Modeling the profitability of investing in cooling systems in dairy farms under several intensities of heat stress in the Mediterranean

Heat stress (HS) in dairy cows affects dry matter intake, milk yield, reproduction, and culling rate. Cooling systems (CS) may partially revert these effects, but their profitability depends on the price of milk and effectiveness and cost of the CS. Because these effects may interact over time, stochastic dynamic models are useful tools to evaluate the effects of HS and the profitability of CS. Several HS intensity scenarios, from 1,000 to 31,000 temperature and humidity index load (THI_Load, units/yr), were simulated in a stochastic dynamic dairy herd simulator, with 3 milk prices (€0.28, €0.32, and €0.36/L) and 2 initial investment costs in fans and sprinklers (€100 and €200/cow). The HS and CS scenarios simulated were modeled as a function of the THI_Load to predict the technical and economic performance in 21 selected locations of the Mediterranean. The THI_Load mean of the 21 selected locations was 12,530 (ranging from 6,908 to 31,424). Heat stress reduced milk yield in a range of 346 to 1,696 L/cow per year, feeding costs in a range of €63 to €266/cow per year, and pregnancy rate in a range of 1.0 to 3.0%/yr and increased culling rates in a range of 5.7 to 16.4%/yr compared with the control scenario. The implementation of CS increased milk yield in a range from 173 to 859 L/cow per year, feeding cost in a range from €26 to €139/cow per year, and pregnancy rate in a range from 0.1 to 1.0%/yr and reduced culling rate in a range from 1.0 to 3.9%/yr compared with HS scenarios. When the THI_Load was ≤6,300, the implementation of CS was never profitable, from 6,300 to 11,000 was dependent on milk price and CS cost, and over 11,000 was consistently profitable. The Δnet margin (€/cow per year) for CS at an initial investment cost of €100/cow ranged from -9 to 239 and at an initial investment cost of €200/cow ranged from -24 to 225. The profitability of CS depends on the THI_Load, milk price, and CS cost.

A pilot study for the isolation of Eimeria spp. oocysts from environmental straw samples in comparison with individual faecal examination of fattening calves

The diagnosis of eimeriosis in calves mainly relies on the presence of diarrhoea and the excretion of Eimeria oocysts in the faeces. Restraining the animals to collect rectal samples for diagnostic purposes is stressful and time-consuming. The aim of this study was to evaluate a method for the quantification of oocysts in environmental barn straw samples. To investigate the recovery rate of the method, straw and Eimeria negative faeces were spiked with Eimeria oocysts in plastic bags and mixed with water and 0.05% Tween 20 (v/v); the liquids were filtered twice through sieves (mesh size 300 and 52 μm), centrifuged and the number of oocysts in the sediment determined using a McMaster counting chamber. A recovery rate of 52.4% (95% confidence interval: 48.2-56.5%) was obtained. In the following, field straw (n = 156) and individual faecal samples (n = 195, also analysed by McMaster counting chambers) were collected on four different farms. Eimeria oocysts were present on all farms in faecal (84/195, 43.1%) and straw samples (119/156, 76.3%). In 37 (23.7%) straw samples, sporulated oocysts were observed, with a sporulation rate ranging from 0 to 40%. Despite high variability between farms and examination days, mean numbers of oocysts in the straw positively correlated with mean numbers of oocysts excreted in the faeces (ρ_Spearman = 0.60). The examination of environmental straw samples may represent an easy-to-perform, non-invasive, inexpensive preliminary diagnostic approach for surveillance of eimeriosis at group level, having the potential to assess the infection pressure.

Comparing thermal conditions inside and outside lactating dairy cattle barns in Canada

