Jul 142010
 

Summer is a great time for riders and horse owners alike, the long days and hopefully sunny weather bring greater opportunities for spending time with our much loved, four-legged friends. However, for some horse and pony owners summer can also be a worrying time and the start of an ongoing battle with their horse’s waistline. Despite our best intentions summer comes and our horse’s stomachs begin to expand like balloons at a birthday party. Some horses come out of winter the perfect weight but can start to inflate the minute the first spring grass appears, for others the issue of weight is a constant factor, especially for those with pony or cold blood genes in their DNA. If you own a horse who is a ‘good doer’ and he can seemingly live off air alone, it can seem like no management strategy or exercise regime will stop the spread. So what are the real risk factors of obesity and how can we prevent our horse’s becoming overweight this summer?

Obesity, in both horses and humans, is becoming an epidemic in the UK. The horse charity, World Horse Welfare, estimates that between 35 and 45 per cent of the UK’s 1.35million horses are obese[1]. There are many worrying disorders that obesity is associated with, including; Laminitis, Equine Metabolic Syndrome and oxidative stress[2]. All of the above disorders are of grave concern to owners! Laminitis is inflammation of the digital laminae of the hoof. The digital laminae are necessary for suspension of the skeleton within the hoof and spread the concussive forces experienced by the hoof during the horse’s locomotion. Inflammation of the laminae weakens the hoof and can have devastating effects on the horse’s physiology included; sinking and rotation of the coffin bone (known as founder), separation of the hoof wall from the hoof capsule, rotation of the coffin bone and penetration of the coffin bone through the sole of the hoof[2]. These complications of Laminitis can cause permanent lameness and loss of use and can, in the worst cases, result in euthanasia.

Equine Metabolic Syndrome (EMS) is characterised by obesity, insulin resistance and intermittent bouts of Laminitis[2]. Obese horses suffering with EMS become gradually more resistant to the action of insulin – insulin is a hormone which triggers cells in the liver, muscles and fat to take up glucose from the blood stream and store it as glycogen. This resistance to insulin consequently causes abnormally high levels of insulin to be secreted when the horse ingests food, especially foods high in sugars such as concentrate. In both horses and humans, insulin resistance seems to be correlated with obesity and the altered metabolism of fats[3]. However, unlike in the human species, insulin resistance in horses due to obesity is very rarely type 2 diabetes (diabetes in horses is usually only associated with Cushing’s syndrome), instead insulin resistance is postulated to be a contributing factor to Laminitis and potentially certain vascular diseases[3].

Laminitis and EMS are not the only concerns for the owners of horses who put on weight easily. Several adverse health effects can be correlated with the horses gain of fat deposits. The horse may become intolerant of exercise and his athleticism will be compromised. Just as obese humans can experience oxidative stress, fatigue and increased concussion on joints during exercise, horses can also experience these consequences of obesity. The performance of horses competing in races of duration 1 mile to 160km has been found to correlate to the horse’s body condition[4-6]. The obese horse may also experience thermoregulatory difficulty, although fat deposits will insulate a horse during the winter months, in the summer excess fat can prevent the horse from effectively dissipating heat resulting in the horse overheating[7]. Finally, abnormal reproductive performance has also been observed in obese mares [8], obesity can cause unnecessary complications in pregnancy and is therefore a welfare concern for both mare and foal. The risks of horse obesity are very worrying for horse owners so why are so many horses becoming obese in the UK?

Although ignorance on behalf of the horse owner is sometimes the underlying cause of equine obesity, most owners are aware when their horses are becoming overweight. Even the least observant owner can see their horse’s stomach increasing in girth, the neck becoming larger and developing a crest, and fat deposits occurring on the shoulders and flanks, but often the owner is struggling to set up a management regime that can control the weight of the horse. Owners are often restricted by factors such as; the residence of the horse, the management of the horse’s pasture or other environmental factors. But do not despair, here are a few ideas which could help to prevent the summertime spread this year.

1. Knowing how much you horse should weigh, finding an accurate way to measure your horse’s weight and keeping a record of change.

The first thing you will need to know when you embark on the battle with obesity is your horse’s ideal weight. Without a goal weight for your horse any measurement of the horse’s weight is going to be arbitrary. Although all horses differ with regards to their ideal weight, approximate ideals for your horse’s type and height can be found below. For each height range there is a range of ideal weights, if your horse is the top end of the height range or a draught bred then the horse’s ideal weight will be the top end of the range, and vice versa.

