Faecal cortisol metabolites, body temperature, and behaviour of beef cattle exposed to a heat load.

Feedlot cattle are at times exposed to high environmental temperatures. Faecal cortisol metabolites were related to possible indicators of heat stress that could be measured under field conditions: respiratory dynamics (respiration rate), body surface temperature and adaptive behaviours, such as water consumption, posture (standing, lying), and activity (eating, drinking and rumination). Twelve (12) yearling Black Angus steers were divided into two treatment groups: a hot treatment (HOT; n = 6) and a thermoneutral-treatment (TN; n = 6) and individually housed in a climate-controlled facility at The University of Queensland, Australia. In the TN treatment, all animals were exposed to an ambient temperature of 20.34 ± 0.25 °C, relative humidity 71.51 ± 3.26% and Temperature humidity index (THI) 66.91 ± 0.33 throughout. In the HOT treatment group, environmental conditions were exposed to different climatic phases from thermoneutral to hot conditions, where they remained for 7 d, and then returned to TN conditions in the recovery period. The dry bulb ambient temperature (TA) and relative humidity (RH) in the pens of cattle in the HOT treatment were increased from 28 °C (daily maximum ambient temperature) and 45% RH at 0700 h to a daily maximum TA and RH of 35 °C (daily maximum ambient temperature) and 50% (THI 77) at 1100 h, which was maintained until 1600 h, after which it declined until it reached the baseline at 2000 h. In both treatments, there was a significant decrease in faecal cortisol metabolite concentration from the start to the end of the experiments they adapted to the experimental facility. The concentration of faecal cortisol metabolites was greater in the HOT treatment, compared to the TN treatment during the heat exposure period, but there was no difference in the transition or recovery periods. Respiration rate was greater in the HOT treatment during heat exposure, and it increased with ambient dry bulb temperature above 26 °C, the latter being the upper critical temperature. Although positive correlations were detected between faecal cortisol metabolites and body surface temperature measurements, particularly the shoulder and rump, as well as standing time, panting score and drinking, a stepwise regression found that faecal cortisol metabolites were only significantly correlated with one variable, respiration rate. It is concluded that respiration rate is the best indicator of the stress induced by hot conditions for cattle.

Comparing the responses of grain-fed feedlot cattle under moderate heat load and during subsequent recovery with those of feed-restricted thermoneutral counterparts: blood cells and inflammatory markers.

Given the climate projections for livestock rearing regions globally, understanding the inflammatory status of livestock under various heat loads will be informative to animal welfare and management. A survey of plasma inflammatory markers was conducted, and blood leucocyte counts followed to investigate the capacity of the ~ 500 kg grain fed Black Angus steer to respond to and recover from a moderate heat load challenge. Two sequential cohorts of 12 steers were housed in climate-controlled rooms (CCR) for 18 days. A thermally challenged (TC) group (n = 2 × 6) experienced five consecutive periods: PreChallenge, Challenge, and Recovery within the CCR, and 40 days in outdoor pens (PENS and Late PENS). PreChallenge (5 days) and Recovery (7 days) delivered thermoneutral conditions, whereas in Challenge the TC steers experienced a diurnal temperature range of 28-35 °C. A feed-restricted thermoneutral (FRTN) treatment (n = 2 × 6) was run concurrently to differentiate between responses to reduced feed intake alone and moderate heat stress. Blood neutrophil counts were particularly sensitive to moderate heat load with higher numbers during Challlenge and in PENs. The plasma concentrations of TNFα and IL-1ß were depressed in the TC group compared to the FRTN counterparts and remained so for 40 days after Challenge. Linear relationships of the concentrations of IL-1ß, IL-10, and haptoglobin with rumen temperature or dry matter intake detected in the FRTN group were altered or absent in the TC group. The findings suggest significant impacts of moderate heat load on the inflammatory status of feedlot cattle.

The effect of day-only versus day-plus-night cooling of dairy cows.

