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International Journal ofBiometeorology ISSN 0020-7128Volume 58Number 7 Int J Biometeorol (2014) 58:1559-1567DOI 10.1007/s00484-013-0760-x

Physiological and production response ofdairy goats bred in a tropical climate

Priscila Teixeira de Souza, Maria GoreteFlores Salles, Antônio Nélson Lima daCosta, Hilton Alexandre Vidal Carneiro,et al.

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ORIGINAL PAPER

Physiological and production response of dairy goats bredin a tropical climate

Priscila Teixeira de Souza & Maria Gorete Flores Salles & Antônio Nélson Lima da Costa &

Hilton Alexandre Vidal Carneiro & Leonardo Peres de Souza & Davide Rondina &

Airton Alencar de Araújo

Received: 29 May 2013 /Revised: 13 October 2013 /Accepted: 23 October 2013 /Published online: 17 November 2013# ISB 2013

Abstract The aim of this work was to determine the adapt-ability of Saanen and ½Saanen×½Anglo-Nubian (½S½AN)goats bred in tropical climates. The study included 30 goats,15 Saanen and 15 ½S½AN. The data was collected during therainy and dry seasons. During the whole experimental period,the environment variables were recorded, as well as rectaltemperature (RT), superficial temperature (ST), respiratoryrate (RR) and heart rate (HR) and milk production (MP).The adaptability coefficient (AC) was calculated for bothgenotypes. The averages were evaluated by ANOVA at 5 %probability. There was a genotype and period of year effect, aswell as the interaction genotype×period of year. Pearson'ssimple correlation analysis was then carried out between milkproduction and physiological and environment variables.There was a statistical difference (p <0.05) between the

seasons for RT, ST and RR. RT, RR and HR were lower for½S½AN than Saanen goats, regardless of the season. MP wasgreater in the dry season (p <0.05) (2.52±0.50 kg/day for½S½AN and 2.41±0.38 kg/day for Saanen) than the rainyseason (2.17±0.27 kg/day for ½S½AN and 2.28±0.53 kg/dayfor Saanen). The MP correlations were very significant(p <0.05), however low and negative, where it was higherwhen correlated with RR in Saanen goats. Under the condi-tions of the present study, it is concluded that the goats wereinfluenced by climatic factors, where the rainy period wasmore likely to cause thermal stress in the animals.

Keywords Adaptability . Tropical climate . Heat stress .

Dairy goat

Introduction

Brazil is ranked 16th internationally in the number of goatswith approximately 9.3 million heads (FAO 2010), and like inother tropical countries, these animals represent an importantsource of meat and milk (Brown et al. 1988; Daramola andAdeloye 2009).

The lower worldwide importance of goat milk production,the little activity in genetic improvement aimed at increasingproductivity, and the supposedly high adaptability to warmenvironments in a general way, explains the little attentionpaid to this species with regard to the effects of thermal stress(Nardone et al. 2010).

Most of Brazil is situated in the intertropical range of theplanet and therefore has high temperatures as a consequence ofthe great intensity of incident solar radiation (Azevedo et al.2005; Souza et al. 2005). Thus, some goat breeds, mainly whennormally very productive and originating from a temperateclimate, can show low productive and reproductive performancein a tropical climate (Medeiros et al. 2008; Lallo et al. 2012).

P. T. de Souza (*) :D. Rondina :A. A. de AraújoFaculdade de Veterinária, Universidade Estadual do Ceará – UECE,Avenida Paranjana, 1700. Campus do Itaperi,CEP 60714-903 Fortaleza, CE, Brazile-mail: priscilatsvet@yahoo.com.br

M. G. F. SallesInstituto de Desenvolvimento Rural, Universidade da IntegraçãoInternacional da Lusofonia Afro-Brasileira – UNILAB, Avenida daAbolição, 3., CEP 62700-000 Redenção, CE, Brazil

A. N. L. da CostaCurso de Agronomia, Universidade Federal do Cariri – UFCA, RuaVereador Sebastião Maciel Lopes, s/n., CEP 63133-610 Crato, CE,Brazil

H. A. V. CarneiroFaculdade de Tecnologia Sertão Central, Instituto Centro de EnsinoTecnológico – CENTEC, Geraldo Bizarria, s/n. Edmilson Correia deVasconcelos, CEP 63800-000 Quixeramobim, CE, Brazil

L. P. de SouzaDepartamento de Biologia, Universidade Estadual Paulista,Avenida 24-A, 1515, CEP 3506-900 Rio Claro, SP, Brazil

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In regions with high temperatures, body temperature andrespiratory rate tend to increase, since heat production exceedsheat dissipation by the animals (Souza et al. 2007). Accordingto Lee et al. (1974), the climatic elements that most influencethe increase in physiological parameters in order of impor-tance are environmental temperature, solar radiation, humidityand air movement.

