Abstract
Rumen fluid of cows with subacute ruminal acidosis (SARA) has high concentrations of short chain fatty acids (SCFA). However, the mechanism of SCFA accumulation is unknown. The solute-linked carrier 5a8 (SLC5A8) plays a key role in the transportation and absorption of SCFA in the intestinal epithelium. The objective of the current study was to investigate (1) SLC5A8 gene and protein expression in various parts of the bovine gastrointestinal tract, (2) the effect of SCFA on SLC5A8 expression in rumen epithelial cells, and (3) SLC5A8 gene and protein expression in SARA and healthy cows. A total of 10 dairy cows, 84 ± 26 days in milk and in their second to fourth parity were allocated to control (n = 5) and SARA groups (n = 5). Three cows from the control group and three calves (1-day-old, female, 45–50 kg, healthy, fasting) were chosen to collect a total of 10 sections of digestive tract, from rumen to rectum, and then bovine ruminal epithelial cells were isolated from the three calves. Gene and protein expression of SLC5A8 was detected in all tested regions of the gastrointestinal tract in calves and adult cows by Western blot and quantitative real-time PCR and were both highest in the rumen. Gene and protein expression of SLC5A8 was more than 50% lower in the rumen epithelium of SARA vs. control cows and was partly restored after therapy of SARA cows. Compared with SCFA concentrations typical for control cows (60 mM acetate, 30 mM propionate, and 20 mM butyrate), gene and protein expression of SLC5A8 in rumen epithelium was lower at elevated SCFA concentrations typical for SARA cows (90 mM acetate, 40 mM propionate, and 30 mM butyrate), specifically for elevated concentrations of propionate or butyrate in contrast to elevated concentrations of acetate increased gene and protein expression of SLC5A8 in rumen epithelium. In conclusion, the elevated concentrations of propionate and butyrate inhibit ruminal absorption of SCFA via downregulation of SLC5A8 in SARA cows; the expression of SLC5A8 plays an important role in the etiology of SARA.
Highlights
Subacute ruminal acidosis (SARA) is a common, difficult to diagnose, and costly digestive disorder in dairy cows
Cows with subacute ruminal acidosis (SARA) have elevated concentrations of short chain fatty acids (SCFA) in the rumen [8, 9], which could be due to greater SCFA production, decreased SCFA absorption across the rumen epithelium [3, 8], or both
The objective of this study was to evaluate the potential role of solute-linked carrier 5a8 (SLC5A8), a low-affinity/high-capacity SCFA−/bicarbonate antiporter [11] in the etiology of bovine SARA
Summary
Subacute ruminal acidosis (SARA) is a common, difficult to diagnose, and costly digestive disorder in dairy cows. It is commonly diagnosed by an occurrence of ruminal pH < 5.6 for >3 h/day [1] and the occurrence of clinical signs, such as intermittent diarrhea, dehydration, poor body condition, depression, decreased rumen motility, laminitis, or decreased milk production [2, 3]. Intestinal SCFA absorption in rats and humans is mediated by solute-linked carrier 5a8 (SLC5A8) [10], a low-affinity/highcapacity SCFA−/bicarbonate antiporter [11], whose affinity in zebrafish in descending order of greatest affinity is butyrate > propionate > acetate [12]. Given the accumulation of SCFA in the rumen during SARA, we, hypothesized that SLC5A8 may play a role in the etiology of SARA
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