Whether you are trying to limit the total caloric intake of your overweight horse, or if you are trying to reduce the amount of sugar an at-risk horse is getting from grazing time, there are specific guidelines to follow to help you accomplish your goals. However, do horses alter their grazing to attempt to eat more in the afternoons when the grass is "sweeter" because of additional accumulated sugars? This information from Kentucky Equine Research looks at a study on that topic.
Grass constantly changes in sugar content throughout each 24-hour period of the growing season. Does this make any difference in grazing rates for horses and other pastured animals? It would seem that grazers would prefer the sweeter taste as plants accumulate sugars through the day, but is grazing time actually influenced by this factor or by hunger, habit, or something else?
Cattle and goats have shown a preference and increased intake for hay that has been cut at the end of the day rather than in the early morning. Sheep have not shown differences in intake or digestibility for hays cut at different times of the day.
In an attempt to find out if horses seem to notice differing sugar content in pasture grasses, a study was conducted from mid-April to mid-May at North Carolina State University. Six light-breed geldings were randomly assigned to morning (six hours) or afternoon (eight hours) grazing treatments for two weeks (period 1). The groups’ grazing times were then switched for an additional two weeks (period 2). The horses were kept in stalls when they were not grazing.
Pasture grass was mostly endophyte-free fescue. Grass height was measured at the beginning and end of each grazing period, and grass samples were freeze-dried before analysis. The horses were also fed oats (200 g, twice daily) except on days 12 and 13 of each period. Fecal samples were collected on days 8 to 12 and were freeze-dried before analysis.
Dry matter intake was higher during period 2, possibly because the forage had matured and had a higher content of stems and seed heads rather than leaves. Afternoon intake was higher than morning intake, indicating that the horses may have altered their eating rate to consume more forage in the afternoons rather than engaging in other activities.
The horses lost an average of 20 kg during the 28-day span of the study, indicating they were not able to consume enough grass during their restricted grazing periods to meet their energy requirement. Supplemental oats did not provide enough energy to make up the difference.