Some studies have shown the adverse effects of environ-ment, especially climate, on the adaptability of goats (Brasilet al. 2000; Silanikove 2000; Silva et al. 2006; Marai et al.2007; Medeiros et al. 2008). However, many of these inves-tigations have been carried out under climatic conditionsdifferent from those found in the coastal region of NortheastBrazil, or under simulated conditions in bioclimatic chambers.

The survival and productivity of animals in tropical regionsdepend on the existence of certain adaptive characteristics(Ogebe et al. 1996). Souza et al. (2005) considered theseaspects to be based mainly on the capacity of animals tomaintain body temperature within a certain range. Differentgoat breeds respond differently to high environmental temper-atures (Brown et al. 1988). The maintenance of homeothermyis a priority for animals and prevails over production functionssuch as milk production and reproduction (Martello et al.2004). According to Baccari Junior (1990), the adaptabilityof animals to warm environments can be determined byphysiological adaptability tests and yield or production.European breeds are more productive only in favorableenvironments.

The low levels of productive performance point to theurgent need for professionals in goat dairy farming to deter-mine the variations that occur in different periods of the yearin tropical climates, with regard to the adaptive characteristicsof potentially productive animals that have not been able toexpress all their genetic capacity. In addition, it is necessary toundertake mitigating techniques such as the development ofbreeds that are less sensitive to heat stress (Kadzere et al.2002) in attempt to minimize the effect of environment onanimals in tropical regions.

Thus, the aim of this work was to determine the adaptabil-ity of Saanen and ½Saanen×½Anglo-Nubian (½S½AN)goats bred confined in tropical climates, examining the inter-action between environment and animal, and how this be-haves in the evaluation of physiological alterations and milkproduction in dry and rainy periods.

Materials and methods

Study location and experimental period

The present work was conducted in the municipality ofPacatuba, state of Ceara—Brazil, with geographic coordinates3°53′49.9″ S, 38°34′32.5″W. The climate of the region is

characterized as being warm and humid. The experimentalperiod involved two seasons: rainy (February to May) anddry (August to November). The division of the seasons wasbased on rainfall data provided by the Fundação Cearensede Meteorologia. There was pre-experimental phase forselection of the animals and their adaptation to the newmanagement.

Experimental animals

The study included 30 goats, 15 Saanen and 15 ½S½AN,between 1 and 2 years old, mean weight of 37.4±6.56 kg,showing a good clinical and healthy history. Care was takenregarding the effect of experimental homogeneity, such thatthe females were in first lactation. Seven Saanen and eight½S½AN initiated their lactation during the rainy season, whilethe other half of the goats, eight Saanen and seven ½S½ANentered lactation in the dry period.

The goats were bred confined in brick facilities covered byclay tiles and kept in common stalls, with a raised slatted floor,with an east–west orientation. Each stall had a solarium thatreceived direct sunlight, to which the animals had free accessduring the whole day. Feed was supplied two times a day(0600 and 1500 hours) and consisted of 70 % elephant grass(Pennisetum purpureum) and 30 % leucena fodder (Leucaenaleucocephala), both in the green chopped form and ad libitum.A concentrated supplement of 45% corn, 21.7 % wheat, 29%soybean, 2 % mineral supply, 1.3 % lime and 1 % commonsalt, was also provided at 1.6 kg concentrate per animal/day(0.8 kg in the morning and 0.8 kg in afternoon). The goats hadfree access to drinking water and mineral salt.

The analyses of dry matter (DM), crude protein (CP), etherextract (EE) and ash of the feed supplied were carried outaccording to methods described by Silva and Queiroz (2002)and those for neutral detergent fiber (NDF) and acid detergentfiber (ADF) according to Van Soest et al. (1991), in theAnimal Nutrtion Laboratory of Universidade Federal doCeará. The composition of the feed is shown in Table 1.

