Tag Archives: amino acids

  • Equine Research: Protein

    Written By Dr. Kristina Hiney

    This month I will begin a new series which tries to summarize some of the new information which has been gathered in equine nutrition.  I will be grouping similar topics together and trying to summarize how this information might be relevant to you and your horse.  We will discuss if this new information means you should change what you have been doing, or you can feel reassured that you are right on track!  And remember not all information may be relevant for your horse.  There is no need to feed your mature gelding who is trail ridden on the weekend like an endurance horse preparing for a 100 mile ride!

    This month we will focus on some new information on protein nutrition in the horse.  Certainly this is the time of year when many of us are busy procuring our hay supplies for the upcoming year.  Often we want the very best for our horses, and typically look for high quality alfalfa hays.  But is that necessary, especially in a year where the weather does not cooperate and hay selection may be more limited?  In a study using mature idle geldings, the digestibility and usefulness of protein from a variety of hays was tested.   Horses were fed diets of either  mixed grass hay alone, the mixed hay with increasing amounts of oats, or alfalfa hay that was either early bloom, mid bloom or late bloom.  As the maturity of alfalfa hay increases, typically its protein content decreases.   Therefore, many horsemen prefer earlier bloom alfalfa.  But is this necessary? In this particular study the horses were also fed at just 1.6% of their body weight as fed, which is typically a little lower than most people feed.  Thus these horses might have been fed at a lower rate than the average horseman would feed.    As expected, the protein intake of the horses increased as they were fed the alfalfa hay, with increased protein intake the earlier the stage of maturity. The digestibility of the protein in the diet also increased when fed straight alfalfa compared with the mixed hay, and digestibility was greater with less mature alfalfa.  That does reconfirm our knowledge that forages of later maturity are indeed less digestible.  However, the nitrogen retention between the groups of horses was not different.  Nitrogen retention refers to how much nitrogen remains in the horse’s body.  So if the horse’s nitrogen intake (which is reflective of protein intake) was higher, but the nitrogen did not remain in the horse’s body, where did it go?  The extra nitrogen was actually excreted in the urine.  You may remember from our earlier series on protein nutrition that excess protein consumed cannot be stored in the horse’s body. Instead, the nitrogen is removed from the amino acid, and the remainder of it can be used for energy or stored as fat.  Overall, for mature idle horses, there is no need to feed these higher “octane” hays, as it all that extra protein just ended up back on the ground!  There was no value to the horse in these high protein hays.

    However, what if you are not feeding a mature, idle horse, but instead are feeding mares and foals?  Their protein requirements are undoubtedly quite higher.  But it is not just protein quantity we must consider, but also the amino acid profile of the diet.  You may remember from previous articles that equine nutritionists have only described the requirements for lysine in the horse.  This is in stark contrast to other species in which the complete amino acid requirements have been well defined for  both growth and lactation. In other species, lysine is also known to be the first limiting amino acid, followed by threonine and methionine.   It is presumed that this may be true in horses as well.   In a study looking at pregnant mares, their subsequent foals and the mare’s themselves during lactation, researchers posed the question if plasma amino acid concentrations would differ after eating.   Theoretically, plasma amino acids which increase the least after eating immediately following a fast indicates the limiting amino acids.  In the weanlings, the amino acids which increased the least were methionine and lysine, for lactating mares it was methionine and for pregnant mares on this particular diet the amino acid which increased the least was leucine, one of the branched chain amino acids.  This study supports the idea that methionine may be the second limiting amino acid for nursing mares and weanlings, but leucine may also need to be considered.  However, this study did not provide information on how much of these amino acids may actually be needed in the diet, but stresses the need for additional studies.

    The final study we will look at did try and examine the question of methionine needs in growing horses.   In a study which looked at the growth rate and plasma metabolites of weanling horses fed differing amounts of methionine, growth rate did not change with addition of methionine. However, weanlings were only fed the diet for 56 d which way not have been long enough to observe differences.    Addition of methionine did result in a decrease in plasma urea nitrogen.  But what exactly does that mean?   Remember that any extra amino acids must be catabolized and the amine group is removed as urea. The urea is synthesized in the liver, but excreted by the kidney.  Urea circulates though the blood prior to its removal.  An increase in plasma urea N indicates an increase in amino acid catabolism, which takes place if protein synthesis is limited by the availability of amino acids.  If we assume that an increase in methionine in the diet allowed more protein synthesis to occur, this would result in more N retention, and less amino acid catabolism.  In this study, the authors did not observe a linear decrease in plasma urea nitrogen as  methionine was increased beyond 0 .2% of the concentrate. In this example, the weanlings were fed at a rate of 1.25% of their body weight in concentrate, or about 8.4 g of methionine.  You may have noticed that many feed companies now include the levels of methionine in their product.  Using this study as an indicator of methionine requirements, at least for weanling horses would indicate that methionine should at least be at the level of .2% of the concentrate if fed in comparable amounts. If less concentrate is fed, than the concentration of methionine should be higher.

    To summarize what we can take from these three studies, we have reaffirmed that mature idle horses don’t really need high protein hays. While their protein may be more digestible, those amino acids remain largely wasted.  For horses with higher protein needs, it may be time for us to turn our attention to more than just protein quantity, but quality as well.  Hopefully soon we will have better knowledge on exact amino acid requirements, but at least we are now somewhat closer to knowing about methionine!