The aim of this study was to assess effects on milk yield (MY), rumen temperature, and panting score when lactating dairy cows were cooled during the day only or during the day and night. The study was conducted over 106 d during using 120 multiparous Holstein-Friesian cows assigned to 2 treatments (60 cows/treatment; 2 pens/treatment): (1) day cooling (DC): overhead sprinklers (large droplet) and fans while in the dairy holding yard only, shade and fans at the feedpad, and a shaded loafing area; and (2) enhanced day+night cooling (EDN): overhead sprinklers (large droplet) and fans in dairy holding yard, ducted air blowing onto cows during milking, plus thorough wetting (shower array) on exit from dairy; shade and fans at feedpad (turned off at night); and shaded loafing area + ducted fan-forced air blowing onto cows at night. The ducted air at night was manually activated at 2030 h when the maximum daily temperature-humidity index exceeded 75 and remained on until 0430 h the next day. The cows were fed a total mixed ration ad libitum, and feed intake was determined on a pen basis. Rumen temperature and cow activity were obtained from each cow at 10-min intervals via rumen boluses. Panting scores were obtained by direct observation 4 times a day at approximately 0430, 0930, 1530, and 2030 h. Cows were milked twice daily: 0500 to 0600 h and 1600 to 1700 h. Individual MY were obtained at each milking and combined to give individual daily totals. The EDN cows had greater daily MY (+2.05 kg/cow per day) over the duration of the study compared with DC cows. Rumen temperature during the third heat wave was lower for EDN (39.51 ± 0.01°C) than for DC (39.66 ± 0.01°C) cows. During the most severe heat wave (heat wave 3), MY for the 2 groups was similar, but over the 6 d following the heat wave, EDN cows had greater daily MY (+3.61 kg/cow per day). Rumen temperature was lower for EDN (39.58 ± 0.01°C) than for DC (40.10 ± 0.01°C) cows.

Comparing the responses of grain fed feedlot cattle under moderate heat load and during subsequent recovery with those of feed restricted thermoneutral counterparts: metabolic hormones.

We set out to determine the impact of moderate heat load on the plasma concentrations of a suite of hormones involved in regulating energy metabolism and feed intake. The responses of the thermally challenged (TC) feedlot steers were compared to those of feed restricted thermoneutral (FRTN) steers. Two sequential cohorts of twelve 518 ± 23 kg Black Angus steers on finisher grain ration were housed in climate-controlled rooms (CCR) for 18 days and returned to outdoor pens for 40 days. The TC group was subjected to a diurnal range of 28-35 °C for 7 days (Challenge) but held in thermoneutral conditions beforehand (PreChallenge), and in Recovery (after Challenge). The FRTN group was held in thermoneutral conditions and feed restricted throughout. Blood was collected over the three periods in CCR and two periods in outdoor pens for 40 days (PENS and Late PENS). Plasma concentrations of prolactin, thyroid stimulating hormone, insulin, leptin, adiponectin and thyroxine (T4) were determined during the five periods. Whilst the pituitary hormones were relatively stable, there were differences in plasma leptin, adiponectin and T4 between the two groups during Challenge and Recovery, and occasionally in PENS. The interaction of the plasma hormone concentrations and rumen temperature and DMI were also investigated. Whilst the positive relationship between DMI and leptin was confirmed, we found a strong negative relationship between adiponectin and rumen temperature, and a strong positive relationship between adiponectin and dry matter intake (DMI) in the TC steers only.

Comparing the responses of grain fed feedlot cattle under moderate heat load and during subsequent recovery with those of feed restricted thermoneutral counterparts: plasma biochemistry.

