Last update: September 8, 2011 08:21:38 AM E-mail Print

 

CAN PROTECTIVE COATS ALLEVIATE THE EFFECT OF COLD, WET AND WINDY CONDITIONS ON ANGORA GOATS?

 

M.A. Snyman# & M. van Heerden

Grootfontein Agricultural Development Institute, Private Bag X529, Middelburg (EC), 5900

#E-mail: Gretha Snyman

 

INTRODUCTION 

Goats are homeothermic animals and are able to maintain a balance between heat metabolism and environmental temperature to avoid either hyper- or hypothermia within the thermoneutral zone (Lu, 1989). Additional energy is required to maintain core body temperature under extreme environmental temperatures. This additional energy expenditure causes physiological and behavioural adaptations under thermal stress, and can lead to impaired production or even death.

 

High mortality rates of Angora goats during periodic cold climatic spells cause considerable annual monetary loss in the mohair industry. According to Mohair South Africa (Personal communication, 2010), an estimated 60 000 to 70 000 goats died from exposure to cold conditions over a ten year period from 1997 to 2007. This implies a financial loss at producer level in terms of mohair production of R14 million, and a direct loss in terms of animals of R21 million. Angora goats are most susceptible to cold spells during the first few weeks after shearing.

 

Various measures are taken to prevent losses during cold spells, of which kraaling of goats in sheds is the most common practice. However, the extensive nature of Angora goat farming and the new labour legislation has decreased the viability of this practice. Other practices to prevent losses, such as supplementation of alkali-ionophore treated grain (Wentzel et al., 1979) to Angora goats during cold spells to increase blood glucose concentration, as well as dipping of Angora goats after shearing in an oil-based emulsion (Snyman et al., 1998), have been done in the past, with varying success rates.

 

Some Angora goat producers have also made use of coats for protection against the elements. No scientific evaluation of the effect of coats as protective measure against cold weather has been done in South African Angora goats. Positive results were, however, obtained for sheep in Australia (Ellis et al., 1985). Angora goat producers, who used the coats, are of the opinion that it is effective against cold weather, but various problems were encountered. Due to the varying sizes of the animals within a specific age group, the coats do not fit all animals equally well, leading to coats being torn easily and getting lost. Furthermore, the coats have to be waterproof, but allow sweat to evaporate.

 

A request was made by the mohair industry to Grootfontein Agricultural Development Institute to investigate the suitability of coats as protection against adverse weather conditions. The aim of this project was therefore to determine if protective coats will enable Angora goats exposed to cold, wet and windy conditions to maintain their normal physiological parameters better than animals without any protective covering.

 

MATERIAL AND METHODS

The study was conducted at the Grootfontein Agricultural Development Institute under kraal and veld conditions during 2009 and 2010. Twenty-four ten-month-old castrated male Angora goat kids from the Grootfontein Angora herd were used for the 2009 study, while 30 nine-month-old castrated male Angora goat kids were used for the 2010 trial. The GADI ethical committee approved the project procedures (Approval number GVE/AP5/28).

 

2009 Cold stress trial

All animals were shorn during the first week of August 2009. The animals were weighed and then divided into two groups on a stratified body weight basis. The first group of 12 animals received no protective body covering (Control group), while the second group received protective coats (Coats group) on the day after shearing. The coats used in this trial were the Bisa sheep coats. These were made of a new material, consisting of Nylon 6, which has been developed to overcome some of the problems encountered with previous designs. This material will prevent contamination of the fleece. It is also Teflon-treated to make it water-resistant, as well as electrostatically treated against bacterial and fungal infestation.

 

The cold stress experiment was carried out one week after shearing on a cold day. The temperature was 0 °C at the start of the trial at 07:00 when the pre-rain treatment (0 minutes) readings were taken, and increased to 13 °C at 12:30 when the trial ended. A slight wind (20 – 25 km/h) blew during the trial period. The animals were put into three small pens in a shaded area, exposed to the wind. Animals were divided among the pens in such a way that body weight and number of animals per treatment group were the same for each pen. After the first round of data recording, the animals were subjected to an equivalent of 5 mm of rain every 60 minutes for a five-hour period. Thus the animals received 25 mm rain over the trial period. Lucerne hay and water were freely available during the trial period.