The health, longevity, and performance of dairy cattle can be adversely affected by heat stress. This study evaluated the in-barn condition [i.e., temperature, relative humidity, and resulting temperature-humidity index (THI)] at 9 dairy barns with various climates and farm design-management combinations. Hourly and daily indoor and outdoor conditions were compared at each farm, including both mechanically and naturally ventilated barns. On-site conditions were compared with on-farm outdoor conditions, meteorological stations up to 125 km away, and NASA Power data. Canadian dairy cattle face periods of extreme cold and periods of high THI, dependent on the regional climate and season. The northernmost location (53°N) experienced about 75% fewer hours of THI >68 compared with the southernmost location (42°N). Milking parlors had higher THI than the rest of the barn during milking times. The THI conditions inside dairy barns were well correlated with THI conditions measured outside the barns. Naturally ventilated barns with metal roofs and without sprinklers fit a linear relationship (hourly and daily means) with a slope <1, indicating that in-barn THI exceeded outdoor THI more at lower THI and reached equality at higher THI. Mechanically ventilated barns fit nonlinear relationships, which showed the in-barn THI exceeded outdoor THI more at lower THI (e.g., 55-65) and approached equality at higher THI. In-barn THI exceedance was greater in the evening and overnight due to factors such as decreased wind speed and latent heat retention. Eight regression equations were developed (4 hourly, 4 daily) to predict in-barn conditions based on outdoor conditions, considering different barn designs and management systems. Correlations between in-barn and outdoor THI were best when using the on-site weather data from the study, but publicly available weather data from stations within 50 km provided reasonable estimates. Climate stations 75 to 125 km away and NASA Power ensemble data gave poorer fit statistics. For studies involving many dairy barns, the use of NASA Power data with equations for estimating average in-barn conditions in a population is likely appropriate especially when public stations have incomplete data. Results from this study show the importance of adapting recommendation on heat stress to the barn design and guide the selection of appropriate weather data depending on the aim of the study.

Using publicly available weather station data to investigate the effects of heat stress on milk production traits in Canadian Holstein cattle

Heat stress imposes a challenge to the dairy industry, even in northern latitudes. In this study, publicly available weather station data was combined with test-day records for milk, fat, and protein yields to identify the temperature-humidity index (THI) thresholds at which heat load starts affecting milk production traits in Canadian Holstein cows. Production loss per THI unit above the threshold for each trait was estimated. Test-day records from 2010-2019 from 166,749 cows raised in Ontario and from 221,214 cows raised in Quebec were analyzed. Annual economic losses due to heat stress were estimated from the average losses of fat and protein yields based on the annual average of 156 days with THI exceeding the calculated thresholds. Average thresholds for the daily maximum (THI_max) and daily average (THI_avg) THI estimated across lactations in both provinces were THI_max (THI_avg) 68 (64), 57 (50), and 60 (58) for milk, fat, and protein yield, respectively, indicating that milk components are more sensitive to heat stress. An economic loss of about $34.5 million per year was estimated. Our findings contribute to an initial investigation into the impact of heat stress on the Canadian dairy industry and provides a basis for genetic studies on heat tolerance.

Impact of heat stress on embryonic development during first 16 days of gestation in dairy cows

Objective was to elucidate the effects of heat stress (HS) on embryo development during first 16 gestational days (GD) and circulating hormone concentrations on GD-16 in lactating Holstein cows. Cows in HS and control (CON) groups were exposed to temperature humidity index (THI) of ≥ 73 and < 73, respectively, for 3 weeks before the experiment. GD-7 (67 vs 49%) and GD-16 (52 vs. 31%) conception rates following single insemination were greater (P < 0.01) for CON compared with HS cows. Control cows produced more GD-7 transferrable embryos following superovulation compared with HS cows (84.8 vs 53.1%; P < 0.001). Mean (± SEM) length (45.2 ± 10.6 vs. 59.2 ± 9.1 mm) and weight (31.4 ± 4.3 vs. 42.4 ± 6.2 mg) of GD-16 conceptus were greater for CON compared with HS cows (P < 0.05). Control cows yielded more filamentous conceptus (≥ 25 mm) compared with HS cows (71 vs 45%; P < 0.05). Progesterone (2.09-fold) was higher, and cortisol (1.86-fold), prolactin (1.60-fold), substance-P (1.55-fold), Isoprostane-8 (1.34-fold) and prostaglandin F metabolites (1.97-fold) were lower in CON compared with HS cows (P < 0.05). Progesterone positively, and substance-P, isoprostane-8 and the THI negatively were associated with GD-16 conceptus length (P < 0.05). In conclusion, altered hormones concentrations in heat-stressed cows plausibly resulted in lower GD-7 and GD-16 conception rates, fewer GD-7 transferable embryos, and stunted GD-16 conceptus elongation.

Microclimate modeling in naturally ventilated dairy barns during the hot season: Checking the accuracy of forecasts

Monitoring and predicting the microclimate in naturally ventilated barns (NVB) is important given the adverse effects of high summer temperatures on dairy cows in the context of global climate change. The aim of the work was to verify the accuracy of the microclimate forecast in a NVB using linear regression (LR). Our working hypothesis suggested that multiple periodic measurements of air temperature and relative humidity outside and inside the barns at the same time will allow us to build LR models for predicting the temperature-humidity index (THI). This was done not only for a specific dairy barn based on this indicator outside, but also in other dairy barns with a similar design, located in similar weather conditions. The results of the research indicate that the use of LR had a high accuracy of forecasting (93-96%) the THI in NVB of various designs during the summer heat. At the same time, differences were found between traits (air temperature, relative humidity as well as resulting THI) provided by meteorological weather stations and these data measured simultaneously next to the dairy barns. The proposed LR models can be used to predict THI in NVBs of different designs.

