A. HERNÁNDEZ
Laboratorio de Alteraciones Funcionales, Facultad de Medicina Veterinaria y Zootecnia, Universidad Veracruzana,Veracruz, México.
Corresponding author; e–mail: anhernandez@uv.mx

B. DOMÍNGUEZ
Laboratorio de Fisiología, Facultad de Medicina Veterinaria y Zootecnia, Universidad Veracruzana, Veracruz, México

P. CERVANTES
Laboratorio de Alteraciones Funcionales, Facultad de Medicina Veterinaria y Zootecnia, Universidad Veracruzana,Veracruz, México

S. MUÑOZ–MELGAREJO ]]> Laboratorio de Bioquímica, Facultad de Medicina Veterinaria y Zootecnia, Universidad Veracruzana, Veracruz, México

S. SALAZAR–LIZÁN
Grupo Ganadería, Facultad de Medicina Veterinaria y Zootecnia, Universidad Veracruzana, Veracruz, México

A. TEJEDA–MARTÍNEZ
Grupo Climatología Aplicada. Licenciatura en Ciencias Atmosféricas, Universidad Veracruzana, Xalapa, Veracruz, México

Received June 17, 2009; accepted May 18, 2010

RESUMEN

Se presentan resultados del análisis de datos de temperaturas (°C) y humedad relativa (RH) combinados, para obtener el índice de temperatura y humedad (THI por sus siglas en inglés) en ganado para la región de Veracruz, México, con el propósito de hacer comparaciones climáticas en diferentes periodos de estudio (1917–1960, 1961–1990, 1991–2008), así como futuros escenarios a 2020, 2050 y 2080. Los resultados indican que las posibilidades de confort animal son reducidas. Para los periodos pasados se encuentra un THI creciente: 83, 85 y 86, respectivamente, considerando las temperaturas máximas para el mes de mayo. Para el futuro los THI fueron obtenidos a partir de los escenarios de emisiones A2 y B2 del IPCC para los modelos GFDL 2020 (80.87), 2050 (81.58), 2080 (82.82); ECHAM 2020 (81.27), 2050 (82.74), 2080 (83.95) y PRECIS HADCM2 2020 (81.24), 2050 (82.65), 2080 (83.95), que resultan en la categoría de peligrosos.

ABSTRACT

Results of the analysis of combined temperature (°C) and relative humidity (RH) data are presented in order to obtain the temperature–humidity index (THI) in livestock for the region of Veracruz, México, in order to make climate comparisons in different study periods (1917–1960, 1961–1990, 1991–2008), as well as future scenarios for 2020, 2050 and 2080. The results indicate that the possibilities for animal comfort are scarce. For the past periods a growing THI has been found: 83, 85 and 86, respectively, considering the maximum temperatures for the month of May. For the future, the obtained THI were obtained from IPCC emissions scenarios A2 and B2 for the GFDL 2020 (80.87), 2050 (81.58), 2080 (82.82); ECHAM 2020 (81.27), 2050 (82.74), 2080 (83.95) and PRECIS HADCM2 2020 (81.24), 2050 (82.65), 2080 (83.95) models, whose results are in the category of dangerous.

Keywords: THI, climate change, livestock comfort, animal heat stress.

1. Introduction

A contest between farmers and climate has been going on for centuries. Farmers related their agricultural tasks with the state of atmospheric changes on a daily basis (Belliveau et al., 2006). While livestock breeding has been around for nearly 500 years in Veracruz, on the east coast of México, with the arrival of the Spanish conquerors (Malgrejo–Vivanco, 1980; Velasco Toro and Skerritt, 2004), in recent years variations in climate have stopped being a daily occurrence and have become a constant concern among meat and milk producers. Climate change is even beginning to cause unease associated with the increase of global greenhouse gases (Salazar et al., 2008).

This concern is justified, since according to Morton (2007), Allen et al. (2007) and Herrero et al. (2010), the most important impacts of climate change will occur precisely among producers with a subsistence economy in tropical regions of developing countries.

