Maximum Temperature-humidity Index Research Articles

Effects of perinatal exposure to daily maximum THI and THI fluctuations on serum total proteins and health of preweaned Holstein heifers raised in a dry climate.

The objective of this study was to assess the effects of the exposure to daily maximum and temperature-humidity index (THI) and to daily THI fluctuations (∆THI = maximum THI - minimum THI) at exposure periods comprising 2 d before birth to birth (-2 d), birth date (0 d), birth to 2 d of age (+2 d), and birth to 7 d of age (+7 d) on serum total proteins (STP), transfer of passive immunity (TPI), and the occurrence of scours and respiratory disease. A total of 841 Holstein heifer calves were retrospectively observed from -2 d until 65 days of age. Colostrum quality was assessed using a colostrometer to ensure a minimum globulin concentration of 52mg/mL in the colostrum fed to the study calves. Two temperature and relative humidity sensors were installed at the calf yard. Maximum, minimum, and ∆THI values were obtained for each exposure period, and thermal exposure categories were defined as heat stress (HS: maximum THI>70 units; non-HS: THI≤70 units) and ∆THI (low <20 units, medium ≥20 to ≤30 units, high >30). The TPI was classified as poor (STP <5.1g/dL), fair (5.1 and 5.7g/dL), good (>5.7 and 6.1g/dL), and excellent (≥ 6.1g/dL). Associations between the thermal exposure categories and the study outcomes were examined using ANOVA, logistic regression, and survival analyses. No differences in STP at -2 d were observed between HS and non-HS calves (6.83±0.05 vs. 6.91±0.05g/dL), whereas HS exposed calves at 0 d tended to have lower STP compared with non-HS calves (6.82±0.05 vs. 6.92±0.05g/dL). Calves exposed to small ∆THI at 0 d had greater STP compared with calves exposed to medium ∆THI (7.00±0.06 vs. 6.75±0.05g/dL). No association was found between HS, and ∆THI categories and the TPI category. The odds of scours were about two times greater in HS calves compared with non-HS calves at all exposure periods. In addition, HS calves were affected by scours between 9 and 15 days earlier than non-HS calves. Furthermore, high ∆THI favored the development of respiratory problems compared with medium and low ∆THI. Assessment of extreme THI values and THI fluctuations provides a research opportunity for assessing thermal stress in dairy heifer calves raised in dry climate.

Effect of the Season on Blood Changes of Oxidative Stress Index in the Italian Mediterranean Buffalo (Bubalis bubalis).

Studies in cattle have shown that high temperatures increase the production of reactive oxygen species (ROS) causing an imbalance between ROS and the ability of antioxidant systems to detoxify and remove the reactive intermediates. As such studies remain limited in buffalo, the effect of temperature on oxidative stress was investigated through the oxidative stress index (OSi). Blood samples were collected from 40 buffaloes over 12 time points distributed over two years (2021, 2022). Samples were taken monthly during the hot and cold seasons. Plasma free oxygen radicals were determined using the d-ROMs test (Diacron, Italy), modified for a microplate procedure, and the results were expressed in arbitrary Carratelli Units (U.CARR). Plasma antioxidants were determined by using the BAP test (Diacron) in a dedicated spectrophotometer (Carpe Diem Free, Diacron). The OSi parameter was calculated as d-ROMs/BAP × 100. Temperature and humidity were recorded daily during the trial to calculate the Temperature Humidity Index (THI). For statistical analysis, year and season and their interactions were included in the model. The results of this study showed for the first time the effect of season on the oxidative stress in buffalo. The minimum and maximum THI values for the hot and cold season recorded during the experimental period were 79.27 ± 2.20 and 63.42 ± 3.20, respectively. Levels of d-ROMs and BAP were affected by the seasons (133.0 vs. 145.1 U.CARR, p = 0.0189, and 2489.19 vs. 2392.43 mml/L, p = 0.033, in the hot and cold season, respectively). A significant year × season interaction was found both for d-ROMs and BAP (p = 0.06 and p < 0.0001, respectively). Moreover, OSi was affected by season, showing a growing trend from hot to cold season (5.35 vs. 6.17, p < 0.0001), but, interestingly, it was unaffected by annual variation. Therefore, Osi could be considered a better and independent marker of oxidative status in buffalo, with respect to the evaluation of single determinations of d-ROMs and BAP. Lastly, there were no differences in the plasma 25OHD levels between seasons; concentrations were 12.24 and 10.26 ng/mL in the hot and cold season, respectively.

