Heat tolerance index , food intake and weight gain of Santa Ines sheep in the agreste region of Pernambuco State , Brazil

This study evaluated the influence of coat color on the heat tolerance and performance of 21 Santa Inês lambs, non-pregnant, non-lactating, seven animals of each coat color: black, brown and white, with an average initial weight of 25.71, 24.85 and 25.00 kg, for white, brown and black animals, respectively, and 12 months of age. The study was conducted during summer in the agreste region of Pernambuco State, Brazil. Twenty-one sheeps were assigned to a completely randomized design with three treatments and seven replicates. The heat tolerance index and the animal performance were evaluated once a week for eight weeks. White sheep were slightly superior in heat tolerance to brown and black sheep, 88.3, 85.5 and 86.6 respectively, but this was not reflected in the growth performance of the animals, which showed average daily weight gain of 170.10, 193.69 and 199.50 g for animals white, brown and black, respectively.


Introduction
Environmental factors such as the climate can interfere with the animal performance, reducing the food consumption and weight gain of animals.
High temperatures and strong sunlight predominate during almost the whole year in arid regions and semi-arid region of Northeastern Brazil and may lead the animals to the caloric stress causing decline in production due to the drop in consumption of dry matter, as shown by several studies with sheep, even with animals of Santa Inês breed.
In tropical conditions, environmental factors are generally not compatible with the ideal range of thermal comfort efficiency for optimal animal performance (PEREIRA, 2005).It would be ideal that determining the adaptability of an animal to a given environment had high correlation with the yield or growth performance.Adaptive characteristics are very important in the process of adjustment of the animal to the adverse weather conditions, and among them stands out the coat color that determines the amount of thermal radiation that the animal reflects and absorbs, which may change their caloric balance.
This study aimed to verify the influence of the coat color on the heat tolerance and pasture intake of Santa Inês sheep.

Material and methods
The survey was conducted from January to March 2008, in Riachão Farm, located in the municipality of Sairé, Agreste region of Pernambuco State.The rainfall in the region ranges from 600 to 900 mm year -1 , concentrated in the months from March to July, and the climate is dry sub-humid (CONDEPE, 1980).
The animals went through an adjustment period of 14 days to the management and diet and were kept in a 3 ha-paddock with pangola grass pasture (Digitaria decumbens Stent).The stocking rate was seven animals per hectare.The paddock was provided of a weir and natural shade.
The experiment lasted eight weeks with 21 Santa Inês lambs with 25 kg average weight and 12 months of age, being seven of each coat color: white, brown and black.The experiment consisted of a completely randomized design with three treatments and seven repetitions.At 6:00 AM, animals were released into a paddock without shading, and were given forage and water ad libitum.The rectal temperature (TR,°C) was obtained at 9:00 AM and 2:00 PM, which was measured with a clinical digital thermometer inserted into the rectum of the animal.After the data measurements in the afternoon, animals were released into the pasture and at 5:00 PM collected to the fold.For the calculation of the heat tolerance index we used the specific formula for sheep, proposed by Rauschenbach and Yerokhin, (1975): ITC = 2 (0.5 t2 -10 dT + 30), where : ITC = heat tolerance index (dimensionless) ; T2 = air temperature in the afternoon (3:00 PM); dT = difference between the body temperature in the afternoon and in the morning.
The results were analyzed by the software SAS (2005).It was evaluated the intake and the digestibility of dry matter (DM) and nutrients.Were used the following indicators chromic oxide and indigestible acid detergent fiber (FDAi) for estimating the forage dry matter intake and the apparent digestibility of dry matter and nutrients determined in the samples using the in "situ" degradability technique for 144h.From the concentration of chromic oxide in the faeces and the amount ingested by the animal, it was estimated the fecal excretion.Later, based on the concentration of FDAi of faeces and food, it was estimated the forage dry matter intake.
All animals were given, at the end of the afternoon in the fold, in individual feeders, concentrate prepared with soybean meal, ground corn and mineral supplement, formulated according to the NRC (2007).Animals were weighed every week and the concentrate was supplied on the basis of 1% body weight (BW) with daily weighing of leftovers.The chromic oxide was supplied mixed with the concentrate, in the proportion of 2.88 % DM (dry matter), which was supplied twice a day, in individual troughs.Fecal samples were collected directly from rectal ampulla of ewe lambs at 6:00 AM and 5:00 PM in the last four days of the concentrate supply.

