Defining and evaluating heat stress thresholds in different dairy cow production systems

Abstract

The aim of this study was to assess the impact of heat stress in dairy cows on test-day records for production traits and somatic cell score (SCS) in the state of Lower Saxony, Germany. Three different production systems were defined: A production system characterized by intensive crop production (=indoor housing), a pasture based production system, and a maritime region. Heat stress was assessed by two temperature-humidity indices (THI) modelled as random regression coefficients in an analysis of variance: One (THI Bo ) was defined as an average of hourly THI, calculated from hourly recorded temperatures and humidities, the other (THI Ra ) was based on daily maximal temperature and daily minimal humidity. In all production systems, THI Bo =60 and THI Ra =70 were identified as general thresholds denoting a substantial decline in test-day milk yield. For daily fat and protein percentage, no universally valid thresholds were identified. In contrast for SCS, especially in the maritime region, heat stress as well as cold stress thresholds were found. Regression analysis was used to study the change in test day milk yield in response to THI of those THI ranges with an obvious decline in milk yield. Regression coefficients were −0.08 kg/THI Bo and −0.16 kg/THI Ra for the crop production system, −0.17 kg/THI Bo and −0.23 kg/THI Ra for the pasture based system, and −0.26 kg/THI Bo and −0.47kg/THI Ra for the maritime region. Based on statistical information criteria, identified thresholds for THI Bo should be given preference over THI Ra when applying genetic studies on heat stress in German Holstein cows.

Dairy cattle in a temperate climate: the effects of weather on milk yield and composition depend on management

“…A decline in milk protein with THI was reported by several other authors (e.g. Bouraoui et al, 2002;Gantner et al, 2011;Bruegemann et al, 2012;Hammami et al, 2013). Our results also agree with those of Lambertz et al (2014), who reported a more marked decline in total protein yield with increasing THI in cows with access to pasture than those without.…”

“…Other authors have reported similar declines in milk yield at low THIs or cold temperatures (Rodriquez et al, 1985;Bruegemann et al, 2012). The rate of decrease in milk yield in our study was greater at higher values of THI than at lower values, consistent with the idea that endotherms are more tolerant of low than high body temperatures (Hansen, 2009).…”

“…AIC has been used previously to compare temperature indices in explaining milk traits (Bruegemann et al, 2012;Hammami et al, 2013). As the metrics for summarising a given element were closely correlated, and high proportions of shared variance can lead to unreliable estimates, we fitted each metric in a separate linear mixed effects model (LMM) (equation (3)) using maximum likelihood to produce a series of non-nested models.…”

“…Milk yield in dairy cows, Bos taurus, is traditionally said to begin declining at around 72 THI units based on work carried out in subtropical regions (Armstrong, 1994;. Thresholds of 68 (Renaudeau et al, 2012;Gauly et al, 2013) or even 60 units (Bruegemann et al, 2012) may, however, be more characteristic of high yielding herds in temperate zones. The genetic relationship between heat tolerance and productivity is negative , and dairy cattle are becoming more sensitive to heat stress owing to optimisation of breeding and management practices for increased performance (Kadzere et al, 2002;West et al, 2003).…”

Climatic effects in Central Europe on the frequency of medical treatments of dairy cows

“…The threshold of THI 5 60 was identified for the various regions characterized as a coastal region, a pasture-based region and a region of intensive crop production. Above this threshold heat stress effects on milk and protein yield were found (Brü gemann et al, 2010;Brü gemann et al, 2012). Whenever environmental stressors in dairy cows are discussed, their remarkable adaptive ability to mobilize mechanisms against environmental stressors has to be considered (Nienaber and Hahn, 2007).…”