Original Research
A Comparison of Actual and Suggested Digestible Energy Intakes of Miniature Horses Derived from Different Feeding Recommendations

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Abstract

Despite being largely studied as models of equine nutrition, few published data exist on actual nutritional requirements of Miniature horses. Small equines are particularly prone to obesity, insulin resistance, and the metabolic disorders for which these are risk factors. Improper feed rationing, overfeeding in particular, puts horses at risk for these metabolic problems. Feed manufacturers, however, generally supply feeding recommendations for horses weighing ≥360 kg, whereas the average Miniature horse weighs around 100 kg. Lack of nutritional guidelines for small equines makes it difficult for owners to properly estimate the amount of hay and grain to feed their Miniature horse. The purpose of this study was to determine whether feeding recommendations provided by feed manufacturers for average-sized horses could be linearly extrapolated to Miniature horses. This study surveyed nutritional management of 12 mature Miniature horses that represented the ideal body condition of the breed. Each horse’s hay, grain, and pasture intake was recorded and the average daily digestible energy (DE) intake was calculated from those data. The daily DE intake of the surveyed horses was compared with the extrapolated recommendations published by several different sources. When linearly extrapolated to fit the body weight of a Miniature horse, recommendations significantly (P < .002) misestimated the amount of daily DE that the surveyed horses were consuming. The majority of recommendations overestimated the DE consumed by the Miniature horses per day. However, one source that was designed specifically for Miniature horses, severely (P < .001) underestimated their required DE.

Introduction

Proper feed rationing is essential for the prevention of digestive and metabolic diseases in the horse as well as for maximizing performance and production. Feed manufacturers usually provide instructions for feeding their product, which are based on the pound of feed per pounds of body weight (BW) system. Instructions for feeding horses that weigh between 360 and 540 kg seem to be the most commonly provided guidelines. This poses a problem for owners of horse breeds that weigh less than the average horse, particularly Miniature horses, which weigh around 100 kg [1]. If specific instructions are not provided for smaller horses, owners of Miniature horses may be tempted to scale down the manufacturer’s feeding recommendations to fit a smaller BW; however, this may result in over- or underestimation of feed intake which could become a problem. This could be either because of inaccuracies in calculations or because of the inability of feeding recommendations to be successfully extrapolated.

Diet, particularly those rich in starch and sugar, is a common contributing factor to obesity which is associated with the development of insulin resistance (IR) [2], [3]. A study by Frank et al. [2] demonstrated that obese, IR horses had higher levels of very-low-density lipoprotein, very-low-density lipoprotein triglyceride, and high-density lipoprotein cholesterol as compared with nonobese horses, which suggests that obesity and IR may occur in tandem. Many obese horses may be described as “easy-keepers,” needing little extra energy to gain or maintain weight. This quality may be a genetic trait in breeds whose ancestors adapted to living off of low-quality forages [3], [4], [5]. This trait seems particularly applicable to ponies and Miniature horses who seem to use the feed rather efficiently and have been discovered to have decreased insulin sensitivity [4], [6] and increased blood lipid concentrations [7] as compared with larger horse breeds. IR is a risk factor for the development of many serious metabolic conditions in horses. Equine Metabolic Syndrome, also known as Syndrome X or IR syndrome, is a phenotype consisting of characteristics including obesity, IR, fasting hyperglycemia, hypertension, and increased triglyceride concentration [8]. Although further research on the mechanisms involved is needed, these characteristics may put horses at risk for or exacerbate the devastating hoof condition laminitis [4], [5], [9], [10].

Miniature horses and ponies have historically been used in equine research studies because of the advantages of their small size. They are easy to handle and less expensive to maintain [7], [11]. However, there are discrepancies as to whether Miniature horses provide accurate models of larger horse nutrition and metabolism. An early study by Slade and Hintz [12] justified the use of ponies as nutritional models for larger horses despite the fact that they were more efficient digesters. Later studies disagreed with this concept, and argued that energy utilization [7] and maintenance requirements [13] of ponies and Miniature horses cannot be effectively compared with larger horses. Other studies find Miniature horses to be suitable models for traits such as mineral balance [11], forage utilization [14], and omega-3 and -6 fatty acid supplementation [15].

Although much work has been done to predict the requirements of large horses, none has been published detailing requirements of equines weighing <200 kg. In fact, the smallest values for which the National Research Council (NRC) provides recommendations are for mature horses weighing 200 kg [16], [17]. Specific research in this area could help Miniature horse owners formulate a more balanced ration and lessen the risk of metabolic disturbances. The purpose of this study was to determine whether feeding recommendations for larger horses could be linearly extrapolated to accurately reflect the digestible energy (DE) intake of Miniature horses maintaining a healthy weight and body condition score (BCS). DE, defined as gross energy intake minus gross energy in the feces [17], was measured because this is the most basic measurement of usable energy in feed. This initial research trial was designed to provide a better estimate of the energy requirements of Miniature horses in the hope that it will stimulate future studies to determine the specific needs of horses weighing <200 kg.

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Materials and Methods

Miniature horses, participating in an American Miniature Horse Association-sanctioned show in the Bluegrass region of Kentucky (July 2008), were surveyed for those representing the ideal body condition of a Miniature horse as described by the American Miniature Horse Association [18]. Of the 17 horses that were originally evaluated, only 12 that were mature, healthy, and whose weight and feed intake had stayed constant for at a minimum of 6 months before this study, were used. These horses,

Results

A significant difference (P < .001) between the mean DE of all groups as well as (P < .002) between the reference group and all feeding standards was observed (Fig. 1). The majority of feeding recommendations overestimated actual DE intake. However, one resource, the Miniature horse-specific feed, significantly underestimated (P < .001) actual DE intake (Fig. 1). The 7th Edition of Nutrient Requirements of Horses, which is the currently accepted source of feeding guidelines, did come closest to

Discussion

The degree of significance between the actual DE intake of the reference group and the recommended DE intakes suggests that the currently published sources of feeding recommendations evaluated, when extrapolated linearly to fit a lighter BW, incorrectly estimate the DE that Miniature horses need to consume to maintain an acceptable BW. Therefore, the extrapolated guidelines for feeding larger horses may not be the best model for feeding Miniature horses. Pagan and Hintz showed that the

Acknowledgments

The authors thank Dr. Joe Pagan, Alan Howard M.S., Dr. Josie Davis, Dr. Brenda Tessmann, Dr. Carey Williams, and Dr. Lyndon Carew for their assistance with this research project.

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    They are easy to handle and less expensive to maintain. Miniature horses are suitable models for traits such as mineral balance and forage utilization [20]. The present study was amid to examine the potential applicability of serum or hair samples as a biological indicator to evaluate the horses responses to (un)sufficient-mineral diets offered daily at 50% and 100% of the requirements recommended by National Research Council [21].

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