Summer Incentives Present a Cool Challenge! By David Arseneau
David Arseneau
David Arseneau
Photo : Martine Doyon

Summer means vacation time! City-dwellers are happy and feeling good, but summer has a completely different meaning for dairy farmers. Most of you are anxiously waiting the first days of fall. Civilians would certainly think this odd! For several years now the Fédération des producteurs de lait du Québec has offered to boost production rights, usually from August to December. Some dairy farmers are quite successful and benefit from this opportunity by adapting their management system to the needs of the market and consequently enjoy significantly more income. Several strategies can be put into practice; in fact one of them is to synchronize cow and heifer calving to ensure maximum production during that period.

Adjusting your Sights in 2011
This year, you need to go about things differently… In fact, 2011 is a lucky year in terms of dairy production because in addition to fall milk, the Fédération is offering the possibility of producing ‘summer milk’. This is excellent news! However, you need to quickly adjust your strategies. Management will need to be tweaked: Some of you intended to slow down production during the summer since more cows are reaching the end of lactation and you’re getting ready for the fall push, which means shipping as much authorized milk as possible at a price per hectolitre that is generally higher than at any other time of year.

To make up for the calendar change in production, some farmers will be thinking of keeping cows that should be taken out of the herd while others will be buying additional cows. So what else can be done? Although vacationers enjoy warm days and nights, cows don’t quite feel the same way: They are not on vacation, they are working hard! Research is conclusive: To maximize animal comfort and performance, you need to reduce heat stress.

Many are inclined to believe that heat stress doesn’t really affect our herds, that this is a problem specific to California dairy farmers. But they would be mistaken. Heat stress is also a reality for animals north of the border and there are two key reasons:

Diagram 1 Stress levels caused by heat, according to temperature and humidity  California, Quebec, South (Quebec – Ontario)

The first reason is the humidity factor. When humidity is combined with temperature the resulting information is referred to as ‘humidex’, which is not only felt by people, but also by animals. For example, let’s compare heat stress in a California cow to that of a Quebec cow (see diagram 1). It is warmer in California than it is in Quebec and seeing the mercury rise to 40°C is not an infrequent occurrence but the air remains very dry. However, in Quebec, the temperature can easily reach 30°C with a humidity rate of 75%. Cows are exposed to high heat stress in both of these cases. At 34°C and 80% humidity, the stress level is considered serious and more severe than heat stress caused exclusively by a temperature of 40°C combined with a humidity level of 20%.

The second reason is the animals’ capacity to produce heat. Some 35 or 40 years ago, Quebec cows suffered much less heat stress. With dairy production having practically doubled since then, the extra heat produced by the animals has also doubled, thereby increasing their own level of heat stress (Kadzere et al, 2002). 

Heat stress is essentially an imbalance of the body’s heat production and its capacity to evacuate the extra heat. Dairy cows, just like all mammals, seek out an environment where free-air temperature is lower than their own body temperature to ensure the evacuation of extra heat per temperature gradient. The hotter the weather outside, the lower the gradient, which means the animal will have a tougher time getting rid of the extra heat to maintain normal body temperature.

The first signs of heat stress include increased respiration: Normal breathing is equivalent to 40 to 50 breaths per minute; at 70 breaths per minute cows are potentially suffering from heat stress. 

Consequences of Heat Stress
Rumen may rapidly be influenced by heat stress, since there is a direct relationship between pH and rumen temperature (see diagram 2). Moreover, saliva contains a much lower concentration of buffers when rumination is affected by stress, which also has an impact on ruminal pH, consumption and in the end, on dairy production and its components (particularly on the percentage of milk fat).

Diagram 2 Progression of rumen’s pH according to temperature

In a different order, it’s always been a given that heat stress may hinder several aspects of reproduction: Follicular dominance, oocyte quality, early embryonic development, not to mention that cows are generally much less demonstrative in the mating period.

