Accelerating sheep genetic improvement in Ireland

Introduction

Animal genetics is a powerful tool that allows farmers to select superior animals to become the parents of the next generation and has been shown to be directly responsible for over half the production gains achieved across livestock species. Genetics involves the passing of genes (favourable and unfavourable) from parents to offspring and unlike feeding or management it is permanent and cumulative. The national genetic indexes is crucial to enable farmers to make more informed breeding and selection decisions to ensure that they have the desirable combination of genetics for their flock. To date rapid increases in genetic gain have been achieved by the Irish dairy and beef industry, the rate of genetic progress in sheep has increased albeit at a slower than desired level. This paper will review the gains achieved to date and highlight future improvements that will accelerate genetic improvement for the national sheep population.

Current status

The Sheep Ireland €uro-star indexes were introduced in 2009 with the aim of providing sheep farmers with an additional tool for the selection of breeding animals. The genetic indexes aim to identify a low cost, easy care sheep with good maternal characteristics, but that also produces a good quality lamb that reaches slaughter at an early age. Each animal’s index is calculated based on its individual animal performance (such as lambing information and weights) and the animal’s relatives (i.e. sire and dam); currently this animal performance data feeds into Sheep Ireland from two main sources: commercial and pedigree data. Commercial farm data are collected on large numbers of commercial animals through the Teagasc BETTER farm programme and the Central Progeny Test (CPT). In the commercial flocks rams from different breeds are mated to a central group of diverse commercial ewes and their progeny performance is recorded. Information on the progeny managed in a commercial environment feeds back into the genetic indexes of the pedigree rams used and also all his relatives. Currently data on over 5,000 commercial animals are included in the genetic evaluations on a yearly basis. Detailed animal performance information is also recorded by pedigree breeders through the LambPlus scheme, with the help of STAP the numbers of pedigree breeders recording information in the last number of years has increased dramatically and currently over 600 pedigree breeders are entering data on their pedigree animals for the national genetic evaluations. This has been reflected in an increase in the number of pedigree rams sold through sales with star rating information.

Sheep Value Indexes

The establishment of a genetic index involves two main steps, firstly a list of traits or animal characteristics that influence the selection of an animal must be identified, thereafter each trait is weighted based on its economic value (€/lambs born) to farm profitability. A star rating is also assigned to each trait that allows farmers to visualise the ranking of animals within their breed (1 star = bottom 20%; 5 stars = top 20% of the breed). The Sheep Value indexes provide a measure of the genetic ability of the animal’s progeny to generate profit at farm level for a combination of traits. The Sheep Value breeding indexes are split into two indexes:

1. Terminal index - ranks animals based on their ability to produce live, fast growing terminal progeny with little lambing difficulty. This takes into account the progeny’s growth rate, carcass characteristics, days to slaughter and also lamb survival and lambing difficulty.
2. Replacement index - ranks animals on the expected maternal performance such as milk yield, lamb survival and the ease of lambing, however it also includes some terminal traits to account for the efficiency at which animal’s progeny are finished.

What to look for in the indexes?

Before selecting a breeding ram each farmer must determine the most suitable animal for their production system. For example, if farmers are interested in finishing all their lambs then they should focus on the terminal index. On the other hand, if a farmer is looking to retain replacements then they should focus on the replacement index. Irrespective of the type of animal that is needed, careful attention should be placed on the €uro-value, star rating and the accuracy associated with the index or trait of interest. The higher the accuracy the greater the information that is known about the animal and the greater the confidence we have that their index value will reflect their true performance potential and thereby reduce the fluctuations in animal star ratings. The €uro-value is the predicted extra profit that will be generated for the animals progeny compared to an ‘average’ lamb. For example a ram with an €uro value of €1.15 is expected on average to produce progeny that will generate €1.15 more profit compared to their average contemporaries. Assuming that a ram produces 100 progeny per year and survives within a flock for 4 mating seasons this ram is expected to generate €460 more profit across his lifetime compared to the average ram.

Does genetics work?

There are many examples of genetics in action internationally, for sheep one of the countries that has witnessed rapid improvements in production due to genetics is New Zealand. The New Zealand sheep population has declined from 68 million in 1985 to 30 million in 2014, however during the same period kilograms of lamb sold per ewe rose from 9.76 kg to 16.83 kg resulting in little change in the overall lamb meat production, much of these production gains have been attributed to genetics. In addition over 90% of rams sold in New Zealand are now sold based on their genetic evaluations which have helped to accelerate the increase in genetic gain for the national population. The contribution of genetics to profitable farming can be witnessed first-hand in both the dairy and beef sectors in Ireland with the dairy and beef indexes used as the main selection criteria for the selection of breeding animals by many commercial farmers.

To increase Irish sheep farmer’s confidence in the national genetic evaluations it is important to demonstrate the benefits of selecting rams with high star ratings. To quantify the relevance and accuracy of the Irish sheep genetic evaluations for improving key profit traits in the national sheep population, animal indexes were compared to their performance on farm.

