Horse v. Cow

There are a lot of controversies surrounding cattle grazing on public lands.  There seems to be even more controversy and upset when horses are brought into the debate.  This is compounded when the activists are involved who strive to protect the free-roaming horses’ right to exist without federal intervention.  Wild horse activists are angered by the high numbers of cattle in comparison to horses.  Appropriate management levels for herd management areas should be increased, while numbers of cattle on the range should be decreased.  These are some common arguments I hear when there is upset surrounding horse gathers.  I am writing this to provide some data that might give some insight as to why more cattle can graze in an area than horses.

In an article I recently read, The Nutritional Basis for Food Selection by Ungulates, it was stated that cows and horses have different digestive systems.  They diverged from common ancestors into two families known as Artiodactyla and Perissodactyla – ruminant and cecal digesters.  Fermentation in the cecum and the rumen is similar.  However, horses are only 70% as efficient as cows at digestion.  This is because cattle regurgitate and chew partially digested food as “cud,” repeatedly.  Food is ground into smaller particle sizes.  Another reason cattle are more efficient is because the food they intake is digested by microbes before it enters the true stomach.  However, for these same facts, cows are less efficient at digesting fibrous plants.  Cecal digesters – horses – are not constrained by this.  Horses can be less selective in their forage, which gives them an up on ruminants in areas where quality forage is lacking.  However, since they are less efficient at digestion than ruminants, horses eat more than cows (Hanley, 1982).

This report explains why cattle are allotted more AUMs (animal unit month) than horses.  Horses, due to their inefficient digestive system, must eat more than a cow.  A study conducted in Europe on wetlands also confirmed that horses ate more than cattle.  If it is true that horses forage more in a highly mesic setting, than I hypothesize that it can also be true in a less mesic landscape where grasses are less nutritious.  (I have not seen any studies done on North American arid or semi-arid grasslands.  If anyone knows of any, shoot them my way!)

Catherine Menard and her research team wrote a paper in 2002 to describe the feeding niches of horses and cows in a European wetland.  They also used a complimentary site in France, where cattle and horse grazing is a conservation strategy.  Their study found that, like Hanley stated, horses ate more than cattle.  In addition, Menard et al. (2002) stated that horses foraged 50% longer than cattle and in one month consumed 63% more.

Both animals consumed less vegetation in spring and summer, and more in fall and winter due to increased energy needs

Cattle were often excluded from grazing sites with shorter grasses.  Due to the fact that horses have two front incisors, they can graze on grasses that are closer to the ground.  Cattle do not have front incisors, so they are restricted to taller grasses for their forage.   Menard et al. (2002) predicted that when this grazing system comes into equilibrium with vegetation, horses will out-compete cattle since their population increases at a higher rate.  They also stated that cattle should only persist in grasslands if there is adequate broad-leaf forage available that is unavailable to horses, or unless horses are highly predated upon.  Otherwise, there will not be enough forage for cows.

Now, linking this to our ranges where cattle and horses graze on the same landscape, I find that several things are relevant from these two papers.  First, horses consume more than cattle due to their different digestive system.  Two, cattle lack front incisors and cannot graze on short grasses.  Horses can.  Therefore, it makes sense to me that horses are allotted less AUMs than cows, especially knowing that horses are on the range year-round, while cattle are only inhabitants for part of the year, usually spring and summer months when energy requirements are not as high.  Thinking of Menard's suggestion, if cattle are to persist in an ecosystem with horses, the horses must be heavily predated upon.  In our rangelands, the BLM is that predating force to allow enough forage for cattle (as the BLM is mandated through the Federal Lands Policy Management Act) and wildlife.

Hanley, Thomas A. (1982). The Nutritional Basis for Food Selection by Ungulates. Journal of Range Management (35)2. 146-151.

Menard, Catherine, Duncan, Patrick, Fleurance, Geraldine, Georges, Jean-Yves & Lila, Marc. (2002). Comparative foraging and nutrition of horses and cattle in European wetlands. Journal of Applied Ecology. (39). 120-133.