Sensible and latent heat loss from the body surface of Holstein cows in a tropical environment

The general principles of the mechanisms of heat transfer are well known, but knowledge of the transition between evaporative and non-evaporative heat loss by Holstein cows in field conditions must be improved, especially for low-latitude environments. With this aim 15 Holstein cows managed in open pasture were observed in a tropical region. The latent heat loss from the body surface of the animals was measured by means of a ventilated capsule, while convective heat transfer was estimated by the theory of convection from a horizontal cylinder and by the long-wave radiation exchange based on the Stefan–Boltzmann law. When the air temperature was between 10 and 36°C the sensible heat transfer varied from 160 to –30 W m^–2, while the latent heat loss by cutaneous evaporation increased from 30 to 350 W m^–2. Heat loss by cutaneous evaporation accounted for 20–30% of the total heat loss when air temperatures ranged from 10 to 20°C. At air temperatures >30°C cutaneous evaporation becomes the main avenue of heat loss, accounting for approximately 85% of the total heat loss, while the rest is lost by respiratory evaporation.Part of first authors doctoral thesis     

Thermoregulatory responses of Holstein cows exposed to experimentally induced heat stress

Heat stress (HS) adversely influences productivity and welfare of dairy cattle. We hypothesized that the thermoregulatory mechanisms vary depending on the exposure time to HS, with a cumulative effect on the adaptive responses and thermal strain of the cow. To identify the effect of HS on adaptive thermoregulatory mechanisms and predictors of caloric balance, Holstein cows were housed in climate chambers and randomly distributed into thermoneutral (TN; n=12) or HS (n=12) treatments for 16 days. Vaginal temperature (VT), rectal temperature (Tre), respiratory rate (RR), heart rate (HR), and dry matter intake (DMI) were measured. The temperature and humidity under TN were 25.9±0.2 °C and 73.0±0.8%, respectively, and under HS were 36.3±0.3 °C and 60.9±0.9%, respectively. The RR of the HS cows increased immediately after exposure to heat and was higher (76.02±1.70bpm, p<0.001) than in the TN (39.70±0.71bpm). An increase in Tre (39.87±0.07 °C in the HS vs. 38.56±0.03 °C in the TN, p<0.001) and in VT (39.82±0.10 °C in the HS vs. 38.26±0.03 °C in the TN, p<0.001) followed the increase in RR. A decrease (p<0.05) in HR occurred in the HS (62.13±0.99bpm) compared with the TN (66.23±0.79bpm); however, the magnitude of the differences was not the same over time. The DMI was lower in HS cows from the third day (8.27±0.33 kg d⁻¹ in the HS vs. 14.03±0.29 kg d⁻¹ in the TN, p<0.001), and the reduction of DMI was strongly affected (r=−0.65) by changes in the temperature humidity index. The effect of environmental variables from the previous day on physiological parameters and DMI was more important than the immediate effect, and ambient temperature represented the most determinant factor for heat exchange. The difference in the responses to acute and chronic exposure to HS suggests an adaptive response. Thus, intense thermal stress strongly influence thermoregulatory mechanisms and the acclimation process depend critically on heat exposure time.     

Thermoregulatory responses of Holstein and Brown Swiss Heat-Stressed dairy cows to two different cooling systems

Thirty-seven Holstein and 26 Brown Swiss dairy cows were used to evaluate the effect of two different cooling systems on physiological and hormonal responses during the summer. A control group of cows had access only to shade (C). A second group was cooled with spray and fans (S/F) and the third group was under an evaporative cooling system called Korral Kool (KK). The maximum temperature humidity index during the trial was from 73 to 85. Rectal temperatures and respiration rates of the C group were higher (P < 0.05) than those of the S/F and KK groups in both Holstein and Brown Swiss cows. Triiodothyronine levels in milk were higher (P < 0.05) in the KK group than in the S/F and C groups, while cortisol levels were lower (P < 0.05) in the C group than in S/F and KK. There was no significant difference in the hormonal response of the two breeds. These results demonstrate that both cooling systems may be used increase the comfort of Holstein and Brown Swiss cows during summer in hot, dry climates.     

