RESEARCH PROJECTS

Tiffany Dobbs, PhD candidate

Equine Consulting Services

Equine Consulting Services, in association with the University of Queensland has commenced a major project funded by the Rural Industries Research and Development Corporation investigating the effect of maternal nutrition and metabolism on skeletal disease in growing foals. In a 1998 publication, skeletal disease, collectively referred to as Developmental Orthopaedic Disease (DOD) was estimated to cost the Hunter Valley Thoroughbred breeding industry approximately $10 million each year. This figure included costs associated with diagnosis and treatment, increased labour, loss of sale value, and training fees. If these figures were applied Australia wide, the costs to the Thoroughbred industry alone are estimated to be as much as $60 million per year ^[1]. OCD, or Osteochondritis Dissecans refers to thickening, cracking and tearing of the joint cartilage of growing horses. Loose fragments of cartilage or bone may be present in the joint space, causing swelling, pain and lameness. It has been estimated that 10% of foals will not be sold as yearlings due to these conditions.

Several studies have identified nutritional factors which influence the incidence and/or severity of OCD. These include:

• Mineral deficiencies, excesses and imbalances (e.g. inadequate levels of phosphorus, calcium, zinc and copper in the diet to support the rate of growth);
• Rapid growth and excessive weight-bearing and other biomechanical stresses on bones and joints;
• Feeding diets excessive in energy and protein.

Potential nutritional causes may also include:

• Feeding diets high in soluble carbohydrates (grain feeds and lush pastures); and
• Glucose intolerance cause by insulin resistance (hypoglycaemia and hyperinsulinaemia)

Both insulin and insulin-like growth factor-1 (IGF-1) play a role in chondrocyte maturation and perturbations of these hormones as a result of chronic hyperinsulinaemia caused by high carbohydrate diets may be manifested by OCD ^{[2, 3]}.

The majority of studies conducted to investigate nutritional causes of OCD in growing foals have focused on nutritional strategies from weaning age (approximately six months) onwards. However, several studies have identified the highest incidence of OCD and other skeletal disorders to be at a younger age than this. In one study, the average incidence of DOD in Thoroughbred foals evaluated between 4 through 18 months of age was 16.1% (range 12.9 – 28.8%) and the highest incidence was recorded at 4 months of age ^[4]. While nutritional strategies during the growing period may reduce the incidence of OCD, it is possible the causative factor exists prior to this time, either during early lactation, or during gestation.

Few studies have evaluated the contribution of the mare’s ration to the incidence of skeletal disease in growing foals and little is known about the metabolic changes that occur during pregnancy and how this may play a role in the prevalence of OCD. Previous research work indicates a possible relationship between the metabolic status of mares and the likelihood of producing hyperinsulinaemic foals. Nutrition during foetal life is thought to be a significant factor influencing animal health and potentially lifetime performance. Therefore, broodmare nutrition and metabolism (or more specifically the intrauterine environment which is thought to influence the metabolic programming of the neonate) may be an important determinant of the development of insulin resistance and the incidence of OCD.

Based on this information, the project examines the following questions:

1)      Is there a relationship between insulin status of mares and foals; and

2)      Does insulin sensitivity influence the prevalence and severity of OCD

Thanks to a number of farms that have enthusiastically assisted with the OCD project so far, a significant number of blood samples have already been collected from mares, foals and yearling groups in NSW. These bloods are to be analysed and correlated with data already collected on each individual horse. These horses will be closely monitored throughout 2009 in conjunction with validated studies being conducted at the University of Queensland, Gatton.

Overall, the goal of this research is to identify key nutritional factors which contribute to the incidence of OCD in the Australian horse breeding industry. Our ultimate aim is to produce a set of nutritional guidelines that can be easily implemented to reduce the incidence and severity of the disease, reducing wastage and improve profitability for Australian breeders. 

We would like to thank our collaborating farms, the University of Queensland and the Rural Industries Research and Development Corporation for their on-going support.

For further information on this project, please contact us today.

References

1.             Aldred, J., Developmental Orthopaedic Disease in Horses. RIRDC Publication No. 97/79., 1998.

2.             Henson, F.M., et al., Effects of insulin and insulin-like growth factors I and II on the growth of equine fetal and neonatal chondrocytes. Equine Veterinary Journal, 1997. 29: p. 441-447.

3.             Ralston, S.L., Hyperglycaemia/hyperinsulinemia after feeding a meal of grain to young horses with osteochondritis dissecans (OCD) lesions. Pferdeheilkunde, 1996. 12: p. 320-322.

4.             Jelan, Z., et al., Growth rates in Thoroughbred foals. Pferdeheilkunde, 1996. 12: p. 291-295.