Behavioural, biochemical and hormonal responses of heat-stressed crossbred calves to different shade materials

^†This article is part of the Ph.D. research work submitted by the first author to the Indian Veterinary Research Institute, Bareilly, India.

ABSTRACT

An attempt was made to study the effect of different shade materials on physiological, behavioural, biochemical and hormonal responses in crossbred Vrindavani calves during the summer seasons in the Cattle and Buffalo Farm of Indian veterinary Research Institute, Izatnagar, India. During experiment, 28 crossbred calves were divided into four groups: thatch shading roof (T1), agro-net shading roof – 60% light diffusion (T2), asbestos with canvas shading roof (T3) and well-grown tree (T4). The daily macro- and microclimate data were recorded at 0900 and 1400 h. The data for each ongoing behavioural activity were recorded by closed circuit television consecutively for three days for each animal in each group from 1000 to 1700 h. Blood was also collected at 0, 15, 30, 45, 60, 75 and 90 days of the experimental period for estimation of different biochemical parameters. The microclimate, that is, maximum and minimum temperatures, relative humidity and temperature humidity index of the roof, was lower in the T2 group. There was significantly more (P < .05) time spent in shade structure by the T2 group as compared to other groups. Among the behaviour, feeding, rumination, resting and sleeping activities were more in the T2 group, whereas standing, moving, drinking, time spent near water tank and abnormal behaviour (cross-sucking, licking) were more in T3 and T4. Among the blood parameters, haemoglobin was significantly higher (P < .05) while, Serum Glutamic Oxaloacetic Transaminase and Alkaline Phosphatase were significantly lower in the T2 group.

KEYWORDS:

• Heat stress
• shade
• crossbred calves
• behaviour
• biochemical
• hormonal

1. Introduction

Heat stress is widely recognized as a stressful condition that affects physiological, behavioural and hormonal responses of an animal. Animal responses to thermal challenges vary among different species. In dairy calves older than 3 weeks, the thermo-neutral zone is about 5–20°C, but this also varies among individual animals. In the temperature above the neutral zone, homeotherms maintain their body temperature within a relatively narrow range and both physiological and behavioural responses help in thermoregulation (Sanker et al. 2012). At temperatures above the Upper Critical Temperature, cattle sweat in an attempt to dispel the excess heat and the animal becomes heat stressed, which can lead to death of the animal. As cattle sweat at only 10% of the human rate, they are much more susceptible to heat stress (Leonel 2012).

In the tropical climate of India, generally calves are housed in the loose housing system and during the daytime, they are let loose in paddocks without being provided with any shade which leaves them exposed to high environmental temperatures. It has been observed that radiation energy flow to an animal is 685 kcal/m²h, but in reality only 340 kcal/m²h of it is from direct solar radiation; the rest is from reflection of floors, dust, walls and so on (Thomas & Sastry 2007). Placing a simple shade over an animal exposed to a hot environment and direct solar radiant energy from cuts the radiant heat load on that animal by about 45% (Blackshaw & Blackshaw 1994). Extended periods of high ambient temperature coupled with high relative humidity (RH) compromise the ability of the dairy calves to dissipate excess body heat (Gaafar et al. 2011). Calves with elevated body temperature exhibit lower feed intake, high water intake and growth with less efficiency (Kendall et al. 2006), thus reducing profitability for dairy farms in hot, humid climates.

For protection from direct solar radiation in open paddocks, different shade materials are used in mangers. The type of roof material generally decides the microclimate under the covered area (Kamal et al. 2014).

There are many ways to provide shade, but little is known about the importance of various design features of shade (e.g. blockage of solar radiation, shade amount/animal etc.). Keeping in mind the importance of animal housing in a tropical country, the present study was taken up to evaluate the effect of different shade materials on the behaviour and biochemical performance of calves.

2. Materials and methods

2.1. Location and climatic condition

The present study was conducted at the Cattle and Buffalo Farm, Indian veterinary Research Institute (IVRI), Izatnagar. The Institute is located at an altitude of 169 m above the mean sea level, at 28°22′ latitude and 79.24°E longitude. The climate of the place touches the extremes of both hot (approximately 45°C) and cold (approximately 5°C) and the RH ranges between 15% and 99%. The average annual rainfall ranges from 90 to 120 cm, most of which is received during July–September.

2.2. Experimental calves

Twenty-eight Vrindavani crossbred calves were chosen for the study after 3 days of their birth (after colostrum feeding) on a staggering basis. Thereafter, the calves were not allowed to suckle the dams but were fed formula milk. Seven calves in each pen were allocated to the following treatments taking average birth weight and sex into consideration. Each group was kept at a different place, which had covered and open areas. However, different shade materials were used for covered areas under each treatment in the following manner.

2.3. Experimental design

• Thatch shading roof (T1): Four-inch-thick layer of paddy straw fixed to a bamboo frame.

• Agro-net shading roof (T2): Green and black coloured knitted fabric made out of 100% high-density polyethylene with ultra-violet light stabilized having 60% light diffusion.

• Asbestos with canvas shading roof (T3): Asbestos sheet on which canvas is laid over outer surface ensuring 2–3 inch gap between them.