 

The parameters indicated in Table 1 were recorded during the five-hour trial period at 0 minutes (before applying rain treatment) and again at 60, 120, 180, 240 and 300 minutes after applying the first rain treatment. The animals were weighed and their rectal temperatures recorded again 150 minutes after the last rain treatment, to assess their recovery status.

 

 

Table 1. Parameters recorded during the 2009 cold stress trial

Trait

Minutes after first rain treatment 

0 min 

60 min 

120 min 

180 min 

240 min 

300 min 

450 min

Body weight

x

 

 

 

 

 

x

Blood samples

x

 

 

x

 

x

 

Skin temperatures

x

x

x

x

x

x

 

Assess shivering

x

x

x

x

x

x

 

Rectal temperature

x

x

x

x

x

x

x

Respiratory rate

x

x

x

x

x

x

 

Heart rate

x

x

x

x

x

x

 

 

Rectal temperature was recorded with a digital thermometer. Animals for which rectal temperature dropped below 32 °C were removed from the pen and placed in a heated room for recovery. Only one animal collapsed at the end of the trial period. Skin temperatures were recorded on the ear, shoulder, britch, front leg and hind leg with an infrared thermometer (Figure 1). The degree of shivering was assessed visually on a scale from 1 to 5, where a score of 1 was allocated if no shivering occurred, and a score of 5 was given for excessive shivering. Veterinarians recorded heart and respiratory rates according to standard clinical methods. Blood samples were collected for determination of serum glucose levels.

 

Figure 1. Positions on the animal where skin temperatures were recorded

 

2010 Subcutaneous temperature recording and cold stress trial

The animals were weighed and then divided into two groups on a stratified body weight basis. On 11 June 2010, temperature data loggers were implanted under the skin on the back between the shoulder blades of all animals. Each data logger was encapsulated in a silicone capsule that would prevent any reaction from the body. All animals were shorn directly after implantation of the loggers. The data loggers were programmed to start half-hourly temperature recordings on 14 June 2010 at 18:00. The treatments were applied the morning of 14 June 2010. The first group of 15 animals received no protective body covering (Control group), while the second group received the same protective coats (Coats group) that were used in 2009.

 

The animals were kept in open pens at the Grootfontein embryo centre. Environmental temperature over the trial period was also recorded with one of the data loggers. The animals received lucerne hay throughout the trial period, which lasted from 14 June 2010 to 12 August 2010.

 

On 13 July 2010, four weeks after treatment, half of the animals in each treatment group were shorn again. On 10 August 2010, a cold stress trial, similar to the one conducted in 2009, was done. The temperature was 2.6 °C at the start of the trial at 08:00 when the pre-rain treatment (0 minutes) readings were taken, and increased to 12.6 °C at 14:00 when the trial ended. A moderate wind (25 –30 km/h) blew during the trial period. The same procedures as during the 2009 cold stress trial were followed. Rectal temperatures were recorded during the five-hour trial period at 0 minutes (before applying rain treatment) and again at 60, 120, 180, 240 and 300 minutes after applying the first rain treatment. The animals were weighed and their rectal temperatures recorded again 60 minutes after the last rain treatment, to assess their recovery status.

 

Statistical analyses

The SAS statistical package (PROC GLM) was used to determine differences in physiological parameters of goats that received protective coats and those without any protection (SAS, 2006). Fixed effects for treatment group and pen were included for the 2009 data, while treatment group, shearing group and pen were included for the 2010 data. Body weight was included as a covariate in both years.

 

RESULTS

2009 Cold stress trial

Initial body weight and body weights before and after the cold stress trial period are given in Table 2. There was no significant difference in body weight between the groups at any stage. Results for the different parameters recorded during the 2009 cold stress trial period are presented in Tables 3 to 9. Individual rectal temperatures for the two groups are also illustrated in Figures 2 and 3.