  • Obesity in Horses: II, Balancing Diet and Exercise

    Written By Dr. Kris Hiney

    In Part I of this series, we talked not only about the difficulty in removing extra pounds from our equine companions, but also the health benefits that our horse will gain from doing so. Our strategies included seeking a more mature grass hay with a lower caloric density and reducing the amount of forage offered to the horse.   The horse will probably need to be confined to a dry lot, but fed in a way to minimize boredom related to reduced  feeding time. This month’s article will look more closely at the diet of our horse, to ensure that we are reducing the calories the horse receives, but are still feeding a balanced diet that provides sufficient amounts of our other nutrients.
    We will continue to use the example of our 1300 lb horse who was at a body condition score of 8 and a goal weight of 1165 lbs. The maintenance requirement for the 1165 lb horse was 17.7 Mcal per day. We decided to feed the horse at a rate of 1.5% of its target weight in order to achieve the desired weight loss. That would mean our horse would consume 17.5 lbs of feed per day. Now, because we specifically chose a lower calorie hay which is more mature, it probably is lower in other nutrients as well. In order to ensure that your horse’s amino acids, vitamin and mineral needs are met, one should look for a low calorie supplement. Fortunately many reputable feed companies produce feeds that are designed for the easy keeper. Typically these feeds will be much higher in crude protein, minerals and vitamins and are designed so that you only need to feed one to two pounds per day. This ensures that your horse will not suffer from deficiencies while we achieve the desired weight loss.
    Additionally, we can accelerate the horse’s weight loss by instituting a regular exercise program. Now, assuming our horse was at a body condition score of 8, it probably wasn’t on a consistent exercise program earlier. The key in implementing an appropriate exercise program is to realize that the horse is relatively unfit and we should begin exercise carefully. Ideally the horse should be ridden or worked five to six days per week.   If this is not possible, try to institute an exercise program at least every other day. Begin with intermittent periods of walking and trotting, and slowly increase the duration of the trotting periods. You should notice that the horse is able to recover its heart rate and respiration rate more quickly during the walking recovery periods as it becomes more fit. Then you can increase the intensity of its exercise program.
    Now let’s take a look at how much exercise your horse needs for increased energy expenditure. For every 45 minutes the horse spends walking per day, it will expend an additional one Mcal/d of net energy.  But what exactly is net energy? To this point in time, we have always discussed the energy needs of the horse in terms of dietary energy or DE. Dietary energy refers to the energy available in the feed once the digestibility of the feed is taken into account. When we determine how much to feed our horse, it is always based on the DE concentration of the diet compared to the horse’s DE requirements. Net energy is more specific about the flow of energy through the horse’s body. Net energy refers to the amount of energy needed to support exercise, growth, lactation, etc. after other energy losses to the horse have been accounted for. These other energy losses include the energy lost from gas production, urine, the work of digestion and the heat lost from the digestion and fermentation of the feed. The energy that is left over after all of these losses is what is available for the animal to use for other purposes.
    The efficiency of conversion of dietary energy to net energy of a horse in light-to-moderate exercise is only about 40%. Therefore, if the horse expends 1 Mcal of net energy, he actually used 2.5 Mcal of DE.  Even regular trail riding will greatly help the horse with our weight loss goals, but increasing the exercise intensity will increase the calorie expenditure even more. If we use the horse’s heart rate as a guide, we can determine how much exercise they need to perform to represent significant calorie expenditure. Let’s say we would like to increase our horse’s energy expenditure to 20% over his maintenance energy requirements. Our goal for our original horse, then, is to use an additional 3.5 Mcal every day.   Our horse’s typical heart rate when he is walking is usually around 60 bpm while trotting will elevate the horse’s heart rate to around 90 bpm. This relates to 24 kcal/min and 56 kcal/min of net energy respectively for walking and trotting.    If we convert that to Mcal of DE, our horse is consuming .06 Mcal /min or .14 Mcal of DE/min. To achieve an energy expenditure of 3.5 Mcal, that would mean we would walk our horse for almost an hour a day, or about a half hour of trotting.  However, these are heart rates of horses which already are fit. For the obese horses we are discussing, the heart rates are usually higher, thus less time will need to be devoted initially to exercising these guys. Good news for them! Heart rates for an unfit horse trotting have been recorded at 120 to 140 bpm! This would correspond to about 0.25 Mcal of DE per minute. Thus only about 15 minutes per day would achieve our increase in energy expenditure of 20%. Remember, this would be 15 minutes total of trotting with intervals of walking. As the horse begins to become more fit and its heart rate lowers, he will tolerate more exercise and will need to increase the amount of time he works to continue using the same amount of calories.
    Alternatively, once our horse is fit, we can also add bouts of cantering or loping to his exercise program.   A horse which is cantering typically has a heart rate between 110 and 130 beats per minute and utilizes about .25 Mcal of DE/min. If we add 10-20 minutes of cantering to our exercise program, the duration the horse needs to be ridden to achieve our target energy expenditure would be about 45 minutes per day, which is probably more realistic for most horse owners. This would include a mix of walking, trotting and loping. Combining this regular exercise program with our restricted diet will help your horse add years to his life.
    Good luck with your weight loss goals.

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