Effects of hot weather on milk production in Canterbury dairy herds

Abstract

To determine the impact of hot weather experienced by dairy cows in Canterbury on their productivity a series of 3 studies was carried out: 1 – to predict the potential for climatic thermal stress in this region of New Zealand, 2 – to study body temperature patterns in lactating dairy cows, and 3 – to analyse milk production records following hot weather episodes. For Study 1, a survey of meteorological data collected in Canterbury from 1998 to 2003 showed that during midsummer (January, February), many sites within the region experienced at least 3 days per month (i.e. approx. 10% probability) when the peak temperature-humidity index (THI) exceeded 72. For Study 2, monitoring of body temperature data in 10 lactating cows every 10 minutes for 46 days at the Lincoln University Dairy Farm during the summer of 2004/2005 revealed regular diurnal changes in body temperature, with peak levels in the afternoons, but there was no evidence of a cause-andeffect relationship with THI until the latter exceeded a value of 72. In Study 3, milk production data recorded from 13 farms in the Selwyn district of Canterbury during two months of summer 2008/2009, when 19 days out of 90 had peak THI values exceeding 72, showed no evidence of a negative relationship between the THI values and the amount of milksolids produced. These findings indicate that the episodes of hot weather which occur in Canterbury do not produce large enough heat loads in dairy cows to impact negatively on their milk production