The effect of low light intensities and red light on heart rate, blood pressure, respiratory rate and activity in dairy cows

Abstract: Today dairy farmers in Sweden are obligated to have lights turned on during night time in addition to the mandatory daylight inlet. This presents a cost for the production but many argue that it can be economically beneficial, especially in loose housing of dairy cows. In loose housing and even more so in herds with automatic milking, well functioning cow traffic during all hours of the day is crucial to optimise production. In order to keep the cow traffic flowing, lights may be an important management tool. It is also perceived among farmers with tied up stall that night light decreases the incidents of cows accidental stepping on their own or neighbours udders. In both these cases economical gain may be potential. On the other hand today it is not clear how well cows see in darkness or at which light intensity they start to distinguish their surroundings, thus it is not clear if night light is really necessary. It may well disturb the cows’ hormone cycle, explicitly the melatonin cycle, or in other ways create stress. The aim of this study was to investigate if stress related properties as heart rate, blood pressure and respiratory rate were affected in cows at different light intensities. Furthermore whether or not these parameters were affected by the presence of red light was investigated. The activity of the cows in different light intensities was also recorded with the help of activity meters attached to their right hind leg. The light intensities aimed for were 0, 5, 20 and 50 lux and the experimental design used was a Latin Square. In the study a total of twelve dry dairy cows were used and during the course of the study two tests were carried out; an obstacle course and a novel object test. The results indicate that heart rate and blood pressure were not affected by different light intensities or the presence of red light, still respiratory rate was slightly affected by the presence of red light. Also the results show that 0 lux with red light increased heart rate, blood pressure and respiratory rate compared to 0 lux without additional light. This suggests that the cows can detect red light and may be stressed by it. However no differences were seen due to the different light intensities and therefore cows are probably not stressed by low light intensities. This make sense since different light intensities is a normal part of their life during the day. The activity meters showed that the cows tended to be lying down a greater proportion of the time in 50 lux, especially in comparison with 20 lux. This could be due to better visual acuity in 50 lux thus making the cows feel more secure.