Semi-feral horses in study show better hoof health than stabled counterparts

The risks of hoof health in horses from intensive management, characterized by stall confinement and overfeeding practices, have been highlighted in a just-published study.

The study, reported in the journal PLOS ONE, centred on 20 horses. The Marajoara and Puruca breeds used in the study originated from horses brought by settlers 300 years ago from the Iberian Peninsula to the island of Marajó, in the Pará State of Brazil.

The Marajoara breed was generated by the interbreeding of these horses with Arabian plus other purebred horses of Iberian origin, whereas the Puruca breed was generated by crossing Marajoara horses with Shetland ponies.

These horses are raised on native grasses grown in low-fertility soils without mineral supplementation. Their hooves do not experience human intervention.

It is hypothesised that during the rainy season, flooded regions are formed, and hooves become submerged in water and are only slightly worn. With rising temperatures in the summer and the transition to the dry season, the soil becomes hard, and the hooves become worn, thus resulting in a self-maintaining balance over the seasons.

Bruno Dondoni Malacarne and his fellow researchers sought to compare the hoof lamellae in Iberian breeds raised in modern domesticated conditions with Marajoara and Puruca horses raised in a semi-feral state.

They hypothesised that the hoof tissue of horses raised in semi-feral conditions – that is, exposed to self-performed daily exercise, limited access to nutrition, and no protection from environmental and pathogenic agents – would exhibit healthier lamellar tissue than horses of similar origin raised under intensive conditions, confined to stalls and fed high-energy diets rich in non-structural carbohydrates.

Samples were taken from six Marajoara horses and six Puruca horses from a ranch on Marajó Island. Although saddle broken, the horses were considered semi-feral as they had not been ridden or handled in years. The horses had body condition scores between 5 and 6.

The eight fully domesticated horses used in the study were of the Mangalarga Marchador breed. The study horses were reported to have higher body condition scores, of 8 and 9.

The researchers used archived lamellar tissue samples from these animals, who had been confined in stalls and received digestible energy in quantities at twice their maintenance requirement over 150 days, as described in a 2020 study that investigated obesity and weight gain in Mangalarga Marchador horses subjected to high-calorie diets. Half of their daily energy needs were provided as concentrates and half as forage at 2% of body weight.

The authors noted that confinement and excessive feed are common in the modern Brazilian horse management system.

All lamellar samples from the 20 horses underwent histological examination (they were examined under a microscope).

Preliminary findings showed that the horses raised in semi-feral conditions had healthier hoof lamellar characteristics than Mangalarga Marchador horses raised under modern domesticated conditions characterized by stall confinement and overfeeding practices.

The Puruca horses, despite their smaller stature, had greater length and width of their primary and secondary epidermal lamellae than other breeds.

The Mangalarga Marchador horses were the only ones that showed signs of fragility in lamellar tissue, they said.

Discussing their findings, the researchers said their study demonstrates that semi-feral horses, despite having microscopic variations related to the environment, nutrition, and hoof self-maintenance process, presented healthier lamellar tissue than horses raised in intensive systems.

The Mangalarga Marchador horses that received high concentrations of non-structural carbohydrates had lesions in their lamellar tissue – unsurprising since hormonal imbalances had been previously identified in this experimental group.

“These findings were consistent with the initial stage of laminitis, with lesions classically described in natural cases associated with hyperinsulinaemia, and in models of insulin-induced laminitis.”

The Mangalarga Marchador horses were in the early stages of insulin dysregulation.

“It is important to consider several undetermined factors when interpreting the present results, including but not limited to the small sample size, differences in age, sex, and breed between the groups, as well as the distinct geographic conditions.

“However, this is the first study to demonstrate that semi-feral horses have lamellar histological characteristics that are very different from those observed in horses confined and excessively fed, which is a common practice in the modern Brazilian horse management system.

“Further studies with larger sample sizes are needed to describe the histological patterns of semi-feral horses.”

The study team comprised Malacarne, Rodrigo Ribeiro Martins, Cahuê Francisco Rosa Paz, João Victor Almeida Alves, Lucas Antunes Dias, Marina Alcantara Cavalcante, Alison Miranda Santos, André Guimarães Maciel Silva, Britta Sigrid Leise, Armando Mattos Carvalho and Rafael Resende Faleiros, from Brazilian and United States institutions.

Malacarne BD, Martins RR, Paz CFR, Alves JVA, Dias LA, Cavalcante MA, et al. (2023) Histological comparison of the lamellar tissue of Iberian origin breed horses created in semi-feral conditions or in an intensive system. PLoS ONE 18(6): e0286536. https://doi.org/10.1371/journal.pone.0286536

The study, published under a Creative Commons License, can be read here.