Table 1 Chemical composition of feeds (%)

Feed Nutrients

DM(%)

CP(%)

EE(%)

NDF(%)

ADF(%)

Ash(%)

Cornmeal 88.77 10.34 3.94 25.91 4.50 1.32

Soybean meal 88.27 52.49 3.62 15.05 10.20 5.83

Wheat meal 88.86 18.08 3.74 44.21 11.72 5.03

Concentrate 89.24 23.51 3.45 32.02 8.16 8.63

Pennisetum purpureum 19.15 15.75 1.50 60.34 37.05 14.90

Leucaena leucocephala 28.67 25.71 1.65 42.31 22.76 6.05

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Environmental variables

During all the experimental period, values of temperature andrelative humidity were recorded (maximum, mean and mini-mum) with the help of a digital thermo-hygrometer placed at aheight of the center of mass of the animals. The temperature-humidity index (THI) was calculated according to the formulaproposed by Buffington et al. (1982):

THI ¼ 0:8T þ RH T − 14:3ð Þ=100 þ 46:3 ; where :T ¼ air temperature in �C and RH ¼ relative humidity

Experimental procedure

We measured the physiological parameters (rectal tempera-ture, surface temperature, respiratory rate and heart rate) of theanimals in lactation (during the first and second months oflactation), twice a week at 1300 hours, during the rainy anddry seasons. Rectal temperature (RT) was obtained using aveterinary clinical thermometer (INCOTERM L279/04) witha scale up to 44 °C, which was introduced directly into therectum of the animal, to a depth of 5 cm, such that the bulbcame in contact with the mucosa of the animal for 2 min.Superficial temperature (ST) was obtained using a 230c Impacdigital infrared thermometer. The measurements were taken atapproximately 7 cm from the surface of the whole body, atfour different points on the animal's body: front, rib, flank andleg, where superficial temperature was expressed as the meanof these five points. Respiratory rate (RR) was determined bymeans of visual evaluation, observing the movements of theflank, counting for 15 s and multiplying by four, determiningthe movements per minute (breaths/min). Heart rate (HR) wasmeasured by auscultation of the heart with a flexible stetho-scope, directly in the left thoracic region, counting the numberof beats during 15 s and multiplying by four, determining thebeats per minute (beats/min).

The individual monitoring of milk production was donedaily by weighing after milking during the second month oflactation of the goats, always carried out in the morning(0330 hours) and afternoon (1330 hours) and recorded inappropriate charts. The sum of values obtained at the twotimes when milking was performed was considered the dailymilk production (MP). Before milking, criteria for good hy-gienic practices were followed.

The tolerance of animals to heat was assessed by theBenezra test according to Muller (1989), with adaptationsfor the goat species (Martins Júnior et al. 2007a), whichcalculates the adaptability coefficient (AC) of animals, wherea value closer to 2 meant more heat-adapted. ACwas obtainedby the following formula:

AC ¼ RT=39:1þ RR=19

where:

RT Rectal temperature (in degree Celsius), measured at1300 hours.

RR Respiratory rate (breaths/min), measured at1300 hours.

39.1 Rectal temperature considered normal for goats.19 Normal respiratory rate for goats.

Statistical analysis

Statistical analyses were performed utilizing the programSYSTAT version 12, where the environmental variables,physiological parameters and milk production were expressedas means and standard deviations and evaluated by analysis ofvariance and F test at 5 % probability, where the comparisonsbetweenmeans were donewith Tukey's test. The experimentaldesign was completely randomized with a 2×2 factorial ar-rangement (2 genotypes×2 seasons), where the effect of ge-notype was evaluated within and between seasons. APearson's simple correlation analysis was then carried out todetermine the magnitude and direction of the proportionalityof variance of the environmental variables and the variousanimal parameters observing the independence of variances ofpairs of the observations utilized.

Results

Table 2 shows that there was a significant difference (p <0.05)between the environmental variables. ATwas higher in the dryseason, while RH and THI were greater in the rainy period.

With respect to the physiological parameters, RT in the dryseason was significantly (p <0.05) lower in ½S½AN goats(38.97±0.26 °C) than in Saanen goats (39.11±0.31 °C).However, there was no difference in the rainy season(p >0.05) between the genotypes (39.18±0.38 °C for½S½AN and 39.19±0.35 °C for Saanen). Considering thevariation between the two periods, there was a clear elevationof RT in the rainy period (Fig. 1).