Behavioural changes to moderate heat load in grazing dairy cows under on-farm conditions

Heat stress poses an increasing risk to welfare, health and productivity of dairy cows, especially for cows on pasture. To apply timely mitigation strategies for grazing cows, simple indicators are needed that signal heat stress. We conducted an exploratory study on the behaviour of grazing dairy cows in relation to the environmental heat load on four commercial dairy farms in Switzerland with herd sizes ranging from 20 to 57 cows. In a scan-sampling procedure standing/lying, feeding/ruminating, low inter-individual distances, proximity to drinker, use of natural shade and insect infestation were observed during 30 days (5–9 days/per farm). Additionally, 10 focal cows per farm were equipped with accelerometers to analyse lying duration and locomotor activity during on average 46 days per farm. On one farm all cows (N = 57) were equipped with GPS devices which were used to calculate inter-individual distances among cows continuously during 69 days. Air temperature and relative humidity were recorded to calculate the temperature-humidity index (THI). For behaviours recorded in direct observations, a principal component analysis was performed for variable reduction. The first three principal components (PC) as well as the variables from automatic measurements were used as outcome variables in mixed effects models with daily maximum THI (THImax), time of day (continuous, in 10 min intervals) and their interaction as explanatory variables. The three PCs could be described as: “feeding and standing”, “proximity to drinker” and “standing in close proximity and seeking shade”. The daily pattern of these PC's differed by THImax (interaction time of day * THImax; all p < 0.01). On days with high THImax compared to days with lower THImax cows were seen more often close to the drinker in the morning, but not in the afternoon when they were observed standing close to each other and in the shade. On days with high THImax, cows also were lying less and increased their locomotor activity towards noon (interaction time of day * THImax; p < 0.001). Data from GPS devices confirmed the findings: On days with high THImax, cows reduced their inter-individual distances over the course of the day, while this was not observed on days with lower THImax (interaction time of day * THImax; p < 0.001). Insect infestation increased with higher THImax. We conclude that a distinct change in daily behavioural patterns, especially a reduction of lying behaviour, an increase in locomotor activity and a decrease in inter-individual distances could be used to monitor heat stress of dairy cows on pasture.

Seasonal influence on follicular and luteal dynamics in dairy cows

The objective of study was to investigate the influence of season, viz. summer, winter, and isothermic (spring and autumn season), on follicular and luteal dynamics in dairy cows. Thirty dairy cows (n=10 in each season) were subjected to the ultrasonographic examination of ovarian structures, i.e. follicle and corpus luteum, during two- and three-follicular waves in an estrous cycle using B-mode and colour doppler mode of ultrasonography. The daily temperature-humidity index (THI) was recorded to envisage its variation among different seasons. In results, the size of the dominant follicle was recorded to be significantly different in all seasons during the second follicular wave. However, all other parameters for follicle, i.e. day of wave onset, length of growth phase, duration of dominance, the maximum diameter of the largest sub-ordinate follicle, as well as luteal morphometric analysis had no significant difference among different seasons. On the other part, the THI varied significantly in different seasons with maximum THI in the summer (72.54), followed by the isothermic (64.7) and lowest in the winter season (54.12). As a part of summation, the seasonal impact was barely noteworthy on different aspects of follicular and luteal dynamics except for the size of dominant and sub-ordinate follicle in dairy cows.

Impact of Climate Change and Heat Stress on Milk Production in Korean Holstein Cows: A Large-Scale Data Analysis.

