Re: High Protein Hay

Eleanor Kellon, VMD

--- In EquineCushings@..., "coppermoonglade" <debbyd@...>

Can the protein content in hay be too high?

The orchard grass I plan to buy is 19.8% crude protein.
The iron is high, but could be dealt with. The protein is risky. For
one thing, crude protein only represents nitrogen. This hay could
have high nitrate levels, a toxin. This can happen when hay is
stressed during growth and does not convert nitrate into protein.
Grasses take up nitrogen from the soil, convert to nitrate and from
there convert to protein/amino acids. High nitrate can also occur if
the hay is overfertilized, either with nitrogen fertilizer or after
years of manure application. Nitrate levels can be tested at the
forage lab.

High protein hay might also cause a significant insulin rise.
Arginine in mares and lysine in both sexes cause an insulin spike.

: J Anim Sci. 2001 Mar;79(3):735-44. Links
Pituitary hormone and insulin responses to infusion of amino acids
and N-methyl-D,L-aspartate in horses.Sticker LS, Thompson DL Jr,
Gentry LR.
Department of Animal Science, Louisiana Agricultural Experiment
Station, Louisiana State University Agricultural Center, Baton Rouge
70803, USA.

Thirty-nine adult light horse mares, geldings, and stallions were
used in two experiments to assess the pituitary hormone and insulin
responses to infusions of arginine, aspartic acid, lysine, glutamic
acid, and N-methyl-D,L-aspartate (NMA). In Exp. 1, 27 horses were
assigned to one of three infusion treatments: 1) physiological saline
(1 L); 2) 2.855 mmol of arginine/kg BW in 1 L of water; or 3) 2.855
mmol of aspartic acid/kg BW in 1 L of water. In Exp. 2, 12 horses
were assigned, in a multiple-square 4 x 4 Latin square design, to one
of four infusion treatments: 1) 2 mL of saline/kg BW; 2) 2.855 mmol
of lysine/kg BW in water; 3) 2.855 mmol of glutamic acid/kg BW in
water; or 4) 1 mg of NMA/kg BW in water. In Exp. 1, an acute (within
20 min) release of growth hormone (GH) was induced (P = 0.002) by
aspartic acid. In contrast, acute release of prolactin (P = 0.001)
and insulin (P = 0.002) was induced only by arginine; moreover, the
arginine effect on insulin was present only in mares (P = 0.011). In
Exp. 2, an acute release of GH was induced (P = 0.001) by glutamic
acid and NMA. In males, the glutamic acid-induced GH release was
greater than that of NMA; in mares, the NMA-induced GH release was
greater than that of glutamic acid (P = 0.069). Both lysine and
glutamic acid induced (P = 0.001) acute release of prolactin, whereas
an acute release of insulin was elicited (P = 0.002) only by lysine.
The NMA-induced LH response was due almost entirely to the response
in mares and stallions (P = 0.016), and the NMA-induced FSH release
was due almost entirely to the response in mares (reproductive status
effect; P = 0.004). In the horse, aspartic acid, glutamic acid, and
NMA seem to stimulate GH release; arginine and lysine seem to
stimulate prolactin and insulin release; and NMA seems to stimulate
LH and FSH release. It seems that N-methyl-D-aspartate glutamate
receptors are involved in controlling GH, LH, and FSH secretion,
whereas other mechanisms are involved with prolactin secretion. These
results also indicate that gonadal steroids interact with amino acid-
induced pituitary hormone release in adult horses.

If we take a look at these numbers, a mmol (millimole) of lysine is
0.146 grams so for a 500 kg (1100 pound) horse that's 73 grams of
lysine, quite a lot and it was also given IV. I don't know what
lysine estimate they gave you, but lysine in orchardgrass runs about
3.9% of the crude protein, after adjusting for protein locked in the
ADF fraction. Over the course of a day, that would amount to 75 grams
of lysine from 10 kg (22 lbs) of hay, and arginine content is almost

Is that enough to cause an insulin rise? Don't know! Blood amino acid
levels are eating are highly variable:

J Vet Med A Physiol Pathol Clin Med. 2006 Nov;53(9):439-44. Links
Individual differences and repeatability of post-prandial changes of
plasma-free amino acids in young horses.Hackl S, van den Hoven R,
Zickl M, Spona J, Zentek J.
Department of Veterinary Public Health, Institute of Nutrition,
University of Veterinary Medicine, Vienna, Austria.

Few data are available on post-prandial changes of plasma amino acids
(AAs) in horses and on the repeatability and the individual variance
on different sampling days. The objective of the present study was to
measure pre- and post-prandial concentrations of plasma AA in 10
yearling horses. Blood samples were taken on days 1 and 40 of the
study before feeding of hay, oats and soya meal and over an 8 h post-
prandial period in 2-h intervals. The plasma AAs were measured by
high-pressure liquid chromatography after ortho-phthalaldehyde
derivatization. Mean fasting concentrations of the AAs were not
significantly influenced by the individuum and sampling day.
Repeatability of the fasting AA levels in the individual horses on
two different sampling days was only found for histidine, 3-
methylhistidine, methionine, tryptophan and taurine. While the
absolute post-prandial AA concentrations differed between sampling
days, the relative changes were comparable. All AA concentrations
except 3-methylhistidine increased after feeding by 13% to more than
200% of their fasting values if the combined data of both days were
analysed. Four hours after feeding the concentrations of arginine,
asparagine, lysine, leucine, isoleucine and threonine, decreased more
than 20%. Histidine, methionine, phenylalanine, valine, tryptophan,
glutamine, glycine, tyrosine and taurine concentrations decreased by
less than 20%. Concentrations of aspartic acid, glutamic acid,
ornithine, serine and citrulline remained elevated.....

In normal horses, alfalfa causes only a slight insulin rise in

If you want to use this hay, I would first have it checked for
nitrate level, and just to be safe get a postfeeding (1.5 to 2 hours)
insulin level checked.

The other thing you will have to deal with is higher water
consumption and urine production. Excess protein is metabolized to
urea and excreted in the urine. That's going to mean a lot of extra
bedding over the winter, and a lot of extra stall cleaning to avoid
ammonia build up (bacteria in the stall break the urea down to


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