The potential effect of climate change on cattle has been linked to the economic viability of the various animal production systems, since the increase of ambient temperature during summer periods is associated with the decrease of voluntary intake of food, causing reductions in weight in feedlot cattle and a drop in milk production in dairy cattle (Frank et al., 2001; Arias et al., 2008).

The easiest way to assess the effect of increasing temperatures in livestock is the use of indexes like the so–called temperature–humidity index (THI), precisely because they combine data from ambient temperature (T) and relative humidity (RH) (Collier et al., 2007).

The THI has been used as a heat stress indicator, which has proven useful to assess the differences in the degree of cattle comfort at different times of the year in the state of Tabasco, México (de Dios–Vallejo et al., 1987), as well as the heat stress effects on milk production and pregnancy rate in cows (Lozano et al., 2005). In the state of Veracruz, México, it was used to determine different groups of cows according to animal responses to heat stress and associate them with their bioproduction (Hernández et al., 2007). According to Vitali et al. (2009), a high THI is a risk factor for the survival of cattle, especially for neonates and mature cows.

In the mid 90s, the first regional climate change scenarios were created in the country (Conde et al., 1994, 2000; Gay, 2000). In these studies, the scenarios of extreme temperatures, precipitation and solar radiation were generated for doubling conditions of the carbon dioxide (2 × CO₂) concentration, based on the base scenario obtained form the normal means of the period 1941–1970 for 23 sites in México. Subsequently, Conde et al. (1995) and Magaña et al. (2000) created base scenarios of temperature and precipitation from the normal monthly mean of temperature and precipitation from the period 1951–1980.

More recently, from models of the Canadian Centre for Climate (CCC) and the Geophysical Fluid Dynamics Laboratory (GFDLR30), Conde et al. (2000) made scenarios of possible changes in temperature and precipitation for México and also for 2 × CO₂ atmospheric conditions. The results of the cited models show that temperatures may increase between 1 and 2 °C for the CCC model, while the GFDLR model changes will vary between 2 and 3 °C.

This work aims to estimate, for the livestock of Veracruz, the degree of thermal comfort in the past and present, and the alterations in animal comfort for the years 2020, 2050 and 2080.

2. Methods

The data used was provided by the Servicio Meteorológico Nacional (National Meteorological Service, SMN). It comes from the Centro de Previsión del Golfo (Gulf Forecast Center –CPG), meteorological station number 3091 692, located in the city of Veracruz, to the east of México, off the coast of the Gulf of México at 19° 08' 32" north latitude and 96° 06' 40" west longitude; with an altitude of 15 meters above sea level. According to Vidal (2004), in the state of Veracruz from sea level to 1000 m in altitude, the climate is warm, with an average annual temperature of 22 °C, to very warm, over 26 °C.

The degree of climate security for livestock was established by the THI, using the following equation:

T = Daily mean temperature (°C)

RH = Mean relative humidity in Valtorta et al. (2000).

The LWSI by Hahn et al. (2000) considers four categories of the THI to evaluate the impact of thermal environmental conditions and associates them to the respirations per minute. Nienaber et al. (2007), consider the increase of the respiratory frequency as a proportional compensatory response to heat stress (Table I).

The data corresponds to the period 1917–2008 and were analyzed to obtain the monthly mean values (normal 1961–1990) of temperature (°C) and relative humidity in tenths and from them the THI was calculated to establish the LWSI.

The THI was calculated from the minimum, mean and maximum temperatures with the average relative humidity. Furthermore the THI were obtained in an hourly form (6:00–8:00 a.m.; 1:00–3:00 p.m. and 5:00–7:00 p.m., local time), corresponding to periods of the day in which changes occur in animal behavior (Hernández et al., 2007).

The averages of temperature (°C) and relative humidity of an hourly form were calculated from the mean maximum temperatures (Tmax) and mean minima (Tmin) of climate normals (1961–1990). That data was used to make climate (not meteorological) comparisons of the THI in different periods of study (1917–1960, 1961–1990, 1991–2008), as well as future scenarios for 2020, 2050 and 2080.

The procedure for obtaining the hourly temperatures (Thor) and relative humidity (RHhor) was obtained from the reported methodology by Tejeda–Martínez and García–Cueto (2002).

