Lack of effect of hot summer conditions in Canterbury on milk production of dairy cows

摘要

The occurrence of hot weather in Canterbury over 90 days during the 2008/2009 summer provided an opportunity to investigate the effects of climatic heat challenge on milk production by cows on commercial dairy farms in that region. An analysis of daily milksolids production and the peak temperature-humidity index (THI) recorded on each previous day was conducted for 13 farms in mid-Canterbury using data from 1 December 2008 to 28 February 2009. There were 19 days when dry bulb air temperature exceeded 27°C and the THI was 72 or higher, conditions at which heat stress has been suggested to occur in dairy cows. However, there was no significant inverse relationship between THI and milksolids production (P ranged from 0.193 to 0.897) on any of the farms using either all the data or only the data for days on which THI exceeded 72. With relative humidity being strongly inversely related to dry bulb temperature in Canterbury summers, THI values rarely exceed 75 in this region. As there were no discernable effects on productivity of these dairy cows during the episodes of hot weather, it is also unlikely that there would be any animal welfare concerns that could be attributable to climatic heat challenge in these conditions.