Identification and bioinformatics analysis of microRNAs associated with stress and immune response in serum of heat-stressed and normal Holstein cows

MicroRNAs (miRNAs) are small single-stranded non-coding RNAs that have an important regulatory function in animal growth and developmental processes. However, the differential expression of miRNA and the role of these miRNAs in heat-stressed Holstein cows are still unknown. In this study, the profile of differentially expressed miRNAs and the target genes analysis in the serum of heat-stressed and normal Holstein cows were investigated by a Solexa deep-sequencing approach and bioinformatics. The data identified 52 differentially expressed miRNAs in 486 known miRNAs which were changed significantly between heat-stressed and normal Holstein cows (fold change >2, P < 0.001). Target genes analysis showed that at least 7 miRNAs (miR-19a, miR-19b, miR-146a, miR-30a-5p, miR-345-3p, miR-199a-3p, and miR-1246) were involved in the response to stress, oxidative stress, development of the immune system, and immune response among the identified 52 differentially expressed miRNAs. Five miRNAs (miR-27b, miR-181a, miR-181b, miR-26a, and miR-146b) were involved in stress and immune responses and the expression of five miRNAs was striking (P < 0.001). In addition, RT-qPCR and deep-sequencing methods showed that 8 miRNAs among the 12 selected miRNAs (miR-19a, miR-19b, miR-27b, miR-30a-5p, miR-181a, miR-181b, miR-345-3p, and miR-1246) were highly expressed in the serum of heat-stressed Holstein cows. GO and KEGG pathway analysis showed that these differentially expressed miRNAs were involved in a pathway that may differentially regulate the expression of stress response and immune response genes. Our study provides an overview of miRNAs expression profile and the interaction between miRNAs and their target genes, which will lead to further understanding of the important roles of miRNAs in heat-stressed Holstein cows.     

Effects of thermal environment on sleep and circadian rhythm

ABSTRACT: The thermal environment is one of the most important factors that can affect human sleep. The stereotypical effects of heat or cold exposure are increased wakefulness and decreased rapid eye movement sleep and slow wave sleep. These effects of the thermal environment on sleep stages are strongly linked to thermoregulation, which affects the mechanism regulating sleep. The effects on sleep stages also differ depending on the use of bedding and/or clothing. In semi-nude subjects, sleep stages are more affected by cold exposure than heat exposure. In real-life situations where bedding and clothing are used, heat exposure increases wakefulness and decreases slow wave sleep and rapid eye movement sleep. Humid heat exposure further increases thermal load during sleep and affects sleep stages and thermoregulation. On the other hand, cold exposure does not affect sleep stages, though the use of beddings and clothing during sleep is critical in supporting thermoregulation and sleep in cold exposure. However, cold exposure affects cardiac autonomic response during sleep without affecting sleep stages and subjective sensations. These results indicate that the impact of cold exposure may be greater than that of heat exposure in real-life situations; thus, further studies are warranted that consider the effect of cold exposure on sleep and other physiological parameters.     

Differences in body temperature between black-and-white and red-and-white Holstein cows reared on a hot climate using infrared thermography

Heat stress is one of the greatest issues of the dairy industry in regions with hot climate. Since coat color appears to be related to heat stress adaptiveness, we compared rectal temperatures and surface temperatures of Red-and-white (RW, n = 14) and Black-and-white (BW, n = 16) Holstein cows using infrared thermography in both cold (July; mean temperature: 15.5 °C) and hot (March; mean temperature: 30.5 °C) seasons in Southern Brazil. Thermographic images were taken from the left side of the animal at a distance of 4 m. The images obtained were then analyzed using the software Testo IRSoft. The variables obtained by thermography of the body surface include the temperature of non-pigmented patches, obtained using the average of five spots on white patches in a rectangle drawn on the body of the cow from the scapula to the ilium of the cow until the middle of the ribs; the temperature of pigmented patches, obtained using an average of 5 pigmented spots on the same rectangle; the temperature at the hottest spot and the temperature at the coldest spot, within the same rectangle. Rectal temperature measures were taken by a mercury thermometer during milkings. In our findings, during the cold season, RW cows had lower temperatures on the surface of pigmented spots (p = 0.01) but did not differ from BW animals when comparing rectal temperatures (p = 0.70). During the hot season, however, RW cows had lower temperatures on white spots (p = 0.049) as well as lower rectal temperatures (p = 0.029). These results suggest that the red coat phenotype presents less absorption of solar radiation, retaining less heat.     