Here, α, b and c are parameters that depend on the season of the year and latitude (Table II); t is in hours as a function of local time (H) and the local time of sunrise (Ho):

t = H – Ho if H ≥ Ho

t = H + 24 – Ho if H < Ho

In the case of monthly temperatures, the precision of Eq. (2) is greater than the De Wit et al. (1978) model, which is the best model according to a review made by Reicosky et al. (1989, cited by Tejeda–Martínez, 1991).

On the other hand, the values of the mean minimum monthly relative humidity (RHmin) were estimated from the combination of mean monthly vapor pressure and from the maximum saturation vapor pressure. The argument is based on the fact that the vapor pressure is unchanged between the time of occurrence of the mean and minimum RH (approximately between 10:00–11:00 a.m. and 2:00–3:00 p.m., respectively). This idea was initially proposed by Geiger (1957, cited by Tejeda–Martínez and García–Cueto, 2002).

The values of mean monthly vapor pressure, result from the monthly means of temperature and relative humidity, and saturation vapor pressure (Es), derived from the application of a polynomial of third–order to the mean monthly maximum temperatures. This polynomial is a regression model of Es in mb, a coefficient of lineal correlation of Pearson r = 0.9997 and a standard estimation error of 0.5 mb in comparison with observed values of Es for temperatures between 10 to 50 °C (Tejeda–Martínez, 1994).

Finally, as the curve of the daily relative humidity is inverted with respect to the temperature curve, the expression to estimate the hourly monthly average values is:

To determine the THI scenarios for the years 2020, 2050 and 2080 the models ECHA 4 (Roeckner et al., 1992), GFDLR30 (Manabe et al., 1991; Delworth et al., 2002) and PRECIS–HADCM2 (Mitchell et al., 1999) were used with initial and boundary conditions HADCM2 Precis at a resolution of 0.5° of latitude by 0.5° of longitude (Gay et al., 2006), using a base scenario generated with the normals of the period 1961–1990 of CPG (SMN–Veracruz). As will be seen further on, despite the differences in resolutions of the models ECHAM4 (2.25° by 3.75°) and GFDLR30 (2.25° by 2.8°), against 0.5° by 0.5° of the PRECIS HADCRM2 system, the results are very similar, indicating that for future estimates of animal bioclimate, scenarios coming from models with a more or less rough resolution could be useful.

3. Results and discussion

Figure 1, shows a systematic increase of average temperatures, being more noticeable in the maximum monthly temperatures of the years 1917 to 2008, that is heightened by the periods following the sixties decade (1961–1990) and becomes evident in the last 18 years analyzed (1991–2008; Fig. 1C). The alert category, which shows a THI value greater than or equal to 74, reaches its highest value in the last period of study, in which there is an increase in the number of months with averages of THI different to the thermal comfort ones and the danger and emergency categories show a higher frequency especially during summer months (Fig. 1C).

While the increase of temperature is associated to the inadequate comfort indicator, the alert and danger categories are accentuated when relative humidity increases. This situation has become evident in recent years (Fig. 2).

By analyzing the data in an hourly way, with the purpose of observing with more detail the heat stress throughout the day, it is possible to establish that the most adverse conditions for livestock of the area are generate at midday (13:00–15:00), although in some months of the years studied livestock security is compromised even in the morning and evening hours (Fig. 3).

The THI value provides a set of categories that indicate the heat stress of animals (Bohmanova et al., 2007). However, for its interpretation it is necessary to know the predominant climate conditions in the area of study, as well as relative humidity and how it has been used to differentiate the discomfort category according to the type of heat: dry, typical of semiarid climates or moist heat, like the predominant one in the coastal region of the Gulf of México, where Veracruz is situated (Vidal, 2004). Here, during the season of high temperatures and humidity, the natural capacity of cattle to dissipate the load of heat by evaporation and sweating is compromised and the stress is maximized as heat stress.

