An allometric analysis of the cardiac and pulmonary systems of the blue wildebeest (Connochaetes taurinus taurinus)

Abstract

This study describes the growth of the blue wildebeest (Connochaetes taurinus taurinus) cardiac and pulmonary systems with ontogenetic allometric equations, contributing an additional species to the small collection of ontogenetic allometric studies on mammals. Allometric equations of the form 𝑦𝑦=𝑎𝑎𝑥𝑥𝑏𝑏 were derived to describe the changes in cardiac or pulmonary measurements (𝑦𝑦), with change in body mass and heart or lung mass (𝑥𝑥). The body masses used in these equations were calculated from external body measurements, to compensate for temporary changes in individual body mass. Different mass estimation equations were investigated to choose the most suitable method. Forty-three post-natal blue wildebeest (22 male, 21 female; body mass 74 - 258 kg), and five foetuses, with (12 and 15 kg; gestational age approximately 7 months) were measured. All animals were sourced from culling operations on the Bubye Valley Conservancy in southern Zimbabwe, in different seasons, over three years. Body mass (𝑀𝑀𝑏𝑏) in kilograms was most accurately predicted from body length (𝐿𝐿) and girth (𝐺𝐺) in meters: 𝑀𝑀𝑏𝑏=39.08(𝐿𝐿𝐿 2)0.909 (R2 = 0.935, PPEA=8.2%) or 𝑀𝑀𝑏𝑏=64.34𝐺𝐺2.58 (R2 = 0.911, PPEA=9.4%). These equations are mildly affected by both sex and season. The equations predict significantly lower body masses (p<0.001) than similar equations for East African subspecies. Blue wildebeest heart mass (𝑀𝑀ℎ) scales hypoallometrically with body mass and ranges from approximately 0.8% of body mass in the foetus to 0.5% of body mass in adult. Heart growth follows the allometric equation: 𝑀𝑀ℎ=0.0118𝑀𝑀𝑏𝑏0.832 (R2 = 0.846, PPEA=10.9%) in the post-natal animal. While the dimensions of the left heart grow isometrically with heart mass, the thickness of the right ventricular wall does not appear to change significantly after birth. This change in thickness may be due to the change in the function of the right ventricle at birth. The lung mass in kg (𝑀𝑀𝑙𝑙) and tracheal volume in ml (𝑉𝑉𝑡𝑡) follow the allometric equations: 𝑀𝑀𝑙𝑙=0.0260𝑀𝑀𝑏𝑏0.816 (R2 = 0.71, PPEA=16) and 𝑉𝑉𝑡𝑡=3.31𝑀𝑀𝑏𝑏0.905 (R2 = 0.78, PPEA=16) in the post-natal animal, which are not significantly different from isometry (p>0.05). The relative lung masses of foetal wildebeest are significantly greater and the foetal trachea relatively narrower than in post-natal animals. Growing wildebeest heart masses are lower than found in horses and giraffes, larger than in buffalo and similar to those of cattle of the same body mass. Their lung masses are smaller than those of horses but larger than those of giraffes. Interspecific equations for mammals predict larger heart and lung masses than measured in post-natal wildebeest, but not significantly so (heart: p=0.11 and lung: p=0.83). However, the difference between measured and predicted heart mass, when only adult wildebeest are considered, is statistically significant (p=0.016). In conclusion, blue wildebeest body mass can be predicted from external body measurements and heart, lung and tracheal measurements scale with body mass. Heart growth is hypoallometric to body mass and lung mass scales isometrically with body mass. Throughout growth, the heart and lung masses of wildebeest are not different from those predicted for average mammals.