Effects of ambient air temperature, humidity, and wind speed on seminal traits in Braford and Nellore bulls at the Brazilian Pantanal

Bioclimatic thermal stress indices and their relationships with andrological characteristics in hair rams

This study evaluated relationships among reproductive parameters and the bioclimatic indices: temperature and humidity index (THI), equivalent temperature index (ETI), black globe temperature and humidity index (BGTHI), and thermal comfort index (TCI), during the first 45 days of spermatogenesis (SP-45) and during the 15 days of sperm transit through the epididymis (STP-15) that preceded the reproductive assessments (ReA). Such information is useful in determining the optimal breeding season in Northeast Brazil. Santa Inês rams (n = 25) underwent two ReA in three periods of the year (D-P = dry; R-P = rainy and RD-P = rainy/dry transition), and the bioclimatic indices were calculated at the corresponding SP-45 and STP-15 timepoints prior to each ReA. Sperm kinetic parameters in D-P were depressed compared to R-P and RD-P (P < 0.05). The index values had an antagonistic relationship with most parameters and regression analysis demonstrated that the BGTHI and the TCI had a negative association with the progressive motility, curvilinear, straight line, and average path velocities, and a positive association with slow sperm in the ejaculate in SP-45 and STP-15 phases (P < 0.01). Semen quality kinetics is affected throughout the year by the environment and it is apparent that it is impaired in D-P and better in R-P and RD-P seasons. The BGTHI and TCI measured in the sperm production phase classified the environment most coherently and presented better association with the behavior of sperm kinetics.

Differential impacts of particulate air pollution exposure on early and late stages of spermatogenesis

BACKGROUND

Despite increasing evidence that particulate air pollution has adverse effects on human semen quality, few studies examine the impact of air pollution on clinically relevant thresholds used to diagnose male fertility problems. Furthermore, exposure is often assessed using average air pollution levels in a geographic area rather than individualized estimates. Finally, physiologically-informed exposure windows are inconsistent.

OBJECTIVES

We sought to test the hypothesis that airborne particulate exposures during early-phase spermatogenesis will have a differential impact on spermatogenic formation compared to late-phase exposures, using an individualized model of exposure to particulate matter ≤ 2.5 µm and ≤ 10 µm (PM_2.5 and PM₁₀, respectively).

METHODS

From an original cohort of 183 couples, we conducted a retrospective analysis of 130 healthy males seeking to become parents, using spermatogenesis-relevant exposure windows of 77-34 days and 37-0 days prior to semen collection to encompass sperm development stages of mitosis/meiosis and spermiogenesis, respectively. Individualized residential exposure to PM_2.5 and PM₁₀ was estimated by selecting multiple air pollution sensors within the same geographic air basin as participants and employing inverse distance weighting to calculate mean daily exposure levels. We used multiple logistic regression to assess the association between pollution, temperature, and dichotomized World Health Organization semen parameters.

RESULTS

During the early phase of spermatogenesis, air pollution exposure is associated with 1.52 (95% CI: 1.04-2.32) times greater odds of < 30% normal heads per 1-unit increase in IQR for PM_2.5. In the late phase of spermatogenesis, air pollution exposure is associated with 0.35 (95% CI: 0.10-0.74) times greater odds of semen concentration < 15 million/mL per 1-unit increase in IQR for PM_2.5, and 0.28 (95% CI: 0.07-0.72) for PM₁₀.

CONCLUSION

Particulate exposure has a differential and more deleterious impact on sperm during early-phase spermatogenesis than late-phase.

Association between meteorological variables and semen quality: a retrospective study

Spermatogenesis is a temperature-dependent process, and high summer temperatures have been linked to lower sperm concentration and count. However, reports describing the association between other meteorological variables and semen quality are scarce. This study evaluated the association between semen quality and temperature, humidity, pressure, apparent temperature (AT), temperature-humidity index (THI), simplified wet-bulb global temperature (sWBGT), and sunshine duration. Semen samples were obtained at the Laboratorio de Andrología y Reproducción (LAR, Argentina), from men undergoing routine andrology examination (n=11657) and computer-assisted sperm analysis (n=4705) following WHO 2010 criteria. Meteorological variables readings were obtained from the Sistema Meteorológico Nacional. Sperm quality parameters were negatively affected in summer when compared to winter. Additionally, there was a significant decrease in sperm kinematics between winter and spring. Branch and bound variable selection followed by multiple regression analysis revealed a significant association between semen quality and meteorological variables. Specifically, changes in sunshine duration and humidity reinforced the prognosis of semen quality. Highest/lowest sunshine duration and humidity quantiles resulted in decreased sperm concentration, count, motility, vitality and membrane competence, nuclear maturity, and sperm kinematics associated to highest sunshine duration and lowest humidity. Findings from this report highlight the relevance of environmental studies for predicting alterations in male reproductive health associated to variations in meteorological variables, especially considering the current climate changes around the planet due to global warming and its consequences for human health.

