Changing views on the role of the uterus in post-partum reproductive function in beef cows1.

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The paradigm for post-partum management of well-being and reproductive function in beef cows is changing. For many decades, research focused on the hypothalamic-pituitary-ovarian axis in attempts to manage beef cows to resume estrous cycles more quickly, because uterine involution was not considered a factor that was limiting to reproductive function in post-partum beef cows (Kiracofe, 1980). Questions remained, however, about the prevalence of subclinical endometritis in beef cows, and about the impact of sub-clinical reproductive tract health on subsequent reproductive performance and well-being (McNeel et al., 2017a). In a pair of papers published in this issue of the Journal of Animal Science, Ault and colleagues (Ault et al., 2019a,b) investigated the uterine and vaginal microbiome in post-partum beef cows using next generation sequencing and demonstrated that a less diverse uterine microbiome in the post-partum interval close to breeding was associated with a decreased risk of conception to timed artificial insemination. A similar result was reported for the vaginal microbiome of post-partum dairy cows (Bicalho et al., 2017). Beef cows, therefore, may not have as many cases of clinical metritis, but some of the same components of post-partum reproductive health may be influencing post-partum re-breeding efficiency in beef cows as in dairy cows. The results of studies examining the influence of endometrial cytology on reproductive performance in post-partum beef cows have been mixed (Santos et al., 2009; Ricci et al., 2017); however, the papers by Ault and colleagues indicate that the application of next generation sequencing technologies may allow more accurate determination of the relationships between post-partum reproductive tract health and re-breeding efficiency.