 

Table 2. Initial body weight and body weights (kg ± s.e.) before and after the 2009 cold stress trial period

 

Coats

Control

Initial body weight (kg)

19.57 ± 0.80

19.47 ± 0.80

Body weight at start of the cold stress trial (kg)

20.71 ± 0.97

20.58 ± 0.97

Body weight at end of the cold stress trial (kg)

18.54 ± 0.91

18.41 ± 0.91

 

Table 3. Rectal temperature (°C ± s.e.) of the treatment groups over the 2009 trial period

Minutes after rain treatment started

Coats

Control

0

39.53 ± 0.12

39.83 ± 0.12

60

39.22 ± 0.18

39.47 ± 0.18

120

38.46 ± 0.16

38.41 ± 0.16

180

38.18 ± 0.19

37.67 ± 0.19

240

37.38a ± 0.32

36.32a ± 0.32

300

36.49a ± 0.45

34.58a ± 0.45

450 (Recovery)

38.88 ± 0.35

38.27 ± 0.35

Difference between start and end values

-3.04a ± 0.48

-5.25a ± 0.48

a Values with the same superscripts differed significantly (P<0.05)

 

Initial rectal temperatures did not differ among treatment groups. This situation prevailed until 240 minutes after the trial started, when rectal temperatures of the Control group animals dropped significantly lower than that of the Coats group animals. At 300 minutes after treatment started, rectal temperature of the Coats group was 1.91 °C higher than the Control group (P<0.05). Coats group animals showed, on average, a 2.21 °C less drop in rectal temperature over the trial period than the Control group (P<0.05).

 

When evaluating the individual temperature curves of the animals in the different treatment groups, it is obvious that most of the animals whose rectal temperature dropped below 34 °C were from the Control group (six animals – Figure 3). Only one animal from the Coats group’s rectal temperature dropped below 34 °C (Figure 2). Only one animal, from the Control group, collapsed after its rectal temperature dropped below 32 °C. It was revived in a heated room after receiving an intra-peritoneal injection of an isotonic glucose solution.

 


Figure 2. Individual rectal temperatures of the Coats group animals over the 2009 trial period

 

Figure 3. Individual rectal temperatures of the Control group animals over the 2009 trial period

 

Animals in both groups showed an increased heart rate over the first two hours of the trial (Table 4), after which it decreased to below the initial values at the end of the trial period. No significant differences in heart rate were recorded between the treatment groups at any stage. Animals in both groups showed an increase in respiratory rate during the first hour after treatment (Table 4). For the remainder of the trial period, the two groups showed different responses in respiratory rate. The Control group animals had a progressively slower respiratory rate, while the Coats group animals had an increasing respiratory rate up to 240 minutes, after which their respiratory rate also decreased. However, no significant differences in respiratory rate were recorded among the treatment groups at any stage.

 

Table 4. Heart rate (beats/min ± s.e.) and respiratory rate (breaths/min ± s.e.) of the treatment groups over the 2009 trial period

Minutes after rain treatment started

Heart rate

Respiratory rate

Coats

Control

Coats

Control

0

142.25 ± 5.70

147.67 ± 5.70

27.75 ± 1.89

29.50 ± 1.89

60

149.00 ± 6.87

159.67 ± 6.87

29.42 ± 1.78

31.75 ± 1.78

120

158.00 ± 7.23

177.83 ± 7.23

30.33 ± 2.07

31.35 ± 2.07

180

153.00 ± 6.42

154.67 ± 6.42

30.33 ± 1.79

30.75 ± 1.79

240

142.33 ± 7.87

132.17 ± 7.87

31.00 ± 2.00

29.92 ± 2.00

300

124.33 ± 7.61

119.17 ± 7.61

27.58 ± 1.62

27.17 ± 1.62

Difference between start and end values

-17.92 ± 7.45

-28.5 ± 7.45

-0.16 ± 2.04

-2.33 ± 2.04

 

Table 5. Skin temperature on the ear (°C ± s.e.) of the treatment groups over the 2009 trial period

