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Emerging data highlighting gut microbiome influences on health support evaluation of how microbial fermentation end-products influence postabsorptive systems. This study aimed to investigate the effect of increased propionate status on progesterone profiles and insulin sensitivity in dairy heifers. Eleven Holstein heifers, synchronized in estrus, were assigned to one of two continuous, 5-day IV treatments: sodium propionate (PRO; n = 5) or saline (CON; n = 6). These infusions culminated in a hyperglycemic clamp with daily blood samples for an additional 7 days. Plasma propionate concentrations increased over the first 9 h in PRO heifers, then decreased until day 3 when they matched CON heifers. Maximum plasma progesterone concentrations tended to be greater in PRO heifers than CON heifers (4.19 vs 3.73 ng/mL; P = 0.087). Plateau insulin concentrations in CON animals were significantly greater than those in PRO animals (249.4 ± 25.1 vs 123.9 ± 35.8; P = 0.008) with a trend for an increased insulin sensitivity index in PRO heifers compared to CON heifers (P = 0.06). These changes in plasma propionate clearance leading to increased progesterone response and changes in insulin sensitivity suggest a role for SCFA metabolism in reproductive hormone regulation.

Reproductive efficiency is a key component of sustainable dairy production, significantly influencing herd profitability. Because of the known interactions between energy status, insulin sensitivity, and the hypothalamus- pituitary-gonadal axis, volatile fatty acid dynamics are likely to influence reproductive status via downstream signaling. Altering volatile fatty acid dynamics has been minimally explored in relation to reproductive status and could be a viable strategy for improvements in this area. The objective of this study was to investigate the effect of increased propionate status on progesterone profiles in dairy heifers. Eleven Holstein heifers, 8 to 10 months of age and 550 to 800 lb, were subject to an OvSynch + CIDR procedure, then assigned to two treatments and given a continuous IV infusion of either sodium propionate (PRO; 61.6 mmol/hr; n=5) or saline (CON; n=6) at a matching infusion volume for 5 days. Daily blood samples were taken from animals for an additional 7 days after the end of the infusion. Plasma propionate concentrations increased over the first 9 hours in PRO cows. Between hour 9 and day 3, plasma propionate concentrations decreased in the PRO group until they matched levels seen in CON cows. No difference in plasma propionate concentrations were identified after day 3. There were no differences in daily plasma acetate or beta-hydroxybutyrate levels seen between treatments for any timepoints within the experimental period (P > 0.10). Plasma progesterone levels rose at a similar rate in both PRO and CON cows, however, PRO cows had the tendency to reach greater maximum progesterone levels (4.19 vs 3.73 ng/mL; P = 0.087). The results of this study indicate that although infusing propionate to dairy heifers initially increases plasma propionate levels, there appears to be a metabolic shift allowing the animal to clear the surplus propionate and return plasma concentrations to basal levels. This phenomenon warrants further investigation because it suggests ample capacity of the animal to metabolize propionate, provided ruminal fermentation can be manipulated to deliver additional quantities to the bloodstream. Further, the increased magnitude of progesterone response suggests a role for propionate, and volatile fatty acid supply and subsequent metabolism, in modulating reproductive performance. [ABSTRACT FROM AUTHOR]