Skin temperature was lower (p <0.05) in Saanen goats(33.75±0.99 °C) compared with ½S½AN goats (33.92±1.06 °C) in the dry season. As with RT, ST did not differ(p >0.05) between the genotypes (31.96±1.28 °C for½S½AN and 31.93±1.26 °C for Saanen) in the rainy season.Regardless of genotype, ST was higher (p <0.05) in the dryperiod (Fig. 2).

However, in the evaluation of the physiological parameters,RRwas also found to be lower (p <0.05) in the½S½AN than inthe Saanen goats, in the dry season (54.55±18.59 breaths/minfor ½S½AN and 72.93±22.69 breaths/min for Saanen) as wellas the rainy season (44.19±15.92 breaths/min for ½S½AN and

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57.40±20.12 breaths/min for Saanen). RR was higher in thedry season for both genotypes (p <0.05; Fig. 3).

Heart rate showed the same pattern as RR, as it was lower(p <0.05) in ½S½AN goats (90.07±14.27 beats/min in the dryseason and 91.28±15.25 beats/min in the rainy season) than inSaanen goats (106.70±15.27 beats/min in the dry season and107.10±17.08 beats/min in the rainy season), with no differ-ence being found between the periods (p >0.05; Fig. 4).

There was no significant difference between the genotypeswith respect to MP, regardless of period (p =0.06). The meanMP observed in the dry period was 2.52±0.50 kg/goat/dayfor ½S½AN goats and of 2.41±0.38 kg/goat/day for Saanengoats. During the rainy season, mean production was 2.17±0.27 kg/goat/day for ½S½AN and 2.28±0.53 kg/goat/day forSaanen. Mean MP was greater in the dry season for bothgenotypes (p <0.05; Fig. 5).

According to Fig. 6, the ½S½AN goats showed a lowerAC, independent of period of year (rainy season, 3.85±0.83for ½S½AN and 4.54±1.06 for Saanen; dry season, 3.86±0.97 for ½S½AN and 4.83±1.20 for Saanen). No difference(p >0.05) was found between the two periods for eithergenotype.

The correlations of MP with the physiological parametersand environmental variables are given in Table 3. ST and HRwere removed, since the correlation was not significant. Thecorrelations were very significant (p <0.05), negative and lowin most cases, but high with RR of Saanen goats.

Discussion

In the dry season with higher AT, RH decreased, in contrast tothe rainy season. It is a desirable characteristic, because in thehottest hours, it is possible for the animal to lose heat byevaporation (Souza et al. 2008; Silva et al. 2012).

The animals were subject to conditions of heat stress duringboth periods, in agreement with Silanikove (2000). The higherTHI observed in the rainy period was due to the substantialincrease in RH in this period because of the greater rainfall, atthe same time during which AT did not decrease. Thus, thisperiod is characterized as being the most favorable for causingheat stress in animals.

According to Silanikove (2000), a THI value less than orequal to 70 indicates a condition of comfort, while values 71 to

Table 2 Average, maximum and minimum environmental variables, air temperature (AT), relative humidity (RH) and temperature-humidity index(THI) during the dry and rainy seasons

Season Average Maximum Minimum

AT (°C) RH (%) THI AT (°C) RH (%) THI AT (°C) RH (%) THI

Rainy 29.5±2.2a 79.1±11.7a 81.8±2.4a 30.5±2.1a 80.1±11.3a 83.6±2.2a 28.8±1.7a 73.1±10.5a 79.8±1.9a

Dry 32.9±0.9b 43.5±8.3b 80.8±1.0b 33.2±1.2b 49.0±9.6b 82.2±1.6b 29.8±0.9b 42.2±8.3b 76.7±1.2b

Means with different letters in the same column differ (p <0.05)

Fig. 1 Rectal temperature of Saanen goat and ½S½AN goat during rainyand dry season in tropical climate. Black columns ½S½AN goat, Graycolumns Saanen goat. Different lower case letters are different in thesame season (p <0.05). Different upper case letters are different betweenthe seasons to the genotypes (p <0.05)

Fig. 2 Skin temperature of Saanen goat and ½S½AN goat during rainyand dry season in tropical climate. Black columns ½S½AN goat, graycolumns Saanen goat. Different lower case letters are different in thesame season (p <0.05). Different upper case letters are different betweenthe seasons to the genotypes (p <0.05)

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78 are considered stressful and higher than 78 cause greatsuffering to the animal, where it is unable to maintain thermo-regulatory mechanisms and normal body temperature.However, these values are generalized for domesticated rumi-nants, where more specific ranges are needed for differentcategories of animals, with respect to species, breed and fitness.

