Effects of Heat Stress on Grazing Behaviour of Farm Animals
NazanKOLUMAN1*, SerapGÖNCÜ1
1 Department of Animal Science, Faculty of Agiculture, Cukurova University, Turkey
*Corresponding Author: nazankoluman@gmail.com
Abstract
In hot and humid climate, particularly under the intensive grazing system, farm animals encounters multifaceted problems viz., climatic influences, pasture type and condition, and grazing competition with co-inhabitants in the grassland. Farm animals first react to the environmental influences by changing their behavioral pattern in field, in order to avoid climatic stress. Sustainable production of livestock requires advanced planning of production management systems, with an understanding of negative animal responses that signal environmental stress and the ability to implement appropriate practices to ameliorate stress effects. With production systems located in many climate zones currently experiencing greater variation in climate extremes, an essential question becomes “How do we adapt our livestock production systems to meet the thermal challenges of current and future climates. In the pasture animal adopt foraging strategy by changing its ingestive behavior to meet nutrient requirement. Thus animals’ strategy of changing their behavior must be regarded as their adaptation. Grazing of forage generally provides the least expensive way of supplying nutrients to animals. Therefore, it is advantageous to develop a year round forage program which allows for as much grazing as possible every month of the year. However, good pasture management involves much more than simply turning the animals to pasture. The principles of grazing of goats are similar to those used for cattle. The primary goal is to have control of the animal's grazing pattern so that one can dictate the degree of defoliation and the frequency of defoliation. To obtain efficient animal production over a number of years, the needs of the plants as well as the needs of the animals must be taken into consideration.
The objectives of this paper are to: define the thermal challenges that create negative animal responses during direct effect of solar radiation at grassland, to characterize those animal behaviors that they can be recognized and ameliorated.
Keywords:Farm animals, heat stress, grazing, behaviour, Mediterranean region.
Introduction
Under the intensive grazing system, animal encounters multifaceted problems viz., climatic influences, pasture type and condition, and grazing competition with co-inhabitants in the grazing field. Animals first react to the environmental influences by changing their activity pattern in field, in order to avoid climatic stress (Solaniki, 2000). Sustainable production of livestock requires advanced planning of production management systems, with
an understanding of negative animal responses that signal environmental stress and the ability to implement appropriate practices to ameliorate stress effects. Thermal challenges range from cold to hot and are species- and life-cycle-dependent. Livestock managers have always had to address such challenges for the benefit of their animals from the standpoints of managerial acceptability, technological feasibility, and economic return. Modern production systems can be designed to manage thermal challenges in specific locations; however, sustainability ultimately determines which options are most appropriate. With production systems located in many climate zones currently experiencing greater variation in climate extremes, an essential question becomes “How do we adapt our livestock production systems to meet the thermal challenges of current and future climates?” (Nienaber andHahn, 2007). Secondly, in the pasture animal adopt foraging strategy by changing its ingestive behavior to meet nutrient requirement. Lastly for the survival among fellow competitors in the same grazing land, they select a feeding niche whereby competition for food material could be avoided and feed requirement can be fulfilled. Thus animals’ strategy of changing their behavior must be regarded as their adaptation (Solaniki, 2000).
Faced with new social concerns, such as those relating to agricultural de-intensification and biodiversity conservation, livestock farmers have to cope in particular with problems linked to grazing land heterogeneity and variability. It may therefore contribute to designing new animal behavior management on the way to manage grazing so as to ensure both animal feeding and better control of vegetation dynamics in varied environments (Meuret and Dumont, 1999).
Grazing of forage generally provides the least expensive way of supplying nutrients to animals. Therefore, it is advantageous to develop a year round forage program which allows for as much grazing as possible every month of the year. However, good pasture management involves much more than simply turning the animals to pasture. The principles of grazing of goats are similar to those used for cattle. The primary goal is to have control of the animal's grazing pattern so that one can dictate the degree of defoliation and the frequency of defoliation. To obtain efficient animal production over a number of years, the needs of the plants as well as the needs of the animals must be taken into consideration (Luginbuhl et al, 1998).
The objectives of this paper are to: define the thermal challenges that create negative animal responses during direct effect of solar radiation at grassland, to characterize those animal behaviors that they can be recognized and ameliorated.