Responses to heat stress in ruminants reflect the integration of local climatic conditions, environment/production system and the animal's homeostatic and homeorhetic capacities. Thus, the goal of ameliorating heat stress requires experimental settings that, within limits, closely resemble the target production system and cohort. We investigated the blood biochemical changes of two sequential cohorts of twelve 518 ± 23 kg grain fed Black Angus steers. Each cohort consisted of two treatments of 6 head/group: a thermally challenged (TC) treatment and a feed restricted thermoneutral (FRTN) treatment. Both groups were housed in climate controlled rooms for 19 days, with the TC group experiencing three distinct periods: PreChallenge, Challenge and Recovery. PreChallenge and Recovery delivered thermoneutral conditions, while Challenge consisted of 7 days of moderate diurnal heat load. The FRTN group was maintained in thermoneutral conditions at all times. Both groups were then relocated to outdoor pens for a further 40 days to detect any enduring change to metabolism as a consequence of the treatments. We compared blood biochemical responses of the treatments and inferred likely metabolic changes. Relative to the FRTN group, the TC animals experienced limited supply of triglycerides, cholesterol and glutamine during moderate heat load, suggesting constraints to energy metabolism. Lower blood urea during Recovery and in outdoor pens implied a requirement to capture N rather than allow its excretion. Altered liver enzyme profiles indicated a higher level of hepatic stress in the TC group. By the completion of feedlot finishing, the groups were not separable on most measures.

The use of percutaneous thermal sensing microchips for non-invasive measurement of body temperature in foals during summer seasons in a subtropical region.

Continuous accurate attainment of the body temperature of foals is important to detect early stages of severe heat stress or fever due to a systemic illness. Among a number of methods to measure body temperature, measuring rectal temperature with a digital thermometer is most frequently used due to being relatively fast and simple method. It is also comparatively accurate and correlates well with the core body temperature. However, this method requires restraining the foal for a few seconds to obtain the temperature, and it can be dangerous for the handling person. Percutaneous thermal sensing microchips (PTSMs) are a means of monitoring the body temperature of horses, which offers a non-invasive, hygienic, quick, and accurate way to measure body temperature and provide an identification number for each individual, once it is implanted. This study tested the hypothesis that PTSM has a strong relationship with a conventional body temperature measurement, i.e., measuring rectal temperature with a digital thermometer of foals during summer seasons. Thirty-two foals in three consecutive foaling seasons (2018, 2019, and 2020 season) were implanted a PTSM into the right pectoral muscle, the right splenius muscle, the right gluteal muscle, and the nuchal ligament as early as two weeks after birth. The four PTSM temperatures, rectal temperature, and climate conditions (air temperature, relative humidity, and wet-bulb globe temperature) were obtained simultaneously during the three summer seasons and paired for comparison analysis. Among the PTSM temperatures, the pectoral muscle had the highest correlation and the least differences with rectal temperature. Using PTSM was safe, easy, and reliable for attaining body temperature in foals.

Thermoregulation of the bovine scrotum 2: simulated acute and chronic heat waves reduces the scrotal thermoregulatory capability of Wagyu bulls.

The objective of this study was to investigate the effect of acute and chronic heat load events on scrotal temperature (ST), body temperature (BT) and bull behaviour, and to examine the interrelationship between these parameters; the underlying hypothesis was that adverse heat treatments delivered in a temperature controlled environment will lead to thermoregulatory dysfunction of the bull scrotum. Six sexually mature Wagyu bulls were used in this study with data loggers surgically implanted into the abdominal cavity and scrotum. Body temperate and ST were recorded at 30-min intervals for the duration of the study. There were two housing locations used throughout the study, outdoor pens and climate control rooms. The study was designed as a four-phase crossover design with two heat treatments: (1) a 5-day acute challenge, and (2) a 14-day chronic challenge. The study was also blocked by phase to control for systematic change between phases with a thermoneutral (TN) phase in outdoor pens between each heat challenge. Observations within the climate rooms were conducted at 1-h intervals and data on panting scores (PS), respiration rate (RR), posture (standing or lying) and general behaviours (feeding, drinking, ruminating) recorded. Ambient temperature (AT, °C) and relative humidity (RH, %) were obtained at 10-min intervals and used to calculate the temperature humidity index (THI). Multiple models were conducted using a linear mixed effects model that contained different permutations of date and time factors and interactions as well as inclusion of an autoregressive parameter. The strongest model based on Akaike's information criterion (AIC) was selected and further analysed. Ambient conditions during heat treatments were consistent with heat load and bulls showed typical physiological symptoms of the same. Maximum ST for acute and chronic treatments occurred once AT had exceeded 34 °C for at least 3 h (acute 35.59 °C at 1500 h; chronic 35.18 °C at 1400 h), whereas during TN conditions, maximum ST was at 2100 h. All phases showed variation in ST throughout the day. There were strong cross correlations between ST and RR during the heat treatments (acute r = 0.918, P < 0.0001; chronic r = 0.916, P < 0.0001), but not during TN (r = 0.411, P < 0.05). Our results confirmed that the ST of the bulls used in this study was not held at a constant temperature and that there was a possible connection between ST and RR. We have shown that during a period of heat load, the thermoregulatory mechanisms thought responsible for maintaining bovine ST appear to breakdown.

