Pregnancy-associated changes in material properties of the third metacarpal cortical bone in mares.

This research investigates how late pregnancy, age, and the number of pregnancies (parity) affect the material properties of the third metacarpal cortical bone in horses. It has revealed that late pregnancy can cause changes in the bone that may make it more prone to fractures. These changes seem to be more linked to the age of the horse and the number of times it has given birth, rather than the state of pregnancy itself.

Study Methodology

• The study involved a sample of eight pregnant mares that had either died or were euthanized within a day after giving birth due to complications during foaling. To provide a comparison, a control group of six healthy, nonpregnant mares of similar ages was also included.
• The mid-section of the third metacarpal bone from each mare was divided into lateral, dorsal, and medial regions for testing. Small cylinders of bone from each region were subjected to a single cycle of compression until they failed or broke. Microradiographic imaging was employed to assess the bone mineral density and porosity of samples obtained from these regions.
• Research was conducted with a scientific approach involving statistical analysis to determine correlations between the variables of age, parity, and treatment group.

Key Findings

• The study found that mares that had recently given birth showed lower yield strain (a measure of how much stress a material can withstand before being permanently deformed) in the dorsal and medial regions of the bone. The failure strain (the stress at which a material breaks) was also lower in the medial region.
• It was observed that the more times a mare had given birth, the more the elasticity of the bone diminished. This decrease was specifically noted in the dorsal region of the bone and in the stress at which the material yielded and failed in the lateral region.
• Strong positive correlation was identified between the age and parity of the mares. However, no significant correlation was discovered between the state of pregnancy (treatment group) and age or parity. This suggests that the changes in the bone’s properties may have been more directly related to age and the number of pregnancies (parity) rather than the state of pregnancy itself.
• The research further revealed that as the mares got older and the number of pregnancies increased, there was an increase in the porosity in the outermost layer of the bone (periosteal).

Conclusion

• Based on this research, it is suggested that any increased risk of fractures in late-pregnant horses may be more related to their age and the number of times they have given birth rather than the condition of pregnancy per se.
• This can help inform future research on bone health in horses and could potentially contribute to the development of targeted treatments or preventative measures to mitigate the risk of bone fractures in older or parity-rich mares.