What do we really mean by trickle feeding: understanding the equine feeding strategy
By Dr. Stephanie Wood (Ph.D., PgDip., BSc (Hons), RNutr, R. Anim. Tech.)
We often hear the phrases that horses, ponies, and donkeys, are trickle feeders who need to eat little and often, and that they should spend the majority of their time eating. Whilst these statements are true, it’s important to understand that providing sufficient access to food is not the only consideration when developing a feeding regime for your equine.
Observations of wild horses, ponies, and donkeys show the strategies that equids use to meet their nutritional requirements. These ‘feeding strategies’ enable them to survive and thrive in a range of environments, utilising the different plant species available. The really interesting part is that the feeding strategy adapts to the animal’s environment, whilst maintaining some core activities. This adaptation shows that equids are more robust than is often portrayed, and that they can cope with changes in diet and food source if that change is actioned appropriately.
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For simplicity, in this article the terms equine and equid are used to describe horses, ponies, and donkeys as they are three of the eight species within the genus Equus
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Diet selection
The diet of modern horses, ponies, and donkeys comprises mainly grass species, with legumes (such as clover) being preferentially selected when available (Hunt, 1995). Browse forms a smaller portion of the diet and is mainly utilised when grass availability is reduced, such as during winter (Putman et al., 1987; Moehlman, 1998; Lamoot & Hoffmann, 2004). The exception to this is the eating of browse by donkeys even when grazing is available (Rutagwenda et al., 1990; Moehlman, 1998). This ability of donkeys to utilise browse as additional food sources is thought to be due to increased upper lip mobility compared to the horse and pony (Moehlman, 1998). In the domestic situation this increased selectivity would place donkeys at an advantage when offered diets ad libitum (unrestricted amounts with free access), enabling selection of more nutritious plant species and plant parts. Domestic grazing donkeys will also browse on hedges even when grazing is abundant (personal observation). The ability of donkeys, and to a lesser extent horses and ponies, to utilise browse, increases the choice of plant species available to eat. In winter, when availability of grass is reduced, increasing browse intake helps to maintain dry matter intake (DMI) and satisfy nutrient requirements. In summer, when grass availability is greater, browse consumption is generally lower, although it should be considered if your horse, pony, or donkey has access to hedges and trees. The effectiveness of a carefully thought-out grazing restriction plan can be undermined if the area they have access to is surrounded by accessible hedges and trees.
Figure 1: Pony browsing on a gorse bush in colder weather.
The nutritional quality of plants varies with plant species, plant part (leaf versus stem), plant stage of growth, and growing conditions. Despite these variations, even when including younger, more nutritious plants when availability allowed, the natural diet equids evolved eating is classed as being of low nutritional quality due to the low energy and protein, and high fibre content. This low nutritional quality required a specific feeding strategy and digestive solution.
Feeding strategy
To consume enough energy and nutrients to meet requirements, equids developed a feeding strategy of high input and limited utilisation compared to other large herbivores such as ruminants (Uden & Van Soest, 1982; Clauss et al., 2023).
Input is measured as daily DMI and equates to the animal’s daily appetite. On average, equids consume 2-2.5% of their body weight on a dry matter (DM) basis per day, although some domestic horses and ponies will consume up to 5% of their body weight daily if food availability allows (Kuntz et al., 2006; Longland et al., 2011). Aside from how much food there is available to eat, the fibre content of the food also affects daily DMI. This is because the fibre content affects how much the food must be chewed before it is swallowed. Fibre provides structure to the plant, but it requires more chewing to break down the particles prior to being swallowed than non-fibrous parts of the plant. Mature plants contain more fibre than younger plants, as do stems, twigs and branches compared to leaves (Jung & Allen, 1995; Bach Knudsen, 2001), therefore, when consuming more mature plants, intake rates will be slower than when consuming less fibrous plants (Smith, 1999; Edouard et al., 2008).
Although the feeding strategy was high input, the fibrous nature of the equine diet meant that it was consumed at a relatively slow rate, requiring equids to spend large portions of the day eating. Observations of wild and semi-feral equine populations show grazing and foraging behaviours are performed for 12-19 hours per day (Boyd et al., 1988; López López et al., 2019), with similar lengths of time allocated to eating in domestic populations when food availability allows. The continued requirement to perform eating behaviours for such lengths of time show it is an innate behaviour, a behaviour that the animal performs without having to learn and which is important for their physical and mental wellbeing (Boyd et al., 1988). Moving whilst eating is also an innate behaviour, as equids will take one or two bites then move a step, take another couple of bites and move another step, and so on, linking eating and movement. The slow intake rate combined with long eating times is the basis for the recommendations that domestic horses, ponies, and donkeys should trickle feed and spend the majority of their day eating.
Figure 2: Feral Konik ponies in East Anglia, UK, thriving on poor quality marsh land.
Link to digestive anatomy and food processing
The small size of the equine stomach compared to overall body size and the size of the digestive tract as a whole, demonstrates how the equine digestive tract evolved to process small amounts of food regularly. On average the equine stomach is only 8-10% of total digestive tract volume, whereas the large intestine, where fibrous plant material is fermented, comprises approximately 60% of total digestive tract capacity (Merritt & Julliand, 2013).
