Spring feeding

springturnout

by Dr Derek Cuddeford,  Royal (Dick) School of Veterinary Studies, University of  Edinburgh

In-wintered horses will undergo a major transition in their feeding programme when it comes to spring turn-out. The magnitude of the change rather depends on the quality of the forage that they have been fed overwinter. They may have been fed a very high fibre hay low in non-structural carbohydrates (NSCs) or in contrast they may have been fed a very high quality haylage that was much lower in fibre but higher in NSCs. The latter provides many more calories than the former on an equal dry basis. The NSC content of forage is important because it represents the simple sugars such as glucose and sucrose as well as the storage carbohydrate, fructan. These water-soluble carbohydrates are rapidly digested by the horse and thus a ready source of calories. The significance of the NSC content depends on the animal being fed. If it is overweight and/or prone to laminitis or suffers from Cushings then it is generally recommended to limit the intake of NSCs. Thus, one important task prior to turn-out is to evaluate your animal’s bodily condition/health status. There are various body condition scoring systems but the simplest rely on assessing fat depots (fatness) in key areas of the animal’s body. Fat deposition over winter may not have been that obvious (particularly if the animal has a dense, hairy winter coat) so a careful look is advised. The crest of the neck and tailhead are key indicator areas where for example an insulin-resistant horse may deposit fat. Once you cannot palpate the ribs then you definitely have a fat horse! For guidance on condition scoring visit some of the sites on the Internet such as www.rightweight. The reason I have initially focussed on NSCs is because they can be present in very high levels in rapidly growing spring grass and if you have a vulnerable animal you will have to take particular care with your turn-out procedure. It may be of course that condition has been lost over the winter period and turn-out to grass will present an opportunity to improve bodily condition.

Conserved forage is usually high in dry matter (DM). Hay should contain ~86%, a high DM haylage ~70% and a low DM haylage ~45/50%. In contrast, early Spring grass may only contain ~15% and probably never more than 20% dry material. Thus, there is a massive change in the nature of the horse’s diet, essentially moving from a “dry” diet to a “wet” diet. This transition should be managed gradually as with all changes of diet to avoid disturbances in gut function. An example of the latter would be a gas colic arising through rapid fermentation of easily degraded, low fibre materials since the intake rate of fresh material when grazing would be a lot more than that of a housed horse fed hay. A horse at grass will spend the best part of the day (16 hours) grazing and thus intake is spread out over a longish period. A 500kg horse eating 2.5% of its body weight as DM would consume 12.5kg. This equates to 0.78kgDM/hour or 13gDM/minute when at grass. In terms of fresh material this is more like 80g grass/minute. The housed horse fed 12.5kg hay DM consumes ~14.5kg fresh hay but usually this is consumed over a much shorter period of time, probably more like 12/13 hours maximum since measured intakes have shown that more than one kg is consumed per hour by a 500kg horse. Assuming only one kg/ hour then that equates to nearly 17g fresh hay or 14ghay DM/minute not that dissimilar from the grass DM intake shown above. Obviously, a “greedy” horse may consume its hay ration in a shorter period of time and thus will have to process more than17g fresh hay/minute. However, this pales into insignificance when considering the measured intakes of some horses consuming quality spring pasture. Voluntary intakes measured over a 24h period have revealed intakes as high as 5% of body weight. This equates to 25kg grass DM for a 500kg horse equivalent to 1.56kg DM/h (16h grazing of grazing activity) or 26gDM/minute and in fresh terms, 9.75kg fresh material/h or 162g/minute! Clearly, animals of this type must be carefully managed at spring turn-out and, if not too fat to begin with, they will soon become so!

If animals are overweight, prone to laminitis or possibly likely to be insulin resistant then special steps must be taken to manage their grass intakes. Firstly, it is sensible to limit NSC intakes and this may be achieved by allowing access to pasture only when grass NSC levels are at their lowest which is in the early morning from about 3AM to 10AM. However, it is important to realise that environmental stressors such as frost, drought, water-logging, plant nutrient deficiencies, stage of growth, etc can cause plant NSC levels to double. So putting horses out to grass in the morning after a heavy frost could precipitate problems such as laminitis because the NSC intake could be very high. Generally, grass intake is usually limited by adopting one or all of the following procedures. Limiting time at grass is often tried and when not at grass the animals are housed or kept on an all-weather area having access to poor quality forage such as barley straw. However, it has been shown that when the time allowed for grazing is restricted horses tend to compensate by eating more in the time allowed which of course would be undesirable. Another approach is to use a grazing muzzle through which the animal can drink but can ingest very little grass. It must be rather frustrating for a horse that is suddenly confronted with fresh pasture after a long winter period to be allowed onto the grass but being hardly able to get hold of any grass with its teeth and lips. Nearly as bad as “dooking” for apples (apple bobbing, apple ducking or snap-apple in Ireland) with your hands tied behind your back!! Other methods rely on pre-feeding poor quality forage prior to grazing so the horse is not so “hungry”.  Reduce grass availability by limiting the grass area available, co-grazing with other species or by harvesting the grass by machine prior to grazing. Clever use of an electric fence can force the animals to walk a long way to get their grass so reduced food intake is combined with increased physical exercise which is, of course, good for the figure…

A major disadvantage of limiting grass intake is that it is not just calories that you are limiting but also protein/amino acids and also vitamins and major and trace minerals. Thus, the ”at risk” groups of ponies and horses whose grass intakes are deliberately limited must be fed a “balancer” or some specially designed protein/vitamin/mineral supplement that will make good the undersupply of these nutrients in the limit-fed animals. It should go without saying that these products are designed for low volume usage and thus do not act as a supplier of calories.

In conclusion, at the end of winter and just prior to spring turn-out it is essential to identify “at risk” animals so that they can be safely managed. Remaining “normal” animals can be turned-out but managed in such a way that they do not become fat because as we have seen many “well” horses can grossly overeat. Rather like humans, horses cannot regulate energy intake to need but instead, eat to appetite…

Author: Dr Derek Cuddeford

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