Original Research
Comparison of Nutrient Digestibility Between Adult and Aged Horses

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Highlights

  • Digestibility differences between adult and aged horses.

  • Digestibility examined for three different diets.

  • No differences in digestibility between the two age groups noted.

Abstract

There is little published work comparing digestibility in healthy adult versus healthy aged horses. Researchers hypothesized that there would be no differences in macronutrient digestibility between eight adult (5–12 years) and nine aged (19–28 years) horses fed three diets in a Latin square design. Seventeen stock-type mares were randomly assigned for a 5-week period to one of three diets: hay only (HAY), hay plus a starch- and sugar-rich concentrate (CHO), or hay plus a fat- (oil) and fiber-rich concentrate (FF). Each diet period comprised 3 weeks of outdoor group drylot feeding, 2 weeks of indoor stalled individual feeding, followed by a 72-hour digestibility trial including total urine and fecal collection. Feed, fecal, and/or urine samples were analyzed to determine dry matter, crude protein, fat, energy, calcium, and phosphorus apparent retention as well as apparent digestibility. Neutral detergent fiber digestibility was also determined. Mean body weight was lower in aged than in adult horses (455 ± 12 kg vs. 500 ± 13 kg; P = .02), but body condition score (BCS) did not differ between groups (aged horses, 4.8 ± 0.2 BCS and adult horses, 5.1 ± 0.2 BCS; P = .20). No age differences in digestibility, apparent digestibility, or apparent retention were seen for any of the variables measured. Based on the results of this study, total tract macronutrient digestibility appears to be similar between healthy adult and aged horses.

Introduction

Although there has been considerable research conducted on the nutritional requirements of the healthy adult horse [1], [2], [3], there is little published work relating to the healthy aged horse. One of the few published studies reported that aged horses had a lower phosphorus absorption and lower fiber digestibility, as well as a trend for lower crude protein (CP) digestibility [4]. However, these findings were not supported in a later report by the same author who speculated that intestinal damage associated with parasite infestation may have contributed to the findings of the original study [5]. Although human studies have documented changing nutritional requirements for the aged, such as an increased requirement for vitamin D [6], selenium [7], and a decreased energy need [8], nutritional recommendations are often made on the basis of data collected in studies of aged humans with specific health problems, such as anorexia [6], [9].

The objective of this study was to compare macronutrient, calcium, and phosphorus digestibility between healthy adult and healthy aged horses fed three rations. Rations designed represent those commonly fed to horses including hay only, hay with a high-fat (oil) and low-cereal starch concentrate, and hay with a low-fat (oil) and high-cereal starch concentrate. Our hypothesis was that there would be no differences in digestibility of the different diets between healthy aged and healthy adult horses.

Section snippets

Animals

The study was originally designed with 18 mares; however, one animal was excluded because of unrelated health reasons. Thus, 17 stock-type mares completed the study, including nine healthy adult horses (5–12 years of age) and eight healthy aged horses (19–28 years of age). Twelve of the 17 mares (five adult and seven aged) originated from a single facility where they had been housed for several years and therefore were exposed to similar diet and management practices, including regular

Results

Aged horses weighed less (455 ± 12 kg) than adult horses (500 ± 13 kg; P = .02). There were, however, no differences in BCS between the two age groups (4.8 ± 0.2 for aged and 5.1 ± 0.2 for adult horses, respectively; P = .20). There were no interactions between BW or BCS and age, diet, or feeding period (Table 2).

Discussion

This study found no difference in the digestibilities of energy, NDF, CP, fat, calcium, or phosphorus between the two age groups. Diet differences were observed (diet differences are the subject of another manuscript in preparation), but as there were no interactions between age and diet, results were not included within this work. Data from this study support the hypothesis that older horses in good health and body condition do not automatically require changes to their core diet [16]. The

Conclusions

In comparison with previous work, this study evaluated a larger number of healthy horses, all of which had received regular anthelmintic treatment and had acceptable dentition. They were tested on three commonly fed formulated diets (high roughage, high oil and fiber, and high cereal) and underwent a relatively long diet adaptation period of 5 weeks. This study suggests that, under most practical feeding situations, differences in digestive capacity are unlikely to be present in healthy aged

Acknowledgments

The authors acknowledge Waltham Center for Pet Nutrition (Leics, UK) for funding this work.

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