For all the advantages that a herd leader enjoys, there appears to be a potential downside: a higher risk of obesity.
Researchers at the University of Bristol in England recorded social interactions between 203 horses in 42 different herds on continual turnout. A feeding trial was conducted to determine each herd’s social structure by setting out individual buckets of feed and observing which horses displaced others to take their food. Scores were assigned based on how many herdmates a particular horse displaced and how often horses were displaced by others.
Using this data, the researchers calculated a food-context-specific dominance rank for each horse. The researchers also assigned each horse a body condition score.
They found that the more dominant horses generally had higher body condition scores and were more likely to be obese (a score of 7 or higher) than were their lower-ranking herdmates.
Although it’s tempting to assume that dominant horses put on the pounds because they take more food, researcher Sarah Giles, PhD, says this study doesn’t prove that definitively.
“To find this out would require a longitudinal investigation of body condition and dominance status over time in a stable, unchanging herd,” she says. “The reason for their obesity might not be simply down to the amount of food they consume. Being dominant may mean they spend less time moving away from other herdmates and so also expend less energy.”
Furthermore, there was not a strictly linear relationship between body condition score and dominance. In other words, the second-ranking horses weren’t always the second fattest and the lowest ranking horses weren’t always the thinnest. “There were even herds that were complete exceptions, where the most dominant was the skinniest,” says Giles.
This study has important implications for horse owners in terms of informed preventive care of dominant horses, she says: “I don’t think these results suggest by any means that being dominant makes a horse fat, but rather that owners should just be aware and perhaps keep a closer eye on the body condition of dominant animals knowing that they are more prone to obesity.”
Reference: “Dominance rank is associated with body condition in outdoor-living domestic horses (Equus caballus),” Applied Animal Behaviour Science, May 2015