Global warming is part of our daily lives and is the subject of many discussions. Heat waves are becoming more frequent, and longer during the summer. The nights are getting warmer, which does not give people, or dairy cows, a break.
According to the Climate Atlas of Canada, developed by the Prairie Climate Centre, the Montreal region will go from about eight tropical nights (with minimum temperatures above 20degrees Celsius) to just over 22 tropical nights per summer by 2050. It is not just the southern regions of the province that will experience such an increase.
In September 2021, the Uniag Cooperative team unveiled a project which involved installing 250 humidity and temperature probes [in cattle housing areas] as well as ruminal temperature probes[boluses with temperature sensors, placed in cows’ rumens, capable of issuing alerts in case of fever] on 25 farms. The results demonstrate that sustained periods of heat, without night respite,are the most stressful conditions for dairy cows.
The data focuses on the three main months of the summer (June through August, 2021). It shows that for 58 per cent of those summer days, the daily average indoor humidex exceeded 68, which represents the first level of heat stress. Furthermore, for 98 per cent of these days, there was at least one reading above 68.
On very hot days, a link is clearly demonstrated between an increase in indoor humidex and an increase in the number of alerts. We can extrapolate that almost one cow out of four is on heat stress alert during such days.
We also wanted to compare heat stress management in a well-ventilated barn versus one needing improvement. The major difference is ruminal temperature. Although the maximum indoor humidex achieved is not very different, the speed at which the well-ventilated building allows the humidex to be lowered plays a determining role. Indeed, the more efficient ventilation system allows the minimum to go below the low-stress level for nearly eight hours. This critical period allows the animals to cool down when they produce the most heat, in theory.
During the day, the humidex curves increase until they reach their maximum around 3 p.m., while the ruminal temperature curves decrease during the same period. This is mainly because cows spend a lot more time standing during the day, either for milking or for feeding and watering; they can eliminate more heat than when they are lying down during the night. In addition, digestion and milk production at night generates a considerable amount of heat. It is estimated that, depending on its production, a cow can generate between 4,500 and 6,000 BTUs per hour, which is the equivalent of a furnace capable of heating a room.
The results show that ventilation systems with the highest average wind speed are more effective, such as multiple basket fans or frame fans in series that ventilate in the same direction. The increase in wind speed did not directly translate into a drastic decrease in indoor humidex; however, the cows’ ability to manage heat stress peaks, with little or no increase in ruminal temperature, improved.
The primary goal in piloting this project on the part of the Uniag Cooperative was to provide producers with tangible and reliable data to evaluate their ventilation systems and decide whether modifications were necessary in the face of climate change.
This project would not have been possible without the participation of several producers, who jumped at the chance to collaborate with our team. Nor would it have been possible without the contribution of each of the Uniag representatives, who all lent a hand in the data collection. Special thanks to the Sollio Agriculture research and development team, and in particular to Annie Pomerleau, who gave us a huge helping hand with the data analysis.
