TIPS TO MANAGE HEAT STRESS

• Increase airflow, using misters and soakers when appropriate.

• Assess air quality and airflow at cow level.

• Ensure unlimited drinking water is available.

• Monitor cattle for behavioural changes, such as increased standing time, panting and drinking more water.

• Provide fresh feed.

• Discuss summer ration adjustments with your nutritionist.

The study demonstrated milk yield, fat yield and protein yield had different and distinct THI thresholds, making it easy to identify when negative effects were observed. A negative effect was seen for milk yield at THI values of 64 to 68 in Ontario, Quebec, the Maritimes and the Prairies. A negative effect was observed at 61 in British Columbia, with the negative impact on milk yield even stronger at a THI of 72 to 76. For milk protein yields, the negative effects of heat and humidity were seen at THI values of 58 to 62 and worse effects at 72 to 73 were seen in all five Canadian regions. More surprising was that the threshold for reducing milk fat yield happened at THI values of only 54 to 55 and at only 49 in B.C.

Using national data and weather data sets meant information about individual conditions in barns, such as housing, cooling management or any feeding adjustments, were not accounted for in this study. However, results suggest the negative impacts of heat stress for these three production traits may begin to happen at lower temperature-relative humidity combinations than previously thought.

Reference: Rockett, P.L., I. L. Campos, C.F. Baes, D. Tulpan, F. Miglior and F.S. Schenkel. 2023. Phenotypic analysis of heat stress in Holsteins using test-day production records and NASA POWER meteorological data. J. Dairy Sci. 106:1142-1158.

With this in mind, farmers should consider managing to prevent heat stress earlier; alleviating it is important for good production and particularly for milk fat and protein yields.

Tom Wright is Dairy Cattle Specialist, Ontario Ministry of Agriculture, Food and Rural Affairs.

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Kexxtone is approved as an aid in the prevention of ketosis and subclinical ketosis*.

Ask your veterinarian how Kexxtone can ensure your cows receive a consistent monensin dosage each day, to help prevent ketosis and set your cows up for success.

Individual farm results may vary.

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