With regard to the physiological parameters, the highervalues of RT, RR and HR observed in Saanen are probablydue to the European origin of this breed, adapted to a temper-ate climate. The ½S½AN show a 50 % genetic contributionfrom a breed considered hardy, namely Anglo-Nubian,adapted tomore severe climatic conditions with regard to heat.

Many studies conducted with the Anglo-Nubian breed orcrosses of this breed in warm environments demonstrated a highdegree of physiological adaptability for these animals (Santoset al. 2005; Souza et al. 2005, 2008; Silva et al. 2006, 2010).

The mean RT for the two genotypes was within the phys-iological range for the species, in agreement with Reece(1996), oscillating from 38.5 to 39.7 °C, usually observed inthe zone of thermoneutrality. Meanwhile, it is known that heatstress is often momentary, which can only be seen in the dailyevaluation of raw values of physiological parameters. Duringsome collections of data, the raw values of RT of someanimals were higher than 40 °C (data not shown). The in-crease in RT in the rainy period can be explained by the higher

Fig. 4 Heart rate of Saanen goat and ½S½AN goat during rainy and dryseason in tropical climate. Black columns ½S½AN goat, gray columnsSaanen goat. Different lower case letters are different in the same season(p <0.05). Different upper case letters are different between the seasonsto the genotypes (p <0.05)

Fig. 5 Milk production of Saanen goat and ½S½AN goat during rainyand dry season in tropical climate. Black columns ½S½AN goat, graycolumns Saanen goat. Different lower case letters are different in thesame season (p <0.05). Different upper case letters are different betweenthe seasons to the genotypes (p <0.05)

Fig. 6 Coefficient adaptability (CA) of Saanen and ½S½AN goatsduring the rainy and dry seasons in tropical climate. Black columns½S½AN goat, Gray columns Saanen goat. Different lower case lettersare different in the same season (p<0.05).Different upper case letters aredifferent between the seasons to the genotypes (p <0.05)

Fig. 3 Respiratory rate of Saanen goat and ½S½AN goat during rainyand dry season in tropical climate. Black columns ½S½AN goat, graycolumns Saanen goat. Different lower case letters are different in thesame season (p <0.05). Different upper case letters are different betweenthe seasons to the genotypes (p <0.05)

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THI value. Environmental conditions of greater discomfortin this period, characterized mainly by a marked increase inRH, hamper heat loss by evapotranspiration, resulting in anaccumulation of endogenous heat. Other studies have alsofound an elevation in RT in the rainy season when AT andRH were simultaneously high (Martins Júnior et al. 2007b;Rocha et al. 2009).

Medeiros et al. (2008), in evaluating the physiologicalresponses of animals kept in the shade, sun and partiallyshaded environment in a warm and humid climate, found amean rectal temperature of 40.16 and 41.32 °C in the after-noon in Anglo-Nubian and Saanen goats, respectively.

The lower ST observed in Saanen can be explained by thewhite color of the coat that accounts for greater reflection andless absorption of light (Maia et al. 2003; Paim et al. 2012).According toMcManus et al. (2009), breeds with a white coatare more adapted to heat. The physiological alterations anddifferences between the genotypes found in this study do notsupport the notion that Saanen goats are more adapted to heaton the basis of coat color alone. When comparing differentgenotypes, other parameters regarding the tegument should beconsidered, such as pigmentation and thickness of the skinand density, height and length of hairs (Maia et al. 2003;Pereira 2005; Paim et al. 2012). In addition, animals betteradapted to warm environments can have increased peripheralcirculation and lose heat by convection and radiation (Maiaet al. 2009; Cardoso et al. 2010), when there is a thermalgradient between the skin and air (Silanikove 2000; Souzaet al. 2008; Silva et al. 2012), besides possessing a largernumber of sweat glands, allowing the loss of latent heat(Silva et al. 2010).

The higher ST in the dry period could have resulted fromthe higher AT. Maia et al. (2009) found a high and positivecorrelation of AT with skin temperature in lambs (r2=0.81).Many works with goats carried out in tropical climates haveshown a higher ST around the afternoon when AT is alsohigher (Santos et al. 2005; Souza et al. 2005, 2008; Silvaet al. 2006, 2010; Darcan and Güney 2008).

