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What’s New in Horse Nutrition in 2000 The 1999 Equine Nutrition and Physiology Society conference and the 2000 KER Advances in Equine Nutrition Conference have presented a lot of new information and a number of review papers on the current state of affairs in equine nutrition. The information that is relevant to the feeding of growing and breeding horses is summarized in this paper, and a number of practical recommendations for change can come out of these recent conferences.
It would appear from a number of studies in the USA, France and Germany, that we have underestimated the digestible Energy (DE) requirements for growth in weanlings and overestimated the requirements in yearlings. This may lead us to under feed weanlings and restrict growth and over feed yearlings with result they growth too fast or get too fat. The other compounding factor with weanling is the restricted appetite that they face and for this reason their nutritional needs must be placed in a more concentrated package. An additional consideration is the potential for poor weather conditions during Winter which place extra nutritional stresses on the weanling. The bottom line is for optimum growth for weanling you may need to increase the energy supplied as high energy concentrates or forages, whereas for yearlings the amount of grain supplied does not need to increase much on the weanling diet. Yearlings have a larger appetite and can eat more pasture to make up for the small increase in energy requirements. The exception is sale or show preparation where significant increases in grain intake are often needed to produce show or sale condition.
Some recent studies in both France and the USA have indicated that lactating mares can produce a lot more milk than previously thought, and for this milk production they need extra energy in their diet or they will lose weight. The NRC tables had worked on a maximum milk production of 3% body weight in early lactation, however up to 4% of body weight or 25kg per day maybe a more realistic figure in the first few months of lactation. The mare needs higher digestible energy intake to maintain this output. It is amazing that some mares can do that on grass alone, provided they have access to good quality pastures. However many mares need supplementary grain and as their requirements for energy are even greater than the racehorse, it is not surprising some mares need to eat more grain than you would feed a racehorse. The consequence of not meeting the mares energy needs is that she will lose weight and become reproductively less efficient. Another consequence maybe a reduced milk output and this maybe beneficial in a situation where a foal is growing too rapidly. So if you wish to reduce the growth of a foal prior to weaning you may need to restrict the mare’s energy intake by locking her up in a small yard with minimal pasture.
Whilst we don’t experience the same cold temperatures that breeders in Canada do, it is apparent to all keen observers, that growth of foals and weanlings will reduce during winter. Part of this reason is related to cold and the increased maintenance requirement that this imposes, leaving less energy available for growth. The other factor is that wind and rain combine to force weanlings to seek shelter rather than spending their time grazing as they should and this can significantly reduce their energy and protein intake. The result is lower growth and on days of poor weather it is advisable to slightly increase the amount of grain supplied and significantly increase the amount of hay you supply to your young horses. Try and supply feed in a sheltered area so horses will stay with the feed rather than leave it to seek shelter. Hay racks in paddock shelters can be evry useful in these circumstances. It has been noted in growth rate studies in the USA that in late winter, 12 month old yearlings will grow at twice the rate in Florida as they will in Canada . A similar, though not as dramatic trend can been seen in Australia between South Eastern Queensland and Victoria.
All horseman realise that horses lose weight very quickly and gain it very slowly. The reason for the slow rate of gain is apparent when you do the sums on the amount of energy required to put weight on. It is estimated that 1kg of weight gain requires over 100 megajules (MJ) of digestible energy and for a 500kg horse a agin of 1kg/day requires 250% of their maintenance requirement. If you want to get a horse to gain 20kg or 1 condition score level using the Texan 1 to 9 system, it will take 60 days if they are feed 40% more energy than their maintenance requirement, or 120 days if only fed 20% above maintenance. For this reason if you are trying for rapid weight gain, you need individual feeding with high energy concentrates and forages and plenty of them. For mares, good grass must be a part of this package as you won’t get the same results from hard feed alone.
How you feed your mare will influence the composition of the milk and potentially the growth of the foal. Mares that are fed a high concentrate diet have high levels of lactose in their milk, whereas those on a roughage diet produce higher fat levels in the milk. Whilst we don’t want fat in our milk, it is a desirable characteristic for foals as it’s a higher and safer form of energy than carbohydrates such as lactose. For this reason you should satisfy as much of the mares energy needs as you can from good quality roughage and that will help improve mares digestive safety for the mare as well.
Most feeds are labeled with crude protein content. Whilst the first thing you see when you pick up a bag of feed is the crude protein content, it’s actually the quality of the protein and it’s digestibility that are more important to the horse. The amino acids most likely to be limiting in horse diets for growth and reproduction are lysine and threonine and a number of good quality feeds have the lysine content marked on the feed. Research has shown that if you supply a growing horse with the same amount of crude protein in milk powder as you do in barley, there is increased growth on the milk powder diet because of the higher amino acid intake and the better protein digestibility. The ideal is to have the amino acids digested and absorbed in the small intestine as there is reduced efficiency from amino acids absorbed after fermentation and microbial amino acid production has occurred in the large intestine. Milk powder, soybean meal and copra meal all have 90% of the amino acids digested in the small intestine. Oats and wheat bran have small intestinal digestibilites of over 80%, whilst barley and corn are lower at around 60%. German and French texts list the protein requirements of various classes of horses in terms of the digestible protein not the crude protein and this is the more accurate way of formulating a diet to meet the horse’s requirements. It is to be hoped that the next NRC will make a change from crude protein to digestible protein and more study will be done on the amino acid digestibility in the small intestine.
A recent study at KER has shown that giving very high levels of supplementary copper will not increase the retention of copper by the horse. The extra copper is not absorbed and ends up in the manure instead. Horses given a diet containing 290mg of copper retained only a fraction more than horses on 180 mg of copper, however this latter diet has a significant advantage over a 150 milligram daily intake in the horses at maintenance. So this study shows twice as much is not always twice as good and as far as copper is concerned, you need to meet the needs of the horse but there is no benefit in a supply well above those needs. This means that feeds or supplements that supply well above daily requirements may be no more effective in meeting copper needs than those that supply the needs. However this study indicted that the KER copper requirements were more realistic than the lower NRC requirements.
The recent University of Kentucky study showed a benefit in mares that received a selenium supplement of 3mg a day compared to those that received only 1mg per day . The higher dose of selenium led to increased selenium concentrations in the milk of the mares and increased immunoglobulin levels in the serum of the foals up to 8 weeks of age. Average daily gain in foals and placental weight or time to placental expulsion were not affected by treatment. This immune boost could be a significant benefit for the foal as the higher antibody levels may help the foal fight off infection in the critical first few months of life.
A similar study was done looking at the influence of supplementary Vitamin E. Mares were supplied with either 800 IU Vitamin E or 1600 IU in the total diet. The mares given higher doses of Vitamin E had increased immunoglobulin levels in the serum and colostrum and foals had increased antibody levels in blood after birth. The conclusion is that supplementary vitamin E given to the mare can boost immunity in the foal and may help ward off diseases.
Chromium has been used in race and performance horses for a number of years and is essential for optimum insulin sensitivity and glucose uptake by insulin sensitive cells. Recent work with yearlings has shown that supplementary chromium did not influence growth or development, but did increase the rate at which glucose was metabolised and lowered glucose and insulin levels after feeding grain. It is thought that high levels of glucose , insulin and cortisol after feeding may be a risk factor for OCD, by reducing thyroid hormone release and maturation of cartilage to bone. Organic chromium supplementation may be useful in to reduce one of the potential risk factors for OCD and other DOD. |