This study investigated the effects of heat stress on milk production in Korean Holstein cows using large-scale data. Heat stress was assessed using the temperature-humidity index (THI). Weather records (2016 to 2020) were collected from 70 regional weather stations using an installed automated surface observing system (ASOS). A dataset of 2,094,436 milk production records from 215,276 Holstein cows obtained from the Dairy Cattle Genetic Improvement Center was analyzed. Stepwise selection was used to select the input variables, including the daily maximum THI (THI_max). Least-squares means were calculated for milk yield, fat and protein corrected milk (FPCM), fat and protein yield, fat-to-protein ratio, solids not fat, and lactation persistency. Segmented linear regression analysis determined the break points (BPs) of the THI_max. Over the five years, heat stress exposure increased, particularly from May to September. This study identified BPs around THI_max of 80-82 for milk yield and FPCM. Similar patterns for other milk traits were observed, which significantly decreased beyond their respective BPs. These findings indicate that THI variations adversely affect milk yield and composition in dairy cows, highlighting the importance of appropriate feeding management strategies to ensure the optimal productivity of Holstein cows under varying climatic conditions.

Effects of the Bamboo Communities on Microclimate and Thermal Comfort in Subtropical Climates

Urban greening is the most effective way to regulate the microclimate environment and thermal discomfort. However, despite being an important type of vegetation, relatively few studies have investigated the effect of bamboo on microclimate characteristics and thermal comfort. In this study, the microclimate characteristics and the differences in the thermal comfort provided by common bamboo communities in East China were investigated in summer and winter, and the effects of canopy structure characteristics on microclimate and thermal comfort were analyzed. The results showed that there were significant differences in microclimate between bamboo communities and the control check in summer, but the differences in air temperature in winter were not obvious. In the daytime during summer, the maximum daily average temperature of the bamboo community decreased by 2.6 °C, and the maximum temperature–humidity index (THI) decreased by 1.1 °C. In the daytime during winter, the maximum daily average temperature increased by 0.5 °C and the maximum THI increased by 0.8 °C. Among the different bamboo communities, Sinobambusa tootsik var. laeta and Pseudosasa amabilis had better effects on improving microclimate and thermal comfort, while the effects of Phyllostachys nigra and Phyllostachys heterocycla ‘Pubescens’ were relatively small. Aspects of canopy structure, especially leaf area index and canopy coverage, had the greatest influence on the microclimate environment, while air temperature made the greatest contribution to thermal comfort. The goal of our study is to quantify the data to confirm the role of bamboo in improving urban climate problems and human comfort and to further select the appropriate bamboo species for urban green spaces and to utilize the ecological benefits of bamboo to optimize the human living environment.

A transgenerational study on the effect of great-granddam birth month on granddaughter EBV for production traits in Italian Simmental cattle

Heat tolerance is a key feature of resilient animals. Offspring of animals that suffer environmental stress during pregnancy could show physiological, morphological, and metabolic modifications. This is due to a dynamic reprogramming of the epigenetics of the mammalian genome that occurs in the early life cycle. Thus, the aim of this study was to investigate the extent of the transgenerational effect of heat stress during the pregnancy of Italian Simmental cows. The effects of dam and granddam birth months (as indicator of pregnancy period) on their daughter and granddaughter estimated breeding values (EBV) for some dairy traits as well as of the temperature-humidity index (THI) during the pregnancy were tested. A total of 128,437 EBV (milk, fat, and protein yields, and somatic cell score) were provided by the Italian Association of Simmental Breeders. The best birth months (of both dam and granddam) for milk yield and protein yield were May and June, whereas the worst were January and March. Great-granddam pregnancies developed during the winter and spring seasons positively affected the EBV for milk and protein yields of their great-granddaughters; in contrast, pregnancies during summer and autumn had negative effects. These findings were confirmed by the effects of maximum and minimum THI in different parts of the great-granddam pregnancy on the performances of their great-granddaughters. Thus, a negative effect of high temperatures during the pregnancy of female ancestors was observed. Results of the present study suggest a transgenerational epigenetic inheritance in Italian Simmental cattle due to environmental stressors.