However, there are different forms of determining the level of heat stress in animals. The interpretation of the comfort classification of livestock has suffered modifications, with a tendency to reduce the stress values in cattle. According to Bohmanova et al. (2007), the first classifications made by Thom (1959) group the THI like: normal between 70 and 74, not comfortable from 74 to 79 and more than 79 seriously not comfortable. Armstrong (1994), proposes indexes under 71 as a comfort zone with values between 72 and 79 as a medium stress, from 80 to 89 as moderate stress and values above 90 as severe stress. Huhnke et al. (2001), group the THI in two categories: danger situation from 79 to 84 and greater than or equal to 84 in an emergency situation. Vitali et al. (2009) defined quantitatively the relationship between mortality risk and the THI in dairy cattle by establishing a THI value greater to 80 as the limit. It should be clarified that for the determination of the majority of these categories the THI values were generated empirically in livestock exposed to heat stress in climate chambers.

Even by choosing any of the different ways of interpreting the THI from the climate values registered for the Veracruz region, it would be observed that they do not result comfortable for livestock during most of the years and months since 1917, according to the records of the CPG. In Figure 4, the frequencies (%) of months, of three different expressions of THI in line with the different periods considered are shown. A percentile substitution is shown in periods of comfort for an increase in those considered typical to discomfort for the animals, situation that is best appreciated for the recent period (1991–2008).

Previous work has been made about cattle farms in the coasts of the Gulf of México, in the sate of Tabasco (De Dios–Vallejo et al., 1987) on the south border of the state of Veracruz. Mean maximum temperatures ranged from 27.4 to 32 °C and a mean maximum RH of 0.80 to 0.86; the average monthly THI showed values greater than or equal to 72 during eight months of the year, as well as records greater than or equal to 72 from 8 to 23 hours every day. Similarly, significant statistical differences were reported (p < 0.01) for the THI between dry and rainy periods, in morning and evening times, showing THI values greater than or equal to 74 in the rainy season during the evening hours, on farms located 20 km from Veracruz (Hernández et al., 2007). This data confirms that the area of study can be classified as one of discomfort for cattle. Countries with similar temperatures and humidity have seen changes in the management of livestock associated to increases in ambient temperatures that are occurring according to the temperature rise, showing changes in the conformation of existing herd predilection for thermo–tolerant animals (Parry et al., 2004).

The climate scenarios for the years 2020, 2050 and 2080 were generated with the data of climate normals of the CPG for the years 1961–1990. They are shown in Tables III, IV and V as monthly temperature values (°C) and relative humidity (%), for the models, GFDLR30 (2020, 2050A2 2050B2), ECHAM4 (2020, 2050A2 2050B2), and PRECIS–HADCM2 (2020, 2050A2 2050B2), respectively. These suggest that climate conditions for these years are conducive to the existence of and adverse environments for the development of livestock in the region of Veracruz, as seen in Figure 5, where scenarios for an average THI are shown deriving from tables III, IV and V. The base scenario was, calculated from the climate normals (1961–1990) and from the selected models (GFDLR30, ECHAM4 and PRECIS–HADCM2 for 2020, 2050 and 2080).

4. Conclusions

The practice of cattle breeding in the region of Veracruz, México, is now carried out in a climate that offers a reduced comfort margin for the animals, a condition which has worsened over time and has become more evident in recent years (1990–2008). According to the PRECIS–HADCM2 (A2) model, used to estimate regional models, the scenarios made for the THI from three different models suggest that the situation will become more critical in the future, so that for 2020 in the month of August, a relative humidity of 79% and an ambient temperature of 29.2 °C, will be sufficient to exceed the THI value of 80 considered as dangerous (82). In the same way for 2050 and 2080, this critical THI value will be exceeded with temperatures of 30.5 and 32.3 °C and with a relative humidity of 0.76 and 0.68 (83 and 85), respectively. It should be emphasized that despite the differences in spatial resolutions of surveyed climate change models, the results are highly coincidental for future estimates towards 2020 and 2050.

Acknowledgements

To the Centro de Previsión del Golfo de México (Forecast Center of the Gulf of México) of the Servicio Meteorológico Nacional (National Meteorological Service), under the Comisión Nacional del Agua (National Water Commission), for its invaluable assistance in collecting data and to the Program for the Generation of Scenarios and Development of Climate Change State Programs UNAM–SEMARNAT.

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