Seventeen stock-type mares were randomly assigned for a 5-week period to one of three diets: only, hay plus a starch- and sugar-rich concentrate, or hay plus a fat- and fiber-rich concentrate. 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. All horses were clinically healthy for the duration of the experiment. Feed, fecal, and/or urine samples were analyzed to determine dry matter, crude protein, fat, energy, calcium, phosphorus, apparent retention and apparent digestibility. Neutral detergent fiber digestibility was also determined.
Mean body weight was lower in aged than in adult horses (1,003 pounds vs. 1,102 pounds), but body condition score (BCS) did not differ between groups (aged horses: 4.8 BCS and adult horses: 5.1 BCS). 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. 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. However, owners should monitor changes in body condition and muscle mass as horses age. It is also important to note that the nutrient digestibilities of diseased aged horses and those with dental disorders may differ. For more information, click here.
Summarized by: Krishona Martinson, PhD, University of Minnesota