In tropical regions, in which the mean radiant temperatureis greater than the air temperature and body temperature of theanimals, sensible heat loss is hampered resulting in an increasein RR (Silva et al. 2012). As seen in the present study, the

goats showed a higher than physiological RR, independent ofgenotype and period. RR of 15 breaths/min, with a range of 12to 25, is considered normal for goats (Reece 1996).

The largest averages of RR for as Saanen are due, probably,to its origins and more productive breed characteristic, while½S½AN also presents in their ancestry, Anglo-Nubian, abreed more adapted to warm climates, but less productivethan Saanen. Lactating animals with a high level of milkproduction possess a higher metabolic rate, which results inincreased generation of endogenous heat, making it difficultfor them to maintain thermal balance in warm environments(Brasil et al. 2000; Azevedo et al. 2005). Thus, the increase inRR in attempt to lose heat was more pronounced in Saanenthan ½S½AN goats.

Lallo et al. (2012), with the aim of determining the goatbreed most adequate for humid tropical climate, found highermean RR values in Saanen than in Anglo-Nubian, with valuesof 105, 65, 76 and 51 breaths/min for imported Saanen parentstock, imported Anglo-Nubian parent stock, Saanen F1 gen-eration and Anglo-Nubian F1 generation, respectively.Medeiros et al. (2008) assessed the physiological responsesof goats in a humid tropical climate and also obtained a higherRR in Saanen goats (75.47 breaths/min) than in Anglo-Nubian goats (48.33 breaths/min).

In other studies of adaptive physiological traits comparingdifferent goat breeds, the Anglo-Nubian and crosses of thisbreed showed lower values of RT or RR (Santos et al. 2005;Souza et al. 2005; Silva et al. 2006, 2010). This is an indica-tion that better results for physiological parameters, exhibitedby ½Sx½AN animals in the present study, was due to thedescent of the breed from African roots.

In the two periods, the increase in RR was important formaintenance of homeothermy. The mean values of RR in thedry period indicate that, exactly in this time when RH valueswere lowest, the use of respiration for heat dissipation wasneeded more and efficient. Consequently, mean RT valueswere lower in the dry season than rainy period. Thus, in theenvironment with lower humidity, evaporative thermolysis isfacilitated, resulting in increased respiratory rate for mainte-nance of body temperature.

Heart rate, in both genotypes and periods, was above thenormal range proposed for goats of 70 to 80 beats/min at rest(Reece 1996). The increase in HR can be attributed to thegreater muscular activity needed due the elevation in RR, aswell as to the reduction of peripheral vascular resistance whichcauses an increase in superficial blood flow for heat dissipa-tion through the skin (Al-Tamimi 2007). However, accordingto Souza et al. (2007), the exacerbated and prolonged eleva-tion of HR can exhaust the metabolic systems of the heart,causing weakness, impairing production processes.

As in the present study,Martins Júnior et al. (2007a) did notfind a difference between the dry and rainy seasons withrespect to HR of Boer and Anglo-Nubian goats. Meanwhile,

Table 3 Pearson's correlation coefficients between milk production(MP) and rectal temperature (RT), respiratory rate (RR), air temperature(AT), relative humidity (RH) and temperature-humidity index (THI) fordairy goats in a tropical climate

½S½AN Saanen Environment

RT RR RT RR AT RH THI

PL (kg/goat/day) −0.30 −0.24 −0.40 −0.74 −0.23 −0.33 −0.26p value 0.002 0.018 0.000 0.000 0.032 0.000 0.006

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Rocha et al. (2009) demonstrated in Saanen goats values of79.44±14.89 beats/min and 65.75±7.29 beats/min for HR inthe rainy and dry periods, respectively. The contrary wasobserved by Ogebe et al. (1996) in studying an African goatbreed, in which a higher HR was found in the dry season.

The results of the physiological parameters obtained underthe climatic conditions of the present study indicate greatertolerance to heat by ½S½AN animals than Saanen, which wasconfirmed by the AC. Medeiros et al. (2002) applied a heat-tolerance test to goats and observed a worse performance bythe Saanen breed compared to the Anglo-Nubian breed.