The influence of shade availability on the effectiveness of the Dairy Heat Load Index (DHLI) to predict lactating cow behavior, physiology, and production traits.

Numerous climatic indices have been utilized to predict the effect 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 effects of heat load mitigation strategies, such as shade, which decreases the negative effects of hot climatic conditions on lactating cows. Therefore, this experiment aimed to determine the effectiveness 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 (TVAG, °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 TVAG 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 effective heat load management tool.

Influence of feeding Saccharomyces cerevisiae on the heat load responses of lactating dairy cows during summer.

The objective of this study was to evaluate the influence of supplementing lactating dairy cows with Saccharomyces cerevisiae on milk production and composition, cow behavior, and physiological responses during summer. Twenty primiparous cows were used and two treatments were imposed: (1) control (CON); and (2) probiotic supplementation (PRO; S. cerevisiae, providing 1010 colony forming units (CFU) per day). Rumen temperature (TRUM, °C) and pH were obtained via rumen boluses. Rumen temperatures were obtained from all cows (n = 20) at 10-min intervals and ruminal pH were obtained from five cow pairs (n = 10) at 10-min intervals. Ambient temperature (TA; °C), relative humidity (RH; %), wind speed (WS; m/s), and solar radiation (SR; W/m2) were recorded at 10-min intervals. The temperature humidity index (THI) was calculated using TA and RH. Cows were milked twice daily. Milk fat (%), protein (%), lactose (%), and somatic cell count (SCC, '000) were evaluated on 16 occasions. Cows were observed three times (0800 h; 1200 h; and 1400 h) daily for panting score (PS); respiration rate (RR); posture (standing/lying); shade utilization; and cow activity (eating/drinking/ruminating). Individual PS were used to calculate a mean panting score (MPS) for CON and PRO treatments for each observation. S. cerevisiae did not influence milk yield (P = 0.87), fat (P = 0.82), protein (P = 0.26) or SCC (P = 0.19), although there was a tendency for PRO cows to have higher lactose (P = 0.06). Probiotics did not influence the proportion of cows utilizing shade (P = 0.42); standing (P = 0.41); ruminating (P = 0.72); or drinking (P = 0.40). All cows exhibited an increase in RR (> 24 bpm) at 1200 h and RR showed a steady increase as THI increased (P < 0.0001), regardless of treatment (P = 0.96). Both CON (35.8%) and PRO (40.2%) exhibited an increase in MPS as THI increased from thermoneutral (THI ≤ 74) to very hot (THI ≥ 84.1; P < 0.001). However, PRO cows had lower (2.19 ± 0.09; P < 0.0001) MPS compared with CON (2.54 ± 0.22) cows when THI was categorized as very hot (THI ≥ 84.1). Rumen pH were not influenced by treatment (P = 0.38), however TRUM of PRO cows were 0.2 °C lower across days (P < 0.0001) and hours (P < 0.0001). These results suggest that supplementing cows with S. cerevisiae may support thermoregulation via decreased TRUM and MPS; however, further studies are required.

Development of a Model for Abdominal Aortic Aneurysms in Swine.