Height in hands11121314151617
Ideal weight in kg120-230230-290290-350350-420420-520520-600600-725

(Adapted from Baileys Horse feeds [9])

Once you know your horse’s ideal weight you will need to be able to measure the horse’s weight. There are many ways to measure a horse’s weight, some more accurate than others. The most accurate method of measuring a horse’s weight is a weighing bridge, however unless you are liveried at a very well equipped yard or have convenient access to veterinary facilities it is unlikely that you will have access to a weigh bridge.

A more common method of measuring a horse’s weight is by using a weight tape. Weight tapes are placed around the girth of the horse, just behind the withers, and give an estimation of the horse’s weight based on the circumference of the girth . The accuracy of these tapes is debatable however, the tape provides a quantitative measure of weight which can be recorded and which will provide notice of the horse’s weight changing over time. Weight tapes can be brought from most equestrian stores, and on occasion tapes specifically designed for draught horses and ponies can be acquired. Buying a tape designed for your horse’s body type will increase the accuracy of the measurement.

As an alternative measure of the horse’s weight and condition there are body condition scoring systems, one of the most popular is based on work by Henneke et al (1983)[10]. Henneke et al’s body condition scoring uses the observation and ranking of the fat tissue present on specific areas of the body to score the condition of the horse. The areas observed for the accumulation of fatty tissue are; the neck, ribs, back, shoulder, wither and the top of the tail. When all the areas are taken into consideration an overall condition score, between 1 and 9, is attributed to the horse – 1 being of very poor condition with no fatty tissue present in the scored areas and 9 being of obese condition with significant fatty deposits visible on the . A picture chart explaining Heneke’s body condition scoring can be found at – http://www.admani.com/allianceequine/images/bodyconditionscoring/horse%20body%20condition%20score%20card.pdf , this picture chart is a good summary of the observations that should be made during condition scoring. A printable record sheet for Henneke et al’s body condition scoring mechanism can also be found at this link – http://www.blm.gov/pgdata/etc/medialib/blm/wo/Information_Resources_Management/policy/im_attachments/2009.Par.52473.File.dat/IM2009-041_att1.pdf

There are potential problems with using body condition scoring as a method of weight measurement in horses. Scoring body condition is a subjective method and it is therefore possible for owners to over or under score their horses and, if no additional methods of weight measurement are used, it is sometimes difficult to ascertain whether the horse is indeed of a healthy weight. Ideally two or three people should score the horse independently and the middle score taken to be correct, such a precaution will help to minimise the effect of subjective bias. The body score of the horse can be recorded and over time any change in the horse’s condition can be monitored accordingly.

Whichever method of weight measurement you decide to use with your horses, try to keep a record at least once a month of the horse’s weight. This record keeping will allow you to see changes in the horse’s condition early and allow you to change his management before serious complications arise.

2. Cutting out the concentrate feed!

This one may seem obvious, but if your horse is overweight it is not necessary to supplement the horse’s roughage feed with concentrate! Removing concentrate feed, and therefore unnecessary calories, from the diet of the horse will help to prevent, or treat, obesity. If the horse is feed ad-lib, quality roughage including pasture, and is a good weight it is not necessary to supplement the horse’s diet with calorie-dense, grain concentrate. Should the horse’s pasture and roughage be of poor quality it may be a prudent idea to add a vitamin and mineral supplement to the horse’s feed, this will prevent any dietary malnutrition. As long as the horse maintains weight and does not become thin, and is not in a heavy exercise regime, i.e. intermediate eventing or above, the horse does not require extra calories. Should the horse be currently in a routine where he is used to receiving concentrate meals at certain times and will become distressed if his routine is changed then some molasses-free chaff or grass chop can be feed at these times to placate him.

3. Pasture maintenance

There are many aspects of pasture maintenance that can be managed to help combat obesity and weight gain in the horse. Below I will tackle the most important factors of pasture maintenance that can be managed by horse and land owners –

The right grass?

Many grassland species have been selectively produced to feed domestic livestock on intensive grazing patterns, as such many grass species commonly found in horse grazing are high in sugars. Grass designed to keep livestock at a good weight is often too rich for horses who are designed by evolution to each a great amount of poorer roughage. See below abstract by Menard et al (2001)[11] on the comparative forage intake of cattle and horses.