The trickle feeding of large amounts of food results in food passing through the equine digestive tract at a much slower rate than species with ‘meal feeding’ strategies such as carnivorous cats and dogs. As predators, these species consume large volumes in short periods of time and then go long periods without eating. The stomach of cats and dogs also comprises 60-70% of their entire digestive tract capacity, enabling them to consume large meals, which is the opposite of the equine digestive tract and feeding strategy.
When equids are compared to other grazing herbivores such as ruminants, food passes through the digestive tract at a significantly faster rate. For example, in a study comparing the passage rate of food through the digestive tract of horses, ponies, and ruminants all fed the same Timothy hay, food took on average 23 hours to pass through the equine digestive tract, whereas for ruminants it took between 41 hours (goats) and 65 hours (large heifers) (Uden et al., 1982). A more recent study comparing passage rate in horses, goats, alpacas, and llamas report similar values, with grass hays taking on average 27 hours to pass through the equine gut, compared to 72 hours in llamas, 71 hours in alpacas, and 54 hours in goats (Sponheimer et al., 2003). In both studies the faster passage of food through the equine gut resulted in less of the food being digested. This lower digestive efficiency of equids is due to reduced time that food is exposed to digestive enzymes in the small intestine, and microbes in the large intestine, reducing digestibility of the food consumed compared to ruminant species.
The lower digestive efficiency of equids is compensated for by a higher DMI compared to ruminant animals, demonstrating the strategy of high input, low utilisation (Sponheimer et al., 2003; Clauss et al., 2023). This can be advantageous when there is plenty of food available (e.g. in summer) as they can increase the amount of food they consume to compensate for less efficient digestion, ensuring DM, energy, and nutrient intake. However, when food resources are limited and high DMI are prevented (e.g. in winter), such compensation is constrained, resulting in lower DM, nutrient, and energy intakes. Such behaviour is seen in wild and feral equine populations, with higher DMI and increases in body weight in summer and autumn, and lower DMI and loss of weight in winter (Scheibe & Streich, 2003; Kuntz et al., 2006).
Similarly, the fibre and nutrient content of food influences DMI, although the picture is less clear. It would seem logical that when food contains less energy and nutrients that equids would increase their DMI to compensate for the poor nutritional value of the food. However, as the energy and nutrient content of plants decreases the fibre content increases, and as previously highlighted, plants containing higher fibre need to be chewed more. More chewing increases the time it takes to process a mouthful of food before it can be swallowed, slowing down the rate of intake. As such, this increase in DMI may not be adequate to compensate for high fibre, poor quality foods. Another strategy equids can use when feeding is to be more selective. When food is not restricted, equids will select the more nutritious plants and plant parts to maintain energy and nutrient intake, however, there is a tipping point when this strategy cannot adequately compensate for poor quality food. When food supply is limited, increasing selectivity just limits food intake even more, so at this point energy and nutrient intakes will decrease and the horse, pony, or donkey will consume a suboptimal diet that will lead to weight loss initially, and nutrient deficiencies if prolonged.
Equids will use a combination of these strategies to select the most appropriate diet with the food resources available, showing that they are able to adapt to changes in food availability and food quality. In nature these changes are not normally abrupt, enabling a gradual change and adaptation. It is this gradual, managed and appropriate change that is needed when we adjust the diet of our horses, ponies, and donkeys.
Practical application
· Feed a diet that is appropriate for the animal – assess the animal and identify requirements (see 5 steps to feeding success), making any changes to the diet gradually over 5-10 days
· Feed a diet high in fibre – the majority of this fibre should be in the form of long forage (grass, hay, haylage) although additional fibre sources such as chaffs, fibre pellets and fibre mashes all contribute to the fibre intake
· Allow natural feeding behaviour to be performed – aim to extend feeding time as much as is practically possible:
o Access to grazing is ideal if the animal can cope with that (does not have metabolic issues)
o Offer forage multiple times throughout the day
o Split forage into multiple smaller feeders/haynets and distribute around field/stable/yard (this promotes movement and mimics innate grazing behaviour)
· Consider providing opportunities for browse – this could be within their stable, field or when out walking or being ridden (be sure to check for poisonous plants, trees and bushes)
· Trickle feeding and constant access does not mean constant eating – they also need time to rest and perform other behaviours so aim for no more than 4 hours without access to food
· Check they are eating what you are offering – spend time watching them eat to see if they are selectively leaving certain parts of the hay or preferring certain parts of the field
· Manage intakes – offer a diet with the right energy and fibre levels that enable them to eat enough:
o For those needing to lose weight, a higher fibre, lower energy forage will take longer to eat, enabling them to satisfy their behavioural need to eat for the majority of the day, with straw being an excellent way of increasing fibre content and slowing DMI rate
o Accept that they can compensate to a certain degree for poor quality forages if fed ad libitum – restricting availability may also be necessary for those who overeat
o For those needing to gain weight, fibre is still important, but it should be a more digestible fibre that can be consumed in large enough quantities within the eating time available
· Balance the diet by providing vitamins and minerals as these nutrients vary in grass and forages, and so forages and grass cannot be relied upon to meet all nutrient requirements
References
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Merritt, A.M., & Julliand, V. (2013). Gastrointestinal Physiology. In: R.J. Geor., P.A. Harris., & M. Coenen (Eds.). Equine Applied and Clinical Nutrition: Health, Welfare and Performance (pp 3-32). Elsevier Health Science.
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