• Well-grown tree (T4): A well-grown tree was used as a circular manger which facilitated feeding.

The long axis of the paddock was oriented east to west. Different shade materials were used to make the covered area measuring 1.5 × 1 m (excluding the manger) for each treatment group. The open paddock measuring 2 × 1 m was made using welded wire mesh. The calves were given an opportunity to loiter freely in the above-mentioned area. The height of the shed at the eaves was 2.5 metres and has brick flooring.

2.4. Feeding and health management for the experimental animals

The calves remained with the dam for two days after calving. On the third day, the calves were shifted to one of the treatment groups and maintained as per the standard recommendation. Whole milk was fed to individual calves as per the body weight. From 4 to 28 days of age one-tenth of body weight, from 29 to 42 days one-fifteenth and from 43 to 56 days one-twentieth of body weight. The desired quantity of milk was offered by pail method and the leftover was also recorded.

Green fodder and calf starter were offered from the first week onwards. The common green fodder supplied included Berseem (Trifolium alexandrium L.)/Maize (Zea Mays L.)/Jowar (Sorghum bicolor) which are the most common green cultivated crop in India. Calf starter prepared by the Feed Technology Unit was utilized for the experiment which includes crushed maize, soyabean oil cake, wheat bran, mineral mixture and common salt.

All the calves were reared under strict management and proper hygienic conditions throughout the period of the study. Deworming was done during the second week of the calf's age. In the subsequent week, disbudding was also followed with precautions. Good sanitation of the pens, feeding utensils, water containers and surrounding experimental area was maintained during the period of the experiment. The pens were cleaned daily and all hygienic precautions were taken to prevent the incidence of infectious and contagious diseases. The calves were given daily morning bath throughout the experiment.

2.5. Environmental observations

Macro- and microclimatic conditions, that is, the climatic condition of the research area and the day-to-day climatic condition within the calves' shed were recorded daily at 0900 and 1400 h. The daily recording of temperature (maximum and minimum) was measured by a maximum and minimum thermometer. The daily RH was recorded in a psychrometric chart using dry and wet bulb reading and the chart was hung by a thread in the covered area underneath the roof. The temperature humidity index (THI) was calculated as per McDowell (1972) using the following formula:

2.6. Blood analysis

Blood samples from all calves were collected at 0, 15, 30, 45, 60, 75 and 90 days of the experimental period.

All the samples were analysed in the Nuclear Research Laboratory (NRL), IVRI, Izatnagar.

The blood haemoglobin was estimated by Drabkin's method. Serum biochemical and hormone level, that is, Glucose, total protein, Albumin, globulin, Alkaline Phosphatase (ALP), Serum Glutamic Oxaloacetic Transaminase (SGOT) and Serum Glutamic Pyruvic Transaminase (SGPT) Cortisol, Serum Triiodothyronine (T₃) and Serum Thyroxin (T₄) were estimated using the kit supplied by Erba Diagnostics Mannheim GmbH, Germany.

2.7. Behavioural observations

The time taken by each ongoing activity was recorded for 7 h (1000–1700 h) after milk feeding by closed circuit television for each animal in each group consecutively for 3 days every month. The time spent in each behavioural activity was recorded and coded in specifically designed coding sheets for the analysis.

2.8. Statistical analysis

The primary data obtained from the study were pooled and analysed through SPSS 14 using ANOVA to compare the treatment and control groups. During analysis, the data were condensed and evaluated at 14-day time intervals

3. Results

3.1. Macro- and microclimatic condition

The mean solar radiation and wind speed during different 14-day intervals of the experimental period are shown in Figure 1. The mean ambient temperature ranged between 23.26 ± 0.82 and 33.65 ± 0.22°C with overall mean temperature being 29.04 ± 0.20°C. The RH during the experimental period at 0900 h ranged between 48.80 ± 2.19 and 60.67 ± 1.98% with an overall value of 53.88 ± 0.80%, whereas at 1400 h, it varied from 36.92 ± 1.58 to 42.09 ± 3.16% with an overall value of 35.29 ± 0.77%. The mean RH during the observation period ranged between 51.38 ± 2.52 and 42.86 ± 1.73% with an overall value of 44.59 ± 1.81%. The THI at 0900 h varied between 69.64 ± 0.80 and 84.28 ± 0.42 with an overall value of 78.16 ± 0.38 and at 1400 h, it ranged between 82.31 ± 0.98 and 89.90 ± 0.35 with an overall THI of 87.51 ± 0.36. The mean THI during the observation period ranged between 75.98 ± 0.87 and 87.09 ± 0.35 with an overall value of 82.84 ± 0.33.

Figure 1. Macroclimatic condition of the experimental location.