Impact of seasonal variation on endocrine profile during an estrous cycle in Jersey crossbred dairy cows

The objective of the study was to investigate the influence of season viz., summer, winter, and isothermic (spring and autumn season), on endocrine profile in dairy cows. The daily temperature-humidity index (THI) was recorded using a dry and wet-bulb thermometer to envisage its variation among different seasons. For analysis of endocrine profile, blood samples were collected from thirty dairy cows (n=10 in each season) at 5-day interval i.e. day 0 (day of estrus) to day 20, of the estrouscycle for ELISA based estimation of estradiol-17β, progesterone, and cortisol. In results, the THI varied significantly (p&lt;0.01) indifferent seasons with maximum THI in the summer (72.54),followed by the isothermic (64.7) and lowest in the winter season(54.12). Among the endocrine profile, the plasma cortisol levels had a significant variation (p&lt;0.05) in different seasons with increased levels in the winter followed by the summer season, however, differences were non-significant (p&gt;0.05) in plasmaprogesterone and estradiol-17β. In summary, seasonal variation barely led to significant changes in the reproductive hormones(estrogen and progesterone) but alleviated cortisol levels during summer and winter season had been suggestive of stress and could result in reduced fertility.

Impact of heat stress on dairy cow rumination, milking frequency, milk yield and quality in a pasture-based automatic milking system

Context Heat stress is an increasing concern for the Australian dairy industry. Aims This study aimed to evaluate the effect of temperature–humidity index (THI) on rumination time (RT), milk yield and quality, and milking frequency in a pasture-based voluntary-movement automatic milking system (AMS). Methods Data were collected from the University of Melbourne Dookie College AMS farm for 3 years (June 2016 to March 2019). Daily RT was collected through the transponder collar (Qwes-HR, Lely). Climatic data (maximum ambient temperature and relative humidity) were obtained from the Dookie Meteorological station to calculate daily maximum THI (THImax). Key results Daily milk yield increased with a rising THImax to 65, then declined after THImax 65. Milking frequency was highest at THImax 90, followed by a steady decline afterwards. Rumination time was maximum at mid-range THImax and declined for high and low values. Conclusions The findings of this study clearly indicated that under pasture-based voluntary-movement AMS, high THI resulted in a drop in the milk yield, milking frequency and RT. Implications With the provision of automation of data collection from AMS, further study with mathematical modelling describing the daily patterns and thresholds in conjunction with the different heat stress levels can be useful for assessing animal welfare and to mitigate heat stress and seek alternative management strategies.

Genotype by environment interaction due to heat stress in Brown Swiss cattle

Due to its geographical position and a highly variable orography, Italy is characterized by several climatic areas and thus, by many different dairy cow farming systems. Brown Swiss cattle, in this context, are a very appreciated genetic resource for their adaptability and low metabolic requirement. The significant heterogeneity in farming systems may consist of genotype by environment (G × E) interactions with neglected changes in animals' rank position. The objective of this study was to investigate G × E for heat tolerance in Brown Swiss cattle for several production traits (milk, fat, and protein yield in kilograms; fat, protein, and cheese yield in percentage) and 2 derivate traits (fat-corrected milk and energy-corrected milk). We used the daily maximum temperature-humidity index (THI) range, calculated according to weather stations' data from 2008 to 2018 in Italy, and 202,776 test-day records from 23,396 Brown Swiss cows from 639 herds. Two different methodologies were applied to estimate the effect of the environmental variable (THI) on genetic parameters: (1) the reaction norm model, which uses a continuous random covariate to estimate the animal additive effect, and (2) the multitrait model, which splits each production pattern as a distinct and correlated trait according to the first (a thermal comfort condition), third (a moderate heat stress condition), and fifth (a severe heat stress condition) mean THI value quintile. The results from the reaction norm model showed a descending trend of the additive genetic effect until THI reached the value of 80. Then we recorded an increase with high extreme THI values (THI 90). Permanent environmental variance at increasing THI values revealed an opposite trend: The plot of heritability and the ratio of animal permanent environmental variance to phenotypic variance showed that when the environmental condition worsens, the additive genetic and permanent environmental component for production traits play a growing role. The negative additive genetic correlation between slope and linear random coefficient indicates no linear relationship between the production traits or under heat stress conditions, except for milk yield and protein yield. In tridimensional wireframe plots, the extreme margin decreases until a minimum of ∼0.90 of genetic correlation in the ECM trait, showing that the magnitude of G × E interaction is greater than the other traits. Genetic correlation values in Brown Swiss suggest the possibility of moderate changes in animals' estimated breeding value in heat stress conditions. Results indicated a moderate G × E interaction but significant variability in sire response related to their production level.

Factors Associated with Farrowing Duration in Hyperprolific Sows in a Free Farrowing System under Tropical Conditions.

