Increasing beef production from dairy cows by implanting embryos from MOET nucleus breeding schemes for beef cattle

Review: Use of assisted reproduction in seasonal-calving dairy herds

A unique aspect of seasonal-calving pasture-based systems of dairy production is the intense focus placed on achieving a concentrated herd-calving period in late winter and early spring. Hence, excellent reproductive performance is required during a short breeding period. A concentrated calving period also produces a problem in the form of a large number of male dairy calves being born at the same time; as these calves have little economic value due to poor beef merit, they present a potential welfare concern. A solution exists in the form of sex-sorted semen, but this is typically associated with poorer pregnancy per artificial insemination, and hence, the use of sex-sorted semen must be carefully considered. The logical strategy to use sex-sorted semen is to target the best genetic merit dams in the herd to generate replacement heifers, thereby accelerating herd genetic gain. On the other hand, if all dairy farmers adopt such a strategy, there will be a corresponding reduction in elite genetic merit male dairy calves being born, potentially reducing availability of the next generation of future bulls to be used for artificial insemination. Use of in vitro embryo production on elite dairy donors could avoid this problem by acting as a multiplier, potentially in tandem with Y-sorted semen to skew the offspring sex ratio towards more male calves. Use of sex-sorted semen on the best genetic merit dams can also facilitate a marked increase in the usage of beef semen on any dams that are deemed unsuitable for sex-sorted semen. The use of "beef on dairy" requires selection of beef bulls that generate offspring with traits that meet the key requirements of both the dairy farmer (e.g., gestation length and calving ease) and the beef farmer that must be motivated to purchase the calves (e.g., growth rate, age at slaughter, carcass value). Beef breed dams that have elite genetic merit for these traits could also be considered for in vitro embryo production, potentially in tandem with Y-sorted semen, to facilitate genetic gain for the growing "beef-on-dairy" market. It is possible to transfer a beef embryo (75-100% beef breed genetics) into dairy dams that are not required to generate replacements, but this is likely to remain a niche practice as there are many barriers to widespread adoption. Such combinations of assisted reproduction have the potential to improve the efficiency and sustainability metrics of seasonal-calving pasture-based dairy herds.

Invited review: Use of assisted reproduction techniques to accelerate genetic gain and increase value of beef production in dairy herds

The contribution of the calf enterprise to the profit of the dairy farm is generally considered small, with beef bull selection on dairy farms often not considered a high priority. However, this is likely to change in the future as the rapid rate of expansion of the dairy herd in some countries is set to plateau and improvements in dairy herd fertility combine to reduce the proportion of dairy breed calves required on dairy farms. This presents the opportunity to increase the proportion of beef breed calves born, increasing both the value of calf sales and the marketability of the calves. Beef embryos could become a new breeding tool for dairies as producers need to reassess their breeding policy as a consequence of welfare concerns and poor calf prices. Assisted reproductive technologies can contribute to accelerated genetic gain by allowing an increased number of offspring to be produced from genetically elite dams. There are the following 3 general classes of donor females of interest to an integrated dairy-beef system: (1) elite dairy dams, from which oocytes are recovered from live females using ovum pick-up and fertilized in vitro with semen from elite dairy bulls; (2) elite beef dams, where the oocytes are recovered from live females using ovum pick-up and fertilized with semen from elite beef bulls; and (3) commercial beef dams (≥50% beef genetics), where ovaries are collected from the abattoir postslaughter, and oocytes are fertilized with semen from elite beef bulls that are suitable for use on dairy cows (resulting embryo with ≥75% beef genetics). The expected benefits of these collective developments include accelerated genetic gain for milk and beef production in addition to transformation of the dairy herd calf crop to a combination of good genetic merit dairy female calves and premium-quality beef calves. The aim of this review is to describe how these technologies can be harnessed to intensively select for genetic improvement in both dairy breed and beef breed bulls suitable for use in the dairy herd.

Optimizing pure line breeding strategies utilizing reproductive technologies

The development of new reproductive techniques has had a great effect on schemes for dairy cattle improvement; AI resulted in progeny-testing schemes, and, more recently, multiple ovulation and embryo transfer has resulted in nucleus breeding schemes. In traditional breeding schemes, the use of multiple ovulation and embryo transfer resulted in only small increases of genetic gains because the selection intensity of bull dams was already high, but the selection intensity of cows in nucleus breeding schemes increased considerably. This increase makes nucleus schemes very competitive, especially when in vitro maturation and fertilization is used to increase female reproductive rates further. The increased genetic gain results in the selection of young females (i.e., optimal generation intervals are shortened). The combined effect of multiple ovulation and embryo transfer and shorter generation intervals increases the rate of gain by approximately 15% but also increases the rate of inbreeding and variances of the selection response (i.e., the risk of the breeding scheme) by about 80%. Recently, selection methods have been developed to reduce the rates of inbreeding or the variance of the selection response in breeding schemes. A scheme that maximized the selection differential while constraining the rate of inbreeding yielded about 30 to 60% more selection response than selection for BLUP estimated breeding value at the same rate of inbreeding. For the future, the combination of juvenile predictors of genetic merit (e.g., DNA markers) and techniques that further increase female reproductive rates seem very promising methods to increase the rates of genetic gain. As an example, the genetic gain of an optimized hybrid nucleus scheme could be increased 24% by the combined use of juvenile predictors and in vitro maturation and fertilization. Fertilization of fetal embryos was predicted to increase rates of gain by up to 18%.