Under the shade materials, the microclimatic parameters like the overall minimum temperature at 0900 h was 23.16 ± 0.1, 19.27 ± 0.19, 23.16 ± 0.20 and 23.09 ± 0.25°C, whereas at 1400 h, these were 33.16 ± 0.18, 32.74 ± 0.22, 34.64 ± 0.20 and 34.61 ± 0.30°C in T1, T2, T3 and T4, respectively. The overall minimum temperature at 0900 h was significantly lower (P < .05) in T2 as compared to other shade materials during all the 14-day intervals, whereas the maximum temperature was (P < .05) recorded more in T3 (34.64 ± 0.20°C) followed by T4 (34.61 ± 0.30°C) and least in T2 (32.74 ± 0.22°C) followed by T1 (33.16 ± 0.18°C). The overall RH was 62.78 ± 0.65, 44.81 ± 0.58, 72.23 ± 0.58 and 76.42 ± 0.58 at 0900 h and 48.87 ± 1.03, 40.82 ± 0.56, 59.98 ± 0.66 and 66.27 ± 0.59% at 1400 h in T1, T2, T3, and T4, respectively. Irrespective of treatment, the RH at 0900 h was significantly more (P < .05) than that at 1400 h. The RH at 0900 and 1400 h was significantly more (P < .05) in T4 (76.42 ± 0.58 and 66.27 ± 0.59%) followed by T3 (72.23 ± 0.58 and 59.98 ± 0.66%) and T1 (62.78 ± 0.65 and 48.87 ± 1.03%) and was the least in T2 (44.81 ± 0.58 and 40.82 ± 0.56%).

The overall THI at 0900 h in T1, T2, T3 and T4 was 74.26 ± 0.40, 72.87 ± 0.41, 75.40 ± 0.34 and 76.12 ± 0.41, whereas at 1400 h, it was 80.72 ± 0.29, 79.68 ± 0.35, 82.86 ± 0.33 and 82.68 ± 0.44, respectively. The data revealed that the THI at 0900 h was significantly lower (P < .05) from the THI at 1400 h in all the treatments groups. The data also showed that the minimum THI (P < .05) was in T2 and the maximum (P < .05) was in T4 followed by T3 and T1 both at 0900 and 1400 h.

3.2. Blood biochemical analyses

3.2.1. Haematological response

The haemoglobin values of crossbred calves under different shade materials have been presented in Table 1. The normal haemoglobin values in calves vary from 5.6 to 12.5 g/dl (Gross 2009). T2 showed significantly higher (P < .05) haemoglobin than T3 during the fourth 14-day interval of the experiment.

Table 1. Mean ± SE of haemoglobin (g/dl) of calves under different shade materials.

14-day period interval	Thatch (T1)	Agro-net (T2)	Asbestos (T3)	Tree (T4)
Initial	8.16 ± 0.85	8.22 ± 0.56	7.68 ± 0.31	9.20 ± 1.10
I	8.80 ± 0.84	9.09 ± 0.85	8.63 ± 0.51	9.07 ± 0.30
II	9.96 ± 0.76	9.97 ± 0.46	8.77 ± 0.46	9.98 ± 0.59
III	10.51 ± 0.77	10.33 ± 0.78	9.79 ± 0.49	10.40 ± 0.56
IV	11.50 ± 0.61^ab	11.98 ± 0.62^b	10.03 ± 0.50^a	11.23 ± 0.61^ab
V	12.17 ± 0.75	12.22 ± 1.16	10.48 ± 0.34	11.96 ± 0.56
VI	12.44 ± 0.73	12.46 ± 1.13	10.93 ± 0.41	12.22 ± 0.37
Overall	10.51 ± 0.43	10.61 ± 0.46	9.47 ± 0.25	10.58 ± 0.36

Note: Means bearing different superscripts in a row differ significantly (P < .05).

3.2.2. Biochemical response

The effect of shade materials on various biochemical parameters is presented in Tables 2 and 3.

Table 2. Mean ± SE of serum biochemical estimation of calves under different shade materials.

