title: Impact of mild heat stress on dry matter intake, milk yield and milk composition in mid-lactation Holstein dairy cows in a temperate climate.
abstract: The aim of the present study was to evaluate the impact of summer temperatures in a temperate climate on mid-lactation Holstein dairy cows. Therefore, a data set was examined comprising five trials with dairy cows conducted at the experimental station of the Friedrich-Loeffler-Institute in Braunschweig, Germany. The temperature-humidity index (THI) was calculated using temperature and humidity data from the barns recorded between January 2010 and July 2012. By using a generalised additive mixed model, the impact of increasing THI on dry matter intake, milk yield and milk composition was evaluated. Dry matter intake and milk yield decreased when THI rose above 60, whilst water intake increased in a linear manner beyond THI 30. Furthermore, milk protein and milk fat content decreased continuously with increasing THI. The present results revealed that heat stress exists in Lower Saxony, Germany. However, further research is necessary to describe the mode of action of heat stress. Especially, mild heat stress has to be investigated in more detail and appropriate heat stress thresholds for temperate climates have to be developed.
authors.affiliation: a Institute of Animal Nutrition, Friedrich-Loeffler-Institute (FLI), Federal Research Institute for Animal Health , Braunschweig , Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Gorniak
authors.forename: Ulrich
authors.initials: U
authors.lastname: Meyer
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: Südekum
authors.forename: Sven
authors.initials: S
authors.lastname: Dänicke
mesh_terms: D000821:Animal Feed; D000818:Animals; D001947:Breeding; D002417:Cattle; D002418:Cattle Diseases / Q000503:physiopathology*; D002980:Climate; D003612:Dairying; D005247:Feeding Behavior; D005260:Female; D005858:Germany; D018882:Heat Stress Disorders / Q000503:physiopathology / Q000662:veterinary*; D006358:Hot Temperature; D007774:Lactation / Q000502:physiology*; D008892:Milk / Q000737:chemistry / Q000378:metabolism*; D012621:Seasons
keywords: dairy cattle; feed intake; heat stress; milk yield; relative humidity; temperate climate