The ongoing selection for increased litter size has had significant impacts on sow husbandry practice. The present study investigated factors associated with farrowing duration and the proportion of sows that had prolonged farrowing in modern hyperprolific sows kept in a free farrowing system in a tropical environment. Farrowing data from 2493 Landrace x Yorkshire cross-bred sows in a commercial swine herd in Thailand were included in the study. The time of farrowing, parity number, litter size, and the birth status of each piglet were recorded. Farrowing duration was analysed using multiple analyses of variance. Total number of piglets born per litter (TB), parity, and time onset of farrowing were included in the statistical models. On average, TB, piglets born alive, and farrowing duration were 13.7, 12.1, and 221.0 min, respectively. Of these sows, 26.4% had TB ≥ 16 and 21.7% had a prolonged farrowing duration (≥300 min). Farrowing duration was positively correlated with TB (r = 0.141, p &lt; 0.001), percentage of stillborn (SB) piglets per litter (r = 0.259, p &lt; 0.001), percentage of mummified foetuses (MF) per litter (r = 0.049, p = 0.015), piglet birth weight (r = 0.068, p &lt; 0.001), and litter birth weight (r = 0.041, p = 0.043). The proportion of SB per litter was higher and piglet birth weight lower in litters that had ≥16 TB than those with 8-12 TB (p &lt; 0.05). The farrowing duration of sows with parity numbers 5-7 (247.7 ± 5.1 min) and 8-10 (237.1 ± 5.1 min) was longer than that of sows with parity numbers 1 (188.3 ± 5.2 min) and 2-4 (214.3 ± 3.9 min) (p &lt; 0.05). Sows that had started farrowing during working hours had longer farrowing durations (229.3 ± 3.6 min) than those that had started farrowing during non-working hours (217.6 ± 3.4 min, p = 0.017). In multiparous sows, the duration of farrowing was positively correlated with the maximum temperature (r = 0.056, p = 0.012) and the maximum temperature-humidity index (r = 0.059, p = 0.008) in the 7 days before farrowing. The present data confirm that TB, sow parity, and time of onset of farrowing are significant risk factors for a prolonged farrowing.

Air Quality, Management Practices and Calf Health in Italian Dairy Cattle Farms.

Simple SummaryCalf mortality is an important factor of economic loss in dairy operations. Among the factors which can affect calf health, air quality in calf housing has rarely been studied. In the present research, the relations among air quality in the calf pens, management practices, microclimatic conditions and calf health and mortality were studied in 25 Italian dairy cattle farms. Microbial air quality in the calf pens was found to be related to temperature and humidity, design and position of the pen, some management practices and calf health and mortality. Maintaining dry bedding and controlling microclimatic conditions in the calf pen can be useful practices to promote good air microbiological quality in the calf pen, improving calf health and reducing mortality.Among factors that can affect calf health, microbial quality of the pen air is poorly studied. In 25 Italian dairy farms, data concerning air quality in the calf pens, hygiene of pens and equipment, microclimatic conditions, calf health and management were collected during the winter season (January-March 2020 and December-March 2021). The average air Standard Plate Count (SPC) of 85 pens was 4.51 (SD = 0.52) log10 cfu/m3 whereas the average air ammonia concentration was 0.66 (SD = 0.53) ppm. Positive correlations were found between average Temperature Humidity Index (THI) in the pen and air SPC, night maximum THI and air SPC and between SPC and yeast, mould and ammonia concentration in the pen air. The concentrations of E. coli, Enterobacteriaceae and yeasts in the pen air were higher and calf cough increased as the renewal interval of bedding material became longer. High bedding dry matter and low THI were associated with low air SPC, good calf health scores and low mortality. Maintaining low bedding humidity and controlling microclimatic conditions can contribute to enhancing air microbiological quality in the pen and reduce calf diseases and mortality.

