Bloodwork

[Sarah Ralston <ralston@AESOP.RUTGERS.EDU>]

Regarding the interpretation of blood work: Susan accurately reported that:
According to Merck and/or Lewis, normal ranges for horses are
 Se .9 - 3.0 mg/dl
Copper .7 - 1.5 mg/l
Ca 1.04 - 1.34 mg/l
Phosphorus .23 - .54 mg/l

However, two caveats: 1. Blood calcium DOES NOT reflect calcium intake! It
is one of my pet peeves that vets will "diagnose" calcium deficiency based
on blood levels! Blood calcium is rigidly regulated through hormonal control-
too little in blood and calcium is mobilized from the bone, too
much-excreted by the kidney. 
Hypocalcemia (Low blood calcium) is usually seen in acute, severe losses, 
such as lactating mares, and in heavily sweating horses that were either 
unconditioned for the work or fed excessive calcium during training 
(gearing the hormone system up to excrete it) and failed to take in enough 
to replace the losses during the competition or exercise bout that caused
the problem.
The horse in question was on good quality hay and alfalfa cubes-no
mention of bran being fed or large amounts of grain-ergo dietary calcium
deficit not
an issue even though blood levels were marginally low. Since all 
of the parameters were marginally low I wonder if it wasn't a dilutional
effect.

2. Blood selenium: Just returned from the KER nutrition conference in
Kentucky (excellent meeting)
There was an excellent poster presented by Vervuert and colleagues from
Germany on 
"Assessment of selenium status in horses". They did an extensive survey of
304 
horses and measured both blood selenium and glutathione peroxidase, a
selenium dependent enzyme thought
to better reflect Se status, plus a full analysis of the feeds. Plasma Se
ranged from 0.16 to
2.91 mg/dl with a mean of 1.16. There was poor correlation between blood Se
and the 
enzyme (r=0.49 for the statistically inclined) and the authors said:"There
was wide variation in measures of
Se status, even if horses received the same feed supplement. 26% of the
horses had plasma Se below 0.7, 
but there was no evidence of myopathy in performance horses or reproductive
difficulties in 
mares associated with low plasma selenium levels"!! The authors concluded
"The results of 
this study raise some questions with regard to the consequences of marginal
selenium supply". 
Food for thought-especially since selenium is potentially so toxic.

BTW-with respect to the blood pH of horses in endurance as Roger mentioned
in Omni's acidosis
(BTW-Good job, Roger, very thought provoking and complete write up of a
difficult situation),
in the past we always assumed endurance horses were alkalotic (high blood
pH) based on studies 
done in the 80's. This is why we absolutely do not give bicarb to them. Has
this changed?
Since they are going so much faster now are we seeing racehorse like
acidosis instead?
Heidi? Sue?

Sarah and Fling (Are you SURE you want to try the OD 100 this year, Mom? Yep!)