Rocha et al. (2009), as in this study, also did not observedifferences between the periods with regard to AC of Saanengoats, finding similar means of 5.13±1.54 and 5.86±1.39 inthe rainy and dry seasons, respectively. The higher values ofAC described by Rocha et al. (2009) are probably due to thehigher THI values obtained in their study. Martins Júnior et al.(2007a) determined AC values for the Anglo-Nubian breedthat were higher in the dry season (dry=3.039±0.038 andrainy=2.678±0.038). The two works with goats of theSaanen and Anglo-Nubian breeds discussed above suggestthat the AC obtained for the ½S½AN goats in the presentstudy is intermediate between the two breeds.

The results presented here corroborate the MP of exoticbreeds found in Brazil (Soares Filho et al. 2001). It is knownthat purebred animals are more productive than their cross-breeds, except when they are forced to produce outside of theirthermal comfort zone. In the present study, no significantdifference was observed between the genotypes. This wasprobably due to the fact that the Saanen goats studied werepurebred animals from the crossing of ascendants longestablished in the region, resulting in a greater selection ofmore adapted descendants. Besides, the meanmilk productionof the Saanen goats can even be in agreement with the meanproduction recorded in the tropics, but far below the produc-tive potential of the breed when in a temperate climate (Esmail1986; Serradilla 2001).

McManus et al. (2008), in evaluating milk production inpurebred Holstein (H) cows and their Gir (G) crossbreeds,observed that the milk production of the former was inferior tothat of ½H ½G and ¾H ¼G groups, demonstrating the adap-tation of the crossbreed animals.

A study carried in Northeast Brazil reported a mean milkproduction for the Anglo-Nubian breed of 1.82 kg/day at thepeak of lactation (Ferreira and Trigueiro 1998), while a meanmilk production of 2.3 kg/day was observed for the Saanenbreed (Barbieri et al. 1990).

According to Gonçalves et al. (2001), the effect of seasonof the year on milk production can be explained, in large part,by climatic changes, which can have a direct or indirect effecton the animals. Thus, the greater MP in the dry seasonobserved in the present study can be explained by climaticvariables, where greater thermal discomfort was detected in

the rainy season, with higher THI and RT values. Scarcity offood was not a problem in the dry period, since the goats werebred confined and received the same diet during the wholeyear. Thus, the climatic factor became the most impacting onproductive performance of animals bred intensively.

Esmail (1986) reported a 36.6 % reduction in dairy pro-duction for Saanen goats imported and introduced in a tropicalregion. Brasil et al. (2000) found that goats in a bioclimaticchamber simulating heat stress produced less milk. However,Baccari Junior et al. (1996) did not find a difference in MP innative Saanen goats in a bioclimatic chamber under conditionsof thermal comfort (1.37 vs. 1.34 kg/day), probably due to thecharacteristic of low productivity in these animals.

Greater MP requires larger amounts of nutrients, whichmeans increased food intake and metabolic heat production,resulting in difficulty in maintaining the thermal balance ofanimals under tropical conditions (Brasil et al. 2000).

The correlation of MP with physiological parameters andenvironmental variables showed, albeit in a subtle way, thatwhen RT, RR, AT, RH and THI are high, MP decreases. Thiseffect was much more pronounced in Saanen goats with highRR.

Darcan and Güney (2008) found a significant negativecorrelation between MP and RR (r =−0.55) of goats bred ina warm climate. However, no significant correlation could bedemonstrated with RT, nor with HR and ST.

In view of the results presented, we conclude that dairygoats are influenced by climatic factors, showing alterations intheir physiological parameters with consequences on theirproductive performance. The rainy season appeared morepropitious for causing heat stress in the animals. Accordingto the results of the physiological parameters and of theadaptability coefficient, the ½S½AN goats appeared moreadapted than the Saanen goats to the tropical climate.Besides, despite that there was no difference in milk produc-tion between the genotypes, we noted a production that wasbelow the genetic potential of the Saanen breed. Therefore,more studies are necessary for the determination of parameterssuch as fertility and resistance to diseases, as well as thedissemination of the utilization of adapted crossbred animals,combining hardiness and productivity.

Acknowledgements To the funding agencies Banco do Nordeste(BNB) and Fundação Cearense de Apoio ao Desenvolvimento Científicoe Tecnológico (FUNCAP) for the financial support. Dr. A. Leyva helpedwith English translation and editing of the manuscript.

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