This study conducted a retrospective analysis of historical Meat Standard Australia (MSA) carcass data in combination with Bureau of Meteorology (BOM) weather data, to evaluate the relationship between climatic conditions prior to feedlot departure on the incidence of dark cutting grain-fed beef. Data records for 2,795,754 carcasses from 17 commercial feedlots over a 6-year period were evaluated within this study. Carcasses were consigned to 16 abattoirs. Weather data from BOM were recorded at 30-min intervals and were obtained from weather stations with the closest proximity to each feedlot. These data were used to calculate the Temperature Humidity Index (THI). Climatic data were amalgamated into daily observations and a series of predictors including ambient temperature (T_A, °C), relative humidity (RH, %), wind speed (WS, m/s), rainfall (mm) and THI. In addition, lag interactions from 24 h out to 28 days prior to exiting the feedlot were generated. The incidence of dark cutting was determined as percentage per cohort with an ultimate pH > 5.7. Data were analysed using three models: model 1 included feedlot, abattoir, hormone growth promotant status and sex as fixed effects. Model 2 incorporated the fixed effects within model 1 and minimum, maximum and standard deviation (SD) of T_A and RH, daily range in T_A, average WS and rainfall as random effects. Model 3 incorporated minimum, maximum, range and SD of THI, average WS and rainfall as random effects in addition to the fixed effects of model 1. The incidence of dark cutting within feedlot had a 10.1% range in estimated means with the lowest incidence was observed at feedlot 17 (0%) and highest incidence at feedlot 10 (10.1%). The inclusion of the climatic variables in model 2 and model 3 accounted for an additional 0.1 to 0.2% of the incidence of dark cutting carcasses. Higher maximum T_A, RH and THI in the 3 to 28 days prior to consignment were all associated with an increased incidence of dark cutting (P < 0.05), but not in the 48 h preceding consignment (P > 0.05). Low minimum T_A and low THI were also associated with an increase the incidence of dark cutting across all lag periods (P < 0.05). Increased variation in THI and T_A in the 48 h prior to consignment increased dark cutting (P < 0.05) while increased standard deviation (SD) of temperature and THI range also increased dark cutting in the 14 and 28 day prior to feedlot exit (P < 0.05). Smaller minimum ranges in TA in the 28 days prior to consignment also reduced dark cutting (P < 0.05). Climatic conditions accounted for a further 0.1 to 0.2% of the incidence of dark cutting, whereas animal management factors, feedlot and abattoir were able to account for 21% of dark cutting. These data suggest that climatic conditions appear to have an inherent role in the incidence of dark cutting, albeit a small impact. Regardless, understanding the influence of climatic conditions on dark cutting allows for the implementation of management strategies within the supply chain to further reduce the impact of climatic conditions on grain-fed cattle.

Context. Annually, millions of sheep are exported from Australia to the Middle East, typically during the southern hemisphere winter to the northern hemisphere summer. During these voyages, sheep can be exposed to relatively rapid changes in ambient conditions within a short period of time (≤29 days); therefore, excessive heat load concerns can arise.

Aims. The aim of this study was to define the responses of sheep to incremental heat load under simulated live export conditions. The study herein describes (1) the heat load imposed, and (2) the effect of this heat load on the growth, performance and behavioural responses of sheep during periods of incremental heat load.

Methods. A total of 144 Merino wethers (44.02 ± 0.32 kg) were included in a 29-day climate controlled study using two cohorts of 72 sheep (n = 2), exposed to two treatments: (1) thermoneutral and (2) hot (HOT). Ambient temperature (°C) and relative humidity (%) for the HOT treatment were modelled from live export voyages from Australia to the Middle East in July. Climatic conditions within the climate control chambers were recorded at 10-min intervals, then used to calculate a temperature humidity index. Sheep posture, rumination, eating, drinking and demeanour (calm, agitated or depressed) were observed four times daily at 3-h intervals between 0800 hours and 1700 hours. Feed intake was recorded daily and water intake was measured using an automated meter. Sheep were weighed on Day 0 and then at 7-day intervals. Sheep were weighed at slaughter and carcass weights were obtained, these data were used to determine carcass dressing percentage. Data were analysed using a repeated measures model, with a compound symmetry covariance structure.