An assessment of skin temperature gradients in a tropical primate using infrared thermography and subcutaneous implants

Infrared thermography has become a useful tool to assess surface temperatures of animals for thermoregulatory research. However, surface temperatures are an endpoint along the body's core-shell temperature gradient. Skin and fur are the peripheral tissues most exposed to ambient thermal conditions and are known to serve as thermosensors that initiate thermoregulatory responses. Yet relatively little is known about how surface temperatures of wild mammals measured by infrared thermography relate to subcutaneous temperatures. Moreover, this relationship may differ with the degree that fur covers the body. To assess the relationship between temperatures and temperature gradients in peripheral tissues between furred and bare areas, we collected data from wild mantled howling monkeys (Alouatta palliata) in Costa Rica. We used infrared thermography to measure surface temperatures of the furred dorsum and bare facial areas of the body, recorded concurrent subcutaneous temperatures in the dorsum, and measured ambient thermal conditions via a weather station. Temperature gradients through cutaneous tissues (subcutaneous-surface temperature) and surface temperature gradients (surface-ambient temperature) were calculated. Our results indicate that there are differences in temperatures and temperature gradients in furred versus bare areas of mantled howlers. Under natural thermal conditions experienced by wild animals, the bare facial areas were warmer than temperatures in the furred dorsum, and cutaneous temperature gradients in the face were more variable than the dorsum, consistent with these bare areas acting as thermal windows. Cutaneous temperature gradients in the dorsum were more closely linked to subcutaneous temperatures, while facial temperature gradients were more heavily influenced by ambient conditions. These findings indicate that despite the insulative properties of fur, for mantled howling monkeys surface temperatures of furred areas still demonstrate a relationship with subcutaneous temperatures. Given that most mammals possess dense fur, this provides insight for using infrared imaging in thermoregulatory studies of wild animals lacking bare skin.     

Lymphocyte functions in dairy cows in hot environment

This study was carried out to ascertain the effects of intense high environmental temperatures (HET) on lymphocyte functions in periparturient dairy cows. The study was undertaken from the beginning of March through the end of July 2003 in a commercial dairy unit located approximately 40 km north of Rome. Thirty-four Holstein cows were utilised in the study. Twenty-two of these cows gave birth in spring (SP cows), from 28 March to 30 April. The remaining 12 cows gave birth in summer (SU cows), between 15 June and 2 July. The two groups of cows were balanced for parity and were fed the same rations. Blood samples were taken 4, 3, 2 and 1 week before calving, and 1, 2 and 4 weeks after calving, in order to evaluate peripheral blood mononuclear cell (PBMC) function in vitro, and to determine plasma cortisol concentrations. After isolation, the PBMC were stimulated with mitogens and their response in terms of DNA synthesis and IgM secretion was measured. During spring, either the day (9–20 h) or the night (21–8 h) temperature humidity index (THI) was below the upper critical THI (72) established for dairy cows. During summer, the mean daily THI values were 79.5±2.9 during the day and 70.1±4.7 during the night. Furthermore, during summer, three heat waves (a period of at least 3 consecutive days during which there were less than 10 recovery hours) occurred. Recovery hours were intended hours with a THI below 72. The first heat wave lasted 5 days, the second 6 days, and the third 15 days. Compared to the SP cows, over the entire periparturient period the extent of DNA synthesis and IgM secretion levels were lower (P ranging from <0.01 to 0.0001) and higher (P<0.01) respectively, in the SU cows. Before calving, the SU cows also presented higher (P<0.01) concentrations of plasma cortisol compared to the SP cows. This study indicates that the effects of HET on the immune response depend on the specific immune function under consideration, and that neuroendocrinal changes due to HET may play a role in the perturbation of immune functions.     

Modeling heat stress effects on dairy cattle milk production in a tropical environment using test-day records and random regression models

In tropical environments, dairy cattle production is constrained by several factors, including climate. The seasonal loss of milk due to heat stress is a recurring challenge for many dairy producers. The objective of this study was to detect heat stress thresholds, milk yield loss and individual animal variations using random regression models for dairy cattle from test-day milk records. Data were obtained from the Kenya Livestock Breeders Organization for the years 2000–2017 and merged with weather data. The weather parameters were grid-interpolated solar and meteorological data obtained from the National Aeronautics and Space Administration/Prediction Of Worldwide Energy Resources (NASA/POWER). After editing, the records comprised 49 993, 45 251 and 36 136 test-day records for first, second, and third lactations, respectively, for the four main dairy breeds: Friesian (68.0%), Ayrshire (21.1%), Jersey (7.6%) and Guernsey (3.3%). Variance components were estimated using Restricted Maximum Likelihood in ASReml software. Random regression models with third-order Legendre polynomials were fitted to the average and individual lactation curves and the reaction norms. An extended factor analytic variance structure for the random cow effects was used to estimate (co)variances between days in milk and thermal load. The daily average temperature (TA) and temperature humidity index (THI) were identified as the most suitable thermal load indicators for assessing milk yield losses. Considering a one day lag, the estimated heat stress thresholds were about 22 °C and 69 index units for TA and THI, respectively. Almost no differences were observed for estimated residual variances between the thermal load indicators, indicating there was no better model fit by TA or THI. The heat stress thresholds and milk loss patterns are important for management of dairy production systems in the tropics with climatic conditions similar to this study. Data recording should be improved as a tool to monitor the expected impacts of climate change and mitigation measures.     

