A breeders’ group has achieved significant improvements in sheep production and profitability writes animal breeding and genetics professor, Dorian Garrick.
Today’s rams produce much more productive and profitable offspring for production circumstances than the offspring of rams that have been available to farmers over the last 50 years. The implementation of effective sheep selection programmes has fuelled this ongoing improvement of successive crops of rams.
The programmes are the result of an ongoing series of global innovations in animal breeding and genetics that were developed by collaborative activities of scientists and ram breeders.
No group of ram breeders has had a bigger impact on New Zealand sheep improvement than the members of the Wairarapa Romney Improvement Group (WRIG). They recently celebrated their first 50 years of partnership aimed at improving and disseminating rams that will increase the profits of their ram-buying clients. Some of the innovations for which WRIG was an early adopter are considered below.
Selection index is a strategy for simultaneously selecting for multiple traits. Most of the work to develop the concept was done at Iowa State University in the 1930s. Before using the selection index breeders either used minimum thresholds for each of the traits of interest or alternated between selection for one characteristic and selection for another.
The logic of a selection index is to weight the gain in any trait by its economic value – the amount of profit that might be expected for a unit increase in the trait.
Professor Rae introduced the concept to the NZ sheep industry more than 50 years ago and it was rapidly adopted by WRIG breeders. They undertook selection that would combine the value of wool with the value of an extra lamb, rewarding the value of heavier lambs.
The same concept is now promoted by Sheep Improvement Ltd (SIL) and used by many ram breeders and ram buyers in NZ, for example in the form of NZ Maternal Worth.
The optimal industry structure to ensure ongoing improvement in livestock has been at the forefront of scientific considerations for more than a century. More than100 years ago Sewall Wright from Chicago showed that the best use of resources would involve partitioning the industry into a commercial sector, which benefited from year-on-year access to improved sires, and a small nucleus or ram breeding sector that generated lines of rams produced by the simultaneous acts of selection and inbreeding.
The inbred lines themselves would not be expected to be particularly productive but would be used to cross with other unrelated inbred lines to produce first-cross animals. The productivity of the industry would benefit greatly from using sires that were the first cross between two lines mated to dams that were the first cross to two different lines.
Four-way crosses
The resulting commercial offspring would be four-way crosses. That strategy is more or less the basis of genetic improvement in broiler and laying chickens, in pigs and in maize but somewhat surprisingly has never found favour with ram or bull breeders.
Some 50 years ago Maurice Bichard from the Pig Improvement Company in the United Kingdom demonstrated that an optimal industry structure would involve the partitioning of the sire breeding sector into “nucleus” and “multiplier” sectors.
Nucleus sires would be used by multipliers, and sires bred by multipliers would be used in the commercial sector. Bichard showed that the annual rate of gain in the commercial sector would be identical to the annual rate of gain in the nucleus sector without the need for pedigree or performance recording in the multiplier or commercial sectors.
The animals produced in the multiplier or commercial sectors would lag in merit behind the animals born in the sector that provided the sires by the amount of gain made in two generations of selection.
In the sheep context this means that a ram buyer purchasing average rams from the same ram breeder year after year will produce offspring about 10 years “behind” the merit of the offspring born in the ram breeders flock. So commercial lambs born in your flock in 2020 will be like the animals that were born in your ram breeder’s flock in 2010. If you purchase above-average rams the lag will be even less. Some of the WRIG breeders were early adopters of the multiplier concept.
Many astute farmers recognised that there were a few exceptional animals in their commercial flocks. In traditional pedigree-based sire breeding, only pedigree-registered animals could be used in the nucleus. The concept of an open-nucleus breeding programme was developed in which elite commercial ewes could become dams in the ram breeding flock. It can result in a quantum leap in the merit of the ram breeding flock when screening of elite ewes first begins, and then it provides a modest improvement in the annual rate of gain thereafter.
No group of ram breeders has had a bigger impact on NZ sheep improvement than the members of the Wairarapa Romney Improvement Group.
It was particularly effective when applied to improving reproductive performance in sheep. Although it was not until the mid-1970s when John James, a scientist at the University of New South Wales, developed the theory to optimise open-nucleus breeding programmes, some WRIG breeders had already effectively adopted the practice and some continue it today.