Key results. Climatic conditions in the HOT treatment increased incrementally between Day 1 (temperature humidity index ≥19) and Day 29 (temperature humidity index ≤34.7). Behaviour, feed intake, average daily gain (g/day), carcass weight (kg) and dressing percentage were not influenced by treatment (P > 0.05). Sheep in the HOT treatment group showed a 137% increase in water intake (P < 0.01) and on average consumed 2.15 L/sheep.day, whereas the thermoneutral group consumed 1.67 L/sheep.day.

Conclusions. These results suggest that these sheep were capable of maintaining feed intake and growth despite exposure to heat load, albeit with a 137% increase in water intake.

Implications. These results highlight the resilience of the Australian Merino genotype, as these sheep were capable of maintaining feed intake and growth during exposure to heat load. As the climatic conditions in this study were modelled based on typical live export vessel conditions, these results may suggest that the climatic conditions experienced by sheep during voyages may not be as critical as previously thought.

The impact of cold stress on feedlot cattle has received limited investigation in temperate climates. However, cold stress has been found to impact cattle welfare and production in temperate climatic conditions, where ambient temperature (T_A), precipitation, relative humidity (RH), wind speed (WS) and solar radiation (SR) all influencing apparent temperature. While there are many indices to quantify cold stress in cattle, there are limited indices that directly relate to cattle and account for all the interactions between climatic variables. This makes cold stress difficult to quantify, with on-cattle measures such as core body temperature and shivering difficult metrics to obtain in feedlot cattle. Moreover, individual cattle will react differently to cold conditions based on their production, age, sex, coat characteristics (colour and type), breed and nutrition. While cold stress can be difficult to measure, the production status, behavioural and physiological effects of cold stress have been identified, but generally under what could be considered as extreme cold stress events. Similarly, while mitigation strategies such as shelter, bedding and windbreaks have been investigated, limited information is available surrounding their usefulness in temperate climates. Further research is needed to fully investigate the effects of cold stress and how to mitigate those effects in feedlot cattle under conditions, such as those found in Australia.

Numerous climatic indices have been utilized to predict the efect of hot, and cold, climatic conditions on animal production and welfare. To date, the dairy industry has relied extensively on the Temperature Humidity Index (THI) to predict adverse climatic conditions" however, neither solar radiation nor air movement is accounted for in the THI equation. The Dairy Heat Load Index (DHLI) was initially developed as an alternative climate index. In its current format, the DHLI does not account for the efects of heat load mitigation strategies, such as shade, which decreases the negative efects of hot climatic conditions on lactating cows. Therefore, this experiment aimed to determine the efectiveness of the DHLI as a predictor of heat load responses in both shaded and unshaded cows, as compared with the THI. Forty lactating Holstein Friesian (n=40) cows were selected and paired based on live weight, milk yield, and days in milk. One cow from each pair was randomly allocated to one of two treatments: shaded (n=20) or unshaded (n=20). Cows were given 7 days to acclimate prior to the commencement of data collection. After 28 days, cows were transitioned into the alternate treatment in a crossover design and given 7 days to acclimate prior to data collection. Behavioral observations (0800, 1200, 1400, and 1800 h daily), daily milk yield (kg), milk composition (various days), and vaginal temperature (T_VAG, °C" 5 pairs/week, over a 4-week rotation) were recorded. Overall, data from this experiment indicated that the DHLI was a better predictor of standing and feeding behaviors in unshaded cows and drinking behaviors in shaded cows. Conversely, the THI was a better predictor of standing behavior and shade usage in shaded cows. Furthermore, the THI was a better predictor of mean panting score (MPS) in shaded cows, whereas the DHLI performed better in unshaded cows. Additionally the DHLI was a better predictor of T_VAG in these cows. Finally, when evaluating the 7-day average of each climatic index, the DHLI was a better predictor of change in milk yield. Incorporation of additional animal and management factors is required if the DHLI is to become an efective heat load management tool.

We would also like to take this opportunity to formally introduce ourselves as the 2020 to 2023 SNP executive committee: Daniel Vecellio, Yuliya Dzyuban and Angela Lees, as your SNP secretary, communications director and chair. On behalf of the SNP, we would like to take this opportunity to sincerely thank Hamed Mehdipoor for leading the SNP group throughout the previous triennium (2017–2020).