To assess the usefulness of the genetic indexes in detecting differences in performance between animals live-weights, lambing and reproduction data for the last three years (2013 to 2015) was extracted from the Sheep Ireland database on 7,644 commercial lambs and sire and dam indexes were compared to the corresponding lamb performance on farm The results clearly show that animals from parents with five star ratings had greater performance compared to lambs from one star parents (Table 2). Progeny from five star parents had less lamb mortality and required less assistance at birth. Ewes with a high star rating for the replacement index were on average 4.18 kg lighter but had a greater number of lambs born (+0.13 lambs) compared to the one star ewes. Progeny from five star parents were also heavier at 40 day weighing and also at weaning compared to progeny from one star animals. These results indicate that selection of breeding animals for favourable maternal and terminal genetic attributes will result in favourable improvements in performance and profitability at farm level.

Replacement Index

Future plans

Although a considerable amount of work has been undertaken in sheep genetics to date, similar to the Irish dairy and beef industry, research is always necessary to further demonstrate the importance of sound breeding decisions on profitability. Some of the new research initiatives that are currently underway are outlined below.

INZAC flock

Previous research has shown that the rate of genetic progress is almost three times higher in the New Zealand sheep industry compared to the Irish sheep industry. Although the New Zealand and Irish indexes are selecting animals for similar characteristics, a genetic comparison of New Zealand versus Irish elite ewes has not been undertaken in a common environment; therefore to date it is difficult to assess the compatibility of the New Zealand ewe to Irish grass based production systems. The INZAC flock was established in Teagasc Athenry to address this question; the flock consists of 180 ewes from two main breeds, Texel and Suffolk, representing the top genetic merit animals in the Irish and New Zealand maternal indexes. The objective of this flock is to allow for the benchmarking of elite Irish genetics compared to elite New Zealand genetics and to validate the Sheep Ireland replacement index. The flock will evaluate the performance potential of New Zealand and Irish for animal characteristics such as lamb growth rates, milk yields, ewe reproduction and lambing traits. The evaluation of the Irish versus the New Zealand ewe commenced at mating in autumn 2015 and ewes will lamb for the first time in March 2016. The trial is expected to run for at least four years and results from this study will allow Irish farmers to assess the suitability of New Zealand genetics for Irish sheep production systems.

OVIGEN – genomic selection for sheep

Genomic selection is a new technology that has gained large traction in the Irish dairy and beef industry over the last number of years and has the potential to rapidly increase the rates of genetic gain for the Irish sheep industry. Genomics is a process that looks directly at the genes or DNA of a ram rather than waiting for his transmitted genes to be expressed in his lambs. DNA remains the same for an animal across its lifetime and therefore the increase in accuracy from genomic selection can be achieved when the ram is still a lamb. Genomic selection was launched for Irish dairy cattle in 2009 and the resultant accuracy of genetic evaluations in dairy increased by 40%, the expected genetic gain may actually be greater in Irish sheep since the current accuracy levels are lower and therefore the potential scope for improvement is greater.

Teagasc, Sheep Ireland and UCD have recently been awarded a research grant, OVIGEN, by the Department of Agriculture, Food and the Marine with the goal of implementing genomic selection for the Irish sheep industry. As part of the OVIGEN project, funding is available to determine the DNA of up to 12,000 animals. A prerequisite for genotyping is accurate performance recording and therefore to date the breeds with sufficient data recorded through the Sheep Ireland system are targeted for genotyping, these breeds include: Texel, Suffolk, Charollais, Vendeen and Belclare. In addition to the genotyping of the major breeds, a subset of 40 animals have been genotyped representing the minority breeds with the goal of quantifying the degree of relationship between the other breeds and the 5 main breeds currently recording in Sheep Ireland. For hill breeders and commercial farmers, low-cost parentage options using the genotyping technology are also under investigation to allow such flocks to start performance recording, as parentage recording is currently the biggest barrier for these groups of farmers to overcome in order to performance record their flocks.

New traits

As part of the OVIGEN project over 12,000 animals will be assessed by Sheep Ireland technicians and this provided an opportunity for additional data to be generated on new and existing traits. The data that is currently being collected includes: weight, body condition score, incidence of mastitis, dag scores and lameness scores. Preliminary results from the OVIGEN data show that on average 10% of ewes and 17% of lambs scored showed some signs of lameness and approximately 2.5% of ewes had mastitis. In addition the heritability estimates for both lameness (0.10) and mastitis (0.07) are moderately heritable, thereby indicating that both traits are under genetic control and can be incorporated into the genetic indexes once research is complete. Research is also on-going into other key traits such as carcass data, lamb vigour scored at birth, ewe fertility and ewe longevity. Future research will continue to focus on evaluating state-of-the-art technologies and statistical methodology to identify “easy to implement tools” to predict traits of economic importance in breeding goals.

Conclusions

Sheep genetic evaluations are now an important tool that allow sheep farmers to make more informed breeding decisions and has the potential to increase profitability at farm level. Teagasc will continue to work closely with the industry to further enhance sheep breeding and ensure that the benefits are clearly seen at farm level.