Farmers had sometimes been disappointed that the offspring of supposedly superior sires did not perform well in their commercial environments. Research had shown that the phenomenon of genotype-environment interaction, which comprised the reranking of sires, was common when environments differed in respect to some form of stress.
The most common stressors were climatic, nutritional, or disease related. Overseas research had shown that animals selected in harder environments could have offspring that performed well in easier environments, whereas animals selected in easy environments often did not achieve good offspring performance when managed in a harder environment.
In the 1960s Professor Rae at Massey University designed an experiment, which ran for many years, where a farm was divided in half and the ewes and their replacements on each half were managed for their entire lives at different stocking rates, but the same sires generated replacement offspring in both halves.
Challenge of commercial conditions
The WRIG members followed the findings of this study and adopted recommendations to avoid problems due to genotype-environment interactions by ensuring their ram breeding flocks were challenged under commercial conditions, often managed within their own larger commercial flocks operating at higher stocking rates than were normal for ram breeders.
Ram buyers were encouraged to purchase rams from breeders whose environments for challenging and selecting rams were similar or harder than their own environments.
The methods for ranking sheep that were adopted in the national evaluation systems prior to SIL were not capable of comparing animals across different cohorts.
The first step in analysing performance records was to deviate them from the cohort average, and this meant that it was not possible to compare rams across cohorts from different years or cohorts from different flocks.
It was therefore not possible to estimate genetic trend from national performance data. Dr Henderson from Cornell University in upstate New York invented an improved method for ranking animals during his PhD at Iowa State University in the 1950s, but algorithms that made it practical to implement his approach were not available until the late 1970s.
During a visit to NZ in 1980 Henderson suggested his method could be used to compare animals across flocks or years and to estimate genetic trend. Dr Blair from Massey University published the research that demonstrated this was the case, and one of my first jobs at Massey from 1982 was to apply those approaches to pedigree and performance records collected in both our pig breeding and sheep breeding industries.
The records from WRIG breeders were among the first I used to demonstrate genetic progress from every flock in the national sheep improvement scheme.
The opportunity to extend these findings to compare animals across flocks was immediately apparent to WRIG members and they formed a core component of the Eastern Romney Sire Reference scheme to test this approach. Each participant used at least one two-tooth ram and at least one older ram from the ram teams that were being used by every other participant in the scheme.
As many as 10% total matings were to reference sires. The prototype across-flock rankings we ran for WRIG members for many years stimulated the rollout of across-flock rankings for connected flocks in SIL. The reference sire concept was adopted by Beef + Lamb NZ for their central progeny testing programme, which provided the links or connections for across-flock analyses that are now widely used by many SIL breeders.
Having established prolific flocks of sheep under commercial conditions as a result of many years of selection on objective sire performance, the WRIG members shifted their attention to consider terminal sire performance of dual-purpose Romneys. New traits were of interest to commercial farmers, such as dressing-out percentage and yield of valuable cuts.
At their own expense WRIG formed a commercial progeny test to directly compare the growth, carcase and meat performance of their dual-purpose animals. Whereas some other breeders were considering ultrasound scanning or CAT scanning to assess carcase attributes, the ability to use ram lambs as sires and to harvest the resulting progeny prior to the next breeding season made a direct measure of terminal performance appealing. The results demonstrated substantial variation in the economic performance of offspring of different sires. Such variation forms the foundation for WRIG breeders to implement effective selection.
Over the last 50 years WRIG members, some of whom are now the third generation of active participants in the group, have experienced the shift in farming from a focus on profit alone to a triple bottom line including welfare of the environment and welfare of all the human and animal lives that comprise or interact with family farms.
Attributes sustainable sheep farming systems will need in the future will be different from what they were in the past. Meeting those needs will not simply be about adopting new tools and technologies but will involve first imagining the future and then implementing technologies both old and new to realise the breeding objectives that accommodate that vision.
I won’t be around in 50 years to enjoy the 100th anniversary of the Wairarapa Romney Improvement Group but the future I imagine involves continued innovation based on collaboration between farmers and scientists, with a suitable business model for funding sheep breeding programmes on family farms.
- Professor Garrick is chief Scientist and director of the Al Rae Centre, Ruakura and in recent years worked at Iowa State University, US.