It has been well-established that dark cutting (DC) is a multifactorial issue that is associated with numerous animal and management factors. However, there is limited understanding of the feedlot-based factors that contribute to the influence of DC. The aim of this study was to evaluate the effect of climate, animal, and feedlot factors on the incidence of pH non-compliance in Australian grain-fed cattle. For this study, feedlot and abattoir records from 142,228 individual cattle over a 1-year period were investigated. These data incorporated records from seven feedlots that consigned cattle to three abattoirs. The average incidence of DC in these carcasses was 2.8%. The production factors that were associated with increased risk of DC included feedlot, sex, hormone growth promotants (HGP), cattle health, and days on feed (DOF). Additionally, DC also increased by reduced solar radiation (SR, W/m² ), lower wind speeds (WS, m/s), increased ambient temperature (T_A, ◦C), higher rainfall, a higher average temperature–humidity index (THI), and increased duration of time above heat-load-index threshold of 86 (HLI ≥ 86) during the 7 days prior to feedlot departure. This study identified the feedlot factors that increase the risk of DC from a feedlot-management perspective.

Context. Approximately 2 million sheep are exported from Australia on live export voyages annually. As voyages travel from a southern hemisphere winter to a northern hemisphere summer, production and welfare issues associated with excessive heat load may arise.
Aims. The aim of this study was to evaluate the responses of sheep to incremental heat load under simulated live export conditions, specifically the influence of heat load on the metabolic and inflammatory status of sheep.

Methods. A total of 144 Merino wethers (44.02 ± 0.32 kg) were used in a 29-day climate controlled study using two cohorts of 72 sheep (n = 2), exposed to two treatments: (1) thermoneutral, and (2) hot. Sheep in the hot treatment were exposed to heat load simulated from live export voyages from Australia to the Middle East. Blood samples were collected from all sheep (n = 144) on Day 1, then at 7-day intervals (n = 5) for the duration of each 29-day period. Blood samples were analysed to determine the cytokine, biochemistry and haematology (data not presented here) profiles. Cytokine and biochemical profiles were analysed using a repeated measures model assuming a compound symmetry covariance. The model fitted included terms for cohort and treatment (hot, thermoneutral), and a term for sample collection day (day) and a treatment × day interaction. The subject factor corresponded to the cohort × treatment combinations.

Key results. There were no consistent trends in plasma cytokine and biochemical profiles. Bicarbonate was the only parameter that was influenced by cohort (P = 0.0035), treatment (P = 0.0025), collection (P = 0.0001) and treatment × collection (P = 0.0025). Furthermore, interleukin-6 and glutamate dehydrogenase were the only parameters that were not influenced by cohort (P > 0.295), treatment (P = 0.2567), collection (P > 0.06) or treatment × collection (P = 0.34).

Conclusions. Overall, these data highlight that the metabolic and inflammatory status of sheep exposed to incremental heat load, during a simulated live export voyage from a southern hemisphere winter to a northern hemisphere summer, were not markedly altered.

Implications. These results provide a preliminary evaluation of the inflammatory and metabolic status of sheep on arrival in the Middle East.

Dark cutting beef is defined by Meat Standards Australia (MSA) as carcasses that have an ultimate pH (pH_u) > 5.70 when measured at grading. Dark cutting beef is associated with deteriorated meat quality, thus beef producers are generally penalised by abattoirs to compensate for reduced saleable quality product. Non-compliant Meat Standards Australia beef, based on pH, has been estimated to cost the Australian beef industry approximately A$55 million per year and the estimated cost to beef producers is approximately A$0.50 per kg carcass weight or A$7.09 for every carcass graded in the Meat Standards Australia system.

Dark cutting (DC) is a complex multifactorial problem that is influenced by nutrition and preslaughter factors which induce stress and exercise and increase muscle glycogenolysis. The condition is generally attributed to low muscle glycogen stores at slaughter, which is either a function of insufficient glycogenesis on farm or too much glycogenolysis during the preslaughter period due to exercise or stress.