“Equids are generalist herbivores that co-exist with bovids of similar body size in many ecosystems. There are two major hypotheses to explain their co-existence, but few comparative data are available to test them. The first postulates that the very different functioning of their digestive tracts leads to fundamentally different patterns of use of grasses of different fibre contents. The second postulates resource partitioning through the use of different plant species. As domestic horses and cattle are used widely in Europe for the management of conservation areas, particularly in wetlands, a good knowledge of their foraging behaviour and comparative nutrition is necessary.

In this paper we describe resource-use by horses and cattle in complementary studies in two French wetlands. Horses used marshes intensively during the warmer seasons; both species used grasslands intensively throughout the year; cattle used forbs and shrubs much more than horses. Niche breadth was similar and overlap was high (Kulczinski’s index 0·58–0·77). Horses spent much more time feeding on short grass than cattle. These results from the two sites indicate strong potential for competition.

Comparative daily food intake, measured in the field during this study for the first time, was 63% higher in horses (144 gDM kg W−0·75 day−1) than in cattle (88 gDM kg W−0·75 day−1). Digestibility of the cattle diets was a little higher, but daily intake of digestible dry matter (i.e. nutrient extraction) in all seasons was considerably higher in horses (78 gDM kg W−0·75 day−1) than in cattle (51 gDM kg W−0·75 day−1). When food is limiting, horses should out compete cattle in habitats dominated by grasses because their functional response is steeper; under these circumstances cattle will require an ecological refuge for survival during winter, woodland or shrubland with abundant dicotyledons.

Horses are a good tool for plant management because they remove more vegetation per unit body weight than cattle, and use the most productive plant communities and plant species (especially graminoids) to a greater extent. They feed closer to the ground, and maintain a mosaic of patches of short and tall grass that contributes to structural diversity at this scale. Cattle use broadleaved plants to a greater extent than horses, and can reduce the rate of encroachment by certain woody species.”

Menard et al (2001)


As horses can consume great amounts of forage it is vital that the high-sugar, easily digestible and nutrient rich grass varieties fed to domestic livestock species are not feed in high quantity to horses. Obesity and laminitis will be difficult to avoid on rich grazing without restricting grazing, which in turn would be detrimental to the welfare of the horse. Sugars present in grass species, especially fructans have been correlated with laminitis in horses. Below is an informative short article on fructans from www.equinescienceupdate.co.uk.

Recent studies suggest that fructans might be involved in pasture-induced laminitis in horses. Fructans are storage molecules produced by the grass when it produces more sugars by photosynthesis than are needed for immediate use. Fructans are poorly digested in the foregut of the horse. If large quantities reach the hindgut they are rapidly fermented by the microorganisms, leading to a cascade of events that may result in laminitis.

In a three year study Jürgen Grässler and Uwe von Borstel, working at the Landwirtschaftskammer in Hannover, Germany, looked at fructan content in the species of grasses that are commonly found in horse pasture. They harvested grass samples every two or three weeks during the growing season. Samples were collected at 11.00 each morning to prevent the results being influenced by time of day.

Dr Grässler presented their findings at the Equine Nutrition Conference held earlier this month in Hannover. They found that Lolium perrene (Perennial ryegrass) and Lolium multiflora (Italian ryegrass) contain the highest amounts of fructans – an average throughout the year of 5.7% on a dry matter basis. However, they found that the fructan content varied throughout the year, being highest in May and October. The fructan content fell during the summer. They also found a difference between strains of perennial ryegrass. One strain (“Anton”) had the highest fructan level of 14.2%DM in autumn 2003 and 13.6% DM in spring the same year.

All other pasture grasses contained low fructan concentrations – on average about 3.5% DM. Again, the highest fructan concentration was found in the first growth in May and in October. The fructan content of the grass was lowest during the summer.

The second part of the study looked at the fructan content of grass mixes that might be used for horse pasture. Grässler and von Borstel found that mixtures with a high proportion of Lolium perrene gave the highest fructan levels . The highest levels were found in pastures containing only Lolium perrene (15.2%). During the growing season the highest fructan content was measured in late June (11.4% DM average) and in October.

Grässler and von Borstel conclude that grass mixes with high amounts of Lolium perrene may contain high fructan concentrations, especially in spring and autumn, and are less suitable for feeding horses predisposed to laminitis.