Methods to quantify heat stress in ruminants: Current status and future prospects

The physiology of hyperthermia or heat stress in mammals is complex. It is a totally systemic condition that in varying degrees involves all organs, tissues and body fluid compartments. The nature and magnitude of the response is influenced by animal specific characteristics (e.g. age, diet, body condition, gender, reproductive stage), environment and animal management. Given the multifaceted nature of heat stress, and the varied ruminant production systems based in varied geoclimatic zones, it has been difficult to find appropriate measures of heat stress for production ruminants. This has become an urgent challenge as production systems intensify globally in a warming climate. Bioclimatic indices such as the Temperature-Humidity Index (THI) have evolved to incorporate some measure of animal physiology. However, these indices do not have strong relationships with core temperature trajectories and altered respiratory dynamics of animals with excessive heat load. In recent decades, the careful physiology studies of the 1950-80s, have given way to numerous studies trialling a plethora of new technologies and computational approached to measure heat stress. Infrared thermography of body surface temperatures, automated measures of respiration rate and radiotelemetry of internal body temperatures are the most intensively researched. The common goal has been to find the 'holy grail' decision-making threshold or timepoint as to the animal's wellbeing. Are we making any progress?

Critical THI thresholds based on the physiological parameters of lactating dairy cows

The severity of heat stress conditions in high-yielding dairy cows is currently underestimated. The present study aimed to determine the heat load threshold of the temperature-humidity index (THI) on physiological parameters of lactating Holstein-Friesian cows under a continental climatic zone in Germany. Physiological parameter measurements, such as respiration rate (RR), measured hourly, and heart rate (HR) and rectal temperature (RT), both measured twice daily, were performed in a total of 139 multiparous cows on three randomly chosen measurement days per week. In addition, the ambient temperature and relative humidity of the barn were recorded every 5 min to calculate the current THI. The physiological parameter data were linked to the THI, and the heat load thresholds were determined using the broken-stick model. The heat load duration effect of each physiological parameter was obtained by regression analysis. Considering the increases in the physiological parameters, our study provided reliable data to determine heat load thresholds for lactating high-yielding dairy cows in a moderate climatic zone. The heat load threshold could be determined for RR in standing cows (THI = 70) and lying cows (THI = 65) and for HR (THI = 72) and RT (THI = 70) in standing cows. The heat load duration also demonstrated a significant effect on the increases in physiological parameters among dairy cows. In particular, the present study enabled a strategy to be devised to initiate heat mitigation in high-yielding dairy cows when they are exposed to THIs above 65.

Daily rumination time of lactating dairy cows under heat stress conditions

The dairy industry in regions with moderate climates, such as Central Europe, will be increasingly challenged in the future by climate change. The problem of heat stress will especially affect dairy husbandry in naturally ventilated barns (NVB). The approach of the study was to determine a heat stress threshold of the average daily temperature-humidity index (THI) that results in changes in the daily rumination time (RT) of lactating, high-yielding cows. The data set was composed of a high sample size of 183 cows and long-duration measurements of 21240 daily observations over two years from June 2015 to May 2017, which were collected in an NVB in Groβ Kreutz, Germany. The THI was calculated in 5-min intervals by data from several sensors in different positions inside the barn. Additionally, every cow from the herd of an average of 53 cows in the experimental procedure was wearing a neck collar with a Lely Qwes HR system that provided the RT 24 h a day (12 2-h recordings were summarized). The study showed that heat stress also negatively influenced RT in moderate climates. The heat stress threshold of 52 THI was determined by broken-stick regression and indicated changes of RT of lactating dairy cows in Germany. During the experimental period, the heat stress threshold for RT was reached from April to September for up to 720 h per month. The changes in RT to the heat stress threshold will be affected by cows' characteristics. Therefore, we considered several cow-related factors, such as milk yield (MY), lactation number (LN), lactation stage (days in milk, or DIM) and pregnancy stage (P) to better understand cows' individual reactions to heat stress. Multiparous, high-yielding cows in later lactation stages are potentially more strongly affected than other cows.