The 2015 Meat Standards Australia Australian Beef Quality audit showed the incidence of dark cutting in grain fed beef was between 1.5% and 2.5% with a peak incidence of 2.5% in March. Australian feedlot producers have anecdotally suggested there is an increased incidence of dark cutting during the summer months. Cattle under heat stress have higher respiration rates and panting to induce evaporative cooling, and have a reduced feed intake. The lowered nutritional intake combined with increased levels of epinephrine (adrenaline) and catecholamine expression during heat stress decrease glycogenesis and stimulate glycogen mobilisation. However, the influence of environmental conditions and/or the duration of exposure to these hot conditions on the incidence of dark cutting had not been established. The overarching objective of this research was to establish whether there was an association between environmental conditions and the incidence of dark cutting in grain fed cattle. This thesis is comprised of four experimental chapters examining the seasonality of dark cutting, a retrospective analysis of historical MSA grading data, plus an in depth examination of feedlot and processor factors affecting the incidence of DC.

The first experiment investigated if there was any inherent impact of seasonality on the incidence of dark cutting in Australian grain fed beef, using a Meat Standards Australia carcass data set. Carcasses were classified as dark cutting when pH measured at grading was > 5.70 in the rib eye muscle (longissimus thoracis et lumborum) of the chilled carcass at the quartering site approximately 12–24 hours post-mortem. Utilizing data from 2,005,925 Meat Standards Australia carcasses, which were supplied from 12 feedlots and sent to 17 different abattoirs over 5 years were analysed. Carcass data were categorised into five groups based on the location of feedlots across geographical regions. These data were then analysed using a seasonal and trend decomposition using locally estimated scatterplot smoothing (loess time series analysis) to establish if a seasonal trend in dark cutting exists in Australian grain fed carcasses. Results show that the majority of feedlots had seasonality scores below 0.3 suggesting that dark cutting in grain fed beef has either low or no seasonality. Three feedlots had slightly higher seasonality scores (0.3 to 0.4), however these are still considered to be low scores. These results highlight there is limited evidence of a seasonality effect on dark cutting in the carcasses evaluated in this study. However, the presence of seasonality scoring above 0.3 for three participating feedlots, highlighted the need for a deeper understanding of the impacts of climatic conditions and specific weather events at the feedlot on the incidence dark cutting.

The second experiment evaluated the relationship between climatic conditions prior to feedlot departure on the incidence of dark cutting in grain fed beef by combining historical Meat Standards Australia carcass data with Bureau of Meteorology weather data. Data records for 2,795,754 carcasses from 17 commercial feedlots sent to 16 abattoirs over 6 years were evaluated in this study. Weather data recorded at 30 minute intervals were obtained from the weather station closest to each feedlot. Climatic data were amalgamated into daily observations and a series of predictors including ambient temperature, relative humidity, wind speed and direction, rainfall, solar radiation and temperature humidity index were included in the analysis. Lag interactions from 24 hours out to 28 days before leaving the feedlot were generated. The incidence of dark cutting was determined as percentage per cohort with an ultimate pH > 5.7. The data were analysed using three separate models. Model 1 included feedlot, abattoir, hormone growth promotants status and sex as fixed effects. Model 2 incorporated the fixed effects within Model 1 and minimum, maximum and standard deviation of ambient temperature and relative humidity, daily range in ambient temperature, average wind speed and rainfall as covariates. Model 3 incorporated minimum, maximum, range and standard deviation of temperature humidity index, average wind speed and rainfall as covariates in addition to the fixed effects of Model 1. The results showed that higher maximum ambient temperature, relative humidity and temperature humidity index in the 3 to 28 days before consignment were all associated with an increased incidence of dark cutting (P < 0.05), but not in the 48 hours before consignment (P > 0.05). Lower minimum ambient temperature and lower temperature humidity index values were also associated with an increase in the incidence of dark cutting across all lag periods (P < 0.05). Increased variation in the temperature humidity index and ambient temperature in the 48 hours before consignment increased dark cutting (P < 0.05) while increased standard deviation of temperature and temperature humidity index range also increased dark cutting in the 14 and 28 day before feedlot exit (P < 0.05). Smaller minimum ranges in ambient temperature in the 28 days before consignment also reduced dark cutting (P < 0.05). Even though many different climatic conditions impacted the incidence of dark cutting, they only accounted for a further 0.1% to 0.2% of variance in the incidence of dark cutting. In contrast, the feedlot and abattoir animal management factors included in the models accounted for 21% of the variation in dark cutting. This analysis showed the major causes of dark cutting in lot fed cattle were driven by factors within the feedlot and abattoir which needed to be quantified further.

