| Abstrakt: |
Limited information is available regarding the utility of ultrasonic measurements of longissimus muscle area and fat thickness as non-invasive and objective means to evaluate body composition in horses. Therefore, 20 stock-type horses (2 to 10 y; 362 to 482 kg BW) were utilized in an 84-d trial to determine the relationship between ultrasonic measurements of lean and fat tissue with several common methods of evaluating body composition in horses. Feeding was divided into 2 phases: in phase 1 (d 0 to 56), horses were individually offered 2.5% BW coastal bermudagrass hay (Cynodon dactylon), and in phase 2 (d 57 to 84), horses received 0.75% BW of a commercially available pelleted concentrate (Cargill Animal Nutrition, Elk River, MN) that was formulated to meet 100% NRC requirements with an additional 1.5% BW coastal bermudagrass hay. All horses were maintained, housed, and exercised in accordance with objectives of the SHSU equine behavior and training course. Intake was adjusted every 7 d according to BW. Biweekly morphometric measurements including height, body length, heart girth circumference (HGC), body condition score (BCS), and topline evaluation score (TES) were obtained. In addition, ultrasonic measurements of rump fat (RF), back fat (BF), intramuscular fat (IMF) and longissimus muscle area (LMA) were collected by a certified technician. All images were evaluated by an independent laboratory (Designer Genes Technologies, Harrison, AR). Data were analyzed using the PROC CORR procedure of SAS to determine relationships between the subjective and objective measures of lean tissue and body fat. A moderate positive correlation existed between LMA and both height (r=0.43) and BCS (r=0.32); however, only weak positive correlations to LMA were observed for the measures of TES (r=0.19), body length (r=0.13), and HGC (r=0.21). Moderately positive correlations also existed between RF and both BCS (r=0.50) and TES (r=0.28), but there was no relationship between BCS or TES and BF. Ultrasonic measurements indicated that LMA has a greater relationship to height and BCS than HGC, body length, and TES. Relationships between ultrasonic measurements and other assessments of body fat were low to moderate with BCS having the strongest relationship. These results indicate that many of the common methods currently used to determine the body composition of horses are inaccurate and a comprehensive investigation regarding the utility of each of these conventional methods is necessary to justify their continued use in the equine industry. |