Unaffected semen quality parameters in Neospora caninum seropositive Belgian Blue bulls

Neospora caninum is a protozoan parasite that causes abortion, perinatal mortality, and subfertility in cattle worldwide. Despite the presence of the DNA of the parasite in semen of infected bulls, the effect on semen quality has not been extensively studied. This study aimed to investigate the effect of a natural Neospora caninum infection on fresh and frozen semen quality parameters in Belgian Blue bulls. Two hundred and fourteen bulls were serologically screened with an indirect ELISA-test specific for anti-Neospora caninum antibodies, every two months during one year. In addition to serological screening, semen was collected twice weekly using an artificial vagina. The following semen quality parameters were assessed: ejaculate volume, concentration, total motility of fresh semen samples, as well as morphology, total and progressive motility for frozen/thawed semen samples. Bulls were semen sampled throughout the whole year, but only semen samples of bulls that had six consecutive positive or negative ELISA-test results were included in our dataset (n = 98). Generalized linear and binomial mixed models were used for statistical analysis of each outcome variable. In these models the explanatory variables were defined as: age, barn location, mean Temperature Humidity Index (THI) during sperm production (14–42 days before sampling), maximum daily THI at collection, season of sperm production, season at collection and the Neospora caninum antibody test results. Initially, individual explanatory variables were tested in univariable models for each outcome variable. Akaike information criterion (AIC) values were used to select explanatory variables to build a multivariable model, where the Neospora caninum test result was forced in all models. The present study reveals an overall apparent seroprevalence of Neospora caninum of 9,2% in the study population. No significant associations were detected between natural neosporosis, substantiated by ELISA-antibody levels, and any of our tested outcome variables on fresh and frozen/thawed semen samples. Based on the results of the present study, we conclude that Neospora caninum seropositive bulls do not have lower semen quality parameters compared with seronegative bulls.

High ambient temperature and humidity associated with early embryonic loss after embryo transfer in mares

Increased ambient temperatures has been identified to contribute to reproductive outcomes for several domesticated species, but its impact on equine reproduction has not been previously investigated. Therefore, this study aimed to examine the relationship between ambient climatic conditions, as measured by temperature-humidity index (THI) between day 7 and day 14 of gestation, and early embryonic loss (EEL) in recipient mares undergoing embryo transfer.The study examined records from 834 embryo transfers at an equine breeding facility in Victoria, Australia. Early embryonic loss was defined as a negative transrectal ultrasound on day 14 of gestation after an embryo was transferred on day 7. Both maximum THI on the day of transfer (day 7) and mean THI between day 7 and day 14 were investigated for association with the outcome of EEL using multivariable logistic regression, controlling for confounders including embryo age and quality, recipient mare quality and embryo transfer quality.EEL was observed in 21% of embryo transfers. A five-unit increase in maximum THI on the day of transfer was associated with an 18% increase in the odds of EEL (p = 0.01). Similarly, the odds of EEL increased by 25% for each five-unit increase in mean THI between day 7 and 14 (p = 0.003).As both single and cumulative episodes of high THI were associated with increased EEL in embryo transfer mares from this equine breeding facility, further studies are warranted to identify similar effects in a broader population, establish causality and evaluate possible mitigation strategies in anticipation of heat waves.

The effect of high temperature and humidity on milk yield in Ankole and crossbred cows

Tropical regions are characterized by high temperature and humidity across the year. At high values of temperature humidity index (THI), there is a risk of heat stress leading to lower milk yield. The objective of this study was to describe the effect of season and the effect of maximum daily THI on milk yield of that day in purebred Ankole and Ankole-Friesian, Ankole-Jersey and Ankole-Sahiwal crosses in a tropical climate. In total, 53,730 records of daily milk yield from 183 cows in Rwanda were analyzed. The results showed that THI had a negative effect on daily milk yield above a threshold, but the effect was small (− 0.11 kg milk/THI unit at most). Purebred Ankole cows had the lowest daily milk yield and the lowest threshold (THI mean 66), as compared to the crossbreds (THI mean 68–69). Ankole-Friesian had a steeper decline in daily milk yield above the threshold than Ankole. The crossbreds, especially Ankole-Friesian, had higher daily milk yield than purebred Ankole also at very high THI. The results indicate some differences between breed groups in the way of coping with a hot and humid climate and raise questions about dairy cows’ adaptation to such a climate.