Bacterial concentrations in bedding and their association with dairy cow hygiene and milk quality

Comparison of bacterial counts (BCs) among common bedding types used for dairy cows, including straw, is needed. There is concern that the microbial content of organic bedding is elevated and presents risks for dairy cow udder health and milk quality. The objectives of this study were to investigate: (1) % DM and BCs (Streptococcus spp., all gram-negatives and specifically Klebsiella spp.) in different types of bedding sampled, and to investigate housing and farm management factors associated with % DM and BCs; (2) if bedding type was associated with hygiene of cow body parts (lower-legs, udder, upper-legs and flank) and housing and management factors associated with hygiene and (3) bedding types associated with higher BCs in cow milk at the farm level and bulk tank milk and management factors that were associated with highest BCs. Seventy farms (44 free-stall and 26 tie-stall) in Ontario, Canada were visited 3 times, 7 days apart from October 2014 to February 2015. At each visit, composite samples of unused and used bedding were collected for % DM determination and bacterial culture. Used bedding samples were collected from the back third of selected stalls. Data were analyzed using multivariable linear mixed models. Bedding classification for each farm were: new sand (n = 12), straw and other dry forage (n = 33), wood products (shavings, sawdust; n = 17) and recycled manure solids (RMSs)-compost, digestate (n = 8). In used bedding, across all bedding samples, sand was driest, compared to straw and wood, and RMS; higher % DM was associated with lower Streptococcus spp. count. Streptococcus spp. and all Gram-negative bacteria counts increased with increasing days since additional bedding was added. Gram-negative bacteria counts in used bedding varied with type: RMS = 16.3 ln colony-forming units (cfu)/mL, straw = 13.8 ln cfu/mL, new sand = 13.5 ln cfu/mL, and wood = 10.3 ln cfu/mL. Klebsiella spp. counts in used bedding were lower for wood products (5.9 ln cfu/mL) compared to all other bedding types. Mean cow SCC tended to be higher on farms with narrower stalls. Farms with mattress-based stalls had a higher prevalence of cows with dirty udders compared to those using a deep bedding system (often inorganic sand). Wider stalls were associated with lower bulk milk bacteria count. Lower % DM of used bedding was associated with higher bulk milk bacteria count. In conclusion, bedding management may have a profound impact on milk quality, bacterial concentrations in the bedding substrates, and cow hygiene.

The relationship between the number of consecutive days with heat stress and milk production of Holstein dairy cows raised in a humid continental climate

Heat stress is known to affect performance of dairy cows experiencing prolonged periods of high temperature and relative humidity. Less is known about its effects in cooler climates. The goals of the present study were to determine the prevalence of days susceptible to cause mild heat stress in dairy cows living in a humid continental climate and to investigate the relationship between the number of consecutive days of mild heat stress and milk, fat, protein, and lactose production. A 6-yr data set (2010-2015) containing 606,031 milk analysis records for 34,360 Holstein dairy cows at different parities was matched with the corresponding daily maximum temperature-humidity index. Exposure to heat stress conditions was divided into 5 categories corresponding to 0, 1 to 2, 3 to 4, 5 to 6, and 7 to 8 consecutive days before milk test date. On average, cows were exposed to heat stress conditions for 135.8 ± 5.9 d/yr in Southwest Quebec and 95.3 ± 10.2 d/yr in Eastern Quebec. Cows experiencing heat stress conditions produced on average less fat, protein, and energy-corrected milk and lower fat and protein concentrations. The decrease in milk fat reached 6% for category 7 to 8 exposure of cows in parity 3 or more. The association between exposure category and milk yield and lactose yield and concentration was weak. Heat stress lowered milk fat and protein production but had little effect on milk volume output. Further research is necessary to better understand the mechanism underlying the effects of sporadic low- to medium-intensity heat stress on dairy productivity.

Short communication: Summer on-farm environmental condition assessments in Québec tiestall farms and adaptation of temperature-humidity index calculated with local meteorological data

