Advancements in 16S rRNA gene amplicon community sequencing have vastly expanded our understanding of the reproductive microbiome and its role in fertility. In humans, Lactobacillus is the overwhelmingly dominant bacteria within reproductive tissues and is known to be commensal and an indicator of fertility in women and men. It is also known that Lactobacillus is not as largely abundant in the reproductive tissues of domestic livestock species. Thus, the objective of this review is to summarize the research to date on both female and male reproductive microbiomes in domestic livestock species (i.e., dairy cattle, beef cattle, swine, small ruminants, and horses). Having a comprehensive understanding of reproductive microbiota and its role in modulating physiological functions will aid in the development of management and therapeutic strategies to improve reproductive efficiency.

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Consumption of zearalenone (ZEN) detrimentally affects tissues and systems throughout the body, and these deleterious effects are especially pronounced in swine. The objectives of this project were to determine the effects of short-term consumption of ZEN (at concentrations that could be found on-farm) on growth, carcass weight, liver weight and reproductive tissues of pubertal gilts, and to determine if the effects are transient or persistent. Cross-bred gilts (107.25 ± 2.69 kg) were randomly assigned to one of three feed additives: 1) solvent only for 21 d (CON; n=10), 2) ZEN for 7 d followed by 14 d of solvent (ZEN-7; 6 mg/d; n=10), and 3) ZEN for 21 d (ZEN-21; 6 mg/d; n=10). Body weights were collected at the beginning and end of the experiment (189.1 ± 0.8 and 211.1 ± 0.8 days of age, respectively). Carcass weights and tissues were collected at harvest. There were no treatment-based differences in growth, carcass, liver or reproductive tissue weights. Histological analyses revealed differences based on treatment and the interaction between treatment and luteal status. The thickness of the ampullary muscularis declined with ZEN exposure (P<0.05), while the isthmic epithelial cell height (P<0.01) and uterine endometrial thickness (P<0.02) increased. Interestingly, the thickness of the isthmic muscularis, uterine myometrium and epithelial cell height only differed in the presence of a corpus luteum. Uterine epithelial cell height in the luteal phase was lowest in ZEN-7 pigs (P<0.01). The isthmic muscularis in the luteal phase was thinner in pigs from both ZEN treatments (P<0.01). Conversely, the luteal-stage myometrium was thicker in pigs from both ZEN treatments (P<0.01). The discovery of these tissue-based differences during the luteal phase is particularly concerning since this corresponds with the time when embryos would be affected by the functional competency of the oviduct and uterus. The results of this work demonstrate that short-term consumption of ZEN produces microscopic, but not macroscopic alterations in reproductive organs which are likely to have negative effects on their subsequent function and that these differences persist even after ZEN consumption ceases. Taken together, these results indicate that it is insufficient to rely solely on outwardly visible symptoms as indicators of zearalenone exposure, as detrimental effects on reproductive tissues were found in the absence of phenotypic and morphologic changes.

Graphical Abstract Summary: Twenty-two multiparous, lactating Holstein cows were enrolled in the experiment, spanning the summer months of June through September. Cows were housed in freestalls where they were individually fed using a Calan gate system. Cows were randomly assigned to the control (Con; no supplement; n = 10) or chromium propionate (CrPro; 12 mg/head per day chromium for 24 d; n = 12) treatment groups. Every 3 days, ovarian structures were counted and measured and blood samples, respiration rates, and rectal temperatures were collected. Every 6 days, a uterine swab was obtained for cytological evaluation to determine the incidences of subclinical endometritis, as determined by polymorphonuclear leukocyte percentage. Chromium supplementation benefited small ovarian follicles, polymorphonuclear leukocyte percentage, and the ratio of plasma progesterone to average corpus luteum volume.