The supply chain experiment analysed the significance of feedlot and abattoir factors including carcass traits, lairage time, weather conditions during lairage and other abattoir factors on the incidence of dark cutting in 142,228 grain fed carcasses. This study analysed data from cattle that were supplied from seven feedlots and processed at three abattoirs over 1 year. The average incidence of dark cutting was 2.8%. Increased wind speed (P < 0.05) and rain (P < 0.001) during lairage at the abattoir was associated with an increased risk of dark cutting, whereas variation in ambient temperature, relative humidity or temperature humidity index in lairage did not influence dark cutting. Heavier carcasses with whiter fat, larger hump heights, more rib fat, higher marble scores and lower ossification had lower incidences of dark cutting (P < 0.001). The abattoir and the grader at the abattoir also had significant effects on the incidence of dark cutting (P < 0.001). Increased time in lairage and reduced time to grading markedly increased the incidence of dark cutting (P < 0.001), which suggests that reducing the time in lairage and increasing the time between slaughter and grading are the two major ways to reduce dark cutting in grain finished carcasses. These factors reduce the opportunity and time for the cattle to experience stressful situations before slaughter and maximise the opportunity for the meat to reach pH_u, reducing the incidence of false positive dark cutting caused by grading too early.

The feedlot component of the supply chain experiment analysed the effect of climate, animal and feedlot factors on the incidence of pH non-compliance in Australian grain fed cattle. Data on the same 142,228 carcasses from seven feedlots processed at three abattoirs over 1 year were analysed. The production factors which were associated with increased pH noncompliance included feedlot, sex, hormone growth promotants, cattle morbidity and longer days on feed. pH non-compliance was also increased by reduced solar radiation, lower wind speeds, increased ambient temperature, more rain, higher average temperature humidity index and more hours spent above heat load index threshold of 86 in the week before consignment. Interestingly transport duration did not impact the incidence of dark cutting.

The causes of dark cutting in grain fed cattle are extremely multifactorial with many small factors having an impact. This thesis identified the main drivers across the supply chain which increased the risk of dark cutting in Australian grain fed cattle. This will help lot feeders identify cattle that are at higher risk of dark cutting and alter their pre-slaughter management to ensure cattle have minimal time in lairage and maximal time post-mortem before grading. Climatic conditions do impact the incidence of dark cutting, however management of cattle before slaughter and of carcasses after slaughter has a larger effect on the incidence of dark cutting.

The study was aimed at assessing heat load-related risk of clinical mastitis (CM) in dairy cows. Records of CM for the years 2014 and 2015 were obtained from a large conventional dairy farm milking about 1,200 Holstein cows in central Italy. A case of CM was defined by the presence of clinical signs and veterinary confirmation. Quarter milk samples were collected and bacteriological investigated for each CM. Etiological agents were identified and classified as environmental or contagious pathogens. Hourly weather data from the nearest weather station were used to calculate heat load index (HLI). Upper and lower thresholds of HLI, at which the animal accumulates or dissipates heat, were settled and used to measure heat load balance through the accumulated heat load (AHL) model. Zero and positive values of AHL indicate periods of thermo-neutral and heat accumulation, respectively. Each case of CM was associated with HLI-AHL values recorded 5 d before the event. The risk of CM was evaluated using a case-crossover design. A conditional logistic regression model was used to calculate the odds ratio and 95% confidence intervals of CM recorded in thermo-neutral (AHL = 0) or heat load (AHL > 0) days, pooled or stratified for pathogen type (environmental or contagious). Classes of AHL as low (<6.5), medium (6.6-34.9), and high (>35) were included in the model. Other variables included in the model were milk yield as liters (<20, 20-30, and >30), days in milk (<60, 60-150, and >150), and parity (1, 2-3, and >3). A total of 1,086 CM cases were identified from 677 cows. Escherichia coli, Streptococcus spp., and Streptococcus uberis were the environmental pathogens isolated with the highest frequency; Staphylococcus aureus prevailed within contagious species. The analysis of pooled data indicated a significant effect of heat load on the occurrence of CM in the contagious pathogen stratum. Higher milk yield, middle and late stage of lactation, and older parity increased the risk of CM under heat load conditions. However, the association between pathogen type and these factors was not clear because the model provided significant odds ratios within all pathogen categories. The present study provided the first evidence of an association between HLI and CM in dairy cattle and suggested the ability of the AHL model to assess the risk of mastitis associated with heat load.