Abstract
Heart rate variability (HRV), heart beat-to-beat variations, is a measure of cardiac autonomic functions, and HRV monitoring using sensor technology can be a non-invasive way to assess stress of animals. The objective of this study was to investigate the effect of dietary vitamin A (VA) restriction to enhance beef quality on the physiological status of fattening steers by HRV analysis. Six Japanese Black steers were equally allocated into VA-restricted (RES) and VA-supplemented (SUP) groups. The RES steers were fed VA-restricted diets from 11 to 20 months of age. The inter-beat intervals and blood VA concentration were measured at 18 and 24 months of age. HRV parameters in time, frequency, and non-linear domains were calculated using the inter-beat intervals. Blood VA concentration was significantly lower in RES steers than in SUP steers at 18 months of age (P < 0.05) but did not differ between the groups at 24 months of age. The HRV analysis indicated greater sympathetic and lower parasympathetic activities in RES steers than in SUP steers (P < 0.05). However, there were significant interactions of the group and age on HRV parameters (P < 0.05), indicating that although RES steers at 18 months of age might suffer from slight stress, the response could recover to a level similar to SUP steers at 24 months of age by the increase in blood VA concentration.
Highlights
Healthy cardiac variation is characterized by irregular time intervals between heartbeats (von Borell et al, 2007)
Blood vitamin A (VA) concentration for steers was significantly lower in RES steers (54.7 IU/dL) than in SUP steers (92.0 IU/dL) at 18 months of age (P < 0.05) but was not significantly different between the two groups at 24 months of age (77.7 and 68.7 IU/dL for RES and SUP, respectively)
The effect of physical activity quantified by vectorial dynamic body acceleration (VeDBA) was significant for heart rate (HR) and all heart rate variability (HRV) parameters when HRV of animals was evaluated under free-moving conditions (Oishi et al, 2018; Kitajima et al, 2021)
Summary
Healthy cardiac variation is characterized by irregular time intervals between heartbeats (von Borell et al, 2007). The fluctuation of inter-beat intervals is expressed as heart rate variability (HRV), which reflects the sympathetic and vagal activities of the autonomic nervous system. As a decrease in HRV can be caused by an increase in sympathetic activity and/or withdrawal of vagal activity, HRV is one of good indicators for assessing autonomic nervous system in response to various stressors (Acharya et al, 2006). A variety of studies have investigated internal and external stress factors that affect HRV in farm animals: e.g., diseases such as lameness (Kovács et al, 2015), diarrhea (Mohr et al, 2002), and bovine spongiform encephalopathy (Konold et al, 2011), and heat stress (Kitajima et al, 2021). HRV monitoring has gained notable attention as a non-invasive technique for evaluating the stress levels of animals from the point of view of animal welfare (Kovács et al, 2014).
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