14-day interval	Thatch (T1)	Agro-net (T2)	Asbestos (T3)	Tree (T4)
Serum glucose (mg/dl)
Initial	39.06 ± 1.63	40.11 ± 1.70	39.85 ± 1.74	39.88 ± 0.63
I	42.49 ± 5.82	45.81 ± 3.89	40.48 ± 4.57	42.81 ± 0.86
II	44.26 ± 7.52	53.34 ± 5.21	41.69 ± 4.81	46.20 ± 4.38
III	39.02 ± 4.10^a	52.86 ± 5.11^b	37.82 ± 5.30^a	32.87 ± 2.87^a
IV	35.27 ± 4.32	41.12 ± 3.81	35.31 ± 6.11	31.26 ± 2.62
V	42.16 ± 5.59	47.69 ± 4.86	41.27 ± 4.01	37.66 ± 2.29
VI	39.88 ± 3.46	44.13 ± 3.99	39.87 ± 4.28	32.43 ± 4.16
Overall	40.31 ± 1.53^a	46.44 ± 1.21^b	39.47 ± 1.62^a	37.59 ± 1.31^a
Total serum protein (g/dl)
Initial	7.77 ± 0.44	7.81 ± 0.45	7.73 ± 0.46	7.75 ± 0.55
I	7.42 ± 0.39	7.77 ± 0.36	7.18 ± 0.40	7.10 ± 0.27
II	7.30 ± 0.36	7.18 ± 0.14	7.07 ± 0.15	6.98 ± 0.23
III	7.12 ± 0.38	7.04 ± 0.20	6.89 ± 0.20	6.93 ± 0.30
IV	6.78 ± 0.32	6.96 ± 0.32	6.24 ± 0.24	6.55 ± 0.37
V	6.61 ± 0.37	6.52 ± 0.36	6.10 ± 0.29	6.54 ± 0.17
VI	6.70 ± 0.22	7.05 ± 0.12	6.73 ± 0.45	6.75 ± 0.08
Overall	7.10 ± 0.15	7.19 ± 0.12	6.85 ± 0.14	6.94 ± 0.12
Serum albumin (g/dl)
Initial	3.69 ± 0.08	3.66 ± 0.08	3.71 ± 0.23	3.68 ± 0.23
I	3.78 ± 0.23	3.79 ± 0.26	3.64 ± 0.11	3.59 ± 0.08
II	3.79 ± 0.24	3.99 ± 0.22	3.70 ± 0.14	3.68 ± 0.11
III	4.03 ± 0.33	4.07 ± 0.16	3.88 ± 0.48	3.88 ± 0.47
IV	3.61 ± 0.23	3.81 ± 0.24	3.58 ± 0.27	3.43 ± 0.28
V	3.73 ± 0.24	3.99 ± 0.29	3.72 ± 0.17	3.69 ± 0.24
VI	3.62 ± 0.17	3.77 ± 0.47	3.49 ± 0.20	3.72 ± 0.22
Overall	3.75 ± 0.11	3.87 ± 0.15	3.67 ± 0.12	3.67 ± 0.08
Serum globulin (g/dl)
Initial	4.08 ± 0.46	4.15 ± 0.43	4.02 ± 0.42	4.07 ± 0.63
I	3.64 ± 0.41	3.98 ± 0.45	3.54 ± 0.44	3.52 ± 0.30
II	3.51 ± 0.41	3.19 ± 0.24	3.37 ± 0.24	3.30 ± 0.25
III	3.09 ± 0.35	2.96 ± 0.24	3.02 ± 0.52	3.05 ± 0.45
IV	3.17 ± 0.26	3.15 ± 0.29	2.66 ± 0.35	3.12 ± 0.30
V	2.88 ± 0.37	2.53 ± 0.28	2.38 ± 0.33	2.84 ± 0.31
VI	3.07 ± 0.31	3.28 ± 0.43	3.24 ± 0.54	3.03 ± 0.26
Overall	3.35 ± 0.11	3.32 ± 0.10	3.18 ± 0.18	3.28 ± 0.16

Note: Means bearing different superscripts in a row differ significantly (P < .05).

Table 3. Mean ± SE of Serum enzymes levels of calves under different shade materials.

14-day interval	Thatch (T1)	Agro-net (T2)	Asbestos (T3)	Tree (T4)
Alkaline phosphatase (IU/L)
Initial	104.84 ± 7.25	116.31 ± 7.55	124.66 ± 8.10	120.49 ± 12.02
I	126.18 ± 8.87	110.62 ± 7.23	125.67 ± 15.84	119.18 ± 6.19
II	103.18 ± 6.43	89.88 ± 6.54	98.80 ± 3.93	95.54 ± 6.71
III	112.78 ± 24.04	98.44 ± 28.4	126.74 ± 33.54	155.42 ± 14.82
IV	110.46 ± 21.41	85.65 ± 16.2	117.82 ± 18.92	144.56 ± 21.08
V	152.70 ± 16.40^ab	132.16 ± 14.9^a	196.11 ± 19.9^b	193.79 ± 11.0^b
VI	148.04 ± 9.19	129.05 ± 10.6	171.68 ± 24.90	188.73 ± 26.25
Overall	122.60 ± 5.45^ab	108.87 ± 5.21^a	137.35 ± 11.8^b	145.39 ± 4.99^b
SGOT (IU/L)
Initial	87.14 ± 13.29	82.09 ± 8.12	85.87 ± 11.69	101.03 ± 12.92
I	109.87 ± 12.92^ab	80.82 ± 4.49^a	137.65 ± 12.0^b	118.71 ± 9.62^b
II	83.35 ± 20.40	79.56 ± 8.63	116.18 ± 14.75	117.45 ± 14.27
III	137.65 ± 11.22	84.61 ± 8.81	136.39 ± 37.00	126.29 ± 8.12
IV	70.72 ± 8.41	82.09 ± 6.60	118.71 ± 28.28	116.18 ± 18.45
V	84.61 ± 29.50^a	89.66 ± 13.00^a	190.69 ± 6.64^b	184.38 ± 30.4^b
VI	97.24 ± 14.31	98.50 ± 12.71	103.55 ± 11.85	133.86 ± 18.24
Overall	95.80 ± 4.26^a	85.33 ± 2.79^a	127.01 ± 5.10^b	128.27 ± 4.82^b
SGPT (IU/L)
Initial	33.34 ± 5.34	30.81 ± 5.76	30.56 ± 6.24	31.82 ± 4.93
I	37.13 ± 4.93	35.87 ± 8.65	38.90 ± 8.43	37.89 ± 8.60
II	33.84 ± 7.00	34.10 ± 5.60	40.92 ± 6.13	39.15 ± 6.56
III	39.91 ± 5.67	35.36 ± 3.78	45.72 ± 2.87	48.49 ± 4.98
IV	34.35 ± 2.98	30.06 ± 3.32	40.41 ± 7.31	39.65 ± 6.71
V	41.93 ± 2.40	32.58 ± 4.03	43.69 ± 5.37	45.46 ± 7.09
VI	32.33 ± 1.38	33.59 ± 2.25	37.63 ± 3.97	42.68 ± 7.51
Overall	36.12 ± 1.84	33.20 ± 2.56	39.69 ± 4.16	40.74 ± 1.84

Note: Means bearing different superscripts in a row differ significantly (P < .05).