INTRODUCTION: Producing a reliable large-animal model of AAA has proven challenging. We sought to create a reproducible swine model of AAA using enzymatic degradation of the aortic wall. METHODS: Twelve male Yorkshire swine received periadventitial injections of type 1 collagenase and porcine pancreatic elastase into a 4 cm segment of infrarenal aorta. Nine survived until postoperative day (POD) 21. Aortic growth was monitored at 7 and 14 days using ultrasound. The animals were euthanized on POD 21, and the suprarenal (control) and infrarenal aorta were harvested for analysis, after gross measurement of aortic diameter (AD). Tensile strength was measured and additional segments were collected for histopathological analysis. PCR of matrix metalloproteinases (MMP9) was conducted. Groups were compared with paired t-tests, or ANOVA, where appropriate. RESULTS: Average percent growth of AD at POD 21 for treated segments was 27% versus 4.5% for control tissue. The average difference in AD by subject, was 26.7% (P<0.001). Aortic medial thickness was decreased in treated tissue; 235 µm versus 645 µm (P<0.0001). Quantities of both medial elastin fibers, and smooth muscles cells were decreased in treated tissue; 1.8% compared to 9.9% (P<0.0001), and 24% versus 37.4%, respectively. Tensile strength was also decreased in treated tissue; 16.7 MPa versus 29.5 MPa (P=0.0002). A 12-fold increase in expression of MMP9 mRNA was also demonstrated in aneurysmal tissue (P=0.002) CONCLUSION: A reproducible, large-animal model of AAA, with anatomical, histopathological, and biomechanical properties that are clinically translatable, can be achieved with extraluminal enzymatic degradation.

Heat load increases the risk of clinical mastitis in dairy cattle.

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.

Body temperature of free-ranging koalas (Phascolarctos cinereus) in south-east Queensland.

The distribution of the koala (Phascolarctos cinereus) in Queensland is predicted to contract as a result of climate change, driven by the frequency, intensity and duration of heatwaves and drought. However, little is known about the physiological responses of this species to environmental extremes under field conditions. This study aimed to establish the efficacy of surgically implanted thermal radio transmitters and data loggers to measure the body temperature of free-ranging koalas across a range of environmental conditions and ambient temperatures. Five free-ranging koalas in southeast Queensland were implanted with thermal transmitters and data loggers waxed together as a single package. Body temperatures were recorded for variable periods ranging from 3 to 12 months. Diurnal rhythms in body temperature were detected irrespective of season. The long-term diurnal body temperature peak for all koalas occurred between 16:00 and 17:00 h and body temperature was 36.7-36.9 °C, the long-term nadir occurred between 07:00 and 08:00 h and body temperature was 35.4-35.7 °C. Koala body temperatures as low as 34.2 °C and as high as 39.0 °C were recorded. Thermolability became apparent when ambient temperatures were outside the deduced thermal neutral zone for koalas (14.5-24.5 °C): heat was accumulated during the day and dissipated during the cool of the night. While this study is the first to report on body temperature of free-ranging koalas in their normal behavioural context, further investigations are necessary to determine the physiological boundaries of the thermal niche for this species, in order to better equip models that will more accurately predict the impacts of climate change on koalas.

Disparities in Treatment for Gallbladder Carcinoma: Does Treatment Site Matter?

BACKGROUND AND PURPOSE: Current treatment guidelines for gallbladder cancer range from simple cholecystectomy to regional hepatic resection. Treatment patterns for radical resection and adjuvant chemotherapy vary. We aim to determine if there is any disparity in treatment or difference in survival between academic versus community treatment centers. METHODS: The National Cancer Database (NCDB) was queried from 2004 to 2014 for gallbladder carcinoma. Cases were stratified into treatment sites as "Community Cancer Center" (CCC) or "Academic Cancer Center" (ACC). Propensity score matching was performed for patient demographics, TNM stage, resection type, and administration of adjuvant chemotherapy. The primary outcome included 30-day mortality, 90-day mortality, and overall survival. RESULTS: There are similar frequencies of radical versus simple resection and administration of adjuvant chemotherapy between ACC and CCC. When propensity-matched for resection type, cases treated at ACC have lower 30-day mortality (4.1% vs. 6.9%) and 90-day mortality (13.2% vs. 18.5%) and increased 5-year overall survival (26.2% vs. 22.4%) (p < 0.01). After propensity matching for adjuvant chemotherapy, cases at ACC have lower 30-day mortality (4.12% vs. 7.71%) and 90-day mortality (13.22% vs. 19.19%) and increased overall survival (13.6% vs. 11.0%) (p < 0.01). DISCUSSION AND CONCLUSIONS: While treatment patterns for gallbladder cancer at ACC and CCC were similar, there was a decrease in 30-day and 90-day mortality and improved overall survival associated with patients treated at ACC. Treatment site may have an impact in the surgical outcomes of gallbladder cancer patients. This disparity warrants further research.