Effect of Heat Waves on Some Italian Brown Swiss Dairy Cows' Production Patterns

Climate change is impacting worldwide efficiency and welfare standards in livestock production systems. Considering the sensibility to heat stress reported for different milk production patterns in Italian Brown Swiss, this study aims to evaluate the effect of heat waves (HWs)of different lengths on some milk production traits (fat-corrected milk, energy-corrected milk, protein and fat yield, protein percentage, cheese production at 24 h, and cheese yield). A 10-year dataset (2009–2018), containing 202,776 test-day records from 23,296 Brown Swiss cows, was used. The dataset was merged both with the daily maximum temperature–humidity index (THI) recorded by weather stations and with the daily maximum THI threshold for each trait in Italian Brown Swiss cows. The study considered 4 different HWs according to their length: 2, 3, 4, and 5 consecutive days before the test-day over the weighted THI threshold. Milk production traits were determined as the difference in losses compared to those after only 1 day before the test-day over the weighted maximum THI. All traits showed to be affected by HWs. Particularly, protein percentage losses increased from −0.047% to −0.070% after 2 consecutive days over the daily THI threshold, reaching −0.10% to −0.14% after 5 days (p &amp;lt; 0.01), showing a worsening trend with the increasing length of HWs. First parity cows showed to be more sensitive to HWs than other parity classes, recording greater losses after shorter HWs, compared to multiparous cows, for protein yield and, consequently, for cheese production at 24 h. This suggests a less efficient metabolic response to heat stress and exposure time in primiparous, compared to multiparous cows, probably due to their incomplete growth process that overlaps milk production, making it more difficult for them to dissipate heat. Although actions to mitigate heat stress are always needed in livestock, this study points out that often time exposure to warm periods worsens milk production traits in Brown Swiss cows.

Avaliação de parâmetros ambientais em uma microrregião no sul do estado do Amazonas e suas relações com estresse térmico de bovinos leiteiros

Abstract Environmental thermal comfort provides higher efficiency in the exploitation of dairy farming, as the responses of animals to the environment are decisive in the activity’s success. This study aimed to evaluate heat stress in dairy cows in the municipality of Humaitá, located in the south of theAmazonas State (AM), Brazil.Air temperature (TA) and relative humidity (RH) data were used to calculate the temperature humidity index (THI) in the dry (August 2020) and rainy seasons (January 2021). The August data were collected at the automatic weather station belonging to the National Institute of Meteorology. The January data were collected by a Hobo® U23-001 thermo-hygrometer installed at Fazenda Nossa Senhora Aparecida. The hourly and monthly means of the data were calculated and, subsequently, boxplots were plotted. TA and RH were 0.65 °C and 0.64% below the provisional climatological normal (PCN), respectively, for August, while January presented 0.77 °C and 3.61% above the PCN, respectively. THI values ranged from 56.25 (comfortable) to 84.68 (emergency) in August and 74.15 (comfortable) to 84.07 (emergency) in January. The maximum THI was observed in August, as well as the largest range. The results allow inferring that heat stress in dairy cows in the municipality of Humaitá-AM presents a state of alert even for cross-breed animals. Thus, the use of shading in pastures is suggested to minimize the effect of heat stress on the productive performance of the animals.

Evaluation of standardized mixture of synbiotic-glyconutrients supplemented in lambs finished during summer season in tropical environment: growth performance, dietary energetics, and carcass characteristics

Twenty-four Pelibuey × Katahdin lambs (36.4 ± 2.9 kg initial weight) were used in a 77 d feeding trial in a randomized complete block design to evaluate the influence of a standardized synbiotic-glyconutrient combination (GLY) on growth performance, dietary energetic, and carcass characteristics of lambs finished during a period of high ambient temperature. Dietary treatments consisted of a high-energy basal diet supplemented (% of diet dry matter basis) with 0% versus 0.4% GLY. Throughout the study, the average temperature humidity index (THI) was 76.23, corresponding to the “alert” range, but daily maximum THI exceeded 80 for 2 to 6 h of each day of the 77 d study. Daily GLY intake averaged 0.10 g GLY·kg−1 live weight. Supplemental GLY increased (P = 0.04) daily water intake, but dry matter intake was not affected. Supplemental GLY increased (P &lt; 0.03) initial 56-d, and overall (77-d) average daily gain, gain efficiency and estimated dietary net energy. Lambs fed GLY had greater (P ≤ 0.05) hot carcass weight and fat thickness, and decreased (P = 0.02) kidney-pelvic-heart fat. Supplemental GLY did not affect (P ≥ 0.16) shoulder tissue composition or relative weight of visceral mass. Synbiotic-glyconutrient combination improved growth performance, dietary energy, and carcass weight in lambs finished in high ambient temperatures. Enhancements in growth performance and dietary energetics were most appreciable during the first 56 d of the 77 d finishing period.