Material and Methods
The animals, used in the experiment were 20 local Hair and 20 imported Saanen goats at private farm conditions of subtropical Eastern Mediterranean region of Turkey, 420 m above sea level. The principal climatic characteristic of Adana Province is high air temperature and humidity in the summer season. The average daily temperature was 34.3 C, while the highest and lowest temperatures were 41 C and 26 C in July, respectively. Average relative humidity and wind speed were observed as 67.9% and 1.2 km/h during the trial, respectively. All goats were 4 years old and 2nd lactation and each of them had only one kid. At the beginning of the experiment, body weights of the Hair (average 68, 9 kg) and
Saanen goats (64,7 kg.) were measured. The kids born at the end of January and sucked their mothers during 2 months. The experiment started after weaning. The study was carried out between June to August 2008 during grazing period. The mating season started at the end of August when the experiment was lasted. The material grazed daytime between 6-12 am and 3.00-7.00 pm together. Within almost 10da grazing area consisting of Aegilops ovate,
Bothriochloa ischaemum, Lolium perenne, Astragalus pinetorum, Poterium sanguisorba, and
a shrub (Quercus humilis). Most of animals grazed at the in-village common property and shrubs at the hilly areas. They were kept in a semi-open barn overnight. All animals were fed as a group on concentrate (12% crude protein and 2300 kcal/kg ME) and ad-lib lentil straw before milking time. Milking was made by hand twice a day. The observation was made by portative camera system (SONY HDR-XR105E 80 GB Hard disc) at the grassland, during grazing period both in morning and afternoon, twice a week. The activities were recorded for grazing, ruminating, walking and lying, and the activities were defined as follows: (1) Grazing-grazing or browsing while walking or standing, (2) Walking-moving from one place to another without grazing or browsing, (3) Ruminating, (4) Lying-simply sitting for rest or for rumination (Solaniki, 2000). Goats were considered lying if their flank was in contact with the ground. They were considered grazing if grass was being ingested or could be seen in the mouth (Tucker et al., 2008). The physiological data (rectal temperature, respiration and pulse rates, and skin temperatures from head and udder) were recorded twice a week at morning 600–700; midday 1200–1300; and 1600–1700; midnight 2400–0100. Rectal temperatures were detected by digital thermometer, and the respiration and pulse rates were recorded using a stethoscope. Skin temperatures were measured via infrared thermometer (Testo BP-960) at a distance of 10 cm. from the head, foot, back side and udder skin.
Air temperature and relative humidity were recorded at 10 min intervals by a portable data logger (Testo 950 humidity and temperature sensor). The climatic data such as air temperature, relative humidity and Thermal Heat Index (THI) of the trial are shown in Table 1.
THI was used as an indicator of thermal comfort for dairy goats and was calculated as follows (Tucker et al, 2008):
THI = (1.8 x T + 32) – ((0.55 – 0.0055) x RH) x (1.8 x T – 26)) where T is the air temperature (°C) and RH the relative humidity (%).
AC method was accepted as the best method suitable for International regulation of milk recording in sheep and goat (Barillet et al,1992). Only one of the three daily milking was recorded, taking into account the total volume of milk produced by the whole goats. It was planned for 5 or 6 test days during the milking period (150-180 days milking period). Interval between two successive test days-30 days. Average suckling period-60 days is fixed as a standard. Only the milked yield during the milking period is taken into account (without that suckled from the kids). Regarding the calculation of milked yield, the Fleischmann method was adapted. There is no difference in the results of calculated milked yield between Fleischmann method and our adaptation. During each control day, 50 ml milk samples were collected from 5 animals from each genotype. Milk contents of animals such as crude pH, fat, crude protein, and dry matter were measured by FOSS Milko Scan FT120 (Denmark).
Physiological values such as; rectal and skin temperatures, respiration and pulse rates; and behavioral traits, milk yield, milk composition of Saanen and Hair goats were analyzed with Student’s t-test to determine the effect of the genotypes. Also, some physiological values accept for respiration and pulse rates were analyzed by One-way ANOVA test to determine the differences among measurement times. After that, the differences were separated using Duncan’s multiple range tests. Respiration and pulse rates were analyzed using Kruskal Wallis test, and any significant findings were further subjected to post-hoc pair-wise comparisons performed by Dunn's Test. The Kruskal Wallis test can be applied in the one factor ANOVA case. It is a non-parametric test for the situation where the ANOVA normality assumptions may not apply. All the computational work was performed by means of MINITAB V.13.20 statistical package program (MINITAB, 2000).
