Epsilon Archive for Student Projects

Abstract

Heat stress in a dairy cow is defined by an increased body temperature leading to decreased welfare and productivity. The increasing number of high producing dairy cows with high vulnerability to heat, in combination with the predicted increase in temperature across the world leads to an urgent need for practical methods to reduce heat stress within the dairy industry. Since the summer of 2018 was exceptionally warm in Sweden, many Swedish dairy herds got considerably affected with lowered milk production compared to a normal summer. Therefore, the aim of this study was to investigate how factors related to housing, preventive measures and experiences influenced milk production during warm periods. Further, the goal was to identify solutions with most potential to counteract the negative effects of warm summer weather in Sweden.
The study is based on 30 phone interviews which included questions focusing on the farmer’s experience of extreme weather and the consequences, housing design, systems, and routines. Risk factors were analyzed using the Mann-Whitney test. Selection of farms for the interviews was based on information from the Swedish milk and disease recording system (SMDRS), including both farms that were negatively affected by the summer 2018 (cases) and farms that were less affected (controls). Information from monthly test-milking occasions was used to calculate the proportional difference in milk production, expressed as energy corrected milk (ECM), between different time periods. First, the production during the warmest period of the summer of 2018 was compared to an average of the previous 7 months and secondly to the production during the corresponding months in 2017.
No significant difference was found regarding year of construction, housing system and ventilation system when analyzing the factors separately. However, the most common combination of these factors was used to create a category of farmers having modern warm housings with controlled ventilation. This combination of factors proved to be the most successful system for maintaining milk production during the summer with a significant difference (1.5% average increase compared to 6% decrease for the other system combinations). Regarding milking system and preventive measures, no results with significant difference could be found. However, although not significant the five farms using extra fans as a preventive measure appeared to have an advantage as they had an average increased milk production of 4% compared to 8% decrease for farms using other preventive measures. Observing early signs of heat stress in form of panting showed to have a positive impact on the milk production, with a significant difference (average 6.5% increase compared to 6% decrease for the other signs). Overall, the result from this study shows that factors have different impact on different farms, meaning that the best solution seems to be different for every farm based on their prerequisites.