PSVIII-18 Effect of rumen temperature on the average daily gain of growing-finishing calf-fed Holstein steers in the feedlot

Abstract Objectives were to evaluate the relationship between ruminal temperature and average daily gain of calf-fed Holstein steers during the extreme summer months characteristic of the Southern California desert region. Thirty-eight calf-fed Holstein steers (395 ±25 kg) were utilized in the 84-d experiment (June 30 – September 20, 2020). Steers were blocked by initial shrunk weight (168 d before the initiation of the experiment) and randomly assigned to 38 pens with 4 other steers (5 steers per pen). Pens were 62 m2 with 25 m2 overhead shade, automatic waterers and 2.4 m fence-line feed bunks. All steers were fed a steam-flaked corn-based growing-finishing diet. A bolus measuring temperature and activity at ten-minute intervals (smaXtec Basic, SmaXtec Animal Care GmbH, Austria) was placed in the rumen of each steer 112 d before the initiation of the experiment (March 10, 2020). Air temperature for the trial averaged 34.90 ± 3.03°C (maximum = 43.8 ± 2.97° C; minimum 24.72 ± 4.00°C). Average temperature-humidity-index (THI) was 80.1 ±5.4. Maximum THI during the 84-d period averaged 89.29 ± 7.85 (steers experience “emergency” THI category for all 84 days of the trial). Maximum (RTmax) and mean (RTm) daily ruminal temperature averaged 40.93 ±0.24 and 40.21 ±0.23°C, respectively. Average daily gain (mean = 1.18 kg/d; maximum = 1.54 kg/d; minimum = 0.88 kg/d) increased (P &amp;lt; 0.01) as RTm decreased (ADG, kg = 19.13 – 0.45 RTm; r2 = 0.28). There was a close association between RTmax and RTm (RTm = 4.57 + 0.87 RTmax; r2 = 0.84). While there are numerous factors that influence ADG of feedlot cattle, differences in ruminal temperature during periods of elevated ambient conditions (ie. temperature, humidity, ration) accounts for an important portion of that variation.

503 Late-Breaking: Using Random Regression Models to Estimate Genetic Parameters for Milk Production Traits under Different Levels of Heat Stress in Canadian Holstein Cattle

Abstract Genetically selecting animals that are heat tolerant can help to maintain production efficiency of the dairy industry under thermal challenges. During the summer months in Canada, dairy cows could be under thermal stress. For instance, in Ontario, cows are expected to be 105 days under thermal stress. The objective of this study was to estimate genetic parameters for milk production traits under heat stress in Canadian Holstein cows. A total of 604,050 test-day records for milk, fat, and protein yields from 78,516 first-lactation Holstein cows were used in this study. The production data was combined with daily maximum temperature-humidity index (THI; ranging from 30 to 83) calculated based on meteorological records from public weather stations. In total, 58 weather stations were located within a maximum distance of 20 km from each of the 1,284 herds included in this study. Single-trait random regressions on THI, fitting linear splines to describe the random additive genetic and permanent environmental effects, were used in the genetic analyses. Based on preliminary analyses, the knots of the spline functions were set to THI = 70, 57, and 58 for milk, fat, and protein yields, respectively. Therefore, the models assumed a linear effect of heat stress beyond the THI threshold, allowing to estimate the additive genetic effect under thermal comfort and at different levels of heat stress. The genetic correlations estimated between thermal comfort and heat stress were -0.09, -0.33, and -0.21 for milk, fat, and protein yields, respectively. This indicates an antagonistic relationship between level of production and heat tolerance. However, small differences in heritability estimates were observed above the THI thresholds (they ranged from 0.20 to 0.22 for milk, 0.18 to 0.15 for fat, and 0.14 to 0.15 for protein yields). This study demonstrates the possibility of genetically selecting for more heat-tolerant animals in Canada.