Standing Romanov versus Lithuanian blackhead sheep heart ultrasound methodology

Abstract

Baseline echocardiographic measurements are essential for accurate and reliable diagnostics of cardiovascular diseases. To avoid misinterpretation of echocardiographic images and measurements, establishing standardized reference values is necessary. Several studies have highlighted the suitability of sheep as models for cardiovascular research due to their morphological similarities to humans, including comparable adult heart size, cardiomyocyte nuclei count, venous drainage patterns, and physiological responses to cardiovascular disease induction [1]. Consequently, sheep are widely used and considered reliable in biomedical imaging studies [2, 3]. Additionally, the increasing popularity of sheep as companion animals, appreciated for their gentle nature and ease of care, has elevated the need for precise cardiovascular diagnostics in veterinary medicine [4]. The aim of this study was to establish cardiac ultrasound methodology of two Lithuanian sheep breads to asses baseline cardiac ultrasound measurements. Physically mature Lithuanian blackhead sheep (LBS) (N = 12) aged 300 to 310 days weighing 33.1 ± 1.47 kg and 20 Romanov sheep (RS) (N = 20) aged 180 to 200 days weighing 22.6 ± 1.80 kg were analyzed in this study. Two-dimensional, M-mode and pulsed wave Doppler echocardiographic studies were accomplished while measuring normal cardiac dimensions, time indices and blood volumes. A 4–5 MHz phased-array transducer was used to acquire the images. The transducer was pressed to the skin approximately 2–3 cm dorsal to the fourth and fifth right intercostal spaces. All the echocardiographic measurements were significantly correlated with body weight and breed. This study demonstrated that it is possible to perform a cardiac ultrasound examination on standing sheep with ease, without disrupting physiology or causing stress to the animal. The sheep remain calm while standing, able to ruminate and breathe without interruption. No anesthesia was used in this study, meaning the physiological parameters of the heart were not affected. This study results showed that it is possible to measure the left ventricle ejection fraction, which was significantly higher in LBS. The left ventricular posterior wall index (LVPi) and the intraventricular septum index were measured, and LVPi was significantly higher in Romanov sheep. Using ultrasound examination on standing sheep makes it possible to calculate early and late diastolic pressure ratio, which was higher in Romanov sheep. The human cardiac ultrasound protocol was adapted for sheep ultrasound measures, and aortic flow acceleration time as well as velocity time integral were observed in both sheep breeds. Depending on the protocol, the left ventricular diastolic and systolic volume as well as the stroke volume were measured. The observed measurements were higher in LBS. This study concluded that echocardiography could be used as a tool in diagnosing and further researching cardiac diseases and disorders of Lithuanian blackhead and Romanov sheep.