return to Farmers Independent Weekly
November 11, 2004
by Alma Kennedy,
Department of Animal Science
Night Lighting in Dairy Barns
Most dairy producers leave a light on in the barn for their cows at night. Light is useful for producers checking their animals and research has proven that cows need some night light to stay healthy. But just how bright should that night light be?
Dairy farmers are divided on the topic. Some provide a bright light greater than 100 Lux despite research proof that bright night light does not promote feeding at night (Tanida et al. 1984) and, in fact, may actually decrease feed intake (Peters et al. 1981). Others, based on experience, use a low light of less than 100 Lux.
Ours is the first research study to examine the effect of exposing dairy cattle to low light intensities during the night. After studying dairy heifers in light-controlled rooms at the University’s Animal Science Research Unit, we now have some important knowledge concerning the “safe” intensity of dim night-light for cattle. Our studies were funded by Manitoba Hydro and ARDI.
The results of our research suggest that producers should be very cautious when using light intensities greater than 10 Lux during the night. Light of 10 Lux intensity is bright enough for humans, and likely cattle, to see fairly well if the eyes are allowed a minute or two to adapt. Thus, use of dim light up to 10 Lux in intensity is a practical and safe alternative for dairy producers who wish to have light in order to check their cattle in free-stall or tie-stall barns during the night.
Animal species differ dramatically in their sensitivity to light. For every species, there is an intensity of light or limit of sensitivity, below which the animal shows no physiological response to the light. Our first study at the University of Manitoba (Lawson and Kennedy 2001), revealed that the threshold in cattle was quite low. The lowest light intensity tested (50 Lux) caused a drop in night-time plasma melatonin level in the heifers.
Melatonin hormone is produced at night by the pineal gland of the brain. In all domestic animals, there is a very regular occurrence of high levels of melatonin in the blood (a high plateau in cattle) at night which falls to levels of essentially zero during the day. This daily rhythm in plasma melatonin is thought to direct other daily rhythms in the body and is important for good animal health. Because light levels of 50 Lux reduced the level of the night-time melatonin plateau in our heifers, we knew that the “safe” intensity of nigh-light was below 50 Lux.
In our next study, Drs. Rob Berry and Alma Kennedy with graduate student Puspa Mutharamalingam measured plasma melatonin levels in dairy heifers exposed at night (8 hours) for two weeks to complete darkness (0 Lux light intensity), to two very low intensities of dim light (5 and 10 Lux) or to the intensity of dim light (50 Lux) previously shown to cause a physiological effect.
The 5 and 10 Lux (0.5 and 1 Footcandles) intensities were chosen as it would be possible for dairy producers to check cows at these intensities of light. An intensity of light less than 5 Lux would be too dim for practical use. Eric Witkowski, lighting engineer, Manitoba Hydro, designed the incandescent and fluorescent lighting schemes set up in four rooms in the Animal Science Research Unit at the University of Manitoba for this experiment.
Statistical analysis revealed that there was a significant treatment by hour effect (Figure 1). Means represent a particular hour of the night treatment period averaged over 12 heifers on days 1, 4 and 14 of the experiment. Of the three light treatments, only the 50 Lux treatment affected plasma melatonin level and this effect had disappeared by the 4th hour of the night. Initially, plasma melatonin only rose to 50% of the normal night level when the 50 Lux light intensity was present.
Plasma melatonin of dairy heifers before and during 8 hours of darkness (0 Lux) or dim night-light treatments ( 5, 10 or 50 Lux). Means represent all heifers over l4 days of the experiment. Shaded bar represents the 8 h night treatment period.
a,b Means with different letters at the same hour of treatment were significantly (**) different.
The negative effect of 50 Lux on plasma melatonin disappeared by 4 hours into the night, but, because melatonin analysis was done only on samples collected at 2 and 4 hours of the night, the negative effect may have lasted for 3 hours or more. This inhibitory effect of 50 Lux was equally dramatic at day 1, 4 and 14 of treatment. Because the ability of 50 Lux to depress melatonin at night occurred consistently throughout the 14 day experiment, we feel confident that the heifers did not become insensitive to the 50 Lux light intensity over time. This is important in that one cannot assume that animals will “get over” the negative effect of 50 Lux on plasma melatonin levels. The results with the 50 Lux light intensity were similar to the results of our previous study.
Melatonin values at night for the 5 and 10 Lux treatments were not different from values found during complete darkness (0 Lux). In Figure 1 it can be seen that the 0, 5 and 10 Lux treatments all caused a normal rise in plasma melatonin at night. Unfortunately, we were limited to having 4 treatments in this experiment and so were unable to test the effects of the intermediate light intensities of 20, 30 and 40 Lux. Results found on day 4 and 14 were identical to results found on day 1 indicating that heifer sensitivity to 5 and 10 Lux does not develop over time.
Our results indicate that dairy heifers are not sensitive to 5 or 10 Lux light intensities during the night but respond to 50 Lux for greater than 2 but less than 4 hours per night. If light with an intensity of 50 Lux is used at night in dairy barns, cows will receive fewer “physiological” hours of darkness than intended, and possibly needed, for good health.
The heifers showed no tendency to develop either increased or decreased sensitivity to dim light over the course of the 14 day experimental period. Dahl et al (2000) has indicated that 6-8 hours of darkness is important for dairy cows in order to ensure the continuation of natural circadian rhythms. Currently there are producers who provide light at 50 Lux or higher at night in dairy barns. In this situation, the presence of light at night may be reducing the length of perceived night to shorter than that which is recommended.
These research results raise the important issue of whether there is a functional consequence of the 50% reduction in plasma melatonin at night which was caused by the 50 Lux treatment. Related information in sheep suggests that the height of the night-time melatonin plateau is of practical importance. As in sheep (Notter and Chemineau 2001), we have observed a high degree of variability among dairy heifers for the normal night level of plasma melatonin. Some heifers consistently had a high plateau while other consistently had a plateau 50 to 25% of the highest levels found. In sheep, night-time melatonin plateau levels are negatively correlated to fertility (Notter and Chemineau 2001). It would be very interesting to examine this relationship in cattle.
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Dahl, G.E., Buchanan, B.A. and Tucker, H.A. 2000. J. Dairy Sci.:83:885.
Lawson, T.J. and Kennedy, A.D. 2001. Can. J. Anim. Sci. 81:153.
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Peters, R.R., Chapin, L.T., Emery, R.S. and Tucker, H.A. 1981. J. Dairy Sci. 64:1671.
Tanida, H. Swanson, L.V. and Hohenboken, W.D. 1984. J. Dairy Sci. 67:585.