The blood glucose values were found to be the highest (P < .05) in T2 than in other grouped calves. The ALP was significantly higher (P < .05) in T4 followed by T3 than T2. Furthermore, the overall ALP value ranged from 95 to 196 IU/L which is under the normal range (64–222 IU/L) given by Gross (2009). The normal values for SGOT vary from 26 to 58 IU/L (Gross 2009) which is lower than the observed value (80–190 IU/L) in all the shade materials. However, there was a significantly higher (P < .05) SGOT level in T4 followed by T3 in comparison to T2 followed by T1. The serum SGPT level fell under the normal range of 18–70 IU/L (Gross 2009)

3.2.3. Hormonal response

The impact of different shade materials on cortisol and Thyroxin (T3 and T4) was studied for a 14-day period and the results are presented in Table 4. The serum cortisol level clearly indicated that the cortisol level for all the groups was more during the initial period and during the last 14-day interval. The overall cortisol value ranged from 7 to 10 nmol/L, which is more than the range given by Gross (2009) (4–6.5 nmol/L).

Table 4. Mean ± SE of hormonal parameters of calves under different shade materials.

14-day interval	Thatch (T1)	Agro-net (T2)	Asbestos (T3)	Tree (T4)
Cortisol (nM/L)
Initial	12.61 ± 0.67	12.65 ± 0.77	12.03 ± 1.21	12.37 ± 0.92
I	10.74 ± 1.48^b	4.56 ± 1.14^a	8.34 ± 2.90^ab	5.75 ± 1.63^ab
II	4.14 ± 1.42	3.25 ± 1.35	4.45 ± 1.72	6.11 ± 2.37
III	3.88 ± 1.47	2.65 ± 1.09	4.60 ± 1.81	7.37 ± 2.30
IV	2.98 ± 1.90	3.64 ± 1.73	7.28 ± 3.04	4.53 ± 1.36
V	18.75 ± 6.73	14.97 ± 4.12	17.91 ± 3.84	20.67 ± 5.57
VI	15.66 ± 3.71	10.01 ± 2.25	18.21 ± 3.44	11.12 ± 2.50
Overall	9.82 ± 1.55	7.39 ± 0.75	10.40 ± 1.04	9.70 ± 1.11
T3 (nM/L)
Initial	3.10 ± 0.25	3.05 ± 0.14	3.14 ± 0.14	3.06 ± 0.36
I	2.73 ± 0.31	2.96 ± 0.14	2.92 ± 0.88	2.86 ± 0.31
II	2.54 ± 0.27	2.63 ± 0.24	2.60 ± 0.30	2.32 ± 0.33
III	2.38 ± 0.28	2.56 ± 0.33	2.36 ± 0.13	2.22 ± 0.19
IV	2.63 ± 0.29	2.99 ± 0.53	2.57 ± 0.19	2.34 ± 0.14
V	2.34 ± 0.20	2.57 ± 0.47	2.18 ± 0.34	2.17 ± 0.17
VI	2.53 ± 0.21	2.81 ± 0.40	2.31 ± 0.10	2.22 ± 0.06
Overall	2.61 ± 0.10	2.79 ± 0.18	2.58 ± 0.25	2.46 ± 0.10
T4 (nM/L)
Initial	57.99 ± 4.50	50.13 ± 2.56	53.85 ± 4.00	56.40 ± 9.93
I	56.33 ± 6.99	62.56 ± 4.65	53.86 ± 8.40	53.97 ± 7.76
II	55.97 ± 5.16	61.54 ± 8.69	53.85 ± 4.47	53.76 ± 8.14
III	54.87 ± 5.77	60.47 ± 8.57	53.54 ± 3.41	52.03 ± 13.72
IV	57.37 ± 9.65	62.68 ± 6.36	55.57 ± 3.27	55.87 ± 9.65
V	61.91 ± 7.15	70.96 ± 16.15	60.88 ± 8.81	60.83 ± 8.69
VI	60.16 ± 5.65	68.11 ± 7.69	58.72 ± 7.27	57.87 ± 7.97
Overall	57.80 ± 2.45	62.35 ± 2.89	55.75 ± 2.71	55.82 ± 4.14

Note: Means bearing different superscripts in a row differ significantly (P < .05).

3.3. Behaviour response

The daily activities of crossbred calves over a period of 7 h (1000–1700 h) for each month of summer, representing time spent in the shade, open and total time spent in particular behavioural activities including the overall effect of the shade material during summer have been presented in Table 5.

Table 5. Mean ± SE of overall behavioural activities (minutes) of calves.

