Effect of low light intensities on dairy cows’ behavior

Abstract: The animal welfare act in Sweden states that dairy cows need to have at least a dim light present at night, but there are no recommendations for what intensity the light should have. It is unknown how cows perceive and react to low light intensities and earlier studies on this topic are limited. Red light as night light has also been suggested, based on the cows’ inability to perceive red light. This have however been questioned. The aim with this study was to investigate how four different light intensities affect dairy cows behavior. The aim was also to investigate how red light affects the cows’ behavior. In the study, twelve cows’ behavior and locomotion pattern were observed at the different light intensities 0, 5, 20 and 50 lux in presence or absence of red light. The cows were asked to pass through an obstacle course and perform a novel object test (NOT) in the different treatments. The study design was following a change-over design with four groups of cows and four different light intensity treatments. The experiment prolonged for four weeks and each treatment period lasted one day. Based on results in this study, it can be concluded that dairy cows can perceive light intensities down to 5 lux. It is further hypothesized that cows may be affected of a light intensity as low as 0.2 lux. This study also show that behavior is significantly affected by a light intensity since step frequency, number of stops, time taken for passing the obstacle course as well as step length and step rate were different at 0 lux compared to 5, 2 and 50 lux. In the NOT, time taken to the first interaction with an object was prolonged at 0 lux compared to the other light intensities. The cows’ behavior was not affected by the presence of red light in light intensities at 5, 20 and 50 lux. At 0 lux with presence of red light the cows had a higher frequency of steps, interacted less with the surrounding and knocked down fewer obstacles in the obstacle course compared to the other three tested light intensities. In the NOT, time taken for the cows to first interact with the objects was longer at 0 lux accompanied by red light compared to the other light intensities and compared to 0 lux in absence of red light. It is unclear if this is a result of a light intensity of 0.2 lux emitted by the red light or due to the precipitation of red light.