Hi,
I have recently become interesting in monitoring the heart rate in a very ambitious young draft horse that I have (5 y/o Belgian/Perch cross mare). I want to make sure she's not working too hard (although she volunteers to work this hard)... At any rate, I have measured her heart rate at rest (25 bpm) and at what I think is her max effort (130 bpm). My trouble is that these numbers seem really low compared to "normal" horse references. Maybe what I think is her max effort really isn't? Either way, what I'm really after is determining the heart rate when her work become anaerobic. I'm only interested in the max heart rate because there are formulas where I can find the anaerobic theshold by plugging in the resting and max heart rate... If I do this with my measured numbers, I get a heart rate of about 105 bpm. This is very different from a "normal" horses anaerobic theshold... Does this seem right???

Just wanted to let you know that I've seen this message but am hoping to get some help from a veterinary exercise physiology expert to try to answer your question. From the little I know on this I suspect that it wouuld be difficult to accuratively determine her anaerobic threshold simply by knowing resting and maximum heart rate. Most determinations rely on testing for blood lactic acid (lactate) levels. I do see that there is a Conconi test that only uses heart rate, but this is a bit controversial. I agree that your heart rate of 130 beats per minute for maximum heart rate is far below the stated 230-260 beats per minute proposed for horses. These would be light horses, though, and a draft such as your mare could be slightly different.

Beth,
Thanks for checking into this. From more reading, I strongly suspect that the rate of 130 bpm is not really her max heart rate, but in actuality the max I can achieve with a heavy sled and a 20% grade. Still, I know she was working really really hard and that she couldn't keep going for more than 1 minute with this load. So, I can't believe that this work is aerobic for her even though 130 bpm is supposed to be aerobic for light horses (from what I've read). The 105 bpm number was obtained by plugging in the resting and max heart rate into a formula that was developed for human athletes. I'm sure the lactic acid test would be more accurate, but I'm looking for something that I can do quickly and simply in the field to make adjustments to her speed or work load. I thought heart rate would be a good simple indicator as endurance riders seem to use it a lot. I even got a stethoscope to listen to her heart beat more accurately, but the whole process seems to have spawned more questions than it's answered... At least I'm learning... :)

You're very welcome. I did get some information from a colleague who confirmed that it would be difficult to know for sure when she has reached maximum heart rate without lactic acid. She also confirmed that there is little information on drafts compared to light horses, but that she would expect higher than 130 for maximum rate, even in a draft horse. More importantly, though, we need to think about her muscles. If she is one of the 2 out of 3 draft related horses (and even more, perhaps, in Percheron related horses) she could be "metabolically different" and developing equine polysaccharide storage myopathy (EPSM). That would limit her ability to work for long periods. I would suggest getting your veterinarian to draw blood for muscle enzyme testing about 4-6 hours after she had performed this workout. If she is has a CK (CPK) over 350 or an AST (SGOT) over 420 then she has EPSM. You could also try sending pulled mane hairs for genetic testing at the University of Minnesota Veterinary College, Dr. Valberg's laboratory (they call it PSSM). Or, you could just change to a high fat (at least 2 cups oil per 1000 lbs of horse per day, increased gradually) and fiber and low starch and sugar EPSM type diet and see how she is going in 4 months or so.