Minutes after rain treatment started

Coats

Control

0

 9.85 ± 0.43

10.2 ± 0.43

60

10.71 ± 0.70

11.24 ± 0.70

120

12.11 ± 0.56

12.83 ± 0.56

180

12.71 ± 0.60

12.30 ± 0.60

240

13.75a ± 0.49

11.52a ± 0.49

300

10.78 ± 0.66

 9.41 ± 0.66

Difference between start and end values

0.94 ± 0.82

-0.84 ± 0.82

a Values with the same superscripts differed significantly (P<0.05)

 

Skin temperature on the ear of the Coats animals increased up to 240 minutes, after which it decreased, while that of the Control animals started declining after 120 minutes (Table 5). Skin temperature on the ear of the Coats animals was higher towards the end of the trial period than the animals of the Control group (P<0.05).

 

Skin temperature on the front leg of the treatment groups remained constant up to 180 minutes in the case of the Control animals and 240 minutes in the case of the Coats animals (Table 6). No significant differences were recorded at the end of the trial period. Skin temperature on the hind leg (Table 7) of the Coats and Control groups showed a steady decline over the trial period up to 240 minutes. After 240 minutes, the Coats group showed a marked dropped in skin temperature, while the Control group only slightly dropped in temperature. At the end of the trial period, skin temperature on the hind leg of the Control animals was 2.76 °C higher than those of the Coats animals (P<0.05).

 

Table 6. Skin temperature on the front and hind leg (°C ± s.e.) of the treatment groups over the 2009 trial period

Minutes after rain treatment started

Front leg

Hind leg

Coats

Control

Coats

Control

0

 10.68 ± 0.42

10.76 ± 0.42

11.35 ± 0.40

11.23 ± 0.40

60

10.98 ± 0.28

10.26 ± 0.28

10.26 ± 0.36

10.68 ± 0.36

120

10.47 ± 0.34

10.92 ± 0.34

9.67 ± 0.27

9.92 ± 0.27

180

10.58 ± 0.42

11.34 ± 0.42

 8.38 ± 0.31

 8.74 ± 0.31

240

10.56a ± 0.32

 9.53a ± 0.32

 8.46 ± 0.28

 8.88 ± 0.28

300

 7.13 ± 0.42

 7.00 ± 0.42

 5.30b ± 0.41

 8.06b ± 0.41

Difference between start and end values

 -3.55 ± 0.55

-3.76 ± 0.55

 -6.05b ± 0.58

-3.16b ± 0.58

a,b Values with the same superscripts differed significantly (P<0.05)

 

Table 7. Skin temperature on the shoulder and britch (°C ± s.e.) of the treatment groups over the 2009 trial period

Minutes after rain treatment started

Shoulder

Britch

Coats

Control

Coats

Control

0

23.07a ± 0.57

19.74a ± 0.57

22.00b ± 0.49

18.58b ± 0.49

60

22.38a ± 0.65

19.93a ± 0.65

22.34b ± 0.63

18.92b ± 0.63

120

24.45a ± 0.67

22.33a ± 0.67

22.80 ± 0.77

21.85 ± 0.77

180

26.06a ± 0.48

22.73a ± 0.48

24.93b ± 0.54

22.92b ± 0.54

240

26.35a ± 0.45

21.45a ± 0.45

25.12b ± 0.45

22.21b ± 0.45

300

23.92a ± 0.64

18.50a ± 0.64

22.86b ± 0.42

18.43b ± 0.42

Difference between start and end values

 0.85 ± 0.81

-1.24 ± 0.81

 0.86 ± 0.56

-0.15 ± 0.56

a,b Values with the same superscripts differed significantly (P<0.05)

 

The Coats group animals had significantly higher skin temperatures on their shoulders (Table 7) over the entire trial period (P<0.05). Their skin temperature increased by 0.85 °C over the trial period, while that of the Control group decreased by 1.24 °C over the trial period. After 240 minutes, both groups showed a drop in skin temperature. As was the case with the skin temperature on the shoulder, again the Coats group animals had significantly higher skin temperatures on their britches over the entire trial period (P<0.05). The Coats group again showed a net increase in skin temperature over the trial period. After 240 minutes, both treatment groups showed a drop in skin temperature.

