Horses that live outside in a herd rapidly establish a hierarchy that affects everything they do, including eat; dominant horses tend to shoo others away from the tastiest grass or hay. A team of researchers wanted to investigate if this meant that horses lower in the pecking order eat less or if they have to spend more time grazing to make up for mealtime shortages.
Drs. Sarah Giles, Pat Harris, Sean Rands and Christine Nicol created a study to investigate the association between social dominance, interruptions to foraging behavior and body condition. The research team used 116 horses from 20 herds, and completed the study during the winter, when pasture was limited and there was competition for food.
The team began by giving each horse a body condition score between 4 and 8.5. They also measured social dominance and observed foraging behavior, tracking the duration and frequency of grazing, as well as the number of interruptions.
The study team found that foraging success of individuals may be partly influenced by their social status, but the relationship between her behavior, dominance and body condition wasn't fully established from the study. They concluded that for horses, the benefits of group living outweigh the costs; individual horses learn to follow behavioral rules that allow them to function as a social unit.
These scientists reviewed over 120 hours of herd monitoring and found that the total time spent foraging wasn't influenced by body condition or social dominance. Horses that had higher social standing also had higher body condition scores, but the main factor behind this was foraging efficiency. The horses that raised their heads more and were hyper-aware of their surroundings, had lower body condition scores. This vigilance was not associated with social status and seems to be an inherited trait.
The study also found that subordinate horses or those with lower body condition scores did not forage more. This suggests that the difference in body condition can be seen when subordinate horses are in the presence of dominant horses and reduce forage intake, they report.
Lower-ranking horse were unlikely to continue to forage when their companions were not, which supports the idea that social factors may result in body-condition score difference in horses living in a herd.
Read the study here.
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