An updated review on cattle thermoregulation: physiological responses, biophysical mechanisms, and heat stress alleviation pathways

Heat stress is one of the main obstacles to achieving efficient cattle production systems, and it may have numerous adverse effects on cattle. As the planet undergoes climatic changes, which is predicted to raise the earth's average temperature by 1.5 °C between 2030 and 2052, its impact may trigger several stressful factors for livestock. Among these, an increase in core body temperature would trigger physiological imbalance, consequently affecting reproduction, animal health, and dry matter intake adversely. Core body temperature increase is commonly observed and poses challenges to livestock farmers. In cattle farming, thermal stress severely affects milk production and weight gain, and can compromise food security in the coming years. This review presents an updated approach to the physiological and thermoregulatory responses of cattle under various environmental conditions. Strategies for mitigating the harmful effects of heat stress on livestock are suggested as viable alternatives for the betterment of production systems.

The specific enthalpy of air as an indicator of heat stress in livestock animals

Along with recognition of environmental effects on the performance and welfare of livestock animals, studies have been proposing new methodologies and parameters to diagnose the heat stress of animals through the physical properties of air. This article aims to present the state-of-the-art on the use of the specific enthalpy of air as an indicator of heat stress in livestock animals. As a starting point, conceptual considerations were made about the connection between homoeothermic animals and the environment. Variables for heat stress evaluation based on psychrometric air properties are then described, including dry bulb temperature and relative humidity, which are often used microclimate variables, and the specific enthalpy of dry air, which acts as a thermal comfort index. Final considerations highlight the recent history of the use of specific enthalpy of air equations as indicators of heat stress in livestock animals, with the intention of better understanding the relationship between animals and the environment. As a conclusion, the specific enthalpy of air is recommended as an indicator in the assessment of livestock housing conditions as, unlike other indices, it is based on thermodynamic air properties and not on linear regressions.

Effect of thermal stress on basic seminal characteristics of Gyr bulls

The objective of this study was to evaluate the influence of thermal stress indices and minimum temperature on the semen quality of dairy Gyr bulls and to determine whether the minimum night temperature is able to balance the thermal stress that occurred during the day. A total of 922 semen samples were collected from 391 bulls aged between 15 and 49 months, which participated in progeny pretest trials, from December 2011 to April 2017. Semen characteristics (ejaculate volume, gross motility, sperm motility, sperm vigor, sperm concentration, and percentage of total defects) and scrotal circumference were analyzed. Meteorological data were recorded daily by the National Institute of Meteorology. The analyses were carried out using mixed models. The following fixed effects were included in the model: test, month of sample collection, scrotal circumference, the age of the bull at sampling as covariate (linear regression), and the climatic variables (equivalent temperature index [ETI], temperature and humidity index [THI], or minimum temperature). The effect of the bull nested within the test was included in the model as a random effect. Two periods were considered to evaluate the effect of the climatic variables on sperm quality: 7 days before collection (period 1) and the day of collection (period 2). There was an effect of ETI on sperm vigor and concentration in both periods and on volume and percentage of total defects only in the second period. The THI exerted a significant effect on volume in both periods and on sperm motility and concentration only in the second period. There was an effect of the minimum temperature on ejaculate volume, sperm motility, sperm concentration, and percentage of total defects only in the second period, which corresponds to the day of semen collection. Taken together, the results show that there was sufficient thermal stress to negatively affect semen quality. However, the minimum temperature during the night was a significant factor that balanced these negative effects of THI and ETI on semen traits of Gyr bulls.

High temperature-humidity index compromises sperm quality and fertility of Holstein bulls in temperate climates

Rising temperatures caused by climate change have adverse effects on cattle physiology, welfare, health, and reproduction. Heat stress in cows affects the oocyte and embryo directly through heat shock on cellular function. Fewer data are available on the effect of high temperatures on male fertility. Temperature-humidity index (THI) is a measure for assessing the risk of heat stress that combines the effects of temperature and humidity. The aim of this study was to determine the relationship between THI and fresh or frozen-thawed sperm quality of Holstein bulls kept in temperate climates. Bull sperm data of 29,170 ejaculates from 933 bulls collected at 3 Dutch artificial insemination centers between 2015 and 2018 were evaluated. The assessed variables included total sperm motility and morphology of fresh semen, and total sperm motility, morphology, and progressive motility of frozen semen 0 and 3 h after thawing. In addition, 56-d nonreturn rates were analyzed. The assessed effects were season and THI on the day of semen collection and during spermatogenesis (30 d before collection), bull, age of bull, year, and location. Bulls were divided into 2 categories according to their age: young (<36 mo) and older (>36 mo). Overall sperm quality of young bulls improved as age increased. No effect of THI on fresh sperm variables was observed in either young or older bulls. However, high THI at spermatogenesis negatively affected the cryotolerance of sperm cells. Sperm cells from young and older bulls showed a pronounced decrease (14-18%) of the assessed variables 3 h after thawing after the increase of THI during spermatogenesis in autumn. Remarkably, older bulls were more sensitive to THI at spermatogenesis compared with semen collection, showing up to a 3.8 times higher negative effect on frozen sperm quality. However, an elevated THI at semen collection produced a tendency toward decreased 56-d nonreturn rates as the age of the bull increased. Although this decrease was up to 4%, rising temperatures may still cause important economic losses in the future. For the first time, the present study confirmed that climate compromises not only sperm quality, but also dairy bull fertility.

