The effect on herd production of "free" electricity on a milking plant

Determination of a stray voltage threshold in Holstein heifers, influence of predictability and past experience on behavioural and physiological responses

Stray voltage (< 10 V) may impair animal welfare. Our objectives were to: i) determine the threshold at which heifers react to voltage and ii) investigate effects of past experience and random applications of voltage. Firstly, forty heifers were trained to eat from two metallic feeders at the end of a test corridor. For 20 heifers, voltage was applied for 2 min (every day in steps of 0.33 V, 0 to 5 V) to the feeder (F1) in which the heifer started to eat (VOLT). Heifers could change to the non-electrified feeder (F2) if they wished. Twenty heifers (CONT) followed the same procedure without voltage exposure. For voltages≥ 2.3 V, percentage of feed eaten from F1 (%FeedF1) was lower, time spent eating in F1 and latency to change to F2 were shorter compared to 0 V. At 2 V and above, more VOLT than CONT heifers performed muzzle-licking and abrupt head movements. Secondly, after four weeks, the same heifers were exposed to 3.3 V for either 11 consecutive days (DAILY, n = 20) or randomly on 4/11 days (RAND, n = 20). CONT heifers had higher cortisol concentrations than VOLT heifers on the first day of test. %FeedF1 was higher for RAND than DAILY heifers. The threshold at which avoidance behaviour started appeared to be 2.3 V in our experimental conditions. Adaptation was more difficult with unpredictable rather than predictable voltage and past experience seemed to reduce the effects of subsequent exposure.

Small electric currents affecting farm animals and man: a review with special reference to stray voltage. I. Electric properties of the body and the problem of stray voltage

The literature on the electrical properties of the body and sensitivity to steady electric current in humans and farm animals is reviewed and the problem of stray voltage is examined. Stray voltage poses a problem to animal health and protection in cattle and pigs and possibly also in other animals. Dairy cattle can perceive alternating currents exceeding 1 mA between the mouth and all four hooves. Behavioural effects in cows usually occur above 3 mA. In practice, the major influence on dairy cows appears to be behavioural. In experimental research on sensitivity to electric current, the effects studied should be related primarily to the actual current densities or electric fields in the affected tissues rather than to the total voltages applied. Under normal conditions, herdsmen are less likely to be affected by stray voltage than their animals.

Small electric currents affecting farm animals and man: a review with special reference to stray voltage. II. Physiological effects and the concept of stress

The literature on the influence of small, steady electric currents on animal health, especially cardiovascular and endocrinological functions and milk let-down, and the effects on milk production is reviewed, with special reference to the problem of stray voltage. Direct physiological effects in cows may occur above 4 mA. How the long-term effects may contrast with the acute effects is not known. Habituation may occur. The altered behaviour and physiological changes due to exposure to stray voltage may be termed a stress response. The type of stress most likely to be encountered is chronic. Whether or not stress occurs depends on the timing and context of exposure and on individual cognition. Hence stray voltage may threaten farm animal health and production wherever modern animal housing is applied.