Heat stress is caused by a combination of high temperature and high humidity. At a temperature of 77°F and a humidity of 60% there is a mild stress. A temperature of 86°F combined with a humidity of 80% already causes severe stress. Heat stress impacts the activity, milk yield and health of the cows. As a result, the number of voluntary visits of cows to the robot will decrease, which implies a negative effect on farm performance. Therefore, it is important to protect the cows from suffering due to heat stress.
Effects of heat stress on the cow
The main effects of heat stress are: reduced dry matter (DM) intake, reduced milk yield with lower fat and protein levels, reduced fertility and increased water consumption. Hence, energy intake may decrease to only 75%. To evacuate surplus heat, cows will raise their respiration rate and start panting. Together with increased salivation, this reduces buffer capacity and augments the risk of ruminal acidosis. Cows suffering from heat stress spend two to three hours/day less lying down. When standing, it is easier to breathe and evacuate heat. However, together with the increased risk of ruminal acidosis, this increases the chance of claw disorders later on. Good claw health is necessary for optimal cow flow to the robot.
Measures to prevent heat stress
These measures do not only apply to lactating cows, but to dried-off cows and heifers as well.
At high temperatures and under heat stress, water consumption increases considerably. High-yielding cows may drink up to 211 quarts per day. As rule of thumb, the water required by a cow equals four times her daily milk yield. In addition, at least 10% of the herd should be capable of drinking simultaneously from, preferably, large open water troughs that are easily accessible. Water quality and cleanliness of the water troughs should be checked daily. The positioning of water troughs in robotic milking barns is important to allow cows to drink after milking. Water troughs should be placed in such a way that cow traffic is not disturbed by drinking cows.
Cows need ventilation to cool off. Natural side-ways ventilation in open-sided barns, together with mechanical ventilation from 68°F onwards, is the most effective. In hot climates, tunnel ventilation is also a good way of cooling off the cows. In addition, isolation of the roof helps to keep the inside temperature low. Sprinkling water over cows helps them to cool off (>78°F), but this can only be applied at regular intervals in combination with mechanical ventilation to prevent udders from getting wet. The robot should be installed within an optimal configuration for the cows. This means: no direct sunlight and the possibility to cool down the area around the robot.
Feeding more often, at cool moments of the day, keeps the ration fresh and tasty as well as stimulating feed intake and preventing fermentation. The following adjustments to the ration are advised: decreased concentrate ration at the feed fence, more easily degradable forages, less energy per kg DM and more rumen non-degradable protein per kg DM. These adjustments reduce the risk of ruminal acidosis, lower heat production during digestion and supply sufficient energy and protein. Due to reduced DM intake and increased use, minerals (Na, P) and vitamins (A, E) should be supplemented as well. Addition of sodium bicarbonate or simply the addition of salt to the ration may also be useful to prevent ruminal acidosis. If PMR feeding (Partly Mixed Ration) is applied, the cows’ consumption of their total ration will be spread more evenly throughout the day. With regard to heat stress, the energy content of the total ration at the feed fence should be adjusted (average milk yield – 7 kg). Figure 3 shows the negative effects of heat stress on the fertility of the cow (as a result of decreased feed intake).
During hot periods, it is advisable to have the cows in pasture only during the night or during the cool moments (evening, early morning) of the day. When in pasture, cows should always be ensured of sufficient shade and fresh water.
Tips and tricks
- Check ventilation capacity and increase ventilation rate when necessary (mechanical ventilation)
- Control water management: at least 10% of all cows can drink simultaneously from large open troughs
- Check cleanliness of water troughs daily
- It is advisable to feed a special ration (supplemented with additional minerals and vitamins) to the cows at least two times a day (to keep the ration fresh and tasty)
- During hot periods, it is advisable to only have the cows in pasture during the night or during the cool moments (evening, early morning) of the day
Sources:Udder Health Centre Netherlands (UGCN), Animal Health Service Deventer, Intervet Schering-Plough
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