Results and Discussion
The climatic factors and THI values of experimental animals are represented in Table 1.
Table 1. Climatic data and THI values of experimental animals
Traits Hours Average Values
Temperature ( C ) 06.00–12.00 15.00–19.00 33.23 ± 0.12 37.15 ± 0.25 Relative Humidity (%) 06.00–12.00 62.81 ± 0.56 15.00–19.00 69.53 ± 0.98 THI 06.00–12.00 78 15.00–19.00 89
THI is a good indicator of stressful thermal climatic conditions. THI values of 70 or less are considered comfortable, 75–78 stressful, and values greater than 78 cause extreme stress and animals are unable to maintain thermoregulatory mechanisms or normal body temperature (Silanikove, 2000). As seen in Table 1, the experimental goats were subjected to stressful conditions (THI: 78 to 89). All data of experimental animals were discussed under the light of THI values.
The physiological traits of experimental goats are presented in Table 2.Average rectal temperatures of Hair and Saanen goats were measured almost same levels during morning times of the day (p>0.05). But when the air temperature increased the rectal temperature of Hair goats increased slightly but did not change significantly (p>0.05), on contrary the rectal temperatures of Saanen goats increased sharply (p< 0.01) during a day (almost +1 C) and slightly decreased at midnight. Head, foot, back side and udder temperature of Hair and Saanen goats increased until night time and returned to normal level at midnight hours.
The Hair goats have long (15 to 20 cm) and black hair while Saanen has short and white hair structure. Finch (1984) reported that white hair permits greater penetration of radiation into the fur than black. The radiation in the visible part of the spectrum (0.3-0.7 µm) is absorbed at or near the surface of the black fur. Little is reflected, but a large amount is reradiated as long wave radiation (>0.7 µm) before it reaches skin. It is clear that due to long
and black hair structure Hair goats might have been more advantageous than that of Saanen goats as indicated by Finch (1984).
Table 2. Some physiological values of Saanen and Hair goats.
Traits Hours Hair goat Saanen Goat Sig.
06.00-07.00 38.12 ± 0.03 38.81 ± 0.03D 0.090 12.00-13.00 38.74 ± 0.03b 39.01 ± 0.03Ba 0.050 RT ( C ) 16.00-17.00 38.16 ± 0.03b 39.88 ± 0.04Aa 0.040 24.00-01.00 38.15 ± 0.04b 39.68 ± 0.05Ca 0.045 Sig. 0.11 0.01 06.00-07.00 44.33 ± 1.28Cb 48.24 ± 1.36Ca 0.050 12.00-13.00 67.32 ± 1.48BCb 75.56 ± 1.83Aa 0.023
RR (breath/min.) 16.00-17.00 62.04 ± 2.03Ab 73.81 ± 1.94Aa 0.048
24.00-01.00 50.34 ± 1.72Bb 67.20 ± 1.77Ba 0.035
Sig. 0.009 0.005
06.00-07.00 81.24 ± 1.15C 94.90 ± 0.99C 0.080
12.00-13.00 92.61 ± 1.17A 104.85 ± 1.20A 0.085
PR (beat/min.) 16.00-17.00 89.98 ± 1.39A 104.64 ± 1.34A 0.078
24.00-01.00 82.43 ± 1.25B 95.36 ± 1.04B 0.063 Sig. 0.004 0.004 06.00-07.00 28.59 ± 0.24Db 29.30 ± 0.20Da 0.048 12.00-13.00 33.68 ± 0.23Bb 36.36 ± 0.19Aa 0.043 Surface temperatures (head C) 16.00-17.00 34.71 ± 0.13A 35.06 ± 0.16B 0.090 24.00-01.00 29.48 ± 0.16C 30.67 ± 0.19C 0.110 Sig. 0.050 0.042 06.00-07.00 27.99 ± 0.18Db 28.75 ± 0.19Da 0.031 12.00-13.00 33.37 ± 0.21Bb 36.46 ± 0.18Aa 0.034 Surface temperatures (back C) 16.00-17.00 34.46 ± 0.17A 34.76 ± 0.16B 0.081 24.00-01.00 29.10 ± 0.17Cb 30.20 ± 0.21Ca 0.025 Sig. 0.034 0.032 06.00-07.00 29.65 ± 0.19Db 30.74 ± 0.27Ca 0.038 12.00-13.00 34.85 ± 0.19Bb 36.45 ± 0.19Aa 0.045 Surface temperatures
(udder C) 16.00-17.00 35.68 ± 0.13Ab 36.10 ± 0.15Aa 0.048
24.00-01.00 30.79 ± 0.23Cb 31.93 ± 0.27Ba 0.048
Sig. 0.012 0.023
06.00-07.00 26.95 ± 0.66C 27.35 ± 0.14 0.098
Surface temperatures 12.00-13.00 30.14 ± 0.29Bb 33.23 ± 0.17a 0.034
(foot C) 16.00-17.00 32.50 ± 0.13A 32.97 ± 0.14 0.078
24.00-01.00 27.85 ± 0.15Cb 28.79 ± 0.17a 0.011
Sig. 0.042 0.053
Differences were illustrated on the groups for RT, RR, PR and ST as a, b Differences were illustrated on the hours for RT, RR, PR and ST as A, B, C, D RT: Rectal Temperature, RR: Respiration Rate, PR: Pulse Rate.