Nitrogen budget and gaseous nitrogen loss in a tropical agricultural watershed

Although agricultural systems in tropical monsoon Asia play a central role in the global nitrogen (N) cycle, details of the N cycle in this region on a watershed scale remain unclear. This study quantified the N budget in a tropical watershed of 221 km² on Java Island, where paddy fields cover 28% of the land, by conducting field surveys. The amount of net biochemical gaseous N loss to the atmosphere (X _GB ), which is generally difficult to determine, was calculated as the residual of the N balance. Assuming that NH₃ volatilization balances deposition, and hence subtracting NH₄–N from the N import with atmospheric deposition, the average total import and export of N per year was found to be 46.5 kg ha⁻¹ year⁻¹ over the watershed. Of this, 71% was imported as fertilizer (M _F ) and 29% with atmospheric deposition (M _AD ). On the export side, 42% was lost as X _GB , 37% with incineration of rice residues and wood fuel (X _GI ), 13% with river discharge (X _D ) and 9% with rice surplus export (X _R ). A large portion of X _GB , and consequently, a small portion of X _D could be explained by the high rate of denitrification resulting from the high temperature and humid climate, and are thought to be common features of tropical watersheds where paddy fields are found.     

Latent heat loss of dairy cows in an equatorial semi-arid environment

The present study aimed to evaluate evaporative heat transfer of dairy cows bred in a hot semi-arid environment. Cutaneous (E(S)) and respiratory (E(R)) evaporation were measured (810 observations) in 177 purebred and crossbred Holstein cows from five herds located in the equatorial semi-arid region, and one herd in the subtropical region of Brazil. Rectal temperature (T(R)), hair coat surface temperature (T(S)) and respiratory rate (F(R)) were also measured. Observations were made in the subtropical region from August to December, and in the semi-arid region from April to July. Measurements were done from 1100 to 1600 hours, after cows remained in a pen exposed to the sun. Environmental variables measured in the same locations as the animals were black globe temperature (T(G)), air temperature (T(A)), wind speed (U), and partial air vapour pressure (P(V)). Data were analysed by mixed models, using the least squares method. Results showed that average E(S) and E(R) were higher in the semi-arid region (117.2 W m(-2) and 44.0 W m(-2), respectively) than in the subtropical region (85.2 W m(-2) and 30.2 W m(-2), respectively). Herds and individual cows were significant effects (P < 0.01) for all traits in the semi-arid region. Body parts did not affect T(S) and E(S) in the subtropical region, but was a significant effect (P < 0.01) in the semi-arid region. The average flank T(S) (42.8°C) was higher than that of the neck and hindquarters (39.8°C and 41.6°C, respectively). Average E(S) was higher in the neck (133.3 W m(-2)) than in the flank (116.2 W m(-2)) and hindquarters (98.6 W m(-2)). Coat colour affected significantly both T(S) and E(S) (P < 0.01). Black coats had higher T(S) and E(S) in the semi-arid region (41.7°C and 117.2 W m(-2), respectively) than white coats (37.2°C and 106.7 W m(-2), respectively). Rectal temperatures were almost the same in both subtropical and semi-arid regions. The results highlight the need for improved management methods specific for semi-arid regions.     

