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Physiological responses of yak under different environments

M. Sarkar, B.C. Das, D.B. Mondal and A. Chatterjee

National Research Centre on Yak, Indian Council of Agricultural Research (ICAR), Dirang 790 101, West Kameng District, Arunachal Pradesh, India

Summary

Adaptability of seven healthy adult female yak ranging in age from 3.54 years and weighing 200250 kg, raised on the farm premises of the National Research Centre on Yak, India, at an altitude of 2730 metres above sea level (masl), was assessed in terms of selected physiological parameters-rectal temperature, pulse rate, respiratory rate and water intake, and level of blood metabolites-glucose and volatile fatty acids (VFA)-during cold humid and moderately cold humid seasons as identifiable in this zone. Rectal temperature, pulse rate and respiratory rate were significantly higher in moderately cold humid season than in cold humid season whereas blood glucose and VFA levels were higher in cold humid season than in the other season. The Dairy Search Index was found to be 0.95 and 1.24 in cold humid and moderately cold humid seasons, respectively. It was apparent from the comparative picture of physiological responses in yak during these two seasons that the animals suffered from considerable heat stress during moderately cold humid season. The common husbandry practice of the yak farmers is that during summer months (moderately cold humid) they take their yak to higher altitudes (45006000 masl) and during winter months (cold humid) they move down to approximately 3000 masl so that their yak live on approximately same weather conditions. The present study presents scientific explanation for the up and down migration of the yak herders during summer and winter months.

Keywords: Yak, adaptability, dairy search index, thermoregulation

Introduction

The adaptability of an animal to the environmental conditions in which it is to be maintained greatly influences its production efficiency. Lack of adaptability of yak, especially to heat, has been an important limiting factor in their large-scale introduction in the tropics. Evaluation of physiological responses of yak under different geo-climatic conditions, is therefore an essential pre-requisite in formulating suitable breeding plan. The present investigation, the first of its kind in our opinion, deals with the evaluation of physiological responses of yak under different environments.

Materials and methods

Experimental animals comprised seven healthy adult female yak, 3.54 years of age and weighing 200250 kg, raised on the farm premises of the National Research Centre on Yak, India, at an altitude of 2730 masl and maintained on a combination of both grazing and concentrate supplement. The study was conducted for 10 days each during cold humid (season 1) and moderately cold humid seasons (season 2) as identifiable in this zone. The meteorological attributes during the two seasons are presented in Table 1.

Table 1. Meteorological attributes during of the two seasons of the study (mean ± SE).

Season

Mean daily temperature (°C)

Mean daily relative humidity (%)

Cold humid

4.7 ± 2.3

74.5 ± 3.9

Moderately cold humid

18.1 ± 0.3

74.2 ± 2.5

Rectal temperature, respiration rate and pulse rate of the animals were recorded at 07:00 and 15:30 h daily. Rectal temperature was recorded by putting a clinical thermometer in the rectum for 1 min., respiration rate with the help of a stethoscope and pulse by placing a fingertip on the coccygeal artery with minimum disturbance of the animal. The morning observations were taken before offering any feed and water. In the afternoon, the observations were recorded about 30 minutes following return from grazing to eliminate the effect of grazing activity. Water was offered ad libitum at 10:00 and 14:00 h and the individual intakes recorded. The water intake per 100 kg body weight was calculated. Blood samples from each animal were also taken daily at 07:00 and 15:00 h for the determination of glucose (Webster et al. 1971) and total volatile fatty acids (VFA) (Gupta et al. 1988). From the data, Dairy search indics (DSI) (Bonsma 1949) were determined from the following equation:

DSI = 0.5 ×  x1/x + 0.2 ×  y1/y + 0.3 × z1/z

where x1, y1 and z1 are the observed rectal temperature (ºC), respiration rate and pulse rate, respectively. x, y and z are normal (expected) rectal temperature, respiration rate and pulse rate, that is 38.33°C, 23/min. and 60/min, respectively. Average of each response for each season was calculated for each animal and used for further statistical analysis (Snedecor and Cochran 1967) (Table 2).

Table 2. Analysis of variance of respiratory frequency, rectal temperature, pulse rate, water intake, dairy search index, VFA and glucose.

Sources of variation

d.f.