The udder temperatures were increased more than the head temperatures for morning measurements in all groups. This observation may be attributed to surface radiation effects of the earth, because the goats are subjected to heat the whole day by way of both convection and radiation. These data matched with results of Koluman Darcan et al (2009), Darcan et al (2008).
Al-Tamimi (2007) reported that, when subjected to environments above the thermoneutral zone and the zone of thermal comfort, homoeothermic animals employ several thermoregulatory mechanisms to offset heat gain by an equivalent loss and maintain their core body temperature and attain thermal equilibrium (IUPS, 2001). Physiological thermoregulatory pathways under heat stress incorporate an increase in respiratory and cutaneous evaporative cooling (Katamato et al, 1998), an increase in peripheral to splanchnic blood flow ratio (Silanikove, 2000).
Respiration rate measurement can provide reliable and practical information for estimating the severity of heat stress in farm animals (low: 40–60 breaths per min; medium: 60–80 breaths per min; high: 80–120 breaths per min; and severe heat stress above 150 breaths per min) (Silanikove, 2000). Respiration rates of experimental animals ranged between 44-67 breath/min. for Hair goats; 48-75 breath/min. for Saanen goats. Thus when it was compared with Silanikove (2000)’s information, it can be said that both groups were in medium heat stress but Saanen goats’ respiration rate almost reached to high heat stress level.
Avendano-Reyes et al(2006) indicated those increased body temperature and respiration rates are normal mechanisms by which animals dissipate heat from their body to maintain thermoregulation in hot ambient conditions (Yousef, 1987). Only if an animal can maintain a rectal temperature below 38.5° C is it considered to have a normal body temperature (Igono et al, 1992). That Hair goats have rectal temperature below this level and they were able to dissipate heat from their body even their skin temperatures were higher than normal levels. Lactation performance and milk contents of experimental animals were given in Table 3.
Table 3. Average milk yield and milk composition of Saanen and Hair goats.
Traits Hair Goats Saanen Goats Sig.
Lactation yield (kg) 120.8 ± 49.9a 270.6 ± 38.5b 0.012
Lactation period (months) Crude fat (%) 5 3.66 ± 0.05 6,5 3.60 ± 0.09 - 0.078 Crude protein(%) 3.83 ± 0.03 3.84 ± 0.06 0.083 Dry matter(%) 12.61 ± 0.09 12.39 ± 0.15 0.092 pH 6.17 ± 0.03 6.99 ± 0.02 0.065
As given in Table 3, lactation milk yields of Saanen goats were recorded as 270 kg. while Hair goats’ were 120 kg Average lactation milk yields of Hair and Saanen goats were reported as 150-200 kg and 500-700 kg, respectively (Darcan, 2000; Darcan and Guney, 2002; Darcan and Guney, 2008). It was seen that production level of Saanen goats was lower than the expected. It could have been due to both heat stress effects and also semi-intensive
conditions. But we have to consider that even heat stress conditions Saanen goats gave two times more milk than Hair goats. Additionally, the milk composition of both groups were almost same which of them matched with previous studies (Yurtseven and Gorgulu, 2004; Gorgulu et al, 2008)
Behavioral aspects of the Saanen and Hair goats were represented in Table 4.
Table 4. Behavioral traits of Saanen and Hair goats
Behavioral traits Hair goats Saanen goats Sig.