Behaviours		Thatch (T1)	Agro-net (T2)	Asbestos (T3)	Tree (T4)
Rumination	Shade	67.03 ± 1.61^b	77.88 ± 0.77^c	22.12 ± 0.68^a	63.92 ± 0.79^b
	Open	12.14 ± 0.53^a	10.40 ± 0.50^a	52.23 ± 1.42^b	10.41 ± 0.58^a
	Total	79.16 ± 1.79^B	88.28 ± 0.93^C	74.35 ± 1.55^A	74.32 ± 0.65^A
Resting	Shade	67.54 ± 1.47^c	75.77 ± 2.07^c	24.15 ± 0.60^a	62.18 ± 0.71^b
	Open	15.05 ± 0.56^ab	12.29 ± 0.44^a	56.63 ± 1.62^c	17.88 ± 0.54^b
	Total	82.59 ± 1.37^A	88.06 ± 1.98^B	80.78 ± 1.91^A	80.06 ± 0.89^A
Standing	Shade	21.30 ± 0.85^b	15.45 ± 0.47^a	25.45 ± 0.54^c	20.77 ± 0.94^b
	Open	18.78 ± 0.59^c	6.63 ± 0.5^a	18.51 ± 0.87^c	13.41 ± 0.38^b
	Total	40.08 ± 1.04^c	22.08 ± 0.56^a	43.96 ± 0.81^c	34.18 ± 0.97^b
Moving	Shade	18.32 ± 0.88	15.31 ± 0.46	17.21 ± 1.06	15.94 ± 0.47
	Open	14.69 ± 0.61^b	10.96 ± 0.48^a	9.97 ± 0.84^a	21.72 ± 0.85^c
	Total	33.01 ± 1.16^b	26.27 ± 0.80^a	27.18 ± 1.42^a	37.66 ± 0.92^c
Sleeping	Shade	30.95 ± 0.84^c	37.35 ± 1.29^d	16.01 ± 0.47^a	26.80 ± 0.49^b
	Open	6.35 ± 0.59^b	4.10 ± 0.27^a	16.56 ± 0.80^c	8.44 ± 0.55^b
	Total	37.30 ± 0.89^B	41.45 ± 1.36^C	32.57 ± 0.77^A	35.23 ± 0.85^AB
Play	Shade	13.94 ± 0.68^a	25.35 ± 1.42^b	11.60 ± 0.46^a	12.67 ± 0.42^a
	Open	14.11 ± 0.80^c	8.31 ± 0.31^a	11.10 ± 0.57^b	12.60 ± 0.45^bc
	Total	28.05 ± 1.02^b	33.66 ± 1.48^c	22.70 ± 0.85^a	25.28 ± 0.53^ab
Grooming	Shade	4.59 ± 0.27^c	3.66 ± 0.17^b	4.81 ± 0.16^c	2.56 ± 0.20^a
	Open	2.55 ± 0.17^a	1.88 ± 0.12^a	4.13 ± 0.27^b	2.23 ± 0.09^a
	Total	7.14 ± 0.34^b	5.54 ± 0.22^a	8.94 ± 0.37^c	4.80 ± 0.26^a
Licking	Shade	2.48 ± 0.18^b	1.48 ± 0.11^a	2.16 ± 0.19^b	2.06 ± 0.14^b
	Open	2.28 ± 0.17^b	1.77 ± 0.09^a	4.69 ± 0.16^c	2.38 ± 0.11^b
	Total	4.76 ± 0.24^b	3.24 ± 0.16^a	6.85 ± 0.31^c	4.43 ± 0.21^b
Cross-sucking	Shade	1.58 ± 0.15^a	1.46 ± 0.07^a	2.43 ± 0.09^b	2.24 ± 0.09^b
	Open	2.18 ± 0.15^a	1.82 ± 0.07^a	2.73 ± 0.14^b	2.26 ± 0.10^a
	Total	3.76 ± 0.21^a	3.28 ± 0.10^a	5.17 ± 0.16^c	4.49 ± 0.16^b
Total time spent	Shade	227.72 ± 1.85^c	253.71 ± 1.59^d	125.95 ± 2.02^a	209.13 ± 1.96^b
	Open	88.13 ± 1.96^b	58.15 ± 1.18^a	176.56 ± 2.64^c	91.32 ± 1.53^b
Feeding	Shade	77.12 ± 1.81^ab	85.48 ± 0.75^c	75.93 ± 1.34^a	81.33 ± 0.64^bc
Drinking	Shade	10.29 ± 0.64^a	9.71 ± 0.31^a	13.67 ± 0.44^b	11.21 ± 0.50^a
Near water tank	Shade	14.42 ± 0.85^b	10.41 ± 0.52^a	25.90 ± 0.53^c	24.02 ± 0.71^c

Notes: Means bearing different superscripts (a, b, c, d) in a row differ significantly (P < .01). Means bearing different superscripts (A, B, C, D) in a row differ significantly (P < .05).

The T2 grouped calves spent maximum time (P < .05) in feeding, rumination, resting, sleeping and playing, whereas the time spent near the water tank, drinking, standing and moving was significantly (P < .05) lower in T2 in comparison with other grouped calves. The time spent in grooming, licking and cross-sucking was significantly higher (P < .01) in T3 and less in T2. The time spent in minor activities like defecation was 1.20 ± 0.07, 1.40 ± 0.15, 1.00 ± 0.06 and 1.44 ± 0.08 minutes, whereas for urination, the time spent was1.13 ± 0.07, 1.11 ± 0.08, 0.99 ± 0.06 and 1.56 ± 0.07 minutes for T1, T2, T3 and T4, respectively. Furthermore, the calves spent more time involving in each activity in the provided shade area in comparison with the open area in all the groups (T1, T2 and T4) except in T3.

