Dairy-Beef integration - 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. This is rapidly changing, however, as the rapid rate of expansion of the dairy herd in some countries is now plateauing 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. Assisted reproductive technologies such as in vitro production (IVP) of embryos can contribute to accelerated genetic gain by allowing an increased number of offspring to be produced from genetically elite dams (both dairy and beef breeds to produce bulls suitable to use on dairy cows). The expected benefits of these collective developments include accelerated genetic gain for milk and beef production, and transformation of the dairy herd calf crop to a combination of good genetic merit dairy female calves and premium quality dairy-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. In Chapter 2, pregnancy outcomes in lactating dairy cows following timed AI or timed ET using either fresh or frozen IVP embryos from dairy or beef breeds were compared. Oocytes collected by transvaginal ovum pick-up on elite dairy and beef donors, and oocytes collected from the ovaries of slaughtered commercial beef heifers were fertilized in vitro with sperm from elite dairy and beef breed bulls. The resulting grade 1 blastocysts were transferred either fresh or frozen into synchronized lactating Holstein Friesian cows. A control group of the synchronized cows received AI. Pregnancy outcomes were compared on d 32 and d 62 by transrectal ultrasound examination. In Chapter 3, using blood samples from a subset of the recipient/AI cows from Chapter 2 and the ultrasound scanning results from Chapter 2, pregnancy outcomes were determined on d 7 (estimated based on serum Progesterone (P4)), d 18 (Interferon Stimulated Gene 15 (ISG15)), d 25 (Pregnancy Specific Protein B (PSPB)), d 120 (ultrasound) and at parturition. This allowed a comparison of pregnancy loss between the AI and ET treatments from the day of initial AI/ET, right up to full-term parturition. Chapter 4 used results from Chapters 2 and 3 regarding increased pregnancy loss in frozen IVP-ET, along with emerging data from Michigan State University (Santos et al., 2023) about a potential predictor of timing of embryo attachment to the uterus, daily PSPB measurement, to compare the incidence of pregnancy loss to the timing presumptive conceptus attachment. Finally, Chapter 5 compared the gestation length, calf birth weight, calving difficulty and overall health status of calves derived from either the AI or ET events in Chapter 2.