Discipline: breeding; Key words: genomic testing, rate of genetic gain, sexed semen
Worldwide, commercialization of genomic testing has irrevocably changed dairy cattle breeding schemes. The high reliabilities being achieved for estimated breeding values (EBV) derived using genomics (EBVG), coupled with reductions in the cost of genomic testing, have seen the number of animals evaluated using genomic data increase exponentially. Genomic testing of commercial dairy females benefits genetic evaluations of populations through regular contributions to reference populations. Herd-level benefits include (1) more reliable decisions in selecting herd replacements, (2) fewer errors in parentage assignment, (3) the development of more targeted breeding objectives, and (4) earlier identification of superior animals to artificially inseminate (AI) with high-value semen or for use in embryo transfer or in vitro fertilization. Relatively few studies consider the cost-benefit of genomic testing of commercial dairy heifers, one reason being that there is little room to apply selection pressure because most heifers are retained as replacements. However, with success shown in selection for fertility more replacements are being born. Furthermore, the use of sexed semen in AI offers an additional opportunity to increase the number of heifer calves and to intensify selection pressure on the female side. Thus, using sexed semen in conjunction with genomic testing may be a profitable strategy. This was the broad aim of a study by Dr J.E. Newton and colleagues in Australia which they published in the Journal of Dairy Science, Volume 101 of 2018, page 6159 to 6173, the title of the paper being: The cost-benefit of genomic testing of heifers and using sexed semen in pasture-based dairy herds.
In their study they modelled the impact of changes to key parameters on the benefit from genomic testing of heifer calves with and without usage of sexed semen in pasture-based systems. A deterministic model was used to evaluate the effect on net benefit due to changes in (1) reproduction rate, (2) genomic test costs, (3) availability of parent-derived breeding values (EBVPA), and (4) replacement rate. When the use of sexed semen was included, they also considered (a) the proportion of heifers and cows mated to sexed semen, (b) decreases in conception rate in inseminations with sexed semen, and (c) the marginal return for surplus heifers.
Scenarios with lower replacement rates and no availability of EBVPA had the largest net benefits. The net benefit of genomic testing realized over the lifetime of genotyped heifers during the time of the study ranged from Aus$204 to Aus$1124 per 100 cows for a herd with average reproductive performance. The cost of a genomic test, a perceived barrier for many farmers, had only a small effect on net benefit. Genomic testing alone was always more profitable than using sexed semen and genomic testing together if the only benefit considered was increased genetic gain in heifer replacements. When other benefits (for example, the higher sale price of a surplus heifer compared with a male calf) were considered, there were combinations of parameters where net benefit from using sexed semen and genomic testing was higher than the equivalent scenario with genomic testing only. In general, the results showed that herd reproduction and replacement rates and the availability of EBVPA have the most influence on whether the investment in genomic testing is profitable at current Australian prices.
It was concluded that by using sexed semen and genomic testing will provide an opportunity to increase net benefit more than genomic testing only, but the outcome will be highly influenced by farm. Benefits from using sexed semen, in conjunction with genomic testing, are most likely to be seen when usage is restricted to heifers. Wide-scale use of sexed semen, in conjunction with genomic testing, will largely depend on achieving conception rates that are comparable to those of conventional semen and the sale price of these surplus heifers. Over time, as the cost of genomic testing decreases and genomic reliabilities increase, the proportion of dairy farmers for whom genomic testing is profitable will increase.