Caution… Intersection Ahead:
Heat Stress, SARA, Leaky Gut, Ad Damna
Even mild heat stress — daily average temperature-humidity index (THI) of 68-71 — can impact dairy performance, especially for high-producing dairy cows. Look for negative effects on feed intake, milk and milk component yields, and possibly somatic cell count.
There also is increased risk of SARA (sub-acute ruminal acidosis) and unhealthy gut permeability — ad damna — leading to serious losses.
Recent nutritional research to combat heat stress goes beyond the basics of increasing dietary cation difference (DCAD) and electrolytes. Researchers today are “thinking outside the rumen box.”Ā Ā The University of Saskatchewan’s Dr. Greg Penner points to studies addressing transient heat stress that can affect high-producing cows in temperate regions, with lower performance apparent even under conditions below a daily average of 72 THI.
Inside the “rumen box,” dietary heat stress precautions involve offsetting the cow’s loss of electrolytes by increasing DCAD concentration, usually by means of buffers such as sodium bicarbonate (NaHCO3), sodium sesquicarbonate (Na3H[CO3]2), potassium bicarbonate (KHCO3), or potassium carbonate (K2CO3).
“What encourages this approach,” Penner notes, “is the hypothesis that heat-stressed cattle may suffer from a ruminal sodium deficiency compromising short chain fatty acid (SCFA) absorption, which would increase the risk of SARA.
“However,” he adds, “recent ex vivo research absent heat stress conditions has found that added sodium ion (Na+) did not affect the uptake of acetate or butyrate across the isolated ruminal epithelium.
“Moreover, follow-up in vivo studies under mild to moderate heat stress conditions — THI 68-72 — showed no effects on SCFA absorption by altering Na+ concentrations. So it seems unlikely that ruminal Na+ concentration limits SCFA absorption.”
In addition, Penner says, such studies point to the potential advantages of optimizing buffers for both rumen and lower gastro-intestinal tract benefits in cows under mild heat stress.
“For example, if heat stress-induced leaky gut occurs independent of rumen acidosis, then there may be advantages in using calcium magnesium carbonate (CaMg[CO3]2), which solubilizes in the abomasum and may help regulate intestinal fermentation while supporting intestinal barrier function.”
Questions?
Email FeedInsight 4U