It’s important to understand that an episode of heat stress may compromise reproduction over a period of time that extends beyond the actual heat stress. A follicle may take 80 to 100 days between the start of its development and the end of the ovule’s maturation and release. Follicles are very sensitive to heat stress. Heat may also damage the ovule contained in the dominant follicle, which can have consequences several days or months after the heat stress episode (up to November).

Minimizing the Effects of Heat Stress in 4 Easy Steps

1 . Adequate Ventilation

Dr Jim Spain and his team at the University of Missouri conducted research to demonstrate how adequate ventilation benefits cows. Using a special chamber where temperature and air flow were properly controlled, they compared the effects of day, night and continuous ventilation over a 24 hour period. Cows produced almost 1.5 litres more milk per day when ventilation was continuous compared with only daytime ventilation (see diagram 3 and 4). Animals build up body heat throughout the day and this means that their body heat is at its highest at 6:00 pm. Then – and only if there is overnight ventilation – body temperature will fall into the normal range around 7:00 am. Over night is definitely not the time to stop the ventilation!

Diagram 3 Effect of ventilation on body temperature Diagram 4 Effect of ventilation on milk production

2 . Don't Forget Dry and Transition Cows
Dr Spain also assessed the effects of heat stress on dry and transition cows. Using the same chamber as that used for lactating cows, heat stress was induced and half of the cows were cooled with a mister and a fan for one hour, twice a day. The result: The dry cows that were cooled produced significantly more milk after calving – around 2 kg/day more during the first six weeks. This kind of volume each day (see diagram 5 and chart 1) over the course of the summer months results in a decent amount of milk!

Diagram 5 Average milk production per week, according to the number of weeks elapsed since the start of lactation

Other experiments produced similar results with about 2 kg more milk when adequate ventilation was provided, as well as increased dry matter intake and reduced water consumption in dry and transition cows. The quality and quantity of colostrum were also improved (Avendano et al, 2006)

Chart 1 Effect of cooled cows on dry matter and water intake and on colostrum and milk production

3 . Water is Critical
Obviously, water consumption cannot be neglected. Having water available at all times is always very important, but we need to consider that in times of heat stress, water loss may be substantial – up to 55 litres per day! (Spain 2010) The cow's requirements increase accordingly. Water plays a very important role in the animal's capacity to regulate its body temperature (thermoregulation) and is critical to milk production. And milk production is easily compromised.

4 . Diet Needs Special Attention.
Photo : La Coop fédérée
There are several strategies that can be implemented in terms of diet to help fight stressful situations, but the aspects of management previously mentioned have undoubtedly the most significant repercussions. Because consumption tends to decrease during episodes of heat stress, we still need to find ways to fulfill nutrient requirements. A cow doesn’t feed on percentages; it eats kilos of dry matter. To get optimal nutrient intake, you could consider adding fat to increase energy density. You can also think about using more cations or buffers to counter the increased risk of ruminal acidosis. Furthermore, consider replacing used cations to compensate for metabolic alkalosis caused by the cow’s rapid breathing during heat stress. The use of more digestible forage is also recommended during episodes of heat stress. Highly digestible forage will reduce the production of extra heat compared with less digestible forage, and it will encourage voluntary intake of dry matter. Mike Allen, from the University of Michigan, stated that an improvement of one unit of NDF (NDF-d) fibre digestibility corresponds to an increase of dry matter intake equivalent to 0.17 kg and an increase in milk production equivalent to 0.25 kg. I hope all the right weather conditions are present for producing the most digestible forage possible!

Everything you do to limit heat stress will have a direct and positive outcome on your herd's potential to produce "summer milk"! The following are a few important facts to remember:

  • Heat stress is not limited to California.
  • Heat stress hinders consumption, dairy production as well as reproduction in the short and long terms!
  • When the risk of heat stress is high, ventilation is needed day and night. Don't forget about dry and transition cows.
  • Always supply fresh water, more water and even more water!
  • In terms of diet, there are key elements to be considered, such as buffers, energy density, the quality of protein and forage

Talk it over with your expert consultant.
Have a great summer!


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