes, (ii) determine which of these SNPs or combinations of SNPs are important – i.e. lead to disturbances in 1C metabolism (many will have no effect and so can be dismissed), and (iii) conduct two ‘proof of concept’ production studies, one with young lambs the other with breeding ewes, to demonstrate that selection on the basis of these SNPs leads to real improvements in lamb growth, ewe fertility and ewe/lamb health.

Deliverables and outreach: By the end of this 3-year study a high-throughput platform will be developed to screen flocks for susceptibility to deficiencies in 1C metabolites such as cobalt (B12). This will facilitate (a) the identification of a manageable numbers of SNPs which will allow the screening of rams across flocks of different breeds with confidence. However, working with a single breed in the first instance will enable the identification of low- and high-risk rams allowing breeders to judiciously select offspring with reduced susceptibility to, for example, cobalt (B12) deficiency. (b) The establishment of a selected resident flock of ewes at Sutton Bonington, with contrasting SNP profiles, for future-industry sponsored studies that could, for example, test the efficacy of various trace-element supplements administered at key stages of the annual production cycle (e.g. mating, late pregnancy, weaning). This will help develop effective strategies for supplementing susceptible animals; the efficacy/benefits of which could be compared to the status of genetically tolerant animals.

The project is being funded by HCC, EBLEX and Agrisearch and is being undertaken by Nottingham University.