Genetic changes in ruminants: Historic trends and future prospects

Abstract

AbstractThe major ruminant species, dairy and beef cattle and sheep, represent a rather heterogeneous group as regards genetic improvement, which to a large extent reflects their respective breeding structures. In the UK, the beef cattle and sheep industries still span many different breeds, have small herds/flocks, and have been relatively unaffected by agribusiness investment, and are assumed to have a traditional pyramid breeding structure, in which progress is determined by a small number of breeders. Recording of production information, which to date has focussed on terminal sire characteristics, is relatively recent, and until the use of across herd evaluations, genetic progress was probably limited. However in recent years there have been gains in both growth and muscling. There is little evidence or concern for undesired consequences in commercial flocks, partly because of the extensive use of crossbreeding in these industries, which exploits both breed complementarity and heterosis.By contrast, the dairy industry is now dominated by purebred Holsteins. Increasingly breeding activities are both global in scope and dominated by a small number of large breeding companies. Because most traits of interest are only expressed in the female, improvement programmes have continued to focus on progeny testing, with test daughters in many herds. Most recording schemes and promotional activities emphasise production and type traits. The dairy industry is also notable for the publication of bull progeny test results, so that top bulls can then be used as sires of the next generation of by all companies. These bull evaluations now extend to international rankings.Data from the US indicates continuing genetic progress for production traits in the Holstein, particularly since the 1960s, by when progeny testing had been established, frozen semen widely used, and adequate statistical procedures in place for evaluating bulls. Genetic progress is also evident for type traits. There is now growing concern and evidence of undesirable genetic changes in fertility, disease incidence and overall stress, despite improved nutrition and general management. Altering this situation will require both the recording of such traits and the use of that information by breeding companies, especially in sire selection.