Can obesity itself exert a direct influence on the hoof structure of horses?
Research has shown the significant role of obesity in equine health, Magdalena Senderska-Płonowska and her fellow researchers noted in the journal Animals.
Horse obesity is an increasingly common problem in developed countries, especially in ponies. It can be an issue in itself, but can also lead to other problems such as systemic inflammation, high blood lipid levels, osteochondrosis, or equine metabolic syndrome.
The latter, they said, is under particular scrutiny because of its similarities to human insulin resistance.
Equine metabolic syndrome is a condition in which the horse develops insulin dysregulation. It especially affects ponies but also hot and warmblood breeds such as Arabian, Spanish, and Morgan horses.
The study team, with the Wrocław University of Environmental and Life Sciences, said there is an ongoing debate over whether obesity in humans is caused by insulin dysregulation or vice versa.
Obesity is often associated with equine metabolic syndrome, which can affect hoof lamellae, causing laminitis. “However, it is not known if obesity itself can cause lamellar failure,” the researchers said. Understanding insulin dysregulation is crucial for equine practitioners, they said.
For their study, the scientists examined the forelimbs of 12 draft horses of the same breed who went to slaughter for meat. Six of the draft horses were classified as obese, and six were classified as being of healthy body weight.
Blood samples taken before their deaths were tested for insulin levels. Insulin concentrations were higher in the obese horses than those of normal body weight, but no horse had insulin concentrations at a level that would give rise to a suspicion of equine metabolic syndrome.
The hooves were x-rayed and assessed under a microscope.
Lamellae differed between obese and lean animals, the study team reported, but damage was found in both groups. “It is hard to say which group had more laminitic changes,” they said.
In the obese group, 89% of the primary dermal lamellae were classified as standard, but in the lean group, the percentage was only 58%. “Therefore, the study did not support the effects of obesity on lamellar failure.”
The changes identified in the lean group were longer secondary epidermal lamellae, more proliferated and separated primary dermal lamellae, and fewer standard primary dermal lamellae. In the obese group, the changes were a lower number of club-shaped and standard secondary epidermal lamellae, and significantly more that were classified as tapered.
The authors noted that previous work has indicated that, in laminitic horses, only 12% of the primary dermal lamella were standard while in healthy horses and ponies it was in the range of 74 to 96%.
“The present study revealed that, in the obese group, 89% of primary dermal lamellae were standard, but in the lean group the rate was only 58%.”
Moreover, in the lean group, some primary dermal lamallae were proliferative and separated, which is recognized as laminitic changes. It is possible, they said, that both the lean and obese groups could have been affected by subclinical laminitis. The lack of differences between groups in the tips of the primary epidermal lamellae may indicate subclinical laminitis, they added.
“In general, the lamellae of obese horses seem to be healthier than in the lean group, which is hard to explain.
“The purpose of these horses may provide a certain explanation; the examined horses were meat horses. We can therefore assume that they were fed more intensively and had less movement than sports or leisure horses.”
This also could mean that the horses which were not obese could have been unwell at some stage, restraining weight gain and causing changes in lamellae.
“Because of the lack of data about the anatomy of lamellae in draft horses, we cannot exclude nor confirm that obtained results are physiological or laminitic.
“What is more, we cannot exclude insulin dysregulation in the examined horses, because it was impossible to perform a dynamic insulin test.”
They said the lamellae measurements taken in the draft horses indicate that they were much longer compared to other hoof studies. “This could indicate that the length of the primary epidermal lamellae depends on the hoof size.”
The findings suggest breed differences in the morphology and length of lamellae may exist, they said, with draft horses appearing to have longer primary epidermal lamellae than previously reported in other breeds.
“As laminitis-like changes were observed in both groups, they are not symptoms directly related to obesity.”
The study team comprised Senderska-Płonowska, Natalia Siwińska, Agnieszka Zak-Bochenek, Marta Rykała, Malwina Słowikowska, Jan Madej, Katarzyna Kaleta-Kuratewicz and Artur Niedźwiedź.
Senderska-Płonowska, M.; Siwińska, N.; Zak-Bochenek, A.; Rykała, M.; Słowikowska, M.; Madej, J.P.; Kaleta-Kuratewicz, K.; Niedźwiedź, A. The Differences in Histoarchitecture of Hoof Lamellae between Obese and Lean Draft Horses. Animals 2022, 12, 1774. https://doi.org/10.3390/ani12141774