Global warming is part of our daily lives and is the subject of many discussions, both personal and political. Heat waves are becoming more frequent and longer during the summer. The nights are getting warmer and 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 8 tropical nights (a tropical night is one where the minimum temperature exceeds 20°C) to just over 22 tropical nights per summer by 2050 (Figure 1). Moreover, it is not just the southern regions of the province that will experience such an increase. According to this document, which brings together 24 studies on climate change, the Saguenay-Lac-Saint-Jean region will go from 0.7 to 3.7 tropical nights, while the Quebec City region will go from 0.9 to 4.9 tropical nights.

Our 250 ruminal probes, installed on 25 farms, have clearly demonstrated that periods of several days of heat without night respite are the most stressful conditions for our dairy cows.


In the September 2021 issue of Le Coopérateur, the Uniag Cooperative team presented the ruminal probe project. We are now proud to share the results with you.

Let’s start with a review of the summer of 2021 thanks to the ruminal probes and the temperature and humidity probes that were installed at the beginning of the season. Graph 1 shows the three main months of the summer, June through August 2021. The green line represents the daily average of the indoor humidex temperature index (ITH) of the 25 farms participating in the Uniag project. This index interprets temperature and percent humidity according to the following formula: [0.8 x temperature (°C)] + [relative humidity x [temperature (°C) – 14.4]] + 46.4.

The first level of heat stress is reached when the ITH exceeds 68 (according to several sources). Our data show that for 58% of the days in the summer of 2021, the daily average was above this first threshold. Furthermore, for 98% of these days, there was at least one reading above 68. The green bars, meanwhile, represent the number of daily alerts on those same days.

Days such as August 21 and 22 clearly demonstrate a link between an increase in HIT and an increase in the number of alerts, with daily average HIT reaching 76.3 and 76.7 respectively. The number of alerts is 56 and 64 respectively, out of a total of 250 probes. We can therefore extrapolate that almost one cow out of four was on heat stress alert during these two days. It is also important to note that on our 25 farms, some had their sample of 10 cows (out of 10 probes!) on heat stress alert, while others managed to have none.

We also wanted to compare the ability to manage heat stress in a well ventilated barn versus one with a lot of potential for improvement. Graph 2 allows us to compare the two facilities during a 24-hour period in August. Ruminal temperatures are represented by the green (T rum enterprise 1) and blue (T rum enterprise 2) lines. The purple and orange lines represent the average August ITH for enterprises 1 and 2 respectively.

The major difference between the two enterprises is ruminal temperature: the enterprise that can improve its ventilation recorded almost 0.9°C more during August. Although the maximum RTI achieved by the two facilities is not very different, the speed at which the well ventilated building allows the RTI to be lowered as well as the minimum achieved play a determining role. Indeed, the more efficient ventilation system allows the minimum to go below the low stress level for nearly eight hours, unlike the other company, which does not manage to go below this level. This critical period allows the animals to cool down when they produce the most heat, in theory.

It is also interesting to compare the curves representing the ITH and the ruminal temperatures, which show an opposite trend. During the day, the ITH curves increase until they reach their maximum around 3 p.m., while the ruminal temperature curves decrease during the same period. This is mainly due to the fact that during the day, cows spend a lot more time standing, either for milking or for feeding and watering. They are therefore able to get rid of more heat than when they are lying down (during the night).

In addition, the digestion and milk production that takes place during the night generates a considerable amount of heat. It is estimated that, depending on their production, cows can generate between 4,500 and 6,000 BTUs per hour, which is the equivalent of a furnace capable of heating a room by itself. We must not forget that these same animals heat the barns during the winter.

From our observations, we were able to identify a type of ventilation that is more effective in resisting the increase in heat stress. For the time being, the systems that achieve the highest average wind speed are proving to be the best. Therefore, ventilation types with multiple basket or frame fans in series that all ventilate in the same direction are proving to be the most effective. The increase in wind speed did not directly translate into a drastic decrease in indoor HTI in companies with such a system. However, it was interesting to observe the improvement in the ability of the cows to manage heat stress peaks with little or no increase in ruminal temperature. Although this system generates electricity and noise, it is the best performing model, according to our observations during the ruminal probe project.

In the third graph, it is possible to observe the difference in performance between a well ventilated enterprise and a less ventilated enterprise. Although the ITH curves (in purple for the well ventilated farm and in orange for the other) do not seem to separate too much, except in the big peaks of increase, the ruminal temperature curves show the advantage of having ventilation. Indeed, the ruminal temperature of the cows on the less ventilated farm (shown by the blue line) increases drastically during hot periods, while the ruminal temperature of the cows on the well ventilated farm (shown by the green line) is much more stable throughout the summer, despite the peaks of heat stress. In this case, the increase in ruminal temperature directly translated into a pregnancy rate problem and the appearance of metabolic disorders at calving.

The fourth and final graphic represents a situation experienced by the Uniag team and a producer participating in the probe project. It is taken from the new visuals that will be on all producers’ Lactascan reports. It represents three different production histories of combined components (kilograms of fat and kilograms of protein): the co-op average, the provincial average and the last three years of the producer.

The producer’s history showed a huge drop in fat production per cow in the last two summers, as shown by the green line on the graph representing the year 2020. The thin dotted line represents the average combined component production of the cooperative the producer deals with, while the thick line represents the same average, but at the provincial level.

Following the 2020 data collection, the producer followed the Uniag team’s recommendation to add fans to the feeder to increase his average wind speed. The results were striking. As shown in the orange curve (summer 2021), the producer was able to maintain a stable production throughout the summer, while moving away from the average, which is dropping like every summer. The stability of component production during the summer is the most pronounced effect on the producer’s performance following the addition of the fans.

In conclusion, the team’s primary goal in piloting this project was to provide producers with tangible and reliable data to evaluate their ventilation system and decide whether or not modifications were necessary. Our team is most proud to hear the testimonials from producers, who tell us, for example, “I did the math quickly, and it was $40,000 I got this summer, compared to previous summers, for a project that cost me $30,000 and will pay for itself over several years!” Or, “Before the addition of the fans, inseminating a cow in the summer was like throwing the semen into the scupper because my arm was so hot. Now, the temperature is the same as it is during the rest of the year, and my breeding performance has stopped decreasing in the summer!”

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.