Ridecamp: [RC] re thumps

Susan Garlinghouse suendavid@xxxxxxxxxxxxxxxx
I'm behind the power curve on this topic, but better late than never, so thought I'd add my comments FWIW...

I agree with the comments already made that calcium depletion alone doesn't cause thumps, it's more of a generalized electrolyte imbalance, with calcium being a major but not unique player.  Lisa, the syndrome you described in freshening dairy cows, lactation tetany, is close, but as Heidi explained, somewhat different in how it affects the phrenic nerve and synchronous contraction.  I do think that DCAD is an issue, but it hasn't been explored in horses nearly to the same extent as it has in dairy.  It's my opinion that reducing alfalfa in the ration to control thumps is much or more a DCAD issue as total ration calcium content is.  However, that also has not been really looked at in research---which I'm actually happy about, as I'm aiming towards calcium metabolism in performance horses, including DCAD, for my PhD dissertation and a already feeling propriety about the topic <g>.

I think another issue that isn't adequately considered in endurance horses is the relationship between calcium availability and acid-base balance.  Coincidentally, there's a concurrent thread about panters, and most endurance horses are shifted more towards alkalosis than acidosis.  However, I think it's significant that the more alkalotic a horse is (virtually always due to respiration to dissipate body heat), the stronger the calcium-albumin bond is, and thus the less available ionized calcium is.  So while this is totally conjecture, I think horses that for whatever reason are panting more (and are thus more alkalotic), are also more likely to be prone to thumps.  Hard to make broad conclusions, though, as there are so many other contributing factors, including the already mentioned genetics, diet, management, etc.

JMO.

Susan G (currently overseeing the Midnight Ruminant Hit Parade: a baby alpaca, a pygmy goat, a 2000-lb Brown Swiss that likes horse cookies and scritches and a metabolic train wreck of a Holstein cow...)




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