Changes in concentrations of hormones, metabolites, and amino acids in plasma of adult horses relative to overnight feed deprivation followed by a pellet-hay meal fed at noon.

This research seeks to understand the changes in hormone, metabolite, and amino acid levels in adult horses with and without access to food. The study analyzes both the effects of a 19-hour fasting period and the response to feeding.

Objective of the Research

The primary aim of this study was to determine the changes in various hormones, metabolites and amino acids in adult horses’ blood in response to overnight fasting and also in response to a meal given at noon. It was performed via two experiments, with Experiment 1 including both male and female horses, while Experiment 2 only included male horses.

Experiment 1

• The researchers observed concentrations of prolactin, growth hormone, cortisol, insulin, glucagon, glucose, nonesterified fatty acids (NEFA), urea N, and 10 critical amino acids in the plasma of mares (female horses) and stallions (male horses) in the last four hours of a 19-hour period of feed deprivation. The evaluation was then continued for eight hours after a meal given at noon.

• The results revealed that, post feeding, there was an increased concentration of prolactin, cortisol, insulin, glucagon, glucose, urea N, and all amino acids apart from methionine. Conversely, NEFA concentrations decreased post feeding.
• Growth hormone concentrations episodically increased in most horses but didn’t associate with feeding or gender.
• Stallions were found to have higher overall plasma urea N concentrations compared to mares, and their prolactin concentrations rise post-feeding was more significant than in mares.

Experiment 2

• Experiment 2 was similar to Experiment 1, the only differences were that the subjects were solely stallions and the experiment design has some stallions fed while others were not.
• Similar to Experiment 1, there were observed increases in prolactin, insulin, glucagon, and glucose levels following a meal, with a decrease in NEFA levels.
• For hormones and metabolites apart from cortisol, there were no time-based fluctuations when the stallions weren’t fed, indicating no inherent diurnal or feeding schedule-associated variations in their concentrations.
• Cortisol and GH concentrations varied with time but didn’t differ between fed and unfed stallions.

Comparison with Other Animals

• Interestingly, the non-impact of feeding on growth hormone secretion in horses was found to be similar to pigs, but this response differs from ruminants, where GH concentrations typically decrease after feeding.