Using a grazing muzzle: Does it affect behavior? (Animal Science Update)
Recently, I hosted a meeting with a few colleagues from around the county — at “An Evening of Wine and Equine”,at Cream Ridge Winery on Aug. 20 — and I would like to take this opportunity to share some very interesting results from some of their practical studies.
The first in the column series featured research performed at the University of Minnesota by Dr. Krishona Martinson, with round bale and square bale feeders.
This second article in the column series will feature research performed at the University of Maryland by Dr. Amy Burk.
She performed a series of studies evaluating grazing behavior and stress level of miniature horses grazing with and without grazing muzzles.
First, to those who do not understand why horses would need a grazing muzzle, it has been commonly studied that some horses can eat up to almost three times their daily recommended intake of pasture forage.
This increase in pasture consumption will cause obesity followed by a host of other problems that come from having an obese horse.
Grazing muzzles are meant to decrease the availability of forage and also slow down eating time.
One study performed at the University of Minnesota found that, “Grazing muzzles can reduce a horse’s pasture intake by about 30 percent, regardless of grass species.”
However, there has been many reports that contradict how long the grazing muzzles should be left on horses for maximal weight control and not impact the horse’s welfare.
Research reports from North Carolina State University have found that horses on a limited turn out time of only four hours each day can consume more than 50 percent of their recommended daily allowance in this time alone once they are accustomed to the schedule.
Therefore, the theory is that leaving the muzzle on for only several hours per day will cause this compensatory grazing pattern and not actually provide any weight loss.
However, many think that if grazing muzzles are left on for a full day of grazing it will create increased stress levels in these horses.
Grazing muzzles are made to allow grazing and drinking through a small hole in the bottom of the muzzle and several small holes around the sides.
However, it can inhibit other natural behaviors like mutual grooming and defensive biting.
These are the reasons for Dr. Burk’s studies.
Each study was designed similarly, but one had horses individually housed in small quarter acre pastures and the other study had horses group housed in a larger pasture. Each horse rotated through three different treatments: no grazing muzzle, muzzled 10 hours per day, or muzzled 24 hours per day. Horses were measured for body weight, muzzle acceptability score (when removing and replacing the muzzle), and percentage of time horses spent moving, grazing, drinking, standing, etc.
Horses also wore a heart rate monitor to measure heart rate variability and had salivary cortisol measured as two measures of stress during the study period.
Results from these studies showed that when muzzled 24 hours per day horses reduced weight however, without a muzzle or when only wearing it for 10 hours per day they actually gained weight.
Grazing muzzle treatment had no effect on salivary cortisol; however, if muzzled 24 hours per day heart rate variability increased which is an indicator that the horse’s stress level is actually decreased compared to the other muzzling treatments.
One theory for the decreased stress might be explained by the behavioral results found.
They showed that there was no difference between treatments in muzzle acceptance, stereotypic or frustration behaviors observed, the amount of voluntary exercise, as well as the dominance hierarchy when group housed.
However, when muzzling 24 hours per day horses had a reduced amount of time they were found resting, and an increase amount of time horses were grazing.
In previous reports, grazing has been shown to have a calming effect as compared to horses in stalls eating hay or confined to a stress lot.
Overall between the two studies, Dr. Burk concludes that wearing grazing muzzles does not induce stress or affect voluntary exercise, but does increase the time horses are grazing and is a good way to prevent weight gain.
If you want more details on both of these studies, see the summary report written by The Horse.com at https://thehorse.com/177303/grazing-muzzles-can-help-horses-lose-weight-without-impacting-welfare/
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