Grazing period (h/day) 3.39 ± 0.55 a 2.44 ± 0.30 b <0.000
Rumination (h/day) 1.09 ± 0.10 a 1.37 ± 0.26 b <0.000
Walking (h/day) 4.31 ± 0.25 a 2.93 ± 0.27 b <0.000
Lying (h/day) 2.01 ± 0.30 b 3.80 ± 0.42 a <0.000
Concentrate feed consumption (g/day) 412,8 556,3 -
Brosh et al (1998) and Mitlöhner et al (2002) reported that, Multiple behavioral adaptive mechanisms play a major role, including, but not limited to, the seeking of shade and cooler surfaces, change in pasture and reduced muscular activity in addition to changing the pattern of feed intake (Al-Tamimi, 2007).
Saanen goats grazed (p<0.001), walked (p<0.001) less but ruminated (p<0.001) and lied (p<0.001) more than Hair goats. McDowell (1985) stated that the major effects of thermal stress are: feed consumption, environment by forage quality interrelationships, digestion and metabolism and requirements of specific nutrients. Feed intake is decreased as temperature and humidity increases. This helps maintain body heat balance by minimizing heat generation from ruminal fermentation. As we discussed before, even they had higher production level, physiological adaptation mechanisms of them indicated thermal stress for Saanen goats. Saanen goats grazed less but they consumed more concentrate at barn conditions.
Due to direct solar energy effects grazing activities of Saanen goats slow down, the animal sat down to restore the energy and ruminates the ingested feed. Darcan et al. (2008), Darcan (2000), Darcan and Guney (2008) reported that goats decreased their activity in heat stress conditions and they ate less food, as well. Saanen goats ate more concentrate, but due to heat stress effects they gave less milk than previous studies (450 vs 270). Saanen goats compensated daily requirements with concentrate feeds. Hair goats were walking more to seek grasses; they were more active than imported Saanen goats. Hair goat’s nails are harder and their udders smaller than Saanen goat. Thus, they were able to walking and standing more at hilly areas. They were affected by direct solar radiation less as well, because these animals locate to subtropical climate and they are able to maintain their body temperature in such environment.
Peischel (2009) reported that stress management is critical to improving the profitability of the farm. Minimizing stress enhances the immune system to achieve profitable health. Management practices can include the physical handling of the stock, well constructed working facilities, animal welfare, an understanding of animal behavior.
Thermal stress could have been severe economic losses with a decrease in reproductive performance of animals. With this study we indicated that genetic heritability of foraging is important in browse, forb and pasture operations, especially in hot and humid regions. As underlined previous studies the goal should be improving herd performance; therefore the economical production traits of goats and their ability to adapt to environmental stress is crucial and a study based on behavioral characteristics and animal welfare should taken into consideration for his aim. But native goats, that resistant to heat stress, should take into consideration and should not have been ignored for improvement studies especially in crucial regions.
Acknowledgements
This study was supported by Scientific Research Fund of Cukurova University project number FAY-2015-3982.
References
Al-Tamimi, H.J., 2007.Thermoregulatory response of goat kids subjected to heat stress,Small Ruminant Research, 71: 280–285.
Avendano-Reyes, L., Alvarez-Valenzuela, F.D., Correa-Clederon, A. et al.,2006. Effect of cooling Holstein cows during the dry period on postpartum performance under heat stress conditions, Livestock Science, 105 : 198–206.
Barillet, F., Boichard, D., Barbat, A. et al.,1992.Use of an animal model for genetic evaluation of the Lacaune dairy sheep.Livestock Production Science, 31(3-4):287-299. Brosh, A., Aharoni, Y., Degen, A. et al.,1998.Effects of solar radiation, dietary energy and
time of feeding on thermoregulatory responses and energy balance in cattle in a hot environment,J. Anim. Sci.76:2671–2677.
Darcan, N., 2000.A study on adaptation mechanism of crossbred goat types in Cukurova subtropical climate conditions, Cukurova Univ., Institute of Science, 97 p. Adana, Turkey.
Darcan, N. and Guney, O.,2002.Comparative Study on the Performance of Crossbred Goats Under Çukurova Subtropical Climate, J. Applied Animal Research, 22 (2): 61-64. Darcan, N. and Guney, O.,2008. Alleviation of climatic stress in crossbred dairy goats in
Çukurova subtropical climatic conditions, Small Ruminant Research, 74(1-3): 212-215, Elsevier.