Results and discussion
Mean values of meteorological elements observed in the morning (8:00 AM) and afternoon (3:00 PM), are shown in Table 1.During the experimental period, it was observed values of rainfall of 71.0 mm (January), 35.0 (February) and 0.0 (March) and the minimum and maximum temperatures were 18 and 35°C respectively.
Table 2 lists the mean values and Pearson correlation coefficients between the heat tolerance index with total weight gain and average daily weight gain for Santa Inês sheep with different coat colors.The ITH, considering the set of animals of the three coat colors, ranged from 58 to 116.Therefore there was a high variability in the tolerance to heat within the breed, a phenomenon also observed by Quesada et al. (2001) in a study with 25 females of the Morada Nova and Santa Inês breeds, aged between two and four years in the Federal District, Brazil under conditions of air temperature and relative humidity ranging from 12.0 to 32.2°C and 22 and 99%, respectively.The high variability in heat tolerance found in this study occurred in the Acta Scientiarum.Animal Sciences Maringá, v. 35, n. 3, p. 307-310, July-Sept., 2013 animals of the three coat colors, which allowed inferring the possibility of performing a selection within the breed to such trait.No significant difference (p > 0.05) was detected in the rate of heat tolerance among animals of different coat colors.However, the white ones showed a slight superiority to the brown and black animals, which were similar to each other; these results confirm those obtained by Neves et al. (2009), who worked on the same property and time of year.
Also, no significant correlation (p > 0.05) was found between the heat tolerance index and the total and daily weight gain.The lack of a significant correlation between the tolerance and weight gain of sheep in the present study is probably due to the small difference among animals of the different coat colors, relative to the adaptability to heat, and also because sheep belonged to the same breed, originated in the conditions at which the study was carried out, and thus, with high adaptability to these stressful conditions.In this way, a single characteristic, such as the color, would be insufficient alone to cause great differences among the animals.
The mean values of intake of dry matter, of forage, of concentrate and total in g day -1 , are presented in Table 3. White, brown and black sheep have not differed (p > 0.05) in relation to the consumption of dry matter, concentrate, forage and average daily weight gain.The average daily weight gain was 170.10,  193.69 and 199.50 (g day -1 ) for white, brown and black animals, respectively.This is probably because animals are of the same breed, with genetic composition favorable to the environment at which they have been subjected to.The results suggested that the coat color is not a characteristic capable alone to impose changes in maintaining heat balance of Santa Inês sheep enough to influence the growth performance of animals.On the other hand, these studies could be conducted with a larger number of animals.
Souza et al. ( 2011) evaluated the feeding behavior of Santa Inês sheep grazing in the semi-arid region of Paraíba State, distributed in environments without shadow (SS), natural shade (SN) and artificial shade (AS), and observed averages regarding maximum and minimum temperature of 35.17 to 20.67°C in the SN, 37.00 to 21.82°C in AS and achieved gains of 120.43, 113.1 and 129.32 g day -1 , respectively, and receiving increasing levels of concentrate supplementation, 0.0; 1.0 and 1.5 % body weight (BW), found values of 85.89, 114.36 and 162.60 g day -1 , respectively.
According to Neiva et al. (2004) Santa Inês sheep kept in the shade, have presented weight gain 30% higher (174 g day -1 ) than those kept under direct solar radiation (122 g day -1 ).

Conclusion
White sheep showed a slight superiority in heat tolerance in relation to brown and black animals, but this is not reflected in the productive performance of animals.From these results, it is suggested that more work should be done in order to strengthen our results.

Table 1 .
Values of meteorological elements by the morning (8h) and afternoon (15h) during the experimental period.

Table 2 .
Mean values and Pearson correlation coefficients between the heat tolerance index (ITH) with the total weight gain (TWG) and average daily weight gain (ADWG) for sheep of Santa Inês of different colors of coat.

Table 3 .
Estimate of daily consumption of dry matter, concentrate, and forage, and average daily weight gain in Santa Inês sheep of different coat colors.