Temperature-humidity index (THI) calculation following the equation developed by the National Research Council (A Guide to Environmental Research on Animals, 1971) requires ambient temperature (AT) and relative humidity (RH). Those data are widely and readily available at local meteorological stations. However, studies showed that using average AT and RH retrieved from the closest stations is not appropriate for estimating on-farm conditions. The present objectives were (1) to study summer on-farm environmental conditions, (2) to explore the relationship between summer THI calculated with on-farm data and summer THI calculated with local weather station data, and (3) to verify whether THI calculated with summer meteorological station data could be adapted to better represent summer on-farm conditions. Six tiestall dairy farms located in 2 regions of the province of Québec [Eastern Québec (EQ) and Southwestern Québec (SWQ)] were enrolled in this study. Within-barn conditions were monitored using 3 remote data loggers from August 2016 through August 2017. Two loggers were installed inside at varying distances relative to the ventilation inlet (L1: closest to inlet; L2: farthest from inlet) and a third was installed just outside of the barn (L3). Values retrieved from each logger and the closest local meteorological station were used to calculate daily THI according to the National Research Council formula and were ultimately compared. Our results showed that THI varied within the barn depending on the proximity relative to the inlet because THI measured by L1 was lower than THI measured by L2 in both regions. Moreover, our results showed that in both regions AT measured on-farm was consistently higher than AT measured at the weather station. The opposite was observed with RH, as it was significantly lower on-farm in EQ and numerically lower in SWQ compared with RH extracted from weather stations. Overall, this led to THI being lower by 4.6 and 3.7 units at the weather stations compared with within-barn conditions for EQ and SWQ farms, respectively. Hence, using local meteorological station data to estimate on-farm conditions would lead to an underestimation of heat stress level in dairy cows. Adapting THI calculations by including daily maximum AT and minimum RH retrieved from the local weather station instead of their average counterparts led to a better estimation of within-barn conditions. However, the difference between THI measured on-farm and the adapted THI calculated with weather station data remained significant. Although the adaption made to THI allowed for a closer relation to on-farm conditions, THI calculated with weather station data should only be used to assess heat stress level in dairy cows when heat stress thresholds are adapted for such data.

Dados de estação meteorológica oficial subestimam o estresse por calor em bovinos leiteiros criados em ambiente tropical

RESUMO Determinaram-se os valores de temperatura do ar, umidade relativa e índice de temperatura e umidade (ITU) de uma propriedade rural de produção de leite a pasto e da estação meteorológica oficial mais próxima, confrontando-os. Na fazenda, as leituras dos dados foram registradas por uma estação meteorológica automática, a cada cinco minutos, de fevereiro de 2015 a setembro de 2016. Depois, calcularam-se a média por hora e o ITU horário. Selecionaram-se os valores diários mínimo, médio e máximo. O mesmo foi feito com os dados da estação meteorológica oficial, que foram horários. As temperaturas mínima e média na estação meteorológica foram maiores que na fazenda durante todo o período experimental e em 16 meses, respectivamente. A temperatura máxima da propriedade rural foi maior que a da estação em seis meses. Já a umidade relativa mínima, a média e a máxima da estação meteorológica foram inferiores às da fazenda. O ITU mínimo foi maior na estação oficial e o ITU máximo superior na fazenda em todos os meses. Por fim, o número de dias com um ITU máximo igual ou superior ao ITU crítico foi maior na fazenda. Assim, dados da estação meteorológica oficial subestimam o estresse por calor.

Thermodynamics of standing and lying behavior in lactating dairy cows in freestall and parlor holding pens during conditions of heat stress

Heat load is a challenge for high-producing dairy cows, with adverse consequences on production, reproduction, and welfare. The objectives of this observational study in 2 commercial dairy herds were to determine the effects of environmental heat stress on standing and lying behavior, to monitor the changes in core body temperature (CBT) of cows during lying and standing bouts, and to compare changes in CBT during standing bouts in freestall pens versus standing in holding pens. High-producing cows were selected for data collection over a period of 6 d of increasing heat stress during a heat wave to which they were not acclimated. A total of 20 cows were fitted with leg accelerometers that recorded lying behavior and with vaginal temperature loggers that recorded CBT. These data were recorded at 30-s intervals. Time in the parlor holding pen was calculated from automated parlor software that recorded milking unit attachment and removal times. Mean daily temperature-humidity index in the pens increased from 68.5 to 79.0 during the 6-d trial, whereas mean daily lying time decreased from 9.5 to 6.2 h/d. The mean number of lying bouts per day remained similar at 11.1 to 12.2, but duration of lying bouts decreased from a high of 49.7 min on the coolest day to 32.8 min on the hottest day. During lying bouts, CBT increased at a mean rate of 0.50°C/h. In contrast, CBT changed at a mean rate of -0.25°C/h when standing in the freestall pens and only -0.09°C/h when standing in the milking-center holding pens. Explanatory models for the CBT at which cows ended either standing or lying bouts were derived from 6 selected lying bouts and 3 selected standing bouts for each cow on each day. The CBT at which a cow ended a lying bout was positively related to CBT and temperature-humidity index at the start of the bout, bout duration, and rate of CBT change during the bout. The CBT at which a cow ended a standing bout was negatively related to bout duration and positively related to start CBT, start temperature-humidity index, and rate of CBT change. Insights into the thermodynamics of standing and lying behavior in dairy cows during periods of heat stress provided by this study may contribute to the development of more effective strategies to mitigate heat load in dairy cattle.