Respiratory frequency

Rectal temperature

Pulse rate

Water intake

Dairy search index

Glucose

VFA

MSS

F

MSS

F

MSS

F

MSS

F

MSS

F

MSS

F

MSS

F

Season

1

2540.3

74.4*

5.7

31.8*

768.8

44.3*

20.2

38.2*

0.41

94.06*

3508.60

339.70*

2628.90

218.90*

Error

18

34.1

 

0.18

 

17.3

 

0.53

 

0.004

 

10.3

 

12.0

 

Total

19

                           
* = P<0.01.

Results and discussion

The average physiological responses in two seasons are presented in Table 3.

Table 3. Average physiological responses of yak during the two seasons.1

Parameters

Cold humid season

Moderately cold humid season

Respiratory frequency/min.

15.024.2 (20.0 ± 1.2)

32.358.3 (42.5 ± 2.3)

Pulse rate/min.

51.660.9 (56.8 ± 0.9)

63.178.2 (69.2 ± 1.6)

Rectal temperature (°C)

100.8102.1 (101.3 ± 0.1)

101.8103.5 (102.4 ± 0.1)

Water intake (L/100 kg body weight/day)

5.27.8 (6.6 ± 0.2)

7.39.8 (8.6 ± 0.2)

Blood glucose (mg/100 mL)

35.647.9 (41.9 ± 1.2)

11.819.1 (15.5 ± 0.7)

Blood VFA (mmoL/L)

68.477.1 (73.7 ± 0.8)

42.257.8 (50.7 ± 1.3)

Dairy search index

0.890.99 (0.95 ± 0.01)

1.11.4 (1.2 ± 0.02)

1. Figures in the parenthesis give the mean ± SE.

Respiratory frequency

The respiratory frequency was significantly (P<0.01) higher in season 2 (18.1°C) than in season 1. The respiratory frequency has been reported to increase significantly around 20°C in the European breeds of cattle and around 32°C in Brahman cattle, although it starts rising around 1618°C and 28°C, respectively (Kibler and Brody 1949, 1950, 1951). At higher temperature, the peripheral warm receptors in the skin become activated and send neural signals to the warm receptors located in the anterior hypothalamus in order to trigger the respiratory activity to increase the rate of heat loss from the body (Hafez 1968).

Rectal temperature

The rectal temperature in all the animals rose significantly (P<0.01) higher during season 2 than that in season 1. Significant rise in the rectal temperature at 27.3°C ambient temperature has been reported in cattle (Singh 1977), and in goats and sheep (Ghosh and Pan 1994). Any imbalance in the ratio of heat production to heat loss, which cannot be manoeuvred by the different thermoregulatory mechanisms, is reflected by the increase in body temperature.

Pulse rate

The pulse rate increased significantly (P<0.01) higher in season 2 in comparison to that in season 1. An increase in pulse rate at higher temperature has been reported in cattle (Worstell and Brody 1953; Beakley and Findlay 1955; Bianca and Findlay 1962; Whittow 1971). In hyperthermia due to severe heat stress, Whittow (1971) observed an increase in the heart rate, which he attributed to the Van Hoff Arrhenius effect.

Water intake

The water intake (per 100kg body weight/day) was significantly (P<0.01) higher during season 2 than that in season 1. The evaporative loss of water in hot environment is expected to be more than that in a cool environment (Thompson et al. 1949, 1951) and an increase in water intake under higher temperature stress has been reported in cattle (Horrochs and Philips 1961; McDowell et al. 1969; Saxena 1976).

Glucose and VFA level

The blood glucose and VFA levels were significantly (P<0.01) higher during season 1 in comparison to that in season 2. The decrease in sugar and VFA level on heat exposure has also been reported in cattle (Riek and Lee 1948) and in sheep and goats (Ghosh and Pan 1994). Cold exposure increases blood glucose level in ruminants due to the increase in circulating thyroid and adrenal hormones and this contributes to metabolic heat production (Weeks et al. 1983).

Dairy search index (DSI)

The DSI during season 1 was 0.95 whereas in season 2 it was significantly (P<0.01) higher (1.24). Much deviation of the index from '1' indicates the decrease in thermal adaptability.

It is apparent from the comparative picture of physiological responses in yak during the two seasons that the animals suffered from considerable heat stress during moderately cold humid season. The natural habitat of yak starts from 3000 masl. The common husbandry practice of the yak farmers is that during summer months (moderately cold humid) they take their yak to higher altitudes (45006000 masl) and during winter months (cold humid) they move them down to approximately 3000 masl so that the animals live on approximately same environmental conditions. The present study provides scientific explanation to the up and down migration of the yak herders during summer and winter months.

Acknowledgments

We thank Mrs S. Pattanaik and Mr K.P. Debnath for their technical assistance.

References

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