Under excessive noise, however, the levels of these free radicals may increase to the point where the enzyme antioxidative capacity is insufficient to alleviate their effects. Noise and metabolic processesįree radicals such as malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (G-Px) are produced during normal metabolism. As indicated earlier, grazing cows equipped with bells tend to decrease head movements to avoid generation of the sound, thereby reducing the amount of pasture plants consumed. Behaviour changes may also contribute to the reduced feed intake. In this way, the animal may have little motivation to eat due to the resulting slower passage of digested feed, distension of the foregut, and the delayed entry of digested feed into the small intestines, thereby contributing to a lower-than-expected rate of body weight gain. Noise and feed intakeįrequent exposure to noise may affect the secretory activity of the adrenal cortex. In the latter case, animals are more severely affected as they do not have the chance to adapt to the noise. Under the same condition, the effects of noise on various production parameters of cattle may also vary depending on whether the animals are exposed to noise on continuous or on an intermittent basis. Above this level, however, the animals are severely affected to a various extent depending on the factors mentioned above. Cattle may tolerate moderate levels of noise and may easily adapt to an intensity level of 60-90 dB. This latter method is not generally used for farm applications, particularly when noise is generated by external sources of unknown technical properties. It can also be measured using various mathematical equations using capacity (in kilowatts, kW), power efficiency, and other electromechanical properties of the device or equipment. The noise intensity associated with any of the above-mentioned sources is best measured in decibels (dB) using a sonometer. Read also: Cow bells and their effect on cow behaviour Measurement and acceptable levels of noise Wearing a bell may further lead to a change in vagosympathetic balance, which is used as an animal welfare indicator allowing comparison of different management procedures. Also, the reduction in rumination time might result in a reduction of saliva production and eventually challenge health through an increased risk of rumen acidosis. The reduction of feeding times inevitably leads to reduced utilisation of pasture plants and lower growth rates of young animals. As a result, the feeding and ruminating durations are decreased because both behaviours include head movements. In this case, animals tend to decrease head movements to avoid generation of the sound. In some parts of the world, grazing cows are often equipped with a bell for several months, to ensure that farmers can locate their animals on the wide pastures. Animals are often exposed to acute noise levels before slaughter in lairages where noise is caused by ventilation fans and operational equipment. The exposure of farm animals to noise has been identified as a potential stressor not only in housing but also during the transport and at the abattoir. In some parts of the world, grazing cows are often equipped with a bell for several months.
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