Four main factors determine how quickly a population can improve genetically.
1. Genetic variation — how much genetic difference exists between animals
2. Selection intensity — how selective we are in choosing the parents of the next generation
3. Accuracy of selection — how close the estimated genetic merit of individuals reflect their true genetic merit
4. Generation interval — how quickly one generation replaces another
It is sometimes assumed that responsibility for genetic gain in a population lies exclusively with breeders and breeding companies. This is not true. Genetic gain in dairy cattle breeding is actually achieved through four different pathways.
1. Sires of sires: bulls selected to produce the next generation of AI bulls.
2. Dams of sires: elite females selected to produce future AI bulls.
3. Sires of dams: bulls selected by farmers to breed replacement heifers.
4. Dams of dams: cows and heifers selected by farmers to produce replacements.
Breeding organisations primarily influence the first two pathways, although farmers contribute by supplying candidate bulls and elite females. Farmers directly control the latter two pathways. While these do not necessarily contribute half of national genetic gain, farmers’ breeding decisions have a substantial influence on the rate of genetic progress.
Several reasons complicate the comparison of genetic gain between countries
1. Different populations have different amounts of genetic variation.
Genetic variation available for selection differs between countries and production systems. For example, genetic variation in milk yield is likely greater in high-input, housed systems than in Ireland’s seasonal, pasture-based system. If the genetic variation for milk production is 500kg and 700kg in two populations, the latter could achieve 40% greater genetic gain at the same selection intensity, accuracy and generation interval. This does not necessarily reflect a superior breeding programme, but rather greater genetic variation expressed in that environment.
2. Reported measures of genetic merit
Some countries report an animal’s full genetic merit, whereas others, including Ireland, report half this value to reflect expected progeny performance. Consequently, reported rates of genetic gain can appear twice as high in countries using full genetic merit.
3. Breeding objectives are not the same
Breeding programmes differ in the traits they prioritise. For example, a programme selecting almost exclusively for milk yield might achieve genetic gain of 100kg annually, while another also selecting for functional traits might achieve only 60kg alongside improvements in these other traits. This does not necessarily make the former superior. Indeed, milk yield in seasonal systems can also increase indirectly through selection for milk solids, improved fertility facilitating longer lactations, and improved survival resulting in a more mature herd.
4. Some breeding programmes prioritise short-term gain over long-term sustainability
Breeding programmes also differ in how they manage inbreeding. While some inbreeding is inevitable, excessive inbreeding can reduce performance and genetic diversity. Intensive use of a small number of closely related elite bulls may accelerate short-term genetic gain, but at the expense of future genetic progress. Ireland’s breeding strategy therefore seeks to balance genetic gain with the preservation of genetic diversity to ensure sustainable, long-term improvement.
5. The unit of measure
Reported genetic gain also depends on the population being evaluated. Some populations report trends in young bulls, others in animals by birth year, while Ireland frequently reports trends in the national female population. These measures are not directly comparable. In populations with relatively low replacement rates, such as in Ireland, superior genetics take longer to spread throughout the milking herd. Consequently, genetic gain in newly born animals can appear substantially greater than that observed across the entire cow population.
Genetic trends for protein yield and fertility for several countries, standardised for the genetic variation within each population and using a common base year of 2015 are presented in figures one and two.
Broadly similar rates of genetic gain exist in Ireland and New Zealand, with faster progress for yield especially in the other countries. However, the rate of inbreeding in some of these populations is approaching, if not exceeding, internationally recommended limits.
Importantly, the seasonal calving season operated in both Ireland and New Zealand imposes significant constraints on efforts to shorten the generation interval in all four selection pathways. This is compounded by the cautious approach of Irish breeding companies to ensure that young bulls are easy calving and only high fertility semen is marketed to farmers. Shortening the generation interval in Ireland by just one year in all four pathways could increase the rate of genetic gain by 25%.
Are Irish farmers investing enough in genetic improvement?
Farmers routinely invest in reseeding, fertiliser and concentrates to improve productivity, carefully considering the return on each euro spent. Genetics deserves the same consideration, particularly as its benefits accumulate over generations. Yet, according to the National Farm Survey, herd artificial insemination costs account for just 2.5% of direct dairy farm costs, compared with 46% for concentrates and bulk feed and 13% for fertiliser.
Despite this relatively modest investment, AI is often perceived as expensive, with an apparent reluctance to pay more for superior genetics. This attitude needs to change.
Maintaining competitive breeding programmes will require substantial investment. Many international dairy breeding companies operate relatively closed nucleus programmes, offering advantages in selection intensity, generation interval, performance recording and mating control.
However, Ireland has a distinct advantage in its national breeding infrastructure, which draws on data from large numbers of commercial farms. This enables selection under real production conditions and identification of genetically superior animals across the national population, rather than relying solely on relatively small elite herds.
In conclusion, farmers have a crucial role in driving genetic progress through their breeding decisions. Sustained investment in breeding programmes and superior genetics is essential to maintaining competitiveness and delivering cumulative benefits to future generations of dairy farmers.