4. Discussion

The highest maximum temperatures were observed in T3 followed by T4. The shade material used in T3 might have been unable to mitigate the radiative heat load; the material absorbed the heat and transferred it to the microenvironment in the shed, which is in agreement with Macfarlane (1981). However, the shade tree (T4) might have provided decreased protection from direct solar radiation compared to other shade structures. The agro-net shading was able to maintain the mean maximum temperature under the shade structure, indicating the superior protective capacity of the shade material used in T2 in comparison with other shade materials. The present findings are in agreement with those of Jat and Yadav (2010) who reported that the maximum temperature and the minimum temperature in thatch and mud plaster roof were lower (P < .05) than in loose housing covered with an asbestos sheet. Similarly, Sivakumar (2002) observed that a house roofed with asbestos had higher maximum temperature and lower minimum temperature than the tile-roofed house. Roy and Chatterjee (2010) found lower maximum temperature in a shed having a tile roof as compared to a Galvanized Iron sheet, polythene sheet.

The lower haemoglobin values in T3 than in T2 may be due to haemodilution, by which more water is transported in the circulatory system for evaporative cooling (Banerjee & Ashutosh 2011). High haemoglobin values are associated with high adaptability to extreme conditions of temperature and it has been suggested that this characteristic might be an index of superior heat tolerance (Johnson 1987).

The higher blood glucose level in the T2 grouped calves might be due to an increased glucose oxidation (Collier et al. 2008), as calves in the T2 group spent more time feeding. Decreased gluconeogenesis and glycogenolysis were observed in cows during heat stress (Itoh et al. 1998). The present finding is in agreement with the report made by Vijayakumar et al. (2011) who found a significantly higher blood glucose level in buffalo heifers treated with sprinklers and fans for reduction of summer stress. The increase in ALP activity due to heat stress under T3 and T4 may be due to alkalosis caused by an increased alveolar ventilation and the resultant alkalosis (Cunningham 2002). With the regulation of cell division and growth, ALP is also involved in maintaining homeostasis and energy generation in the animal body (Vashishth et al. 1998), which seems to be the reason for higher activity in the present study. The present finding is in agreement with Bahga (2007). However, Sejian et al. (2010) found a decrease in the ALP activity after heat stress, whereas Bahga et al. (2009) reported no significant increase in ALP in response to heat stress. The serum SGOT and SGPT activity was higher in T4 and T3 grouped calves because of higher temperature inside the shade material, which increases the serum SGOT and SGPT activity in order to compensate for the other negative effects of thermal stress on the physiological and biochemical homeostatic mechanisms. The present findings were also supported by Srikandakumar et al. (2003); and Brijesh (2012), as they reported an increase in the serum SGOT and SGPT activity during thermal stress under different situations.

The cortisol level was lower during the second time period in the T2 grouped calves which corresponds to a higher macro-temperature during that time period, indicating a comfortable, stress-free environment provided by the agro-net. The present findings are in agreement with Singh et al. (2008) who reported a non-significant difference in the cortisol level within the treatment group (thatch, agro-net and tree) and also observed a significantly higher cortisol level in kids kept under open sky during summer. A non-significant decreasing trend was found in the T₃ and T₄ concentration with an increasing thermal exposure. This can be explained by the findings of Silanikove (2000) who has reported that thyroid hormones take a long time to achieve new steady levels in response to heat stress.