Genetic regulators of mineral amount in Nelore cattle muscle predicted by a new co-expression and regulatory impact factor approach

Mineral contents in bovine muscle can affect meat quality, growth, health, and reproductive traits. To better understand the genetic basis of this phenotype in Nelore (Bos indicus) cattle, we analysed genome-wide mRNA and miRNA expression data from 114 muscle samples. The analysis implemented a new application for two complementary algorithms: the partial correlation and information theory (PCIT) and the regulatory impact factor (RIF), in which we included the estimated genomic breeding values (GEBVs) for the phenotypes additionally to the expression levels, originally proposed for these methods. We used PCIT to determine putative regulatory relationships based on significant associations between gene expression and GEBVs for each mineral amount. Then, RIF was adopted to determine the regulatory impact of genes and miRNAs expression over the GEBVs for the mineral amounts. We also investigated over-represented pathways, as well as pieces of evidences from previous studies carried in the same population and in the literature, to determine regulatory genes for the mineral amounts. For example, NOX1 expression level was positively correlated to Zinc and has been described as Zinc-regulated in humans. Based on our approach, we were able to identify genes, miRNAs and pathways not yet described as underlying mineral amount. The results support the hypothesis that extracellular matrix interactions are the core regulator of mineral amount in muscle cells. Putative regulators described here add information to this hypothesis, expanding the knowledge on molecular relationships between gene expression and minerals.

Semen quality and diversity of morphological sperm abnormalities in bulls: breed and strain effects

At present great attention is paid to studying genetic regulation of farm animal adaptations to environmental conditions. This problem is very important due to a wide expansion of highly productive cattle breeds created in Europe and North America. However, until the present no investigation of changing semen quality in bulls of imported breeds during their adaptations to environmental conditions of Western Siberia has been conducted. The aim of this study was to investigate semen quality peculiarities and the diversity of morphological sperm abnormalities in bulls of imported and local breeds kept in the environmental conditions of the southern part of Western Siberia. We determined sperm concentration, sperm count, and rate of sperm with progressive motility and percentage of morphologically normal spermatozoa. The rate of sperm abnormalities according to Blome’s classifcation was determined too. It was found that the mean values of sperm concentration, sperm motility and percentage of morphologically normal spermatozoa in the bulls investigated were similar to those in bulls kept in European countries. Inter­breed differences in these parameters were not found. However, bulls of the Red Danish, Angler, and Simmental breeds had a higher percentage of misshapen sperm head and pyriform sperm head than bulls of the Black­White breed. An inter­strain difference in sperm motility in bulls of the Black­White breed was observed. It was found that bulls of Reflection Sovereign 198998 strain had lover sperm motility than bulls of Wis Burke Ideal 1013415 strain. No inter­strain differences in sperm production, percentage of morphologically normal spermatozoa and rate of main sperm abnormalities were found. Thus, it has been found that the environmental conditions of the southern part of Western Siberia do not seriously affect the sperm production, sperm motility or percentage of morphologically normal spermatozoa in bulls. However, the increased rate of misshapen and pyriform sperm heads in the bulls of the foreign breeds points to a need to study sperm DNA fragmentation.

Scrotal infrared digital thermography predicts effects of thermal stress on buffalo (Bubalus bubalis) semen

The objective was to use scrotal infrared digital thermography to evaluate effects of thermal stress on semen quality of Murrah buffalo (Bubalus bubalis) breeding bulls. Ejaculates from 109 Murrah bulls maintained at three semen stations were evaluated for: ejaculate volume, sperm concentration (SCON), initial motility (IM), percent live sperm (LIVE), acrosome integrity of fresh semen (AIFS), plasma membrane integrity of fresh semen (PMIFS), head abnormalities of fresh semen (HAFS), midpiece abnormalities of fresh semen (MPAFS), tail abnormalities of fresh semen (TAFS), post-thaw motility (PTM), acrosome integrity of post-thawed semen (AIPT) and plasma membrane integrity of post-thawed semen (PMIPT). Scrotal and ocular surface temperatures were acquired during rainy, winter and summer seasons, using an FLIR i5 infrared camera. Thermographic images were analyzed with Quick Report 1.2 SP2 software and temperature data acquired. Daily mean temperature and mean relative humidity were used to determine the temperature-humidity index (THI). Environmental factors were analyzed using CORR to determine collinearity among independent variables. There was a high correlation among THI, proximal, mid and distal scrotal temperatures (r ≥ 0.73). Therefore, distal pole temperature (DPT), THI, temperature gradient (TG) and ocular temperature (OcT) were used in the analysis of variance (ANOVA) and in regression analysis of dependent variables. The THI, DPT, TG and OcT had significant influences on sperm abnormalities, acrosome and plasma membrane integrity of fresh as well as post-thawed semen. The TG had significant effects on LIVE and SCON. All semen quality parameters were predicted (regression analysis) as a function of the three independent factors. We concluded that scrotal infrared thermography was useful for assessing influences of thermal stress and environmental factors on characteristics of buffalo semen.