Darcan, N., Cedden,F. and Cankaya,S., 2008. Spraying Effects on Goat Welfare in Hot and Humid Climate, Italian J. of Anim. Sci. 7: 77-85.
Finch, V.A., 1984. Heat as a stress factor in herbivores under tropical conditions, Gilchrist, F.M.C. and Mackie, R.I., Editors, 1984. Herbivore Nutrition in the Subtropics and
Tropics, The Science Press, Graighall, South Africa, 89-105.
Gorgulu, M., Boga, M., Sahin, A. et al., 2008. Diet selection and eating behavior of lactating goats subjected to time restricted feeding in choice and single feeding system, Small Ruminant Research, 78 :41–47.
ICRPMA, 1990.International Regulation for Milk Recording in Goats, International Committee for Recording the Productivity of Milk Animals. Italy.
Igono, M.O., Bjotvedt, G. and Sanford-Crane, H.T., 1992.Environmental profile and critical temperature effects on milk production of Holstein cows in desert climate, Int. J. Biometeorol. 36 :77–87.
IUPS, 2001.Glossary of Terms for Thermal Physiology , 3rd ed. Revised by the commission for thermal physiology of the international union of physiological sciences. The Japanese J., Physiol. 51(2): 245-280.
Katamoto, H. , Fukuda, H., Oshima, I., et al.,1998. Nitroblue tetrazolium reduction in heat stressed goats is not influenced by vitamin E and selenium injection, J. Vet. Med. Sci.60 (11):1243–1249.
Koluman Darcan, N., Cankaya, S. and Goncu Karakok, S., 2009. The Effects of Skin Pigmentation on Physiological Factors of Thermoregulation and Grazing Behaviour of Dairy Goats in a Hot and Humid Climate, Asian-Aust. J. Anim. Sci., Vol. 22 No. 5 : 727
Luginbuhl, J-M., Green, J.T. , Mueller, J.P., et al., 1998. Forage needs for meat goats and sheep” In:“Production and Utilization of Pastures and Forages, – Technical Bulletin 305. North Carolina Agricultural Research Service, North Carolina State University, Raleigh.
URL address: http://www.cals.ncsu.edu/an_sci/extension/animal/meatgoat
McDowell, L.R. 1985. Nutrition of Grazing Ruminants in Warm Climates, Chapter 4: 59-71. Academic Press, Inc. Orlando, FL. 32887. ISBN 0-12-483370-5.
Meuret, M. and Dumont, B., 1999.Advances in modelling animal– vegetation interaction and their use in guiding grazing management, Gagnaux, D., Poffet, J.R. (Eds.), proceedings of the Fifth International Symposium on Livestock Farming System, Posieux, Switzerland, 57–72.
MINITAB, 2000. MINITAB Statistical Software, Release 13.20, Minitab Inc. State College, PA, USA.
Mitlöhner, M. Galyean and J. McGlone, 2002. Shade effects on performance, carcass traits, physiology and behavior of heat stressed feedlot heifers, J. Anim. Sci.80 : 2043–2050. Nienaber, J.A. andHahn G.L., 2007 . Livestock production system management responses to
thermal challenges, Int J. Biometeorol 52:149–157.
Peischel, A.,2009. Environmental Factors Affect Nutrient Requirements for Goats,
URL address: http://www.tennesseenutritionconference.org/pdf/Proceedings2007/ Proceedings-Peischel.pdf, 11.06.2009
Silanikove, N. ,2000. Effects of heat stress on the welfare of extensively managed domestic ruminants: a review, Livestock Prod. Sci., 67:1–18.
Solaniki, G.S., 2000. Grazing behaviour and foraging strategy of goats in semi-arid region in India, Tropical Ecology 41(2): 155-159
Tucker, C.B., Rogers, A.R. and Schütz, K.E., 2008. Effect of solar radiation on dairy cattle behavior, use of shade and body temperature in a pasture-based system, Appl. Anim. Behav. Sci., 109: 141-154.
Yousef, M.K., 1987.Principles of bioclimatology and adaptation of livestock, WAS, B5, 17- 31, Elsevier Publ., Holland
Yurtseven, S., Gorgulu, M. 2004. Effects of grain sources and feeding methods, free-choice vs total mixed ration, on milk yield and composition of German Fawn x Hair crossbred goats in mid lactation, Journal of Animal and Feed Sciences. 13: 417-428.