The reason for spending more time on feeding by the calves may be attributed to the fact that the shade material used in T2 provided a comfortable microclimatic condition. However, calves in T3 might be trying to cope with heat load (Kendall et al. 2006), and this change is believed to contribute to a significant difference in the serum biochemical level. Mader et al. (1997) demonstrated that animals with access to 3.5 m² shade/animal had higher feed intake than animals with less shade. At high thermal exposure, thermoregulation was mainly by evaporative heat loss (respiration, sweating or panting) because of which there was loss of body water, resulting in increased osmolarity of the extracellular fluid in the body, leading to activation of the thirst centre in the hypothalamus and thus the drinking time was increased in the T3 grouped calves. Banerjee and Ashutosh (2011) reported similar results in cattle during thermal stress. Widowski (2001) reported that cattle increase their water consumption in summer, particularly when there is no access to shade. The reason for more time spent near a water tank might be attributed to hot environmental conditions under T3 and T4, which make the calves spend more time near the water tank. Calves of T3 and T4 groups might have adopted other behavioural strategies to alleviate heat load, such as increasing time around the water trough. Mader et al. (1997) found that the percentage of beef cattle around the water trough was two to three times greater for unshaded groups compared to groups that had >3.5 m² shade/animal, especially when the heat load was at its peak. They could not fully understand why cows spent more time around the water trough. There are several possible explanations for how cattle may reduce the effects of high heat load by increasing water consumption. A similar finding was reported by Widowski (2001). Higher rumination by T2 and T1 grouped calves may be due to more resting subsequently leading to more rumination, and also indicated comfort in a given situation. Similar findings were reported by Vijayakumar et al. (2011) who concluded that the average time spent on rumination was significantly influenced by summer management practices. Calves in T1, T3 and T4 spent comparatively less time in resting which might be an indication of lack of comfort which reduced the time spent resting and a subsequent increase in the time spent standing. This is also in agreement with Vijayakumar et al. (2011) who concluded that the provision of sprinklers and fans for reduction of summer stress helps the comfort of the buffalo heifer, which was indicated by more time lying down. The findings are also supported by Schutz et al. (2010) who concluded that cows spend nearly half of their lives lying down; a reduction in the time cows spend resting can lead to physiological changes associated with stress and can ultimately have a negative impact on health. By standing, cows maximize evaporation from the body surface and also benefit from convection due to wind, or cows stand to escape conductive and radiative heat from the hot ground surface, which seems to be the reason for higher standing time in the present study. The present finding is in agreement with Widowski (2001) who reported that a change in behaviour associated with heat load is an increase in the time spent standing. Tucker et al. (2008) found that time spent standing increased by 10% (13.8–15.3 h/day) when the heat load increased by 15% (THI = 60–70). Thus, they suggested that cows spend more time standing to increase the heat loss by increasing the amount of skin exposed to airflow or wind. The reason for spending more time on sleeping by the calves in group T2 may be attributed to the comfortable microclimatic condition provided by the agro-net. More play in T2 might be due to the comfortable and healthy environment provided by the agro-net which makes the calf exhibit more play behaviour. Babu (2000) also observed that play behaviour was only found in more comfortable and healthy calves.

Shade by different roofing materials provided a comfortable environment and thus calves spent more time under the shade. However, although calves in the T4 group spent more time in the shaded area, spending more time moving and standing in the shaded area indicated that the calves were not comfortable under T4. The higher time in the shaded area might be due to our assumption. While recording, the shadow of the tiny branch of the tree falling on calves was considered as a shade area. Since the shade was changing depending on the sun's movement, it causes more shade area, which led to higher  value for time spent under T4.

Among the various behavioural activities under the shade in all the four groups during the experimental period, maximum time was spent in resting and rumination followed by standing, sleeping, walking and playing, whereas least time was spent in grooming, licking and cross-sucking. This is also in agreement with Vijayakumar et al. (2011) who concluded that even in the summer in peak stress the major activities were feeding, rumination, resting and sleeping. The result also suggests that the major behavioural activities like resting, rumination and sleeping time were more (P < .01) in the shaded area as compared with the open area in T1, T2 and T4 grouped calves except in the T3 grouped calves, which spent more time in the open area than in the shaded area. However, using the shaded area for resting and rumination was significantly more (P < .01) in the T2 group followed by the T1 grouped calves and was least in the T3 grouped calves. The probable reason may be more comfort for the T2 grouped calves as compared with other grouped calves.

Calves kept in the T2 group had spent more time in the shaded area as compared with other calves. These differences could be due to the more diffused sunlight which created less darkness underneath the covered area with high aeration. This helped not only in reducing the population of flies which was monitored during the experiment, but also provided low temperature underneath the covered area. This helped the calves to spend more time in the shaded area which is also supported by previous reports (Weiguo and Phillips 1991), which indicated that cattle preferred to spend more time in the light. Stookey and Watts (2007) reported that 86% of cattle have a very strong preference for a lighted facility over a dark one. Time spent in other activities like grooming, licking and cross-sucking behaviour was very less and nearly equal in the open or shaded areas. However, among these, time spent for grooming was more in the shaded area.

The present findings are in agreement with Khongdee (2008) who observed significantly lower heat stress conditions in the animal house shaded with polypropylene cloth, which was the result of the incoming solar radiation being reduced by the black woven sheet which allows energy to be absorbed and re-radiated. The finding is also in agreement with the short-term preference shown by beef cattle for shade that blocked more solar radiation (Bennett et al. 1984/1985). In addition, the total amount of time spent in the shade was similar to other studies with pastured cattle (Widowski 2001). Similarly, Tucker et al. (2008) observed that cows spent more (P < .01) time using shade that blocked a greater percentage (50% and 99%) of solar radiation during daytime as compared to 25% protection from solar radiation.

5. Conclusion

During summer season, provision of the agro-net followed by thatch as shade material in the open paddock provided a favourable microenvironment to the crossbred calves which resulted in maintaining the physiological, biochemical and behavioural responses in the normal range. Asbestos sheet could not provide proper microclimate to calves, which was witnessed by high physiological values and less time spent under the covered area. Calves kept under a tree also had high physiological values which indicated that the tree was also insufficient to provide a better microenvironment to calves during summer. It can be concluded that new shade material like the agro-net could be suggested as the shade material for summer for cattle; however, the durability of the material has to be investigated.

Acknowledgement

The authors are thankful to the Director, Indian veterinary Research institute, Izatnagar, for providing all the necessary infrastructure facilities while carrying out the experiment.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

^† This article is part of the Ph.D. research work submitted by the first author to the Indian Veterinary Research Institute, Bareilly, India.