Prediction models, assessment methodologies and biotechnological tools to quantify heat stress response in ruminant livestock.

Livestock industries have an important role in ensuring global food security. This review discusses the importance of quantifying the heat stress response of ruminants, with an emphasis on identifying thermo-tolerant breeds. There are numerous heat stress prediction models that have attempted to quantify the response of ruminant livestock to hot climatic conditions. This review highlights the importance of investigating prediction models beyond the temperature-humidity index (THI). Furthermore, this review highlights the importance of incorporating other climatic variables when developing prediction indices to ensure the accurate prediction of heat stress in ruminants. Prediction models, particularly the heat load index (HLI) were developed to overcome the limitations of the THI by incorporating ambient temperature (AT), relative humidity (RH), solar radiation (SR) and wind speed (WS). Furthermore refinements to existing prediction models have been undertaken to account for the interactions between climatic variables and physiological traits of livestock. Specifically, studies have investigated the relationships between coat characteristics, respiration rate (RR), body temperature (BT), sweating rate, vasodilation, body weight (BW), body condition score (BCS), fatness and feed intake with climatic conditions. While advancements in prediction models have been occurring, there has also been substantial advancement in the methodologies used to quantify animal responses to heat stress. The most recent development in this field is the application of radio frequency identification (RFID) technology to record animal behaviour and various physiological responses. Rumen temperature measurements using rumen boluses and skin temperature recording using infrared thermography (IRT) are making inroads to redefine the quantification of the heat stress response of ruminants. Further, this review describes several advanced biotechnological tools that can be used to identify climate resilient breeds of ruminant livestock.

Evaluating rumen temperature as an estimate of core body temperature in Angus feedlot cattle during summer.

This study was conducted to determine the relationship between rectal temperature (TREC) and rumen temperature (TRUM) and to assess if TRUM could be used as a proxy measure of core body temperature (TCORE) in feedlot cattle. Eighty Angus steers (388.8 ± 2.1 kg) were orally administered with rumen temperature boluses. Rumen temperatures were recorded at 10-min intervals over 128 days from all 80 steers. To define the suitability of TRUM as an estimation of TCORE, TREC were obtained from all steers at 7-day intervals (n = 16). Eight feedlot pens were used where there were 10 steers per pen (162 m2). Shade was available in each pen (1.8 m2/animal; 90% solar block). Climatic data were recorded at 30-min intervals, including ambient temperature (TA; °C); relative humidity (RH; %); wind speed (WS; m/s) and direction; solar radiation (SR; W/m2); and black globe temperature (BGT; °C). Rainfall (mm) was recorded daily at 0900 h. From these data, temperature humidity index (THI), heat load index (HLI) and accumulated heat load (AHL) were calculated. Individual 10-min TRUM data were converted to an individual hourly average. Pooled mean hourly TRUM data from the 128-day data were used to establish the diurnal rhythm of TRUM where the mean minimum (39.19 ± 0.01 °C) and mean maximum (40.04 ± 0.01 °C) were observed at 0800 h and 2000 h respectively. A partial correlation coefficient indicated that there were moderate to strong relationships between TRUM and TREC using both real-time (r = 0.55; P < 0.001) and hourly mean (r = 0.51; P < 0.001) TRUM data. The mean difference between TREC and TRUM was small using both real-time (0.16 ± 0.02 °C) and hourly mean TRUM (0.13 ± 0.02 °C) data. Data from this study supports the hypothesis that TRUM can be used as an estimate of TCORE, suggesting that TRUM can be used to measure and quantify heat load in feedlot cattle.