Attempts to vaccinate ewes and their lambs against natural infection with Haemonchus contortus in a tropical environment

A vaccine containing integral membrane glycoproteins from the intestine of Haemonchus contortus was evaluated in three groups of grazing sheep each containing 13 ewes and their 16 lambs naturally infected with gastrointestinal nematodes. Two groups were vaccinated with either 5 or 50 μg of the antigen per immunisation, while the third, the control group, received adjuvant alone. The sheep were immunised six times at 3 week intervals, partly because the vaccine antigens are hidden and thus no immunological boost would be delivered by subsequent infection and partly because the level of Haemonchus spp. challenge was expected to be high. The vaccinated ewes, first immunised approximately 1 month before lambing, showed a circulating antibody response but no signs of reduced anaemia or Haemonchus spp. egg counts, compared with control ewes. Several ewes with severe haemonchosis in all three groups had to be given precautionary treatment with anthelmintic drugs. In contrast, vaccinating their lambs with either 5 or 50 μg of the antigen per immunisation resulted in 10 fold higher antibody titres. In the case of the lower antigen dose this was associated with significantly less anaemia, 72% reduction in the overall number of Haemonchus spp. eggs produced and significantly fewer worms compared with control lambs. It is hypothesised that the heavily pregnant or lactating ewes did not have sufficient physiological reserves to mount a protective response following vaccination in the tropical weather and high challenge conditions that prevailed. Nevertheless, the vaccine could afford useful protection for lambs against H. contortus.     

The effect of dynamic exercise on resting cold thermoregulatory responses measured during water immersion

The purpose of this study was to evaluate the effect of exercise on the subsequent post-exercise thresholds for vasoconstriction and shivering measured during water immersion. On 2 separate days, seven subjects (six males and one female) were immersed in water (37.5 degrees C) that was subsequently cooled at a constant rate of approximately 6.5 degrees C x h(-1) until the thresholds for vasoconstriction and shivering were clearly established. Water temperature was then increased to 37.5 degrees C. Subjects remained immersed for approximately 20 min, after which they exited the water, were towel-dried and sat in room air (22 degrees C) until both esophageal temperature and mean skin temperature (Tsk) returned to near-baseline values. Subjects then either performed 15 min of cycle ergometry (at 65% maximal oxygen consumption) followed by 30 min of recovery (Exercise), or remained seated with no exercise for 45 min (Control). Subjects were then cooled again. The core temperature thresholds for both vasoconstriction and shivering increased significantly by 0.2 degrees C Post-Exercise (P < 0.05). Because the Tsk at the onset of vasoconstriction and shivering was different during Pre- and Post-Exercise Cooling, we compensated mathematically for changes in skin temperatures using the established linear cutaneous contribution of skin to the control of vasoconstriction and shivering (20%). The calculated core temperature threshold (at a designated skin temperature of 32.0 degrees C) for vasoconstriction increased significantly from 37.1 (0.3) degrees C to 37.5 ( 0.3) degrees C post-exercise (P < 0.05). Likewise, the shivering threshold increased from 36.2 (0.3) degrees C to 36.5 (0.3) degrees C post-exercise (P < 0.05). In contrast to the post-exercise increase in cold thermal response thresholds, sequential measurements demonstrated a time-dependent similarity in the Pre- and Post-Control thresholds for vasoconstriction and shivering. These data indicate that exercise has a prolonged effect on the post-exercise thresholds for both cold thermoregulatory responses.     

Respiratory heat loss and core temperatures during submaximal exercise

1. 1. This study examined the effect of inhaling air supersaturated with water on changes of core temperatures in submaximally exercising males.

2. 2. During exercise with inhalation of supersaturated relative to low-air-humidity air, a significant elevation in tympanic temperature (P = 0.009) and a significant decrease in esophageal temperature (P = 0.004) were observed.

3. 3. Forehead skin temperatures significantly decreased during humidified air inhalation (P = 0.02) supporting that this treatment induced greater thermolytic responses that cooled the skin.

4. 4. The results are consistent with the conclusion that heat loss from the upper airways directly influenced human cerebral temperatures as indexed by tympanic temperatures.

     

Seasonal patterns of heat loss in wild bottlenose dolphins (<Emphasis Type="Italic">Tursiops truncatus</Emphasis>)

This study investigated patterns of heat loss in bottlenose dolphins (Tursiops truncatus) resident to Sarasota Bay, FL, USA, where water temperatures vary seasonally from 11 to 33°C. Simultaneous measurements of heat flux (HF) and skin surface temperature were collected at the body wall and appendages of dolphins during health-monitoring events in summer (June 2002–2004) and winter (February 2003–2005). Integument thickness was measured and whole body conductance (W/m² °C) was estimated using HF and colonic temperature measurements. Across seasons, HF values were similar at the appendages, but their distribution differed significantly at the flipper and fluke. In summer, these appendages displayed uniformly high values, while in winter they most frequently displayed very low HF values with a few high HF values. In winter, blubber thickness was significantly greater and estimated conductance significantly lower, than in summer. These results suggest that dolphins attempt to conserve heat in winter. In winter, though, HF values across the body wall were similar to (flank) or greater than (caudal keel) summer values. It is likely that higher winter HF values are due to the steep temperature gradient between the body core and colder winter water, which may limit the dolphin’s ability to decrease heat loss across the body wall.     

