Tuesday, April 12, 2016

Grazing Muzzles: New research shows grass length affects grazing behavior

It’s that time of year. The grass in the pastures is waking up and springing to life. But animals at risk for laminitis require effective strategies to prevent weight gain and overeating that may trigger insulin dysfunction and possibly lead to mild or even severe laminitis and changes in the structure and integrity of the hoof that could cause diminished performance, even if the horse is not overtly lame.

For many horse owners, the first line of defense is a grazing muzzle, even if their horses do detest wearing them. What are the latest findings on how they affect horses?
New research will be published next month that documents how grazing muzzles may change equine behavior while on pasture, based on the length of grass available. The Hoof Blog is pleased to share a summary capsule of that research, which may be useful when planning pasture management once the grass is higher.
Investigation into the effectiveness of grazing muzzles as a tool to help with weight management has also shown that longer grass can be more difficult for muzzled ponies to graze, and can cause frustration-related behavior in some individuals.

Grazing muzzles have already been shown to reduce the pasture intake of ponies by around 80% by significantly reducing bite size and intake. (1) Ponies fitted with grazing muzzles may spend more time engaging in foraging and eating than their non-muzzled counterparts, yet the majority either lose weight or retain their body condition. This in turn helps reduce susceptibility to obesity and related disorders, such as insulin dysregulation and laminitis.

The new (2016) research was conducted by the United Kingdom's WALTHAM® Equine Studies Group in collaboration with Dr Annette Longland of Equine and Livestock Nutrition Services (ELNS) in Wales. (2)  It will be published in the Journal of Equine Veterinary Science.

Four mature ponies were selected for the study. Their dry matter (DM) and water-soluble carbohydrate (WSC) intakes were measured in spring, summer, and autumn pastures on four, three-hour occasions per pony per season when fitted with or without a grazing muzzle.

In addition, ponies with and without muzzles were allowed to take 10 bites of swards maintained at different heights.

When the ponies wore grazing muzzles, pasture intake was reduced by 77% during spring and summer and by 83% during the autumn. Without muzzles, the ponies generally reduced the sward length by half with the first bite; however, when the ponies were muzzled the reduction of pasture intake was variable and the ponies appeared to experience greater difficulty in accessing the longer versus the shorter swards.

The short (less than 10cm), upright grass appeared to be the easiest to eat, as leaf blades and stems protruded through the holes in the muzzle. The medium and long swards proved more difficult. They bent under the pressure of the muzzle and became flattened, causing the ponies to adopt various strategies to access the grass. 

In some cases, the ponies pawed the ground to unearth the sward and access it through the muzzle. Alternatively they rammed the solid base of the muzzle hard onto the grass, causing it to buckle and make some blades or stems accessible. These were then yanked vigorously, often causing the entire plant to be uprooted and eaten.

Water soluble carbohydrate levels in the sward were similar across the seasons although they were slightly higher in autumn. However, once muzzled, the ponies’ intake of WSC wasn’t significantly different across the seasons; this finding strengthens evidence that the use of grazing muzzles is effective.

Clare Barfoot, RNutr, research and development manager at SPILLERS® said:“While the frustration displayed when the muzzled ponies were on longer grass swards indicates that care should be taken to provide an accessible grass length, grazing muzzles remain an effective weight management tool. They allow turnout over large areas, increasing exercise and allow slow “trickle” feeding, to control weight gain and reduce the risk of obesity-related disorders, without significantly compromising the natural behavior and wellbeing.”

Grazing muzzle use has three basic requirements:
  1. they must be used with care; 
  2. they should be properly fitted; and 
  3. horses and ponies should be adapted gradually to wearing them. 

In addition, follow these recommendations from the SPILLERS® researchers:
  1. Group and individual behavior should be monitored closely to observe any potential concerns caused by changes to the herd dynamics. 
  2. Ensure that muzzled ponies are confident in drinking and eating through their muzzles before turning them out for prolonged periods. 
  3. Muzzles must not be used continuously (not more than 10 hours per day) and total exclusion muzzles are not advised. 
  4. Periodic weight monitoring is recommended as some individuals can still gain weight when muzzled.
References cited in this article:
(1) The effect of wearing a grazing muzzle vs not wearing a grazing muzzle on pasture dry matter intake by ponies, A.C. Longland, C. Barfoot, P.A. Harris, Journal of Equine Veterinary Science, Volume 31, Issues 5–6, May–June 2011, Pages 282-283, http://dx.doi.org/10.1016/j.jevs.2011.03.105.
(2)   Effects of Grazing Muzzles on Intakes of Dry Matter and Water-Soluble Carbohydrates by Ponies Grazing Spring, Summer, and Autumn Swards, as well as Autumn Swards of Different Heights,
Annette C. Longland, Clare Barfoot, Patricia A. Harris,
Journal of Equine Veterinary Science, Volume 40, May 2016, Pages 26-33,
Top photo provided by Spillers and adapted for the Hoof Blog.

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