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

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A better understanding of how livestock respond to weather is essential to enable farming to adapt to a changing climate. Climate change is mainly expected to impact dairy cattle through heat stress and an increase in the frequency of extreme weather
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  Weather affects milk yield and composition 1 Full text available from Cambridge Journals Online: http://journals.cambridge.org/action/displayAbstract;jsessionid=CB6801744E7604776077924FBA2E2BBF.journals?aid=9447136&fileId=S1751731114002456 Hill, D. L. and Wall, E. (2015) Dairy cattle in a temperate climate: the effects of weather on milk yield and composition depend on management,  Animal    9 : 138- 149 DOI: http://dx.doi.org/10.1017/S1751731114002456  --------------------------------------------------------------------------------------------------------------- Dairy cattle in a temperate climate: the effects of weather on milk yield and composition depend on management D. L. Hill *1  and E. Wall 1,2 1  Animal and Veterinary Sciences Research Group, SRUC, King’s Buildings, West Mains Road, Edinburgh, EH9 3JG, UK 2 ClimateXChange, High School Yards, Edinburgh, EH1 1LZ, UK    *Corresponding author: davina.hill@sruc.ac.uk    Weather affects milk yield and composition 2 Abstract 1  A better understanding of how livestock respond to weather is essential to enable 2 farming to adapt to a changing climate. Climate change is mainly expected to impact 3 dairy cattle through heat stress and an increase in the frequency of extreme weather 4 events. We investigated the effects of weather on milk yield and composition (fat and 5 protein content) in an experimental dairy herd in Scotland over 21 years. Holstein 6 Friesian cows were either housed indoors in winter and grazed over the summer or 7 were continuously housed. Milk yield was measured daily, resulting in 762786 test 8 day records from 1369 individuals, and fat and protein percentage were sampled 9 once a week, giving 89331 records from 1220 cows per trait. The relative influence 10 of 11 weather elements, measured from local outdoor weather stations, and two 11 indices of temperature and humidity (THI), indicators of heat stress, were compared 12 using separate Maximum Likelihood models for each element or index. Models 13 containing a direct measure of temperature (dry bulb, wet bulb, grass or soil 14 temperature) or a THI provided the best fits to milk yield and fat data; wind speed 15 and the number of hours of sunshine were most important in explaining protein 16 content. Weather elements summarised across a week’s timescale from the test day 17 usually explained milk yield and fat content better than shorter-scale (three day, test 18 day, test day-1) metrics. Examining a subset of key weather variables using REML, 19 we found that THI, wind speed and the number of hours of sunshine influenced milk 20 yield and composition. The shape and magnitude of these effects depended on 21 whether animals were inside or outside on the test day. The milk yield of cows 22 outdoors was lower at the extremes of THI than at average values, and the highest 23 yields were obtained when THI, recorded at 0900 h, was ~55 units. Cows indoors 24 decreased milk yield as THI increased. Fat content was lower at higher THIs than at 25  Weather affects milk yield and composition 3 intermediate THIs in both environments. Protein content decreased as THI increased 26 in animals kept indoors and outdoors, and the rate of decrease was greater when 27 animals were outside than when they were inside. Moderate wind speeds appeared 28 to alleviate heat stress. These results show that milk yield and composition are 29 impacted by extremes of THI under conditions currently experienced in Scotland, 30 where animals have so far experienced little pressure to adapt to heat stress. 31 32 Keywords 33 climate change, fat percentage, heat stress, protein percentage, THI 34 35 Implications 36 Climate change is expected to bring about drier, hotter summers and an increased 37 frequency of extreme weather events across Europe. Here we show that milk yield 38 and quality decline at the upper extremes of temperature and humidity even under 39 conditions currently experienced in Scotland. We identify the values of temperature 40 and humidity, and of other weather elements, at which performance begins to 41 decrease. These estimates could be used in conjunction with climate projections to 42 help policy makers understand the likely economic impact of climate change on dairy 43 productivity. 44 45  Weather affects milk yield and composition 4 Introduction 46 47 Climate change will have direct effects on livestock performance and welfare, mainly 48 through increases in temperature and the frequency of extreme weather events, and 49 will also affect animals indirectly through changes in the availability of fodder and 50 pasture and the distribution of pests and parasites (Gauly  et al. , 2013). High 51 temperatures are associated with a greater incidence of heat stress in livestock, 52 which can have negative effects on milk yield (Bohmanova  et al. , 2007, Hammami  et 53 al. , 2013), fertility (Hansen, 2009) and health (Sanker   et al. , 2013), and increase the 54 risk of mortality (Vitali  et al. , 2009). Heat stress occurs when animals experience 55 conditions above their thermal comfort zone and are unable to dissipate enough heat 56 to maintain thermal balance (Kadzere  et al. , 2002). This is already costly to the dairy 57 industry in terms of management interventions and lost productivity (St-Pierre  et al. , 58 2003). 59 60  An animal’s tolerance to high air te mperatures depends on the amount of water 61 vapour in the air because this influences the rate of heat loss through evaporative 62 cooling. The association between air temperature and water vapour content can be 63 expressed as a Temperature Humidity Index ( THI ; Thom, 1959). Milk yield in 64 Holstein dairy cows, Bos taurus , is traditionally said to begin declining at around 72 65 THI units based on work carried out in subtropical regions (Armstrong, 1994, 66 Ravagnolo  et al. , 2000). Thresholds of 68 (Gauly  et al. , 2013, Renaudeau  et al. , 67 2012) or even 60 units (Bruegemann et al.,  2012) may, however, be more 68 characteristic of high yielding herds in temperate zones. The genetic relationship 69 between heat tolerance and productivity is negative (Ravagnolo and Misztal, 2000), 70  Weather affects milk yield and composition 5 and dairy cattle are becoming more sensitive to heat stress due to optimisation of 71 breeding and management practices for increased performance (Kadzere  et al. , 72 2002, West  et al. , 2003). The reduction in productivity in heat stressed cows is 73 largely a result of reduced feed intake, but high temperatures also have a direct 74 effect on reproductive physiology and metabolism (Renaudeau et al  ., 2012). Cattle 75 generate metabolic heat as a by-product of milk synthesis and so higher yielding 76 animals experience heat stress at lower THIs than lower yielders (Kadzere et al  . 77 2002). 78 79  A n animal’s thermal tolerance is also affected by solar radiation and the velocity of 80 ambient air (Dikmen and Hansen, 2009, Graunke  et al. , 2011, Hammami  et al. , 81 2013), while increasing precipitation is associated with declining milk production 82 (Stull et al  ., 2008). Weather-related stressors could potentially affect performance 83 immediately or have a delayed impact, and yet few studies have explored the time 84 interval between weather events occurring and impacting milk traits (St-Pierre  et al. , 85 2003). Among those that have, West et al  ., (2003) found that the effects of mean 86 daily THI on milk yield were greatest two out of a possible three days after THI was 87 recorded and Bouraoui et al.  (2002) found that mean daily THI measured 1-3 days 88 before the test day had a greater effect on milk yield than test day THI. These time 89 lags might be related to the duration of digestive processes (Gauly  et al. , 2013). 90 91 Here we used 21 years’ data from a single herd at two dairy research farms on the 92 east and west coasts of Scotland to investigate the effects of weather on milk yield 93 and composition (fat and protein content). The study evaluates a range of weather 94 variables collected from Meteorological Office weather stations located on the 95
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