Effects of the daily heat load duration exceeding determined heat load thresholds on activity traits of lactating dairy cows

In recent years, the problem of the welfare and heat load of dairy cows has become increasingly important in moderate climate zones. The objective of the present study was to determine heat load thresholds of average daily temperature-humidity index (THI) that lead to changes in different activity traits of lactating high-yielding dairy cows. Furthermore, we studied how the activity of the cows to heat load was influenced by the daily heat load duration which exceeded the heat load we had determined as threshold in our experiments. The study was conducted from June 2015 to May 2017 in a naturally ventilated dairy barn in Groß Kreutz, Germany. The climate was measured at several positions inside the barn, and the average THI was calculated every 10 min. The THI was used to define the dairy cows' heat load exposure. In addition, the activity of the cows was measured by pedometers, and different activity traits were recorded in the functional groups "resting behavior" and "locomotion behavior". The heat load thresholds determined by broken-stick models were 47 THI (standing bout duration, number of steps) as well as 67 THI (total lying/standing time, number of lying/standing bouts, lying bout duration). During the experimental period, the most reliable heat load threshold of 67 THI was exceeded from May to September for up to 480 h per month. The analysis model of each activity trait included the effect of the average daily THI values below and above the determined heat load threshold and the effect of the daily heat load duration exceeding the determined heat load threshold. The total lying/standing time and the number of steps showed significant changes related to increasing daily heat load duration. The effect of the daily heat load duration additionally intensified the effect of the average daily THI.

Spatially explicit estimation of heat stress-related impacts of climate change on the milk production of dairy cows in the United Kingdom

Dairy farming is one the most important sectors of United Kingdom (UK) agriculture. It faces major challenges due to climate change, which will have direct impacts on dairy cows as a result of heat stress. In the absence of adaptations, this could potentially lead to considerable milk loss. Using an 11-member climate projection ensemble, as well as an ensemble of 18 milk loss estimation methods, temporal changes in milk production of UK dairy cows were estimated for the 21st century at a 25 km resolution in a spatially-explicit way. While increases in UK temperatures are projected to lead to relatively low average annual milk losses, even for southern UK regions (<180 kg/cow), the ‘hottest’ 25×25 km grid cell in the hottest year in the 2090s, showed an annual milk loss exceeding 1300 kg/cow. This figure represents approximately 17% of the potential milk production of today’s average cow. Despite the potential considerable inter-annual variability of annual milk loss, as well as the large differences between the climate projections, the variety of calculation methods is likely to introduce even greater uncertainty into milk loss estimations. To address this issue, a novel, more biologically-appropriate mechanism of estimating milk loss is proposed that provides more realistic future projections. We conclude that South West England is the region most vulnerable to climate change economically, because it is characterised by a high dairy herd density and therefore potentially high heat stress-related milk loss. In the absence of mitigation measures, estimated heat stress-related annual income loss for this region by the end of this century may reach £13.4M in average years and £33.8M in extreme years.

Causes of declining fertility in dairy cows during the warm season

In the Northern Hemisphere, from June to September and in the Southern Hemisphere from December to March, there are periods of reduced fertility (sub-fertility) in dairy cows that are described as summer infertility. Several factors contribute to sub-fertility during this time, such as ambient temperature, humidity and photoperiod. During the warm season there is a reduction in feed intake that may compromise the energy balance of the cow and/or induce an imbalance in the activity of the hypothalamo-hypophyseal-ovarian axis. These factors reduce the reproductive performance of the cow and compromise the quality of oocytes, embryos and corpora lutea. This paper reviews current knowledge on the metabolic and endocrine mechanisms that induce summer infertility and describe their effects on follicle, oocyte and embryo development in dairy cows.