Thermoregulatory stress during rest and exercise in heat in patients with a spinal cord injury

Twelve subjects with spinal cord injuries and four controls (all male) were exposed to heat while sitting at rest or working at each of three environmental temperatures, 30, 35 and 40 degrees C, with a relative humidity of 50%. Exercise was accomplished at a load of 50 W on a friction-braked cycle ergometer which was armcranked or pedalled. Functional electrical stimulation of the legs was provided to the subjects with quadriplegia and paraplegia to allow them to pedal a cycle ergometer. The data showed that individuals with quadriplegia had the poorest tolerance for heat. As an example, in this group, accomplishing armcrank ergometry while working at an environmental temperature of 40 degrees C resulted in an increase in aural temperature of 2 degrees C in 30 min. The aural temperature of individuals with paraplegia working for the same length of time under the same conditions rose approximately 1 degree C. There was virtually no change in the aural temperature in the control subjects.     

Arginine vasopressin does not mediate heat loss in the tail of the rat

It has been reported that hypothermia induced by arginine vasopressin (AVP) is brought about by a coordinated response of reduced thermogenesis in brown adipose tissue (BAT) and increased heat loss through the tail of rats. However, it is well known that AVP is one of the strongest peripheral vasoconstrictors. Whether the AVP-induced hypothermia is associated with an increase in heat loss through the tail is questionable. Therefore, the present study assessed the relationship between the effects of AVP on tail skin temperature and the induced hypothermic response, and to determine if peripheral AVP administration increases heat loss from the tail. Core, BAT and tail skin temperature were monitored by telemetry in male Sprague–Dawley rats before and after intraperitoneal administration of AVP or vasopressin receptor antagonist. We also analyzed simultaneously of the time-course of AVP-induced hypothermic response and its relationship with changes in BAT temperature, and effect of AVP on grooming behavior. The key observations in this study were: (1) rats dosed with AVP induced a decrease in heat production (i.e., a reduction of BAT thermogenesis) and an increase of saliva spreading for evaporative heat loss (i.e., grooming behavior); (2) AVP caused a marked decrease in tail skin temperature and this effect was prevented by the peripheral administration of the vasopressin V1a receptor antagonist, suggesting that exogenous AVP does not increase heat loss in the tail of rats; (3) the vasopressin V1a receptor antagonist could elevate core temperature without affecting tail skin temperature, suggesting that endogenous AVP is involved in suppression of thermogenesis, but not mediates heat loss in the tail of rats. Overall, the present study does not support the conclusion of previous reports that AVP increased tail heat loss in rats, because AVP-induced hypothermia in the rat is accompanied by a decrease in tail skin temperature. The data indicate that exogenous AVP-induced hypothermia attributed to the suppression of thermoregulatory heat production and the increase of saliva spreading for evaporative heat loss.     

Carbon mineralization by termites in tropical forests,with emphasis on fungus combs

A role of termites in decomposition processes was quantitatively evaluated in a dry evergreen forest (DEF) in Thailand, using respiration rates and biomasses of fungus combs as well as of termites themselves. The termite population and fungus combs mineralized 11.2% of carbon (C) in the annual aboveground litterfall (AAL) by their respiration. Fungus combs were responsible for a major part (7.2% of the AAL) of the C mineralization mediated by termites. For comparison, fractions of AAL mineralized by respiration from termite populations and fungus combs were estimated for tropical forests and savannas where termites have been well studied, assuming that there is the same ratio as for the DEF between biomass of fungus combs and abundance of fungus growers. Termites in dry tropical forests (annual rainfall<2,000 mm) are shown to mineralize about 10% of C in the AAL by respiration from their populations and fungus combs, and their ecological impact in savannahs is comparable in this aspect. A significant negative correlation between fraction of AAL and annual rainfall demonstrates that the importance of termites in decomposition processes is greater in dry tropical forests than in moist tropical forests. Considering that fungus combs contributed significantly to AAL mineralization in most of the tropical forests and savannas, fungus growers are a much more influential group than previously expected in tropical ecosystems.T. Abe deceased on 27 March 2000