Dietary protein and(or) energy restriction in mares: plasma glucose, insulin, nonesterified fatty acid, and urea nitrogen responses to feeding, glucose, and epinephrine.

The study investigates how dietary protein and energy restriction in mares affects their metabolic responses such as glucose, insulin, nonesterified fatty acid (NEFA), and urea nitrogen levels to food intake, glucose tolerance test, and epinephrine injection.

Research Design and Methodology

• The researchers used 16 light horse mares aged between 8 and 9 years. These mares were given Bermudagrass hay and supplement based on corn and cottonseed hull, which either met 100% (control group) or 50% (restricted group) of the recommended protein and energy requirements.
• This diet arrangement followed a 2 x 2 factorial design. They tracked the mares’ intake, body weight, and plasma hormones and metabolites daily for 33 days.
• On the 27th day, they measured plasma glucose, insulin, NEFA, and urea N in hourly samples. On the 29th day, they conducted an intravenous glucose tolerance test (IVGTT) and an epinephrine challenge.

Findings and Observations

• Energy restriction led to increased daily NEFA concentrations and urea N. Conversely, protein restriction led to decreased urea N concentrations. These changes were noticed within the first 24 hours and stayed consistent for the remaining 24 days of the experiment.
• Regular meal consumption raised plasma glucose, insulin, and urea N levels. Plasma NEFA concentrations did not change post feeding in mares on the control energy diet, but decreased in mares on the restricted energy diet.
• Post-IVGTT, the areas under the curve for plasma glucose and insulin were smaller in mares on a restricted protein diet. Glucose area was larger in mares on a restricted energy diet.
• Energy restriction increased the initial NEFA response following an epinephrine injection. However, after 50 minutes, it reduced plasma NEFA levels below the pre-injection concentrations.

Significance of the Research

• This study provides insights into the metabolic responses to dietary restriction in mares. The findings could be important to veterinarians and horse owners in formulating diets for horses and managing their health.
• Specifically, the results show how energy and protein restriction alter the metabolic parameters, impacting glucose, insulin, NEFA, and urea nitrogen levels differently.