Measurement of heat stress conditions at cow level and comparison to climate conditions at stationary locations inside a dairy barn

The objectives of this study were to examine heat stress conditions at cow level and to investigate the relationship to the climate conditions at 5 different stationary locations inside a dairy barn. In addition, we compared the climate conditions at cow level between primiparous and multiparous cows for a period of 1 week after regrouping. The temperature-humidity index (THI) differed significantly between all stationary loggers. The lowest THI was measured at the window logger in the experimental stall and the highest THI was measured at the central logger in the experimental stall. The THI at the mobile cow loggers was 2·33 THI points higher than at the stationary loggers. Furthermore, the mean daily THI was higher at the mobile cow loggers than at the stationary loggers on all experimental days. The THI in the experimental pen was 0·44 THI points lower when the experimental cow group was located inside the milking parlour. The THI measured at the mobile cow loggers was 1·63 THI points higher when the experimental cow group was located inside the milking parlour. However, there was no significant difference for all climate variables between primiparous and multiparous cows. These results indicate, there is a wide range of climate conditions inside a dairy barn and especially areas with a great distance to a fresh air supply have an increased risk for the occurrence of heat stress conditions. Furthermore, the heat stress conditions are even higher at cow level and cows not only influence their climatic environment, but also generate microclimates within different locations inside the barn. Therefore climate conditions should be obtained at cow level to evaluate the heat stress conditions that dairy cows are actually exposed to.

Melatonin modulates tonic immobility and vigilance behavioural responses of broiler chickens to lighting regimens during the hot-dry season

Experiments were conducted with the aim of determining the influence of melatonin administration on vigilance and tonic immobility (TI) responses of Marshall broiler chickens. The broiler chickens were reared on different lighting regimens and subjected to heat stress during the hot-dry season. Simple random sampling was used to assign 300 broiler chicks into three groups, comprising 100 broiler chicks each. Group I (12D:12L cycle) was raised under natural photoperiod of 12-h light and 12-h darkness, without melatonin supplementation. Group II (CL) was kept under 24-h continuous lighting, without melatonin administration. Group III (CL+MEL) was raised under 24-h continuous lighting; with melatonin supplementation at 0.5mg/kg per os, via drinking water using a syringe. Beginning from day-old, broiler chickens in group III were individually administered with melatonin once daily for 8weeks at 17:00h. TI was induced by manual restraint, and vigilance elicited at self-righting graded for three days, two weeks apart, in 15 labeled broiler chickens from each of the three groups; at 06:00h, 13:00h and 18:00h, starting from week 4-8. Each broiler chicken was laid on its back in a U-shaped cradle, covered with cloth. Thermal microenvironment parameters of dry bulb temperature (DBT) and relative humidity (RH) were recorded at the experimental site, concurrently during the vigilance and TI tests. Inside the broiler chickens' house, the weekly temperature-humidity index (THI) was lowest at week 4 of the study, with the value of 48.60±0.08°C. At week 4, the relationship between the THI and TI induction attempts was stronger in 12D:12L cycle (r=0.589, P<0.001) than CL (r=0.264, P>0.05) or CL+MEL (r=0.096, P>0.05) broiler chickens. This indicated that the broiler chickens on 12D:12L cycle were more active compared to their melatonin-treated counterparts, apparently due to adverse effects of high DBT and high RH on the broiler chickens during the hot-dry season. The highest numbers of TI induction trial attempts were recorded at 13:00h in 12D:12L cycle and CL groups (2.13±0.34 and 2.15±0.22, respectively), when the broiler chickens were at week 8. The overall mean values of induction trial attempts differed significantly (P<0.0001) between the groups; with the lowest mean values of 1.22±0.4 recorded in CL+MEL broiler chickens. At day 42, the lowest mean TI duration of 101.87±10.24s in the CL group, recorded at 06:00h rose (P<0.001) to 184.07±23.69s at 13:00h. The overall mean duration of TI differed significantly (P<0.0001) again between the groups; with the highest mean duration of 167.82±8.35s, recorded in CL+MEL broiler chickens administered with melatonin. The overall mean vigilance behavioural ranking values of 1.85+0.07 and 1.70+0.08, obtained in 12D:12L cycle and CL broiler chickens, respectively were higher (P<0.0001) than the value of 1.44+0.05 recorded in melatonin-treated broiler chickens. The results indicated that broiler chickens belonging to both 12D:12L cycle and CL groups were more emotional, fearful or anxious, compared to CL+MEL broiler chickens. It was concluded that melatonin administration elicits boldness and confidence by suppressing freezing behaviour in broiler chickens, and it may improve their welfare and productivity.