A panting score index for sheep.

When exposed to hot conditions, heat dissipation via an increase in respiration rate (RR) is an important thermoregulatory mechanism for sheep. However, evaluating RR under field conditions is difficult. In cattle, a viable alternative has been to assess panting score (PS); therefore, the objective of this study was to evaluate the relationship between RR and PS to determine if a PS index can be used to evaluate heat load in sheep. One hundred and forty-four Merino wethers (44.02 ± 0.32 kg) were used within a climate-controlled study. The study was replicated twice over 29 days, where each replicate consisted of two treatments: (1) thermoneutral (TN) and (2) hot (HOT). Ambient temperature (TA) and relative humidity (RH) were maintained between 18 and 20 °C and 60 and 70% respectively for the TN treatment. For the HOT treatment, heat load increased steadily over the 29 days. Minimum TA was 22.5 °C and maximum was 38.5 °C, while RH decreased (60 to 30%) as TA increased in the HOT treatment. A comprehensive PS classification was developed by enhancing the current sheep PS index and aligning the descriptors with the current PS index utilized in beef cattle studies. Respiration rate and PS were obtained for each animal at 3-h intervals between 0800 h and 1700 h daily. These data were used to determine the mean RR for each PS, across the study and within the TN and HOT treatments. The relationship between PS and RR was evaluated using a Pearson's correlation coefficient. Data were also analyzed using a general linear model to determine the impact of PS, posture and animal identification (animal ID) on RR within each PS. Unsurprisingly, RR increased as PS increased, and PS, 0 and RR, 2.5 were 30.7 ± 0.59 and 246.8 ± 12.20 bpm respectively. There was a strong relationship between RR and PS (r = 0.71; P < 0.0001). As RR increased, sheep were more likely to be observed standing (P < 0.001). Mean PS of sheep within the HOT treatment (1.49 ± 0.02) were greater (P = 0.0085) when compared to the TN (1.17 ± 0.02) sheep. Individual animal ID accounted for approximately 7-37% of the variation observed for RR across PS, indicating that animal ID and climatic conditions were influencing RR and PS. These results suggest that the comprehensive PS index described here can be used as a visual appraisal of the heat load status of sheep.

Review: Adaptation of animals to heat stress.

Livestock plays an important role in the global economy. Climate change effects are not only limited to crop production, but also affect livestock production, for example reduced milk yields and milk quality, reduced meat production and reduced fertility. Therefore, livestock-based food security is threatened in many parts of the world. Furthermore, multiple stressors are a common phenomenon in many environments, and are likely to increase due to climate change. Among these stresses, heat stress appears to be the major factor which negatively influences livestock production. Hence, it is critical to identify agro-ecological zone-specific climate resilient thermo-tolerant animals to sustain livestock production. Livestock responds to the changing environments by altering their phenotypic and physiological characters. Therefore, survivability of the animal often depends on its ability to cope with or adapt to the existing conditions. So to sustain livestock production in an environment challenged by climate change, the animals must be genetically suitable and have the ability to survive in diversified environments. Biological markers or biomarkers indicate the biological states or alterations in expression pattern of genes or state of protein that serve as a reference point in breeding for the genetic improvement of livestock. Conventionally, identification of animals with superior genetic traits that were economically beneficial was the fundamental reason for identifying biomarkers in animals. Furthermore, compared with the behavioural, morphological or physiological responses in animals, the genetic markers are important because of the possibility of finding a solution to animal adaptability to climate change.

Effect of heat stress on rumen temperature of three breeds of cattle.