To minimise the risk of laminitis they suggest that grass mixtures with reduced quantities of Lolium perrene should be used. Pastures with forage grasses such as Alopecurus pratensis (Meadow Foxtail) and Phleum pratense (Timothy) as the main components are suitable to produce low fructan concentrations.

Reference: Fructan content in pasture grass. Jürgen Grässler and Uwe von Borstel. Proceedings Equine Nutrition Conference. Pferdeheilkunde (2005) 21, 75 – 76.”[12]

The key message of the above article is; when planning the reseeding of your pasture please consider the grass species you are using and choose low-sugar grass species, such as Meadow Foxtail and Timothy, which will protect your horses against obesity, insulin resistance and Laminitis. Herbs and legumes can also be included for variety and additional vitamin and mineral availability. Sugar-dense grasses used to feed domestic livestock, such as dairy cattle, should be avoided as they are not suitable for healthy horse grazing. Rye grass is the typical example and is currently very common in the pastures of Britain’s horses. If you are at the mercy of a land owner it may be possible through democratic negotiation to encourage the seeding of horse friendly grass species.

Pasture fertilisation

Traditionally pasture fertilisation is recommended in the spring and autumn months. It is suggested that proper fertilisation will provide pasture with the nutrients to produce a good quantity of grass cover, minimising weed growth. In addition it is postulated that the nutrients needed to provide horses with a healthy diet are also infused into the soil during fertilisation. However, the relationship between fertilisation and grass nutrition is not straight forward, especially when considering non-structural carbohydrate concentrations (sugars). It is often assumed that fertiliser increases the sugar content of grass, however, it is well noted in scientific journals that grass grown in an environment deficient in either nitrogen or phosphorus is observed to be significantly higher in sugars than grass grown in fertilised conditions [13, 14, 15, 16]. The discovery of this correlation between nitrogen availability and the sugar concentration in grass has led to the postulation that nitrogen maybe a limiting factor for growth and therefore if the grass becomes deficient in nitrogen, growth stops and, rather than being used for the production of new plant matter, fibre and energy, the sugars accumulate in the grass[17].

In her 2005 paper titled – A Review of Unlikely Sources of Excess Carbohydrate in Equine Diets, Kathryn Watts considers data collected on the effect of pasture fertilisation on the non-structural carbohydrate (NSC) concentrations of grass, and how pasture should managed to prevent an excess in sugar in the equine diet[17]. She writes “The following data was collected from the first cutting of forage from an established paddock of irrigated pasture at Rocky Mountain Research & Consulting, Inc. Each treatment was replicated 4 times in a randomized block design. The species represented are mostly Paddock meadow brome and Garrison meadow foxtail, which are standard commercial varieties in the area. Ammonia nitrate was broadcast in March, and irrigation was applied as needed for optimum growth to both fertilized and unfertilized plots. When the paddock was starting to head the end of May, samples for NSC were collected 4 PM, frozen immediately, and shipped frozen for analysis. A light frost occurred the night before sampling. The next day, 2 sq yards of plant material were hand clipped to ground level from each plot, and dried in an oven to obtain dry matter yield. The plots fertilized with ammonia nitrate yielded 3 times more dry matter, and were 29% lower in NSC concentration than unfertilized. This inverse relationship between nitrogen content and NSC concentration corroborates that found in plant science literature.

NSC %

Dry matter

Yield Tons

Dm/ acre

Pounds NSC /acre
35 lbs/acre

nitrogen as AmNO3

17.88 b1.8 a643 a
No nitrogen23.10 a.6 b277 b

Analysis by Dairy One, Ithaca, NY

The determination as to whether NSC concentration or pounds of NSC per acre is more important will be dependent on how the individual horse’s intake is managed. If a horse has continual access to pasture, it is possible to limit grass intake by starving the grass for nitrogen and overgrazing such that the amount of available forage does not exceed or even meet caloric needs. In this scenario, additional hay is often required. Because hay is generally lower in NSC than fresh grass, the higher concentration of NSC in nitrogen deficient grass may be offset by the lower concentration generally found in hay. In this type of situation, susceptible horse’s may be at increased risk of over indulging if the pasture is fertilized or irrigated, or a drought breaking rain occurs, which would then create more pounds of NSC per acre, while removing the limitations to intake imposed by slow grass growth.