Mapping rural community and dairy cow heat stress in Southern Ontario: A common geographic pattern from 2010 to 2012

Climate change has increased the occurrence of heat waves, causing heat stress among humans and livestock, with potentially fatal consequences. Heat stress maps provide information about related health risks and insight for control strategies. Weather data were collected throughout Southern Ontario, and the heat stress index (HSI) was estimated for 2010-2012. Geostatistical kriging was applied to map heat stress, heat waves, and control periods. Average HSI for each period ranged from 55 to 78 during control periods, and from 65 to 84 during heat waves, surpassing levels where morbidity is known to increase substantially. Heat stress followed a temporally consistent geographic pattern. HSI maps indicate high-risk areas for heat-related illness and indicate areas where agriculture and human health may be at increased risk in future.

Short communication: Effect of heat stress on nonreturn rate of Italian Holstein cows

The data set consisted of 1,016,856 inseminations of 191,012 first, second, and third parity Holstein cows from 484 farms. Data were collected from year 2001 through 2007 and included meteorological data from 35 weather stations. Nonreturn rate at 56 d after first insemination (NR56) was considered. A logit model was used to estimate the effect of temperature-humidity index (THI) on reproduction across parities. Then, least squares means were used to detect the THI breakpoints using a 2-phase linear regression procedure. Finally, a multiple-trait threshold model was used to estimate variance components for NR56 in first and second parity cows. A dummy regression variable (t) was used to estimate NR56 decline due to heat stress. The NR56, both for first and second parity cows, was significantly (unfavorable) affected by THI from 4 d before 5 d after the insemination date. Additive genetic variances for NR56 increased from first to second parity both for general and heat stress effect. Genetic correlations between general and heat stress effects were -0.31 for first parity and -0.45 for second parity cows.

Invited review: Influence of climatic conditions on the development, performance, and health of calves

The objective of this review is to provide the reader with an overview of thermoregulatory mechanisms and the influence of climatic conditions in different housing systems on the development, performance, and health of calves. Thermic stress is observed in association with extreme temperatures and large temperature variations, but other variables such as relative humidity and wind speed can also contribute to thermic stress. Thermoregulation in calves is similar to that in adult cattle, but especially dystocial calves are more prone to heat loss. Heat or cold stress results in direct economic losses because of increased calf mortality and morbidity, as well as indirect costs caused by reduced weight gain, performance, and long-term survival. The climatic conditions in a variety of housing systems, associated health problems, and strategies to mitigate thermic stress are discussed in this review. The goal of housing is to alleviate the effect of climate on calves and provide a microclimate. Adequate ventilation with fresh air is essential to reduce respiratory disease. Common practices such as raising calves in individual outdoor enclosures have been challenged lately. Recent research seeks to evaluate the suitability of group housing under practical, economic, and animal welfare considerations. Limited results for reducing thermic stress can be achieved by simple measures such as shades or shelter, but additional heat or cold stress relieving strategies can be required depending on the housing system.

Heat stress related dairy cow mortality during heat waves and control periods in rural Southern Ontario from 2010-2012

Background

Heat stress is a physiological response to extreme environmental heat such as heat waves. Heat stress can result in mortality in dairy cows when extreme heat is both rapidly changing and has a long duration. As a result of climate change, heat waves, which are defined as 3 days of temperatures of 32 °C or above, are an increasingly frequent extreme weather phenomenon in Southern Ontario. Heat waves are increasing the risk for on-farm dairy cow mortality in Southern Ontario. Heat stress indices (HSIs) are generally based on temperature and humidity and provide a relative measure of discomfort which can be used to predict increased risk of on-farm dairy cow mortality. In what follows, the heat stress distribution was described over space and presented with maps. Similarly, on-farm mortality was described and mapped. The goal of this study was to demonstrate that heat waves and related HSI increases during 2010–2012 were associated with increased on-farm dairy cow mortality in Southern Ontario.

Mortality records and farm locations for all farms registered in the CanWest Dairy Herd Improvement Program in Southern Ontario were retrieved for 3 heat waves and 6 three-day control periods from 2010 to 2012. A random sample of controls (2:1) was taken from the data set to create a risk-based hybrid design. On-farm heat stress was estimated using data from 37 weather stations and subsequently interpolated across Southern Ontario by geostatistical kriging. A Poisson regression model was applied to assess the on-farm mortality in relation to varying levels of the HSI.

Results

For every one unit increase in HSI the on-farm mortality rate across Southern Ontario increases by 1.03 times (CI_95% (IRR) = (1.025,1.035); p = ≤ 0.001). With a typical 8.6 unit increase in HSI from a control period to a heat wave, mortality rates are predicted to increase by 1.27 times.

Conclusions

Southern Ontario was affected by heat waves, as demonstrated by high levels of heat stress and increased on-farm mortality. Farmers should be aware of these risks, and informed of appropriate methods to mitigate such risks.