Thirty-six steers (12 of each Angus, Charolais, and Brahman) with an initial BW of 318.5 ± 6.7 kg were used in a 130-day study. Two treatments were imposed: un-shaded and shaded (3 m2/animal; 90% solar block shade cloth). On day 1, steers were administered with rumen temperature boluses. Rumen temperatures (T RUM) were obtained at 10 min intervals over the duration of the study to determine differences in T RUM between Bos indicus and Bos taurus cattle. Six feedlot pens (162 m2) were used with six steers (2/breed) per pen with three pens/treatment. Ambient dry bulb temperature (T A; °C), relative humidity (RH; %), wind speed (WS; m/s) and direction, and solar radiation (SR; W/m2) were recorded at 10 min intervals. Rainfall (mm) was collected daily at 0900 h. From these data, black globe temperature (BGT; °C), temperature humidity index (THI), heat load index (HLI), and accumulated heat load (AHL) were calculated. Individual T RUM were converted to an hourly average and then mean hourly T RUM were converted to a mean within hour T RUM across the 130 days. Rumen temperatures were analyzed using an autoregressive repeated measures model. The model analyzed the effect of breed (P < 0.0002), treatment (P = 0.3543), time of day (hour, h; P < 0.0001), breed × treatment (P < 0.3683), breed × h (P < 0.0001), treatment × h (P < 0.0001), breed × treatment × h (P = 0.0029), pen within treatment (P = 0.0195), and animal × breed × treatment within pen (P = 0.1041). Furthermore, there were breed × treatment × hour differences in T RUM (P = 0.0036), indicating that Bos indicus and Bos taurus regulate T RUM differently.

Short communication: using infrared thermography as an in situ measure of core body temperature in lot-fed Angus steers.

Thirty-six Black Angus steers were used in a replicated study; three replicates of 12 steers/replicate. Steers had an initial non-fasted BW of 392.3 ± 5.1, 427.5 ± 6.3, and 392.7 ± 3.7 kg for each replicate, respectively. Steers were housed outside in individual animal pens (10 m × 3.4 m). Each replicate was conducted over a 6-day period where infrared thermography (IRT) images were collected at 3-h intervals, commencing at 0600 h on day 1 and concluding at 0600 h on day 6. Rumen temperatures (T RUM) were measured at 10-min intervals for the duration of each replicate using a radio-frequency identification (RFID) rumen bolus. These data were used to determine the relationship with surface temperature of the cattle, which was determined using IRT. Individual T RUM were converted to an hourly average. The relationship between T RUM and surface temperature was determined using Pearson's correlation coefficient. There were no linear trends between mean hourly T RUM and mean surface temperature. Pearson's correlation coefficient indicated that there were weak associations (r ≤ 0.1; P < 0.003) between T RUM and body surface temperature. These data suggest that there was little relationship between the surface temperature and T RUM.

Measurement of bovine body and scrotal temperature using implanted temperature sensitive radio transmitters, data loggers and infrared thermography.

Synchronous and continuous measurement of body (BT) and scrotal temperature (ST) without adverse welfare or behavioural interference is essential for understanding thermoregulation of the bull testis. This study compared three technologies for their efficacy for long-term measurement of the relationship between BT and ST by means of (1) temperature sensitive radio transmitters (RT), (2) data loggers (DL) and (3) infrared imaging (IRI). After an initial pilot study on two bulls to establish a surgical protocol, RTs and DLs were implanted into the flank and mid-scrotum of six Wagyu bulls for between 29 and 49 days. RT frequencies were scanned every 15 min, whilst DLs logged every 30 min. Infrared imaging of the body (flank) and scrotum of each bull was recorded hourly for one 24-h period and compared to RT and DL data. After a series of subsequent heat stress studies, bulls were castrated and testicular tissue samples processed for evidence of histopathology. Radio transmitters were less reliable than DLs; RTs lost >11 % of data, whilst 11 of the 12 DLs had 0 % data loss. IRI was only interpretable in 35.8 % of images recorded. Pearson correlations between DL and RT were strong for both BT (r > 0.94, P < 0.001) and ST (r > 0.80, P < 0.001). Surgery produced temporary minor inflammation and scrotal hematoma in two animals post-surgery. Whilst scar tissue was observed at all surgical sutured sites when bulls were castrated, there was no evidence of testicular adhesion and normal active spermatogenesis was observed in six of the eight implanted testicles. There was no significant correlation of IRI with either DL or RT. We conclude that DLs provided to be a reliable continuous source of data for synchronous measurement of BT and ST.