If the caretaker were limiting intake by restricting access to grass, by use of grazing muzzle, portable fencing, or removal to a dry lot for part of the day, then fertilization, which decreases the concentration of NSC per mouthful of grass, would be the best option.” [17]

When considering whether it is healthier for your horses to fertilise your paddock or to leave it to grow organically it is necessary to consider whether the higher yield of grass obtained through fertilisation is likely to cause your horse to have higher sugar in his diet than the lower yield, higher sugar concentration grass of organic pasture? If your horse’s residential property has a low horse-acreage ratio, then it is possible that the high yield gained by fertilisation will create to much pasture for the horses to graze without becoming overweight. However, if there are a significant amount of horses grazing the pasture of your horse’s residence the extra grass yield of fertilised pasture should be spread between enough animals that the lower sugar concentration of fertilised grass is beneficial. Optimum fertilisation is a balancing act, one that must be considered carefully by horse owners.

To be continued….

Next time we will consider more pasture management ideas and exercise routines design to fight horse flab.

By Emma Lethbridge

(info@emmalethbridge.com)

References

[1] http://www.worldhorsewelfare.org/

[2] Johnson P.J., Wiedmeyer C.E., Messer N.T., Ganjam V.K. Medical Implications of Obesity in Horses—Lessons for Human Obesity. J Diabetes Sci Technol. 2009; 3(1): 163–174.

[3] Hoffman R.M., Boston R.C., Stefanovski D, Kronfeld D.S., Harris P.A. Obesity and diet affect glucose dynamics and insulin sensitivity in Thoroughbred geldings. J Anim Sci. 2003;81(9):2333–2342.

[4] Kearns C.F., McKeever K.H., Kumagai K., Abe T. Fat-free mass is related to one-mile race performance in elite standardbred horses. Vet J. 2002;163(3):260–266

[5]Lawrence L.M., Jackson S., Kline K., Moser L., Powell D., Biel M. Observations on body weight and condition of horses in a 150-mile endurance ride. J Equine Vet Sci. 1992;12:320–324.

[6]Garlinghouse S.E., Burrill M.J. Relationship of body condition score to completion rate during 160 km endurance races. Equine Vet J Suppl. 1999;30:591–595.

[7] Cymbaluk N.F., Christison G.I. Environmental effects on thermoregulation and nutrition of horses. Vet Clin North Am Equine Pract. 1990;6(2):355–372.

[8] Henneke D.R., Potter G.D., Kreider J.L. Body condition during pregnancy and lactation and reproductive efficiency of mares. Theriogenology. 1984;21:897–909.

[9] http://www.baileyshorsefeeds.co.uk/feedingexplained/calculator.htm

[10] Henneke D.R., Potter G.D., Kreider J.L., Yeates B.F. (1983). Relationship between condition score, physical measurements and body fat percentage in mares. Equine Vet J. 15(4):371-2

[11] Menard C., Duncan P., Fleurance G., Georges J-Y., Lila M. (2001). Comparative foraging and nutrition of horses and cattle in European wetlands. Journal of Applied Ecology. 39 (1); 120-133.

[12] Article at http://www.equinescienceupdate.co.uk/fructan.htm on the paper- Fructan content in pasture grass. Jürgen Grässler and Uwe von Borstel. Proceedings Equine Nutrition Conference. Pferdeheilkunde (2005) 21, 75 – 76.

[13] Smith D. Nonstructural Carbohydrates. In Butler G.W., Bailey R.W. ed. Chemistry and Biochemistry of Herbage, vol 1. London: Academic Press, 1973;105-155.

[14] Belesky D.P., Wilkinson S.R., Stuedemann J.A. The influence of nitrogen fertilizer and Acremonium coenophialum on soluble carbohydrate content of grazed and non-grased Festuca arundinace., Grass Forage Sci 1991;46:159-166.

[15] Donaghy D.J., Fulkerson W.J. The impact of defoliation frequency and nitrogen fertilizer application in spring on summer survival of perennial ryegrass under grazing in subtropical Australia, Grass Forage Sci 2002;57(4):351.

[16] Morvan-Bertrand A., Boucaud J., Prud’homme M. Influence of initial levels of carbohydrates, fructan, nitrogen and soluble proteins on regrowth of Lolium perenne . L. cv. Bravo following defoliation. J Exper Bot 1999;50:1817-1826.

[17] Watts K.A. A Review of Unlikely Sources of Excess Carbohydrate in Equine Diets. Journal of Equine Veterinary Science. 2005; 25(8): 338-344