Increasing global temperatures have resulted in more hot days in many parts of Canada. Given the rise in global temperature there has been an increased focus on understanding the effects of different heat mitigation strategies on dairy cattle health, welfare and production. It is well established that heat stress has negative effects on the health and biological functioning of dairy cows through depressed milk production and reduced reproductive performance. Although it is also generally accepted that heat stress can also increase thirst, there has been little research on this relationship.
The environmental conditions driving heat stress are most often presented using the temperature and humidity index (THI) – a measure that includes the effects of both temperature with relative humidity (RH). At 25 C, THI can range from a low of 67 (at 0% RH), to 77 (at 90% RH). It is generally accepted that dairy cows begin to show signs of heat stress when THI exceeds 68, and that when THI is greater than 74 cows will begin to show more obvious signs, including decreased milk production. Values into the high 80’s can be dangerous.
Water accessibility is always important for dairy cattle, but it becomes critically important for the heat stressed animals, making it especially important that access to fresh water is well managed when THI increases during the summer months. One way to assess if water access is sufficient for cows is to watch their behaviour, including evidence of competitive behaviour at the drinker. As the results of the first study described below illustrate, when THI increases cows are more likely to physically butt or push another cow away from the drinker, taking her place. Even cows that are otherwise more submissive will be more likely to physically displace a ‘boss’ cow from the drinker, illustrating just how motivated these animals are to access water.
Our study followed drinking behaviour and competition among lactating dairy cows at The University of British Columbia’s Dairy Education and Research Centre in Agassiz. Group size was held constant at 20 animals housed in a single pen fitted with 24 freestalls, and with electronic water bins that were used to measure drinking behaviour and water intake. When a cow had completed 21 days in the study she was removed and replaced with a new cow; 69 cows completed the study. Each cow was fitted with an RFID ear tag, allowing us to measure how much time she spent at the drinkers, often she visited the drinkers, and her daily water intake. Using video recordings of cows drinking we could also identify competitive replacements, when one cow displaced another cow from the drinker and then took her place. Analyzing video for many cows over many days is labour intensive, so we developed an algorithm that was able to automatically identify replacements with a high degree of accuracy, based on one cow leaving the drinker and another taking her place within a short interval of time (less than 29 s). We then used this algorithm to automatically record competitive replacements for 24 h/d throughout the study. Ambient temperature and humidity were recorded by the local weather station and used to calculate the temperature–humidity index (THI). We presented the daily maximum THI over a rolling 3-day period.
As THI increased, cows drank more water, spent more time at the drinkers, and visited the drinkers more often. But the greatest effect of increasing THI was, as illustrated in Figure 1, a more than seven-fold increase in competitive replacements at the drinker. More submissive cows were most affected by this competition — these cows were more likely to avoid the drinker at the hottest and most competitive times of day. We also found that the dominance ranking flattened when competition was high during periods of hot weather, meaning that the subordinate cows were sufficiently motivated to drink that they were willing to take on the more dominant cows in the pen.
We also recently completed another study where we studied how changes in stocking density at the feeder (varied between 1 or 2 cows per feeder), and drinker (varied between 6 or 12 cows per drinker) and a temporal feed restriction (14 or 24 h access) impacts drinking in 4 groups of 6 cows each. Cows drank on average 5 litres less water per day when feed availability was restricted and again subordinate cows were most affected, spending spent less time drinking when overstocked. Under times of higher competition, cows were observed drinking in the hours after the peak in drinking observed when not overstocked.
Our findings reinforce the importance of providing easy access to water, especially when THI exceeds 70 and that feed restriction and higher stocking density of cows at the drinker and feeders changes the drinking behavior of cows, with subordinate animals experiencing more pronounced effects.
These results also suggest that changes in behaviour at the drinker, especially an increased number of competitive interactions, indicates that cows are especially motivated to drink and may be used to inform changes in farm management regarding the placement and availability of drinkers.
Figure 1. Number of replacements (one lactating dairy cow displacing another cow within 29 seconds) at the drinker in relation to the maximum THI.
For further information please contact Marina (Nina) von Keyserlingk (nina@mail.ubc.ca) or Daniel M. Weary (danweary@ubc.ca) . The results described in this article are based on two peer reviewed publications: McDonald, P. V., M.A.G. von Keyserlingk, and D. M. Weary. 2020. Hot weather increases competition between dairy cows at the drinker. J. Dairy Sci. 103: 3447-3458. https://doi.org/10.3168/jds.2019-17456; and, Nizzi, E., B. Foris, D. M. Weary, A Boudon, and M.A.G. von Keyserlingk. Accepted. Stocking density at feeders and drinkers and temporal feed restriction affects dairy cows’ drinking behavior. JDS Communications.
General funding for the Animal Welfare Program during the time of this study was provided by NSERC Industrial Research Chair program with industry contributions from the Alberta Milk (Edmonton, AB, Canada), British Columbia Dairy Association (Burnaby, BC, Canada), Boehringer Ingelheim (Burlington, ON, Canada), CanWest DHI (Guelph, ON, Canada), BC Cattle Industry Development Fund (Kamloops, BC, Canada), Dairy Farmers of Canada (Ottawa, ON, Canada), Dairy Farmers of Manitoba (Winnipeg, MB, Canada), Intervet Canada Corporation (Kirkland, QC, Canada), Saputo Inc. (Montreal, QC, Canada), SaskMilk (Regina, SK, Canada), and Semex Alliance (Guelph, ON, Canada).
Research Reports are published six times a year by UBC’s Dairy Education and Research Centre, part of the Faculty of Land and Food Systems, to share applied aspects of research from published articles in refereed scientific journals. The UBC Dairy Education and Research Centre is used by faculty members from the Applied Animal Biology Program located in the Faculty of Land and Food Systems at UBC. Other groups interested in conducting research at the Centre are encouraged to contact Dr Julia Lomb, Research Manager at julia.lomb@ubc.ca.