 

Table 8. Shivering score (± s.e.) of the treatment groups over the 2009 trial period

Minutes after rain treatment started

Coats

Control

0

1.67 ± 0.16

1.75 ± 0.16

60

2.33 ± 0.16

2.75 ± 0.16

120

3.00 ± 0.12

3.25 ± 0.12

180

3.17a ± 0.12

3.58a ± 0.12

240

3.50a ± 0.11

3.92a ± 0.11

300

3.66 ± 0.11

3.92 ± 0.11

a Values with the same superscripts differed significantly (P<0.05)

 

As expected, shivering score increased with time over the trial period (Table 8). At 180 and 240 minutes, the Control animals shivered more than the Coats animals (P<0.05). At 300 minutes, however, all animals shivered to the same extent.

 

Table 9. Serum glucose levels (ng/ml ± s.e.) of the treatment groups over the 2009 trial period

Minutes after rain treatment started

Coats

Control

0

4.50 ± 0.18

4.92 ± 0.17

180

4.46 ± 0.37

4.24 ± 0.33

300

1.33 ± 0.23

1.66 ± 0.21

Difference between start and end values

3.18 ± 0.32

3.23 ± 0.29

 

No significant differences in serum glucose levels were detected in the samples analysed (Table 9). Both groups showed a drop in serum glucose levels between 180 and 300 minutes.

 

2010 Cold stress trial

Initial and final body weights of the two treatment groups are given in Table 10. There was no significant difference in body weight between the groups at the end of the trial period. Results for the rectal temperatures recorded during the 2010 cold stress trial period are presented in Table 11.

 

Table 10. Initial body weight and body weight (kg ± s.e.) at the end of the 2010 trial period

 

Coats

Control

Initial body weight (kg)

26.75 ± 1.02

26.70 ± 1.02

Body weight at end of the trial (kg)

36.73 ± 1.59

38.52 ± 1.59

 

Table 11. Rectal temperature (°C ± s.e.) of the treatment and shearing groups over the 2010 trial period

Minutes after rain treatment started

Treatment group

Shearing group

Coats

Control

Shorn 13/07/2010

Not shorn

0

39.57a ± 0.07

39.34a ± 0.07

39.47 ± 0.06

39.55 ± 0.05

60

39.44a ± 0.09

38.98a ± 0.09

39.10 ± 0.08

39.13 ± 0.07

120

39.16a ± 0.11

38.79a ± 0.11

38.80 ± 0.10

38.93 ± 0.09

180

39.17a ± 0.14

38.37a ± 0.14

38.55 ± 0.12

38.58 ± 0.11

240

39.17a ± 0.16

37.97a ± 0.16

38.06b ± 0.14

38.46b ± 0.12

300

39.17a ± 0.21

38.17a ± 0.21

37.99b ± 0.18

38.58b ± 0.16

360

39.15a ± 0.28

38.28a ± 0.28

37.75b ± 0.24

38.71b ± 0.22

Difference between start and end values

-0.43 ± 0.28

-1.05 ± 0.28

-1.71b ± 0.24

-0.84b ± 0.22

a,b Values with the same superscripts differed significantly (P<0.05)

 

At the start of the cold stress trial at 08:00 in the morning, the Control group animals already had a lower rectal temperature than the Coats animals. From 120 minutes after commencement of rain treatment, the Coats group had higher rectal temperatures that the Control group (P<0.05). Rectal temperature at the end of the trial period of Coats group animals was 0.43 °C, and that of Control group animals 1.05 °C lower than at the start of the trial period. Rectal temperature of animals with four weeks’ hair growth dropped 1.71 °C over the trial period, compared to the 0.84 °C drop of the animals with eight weeks’ hair growth (P<0.05).

 

Subcutaneous temperature recording

Subcutaneous temperature of individual goats that were recorded with temperature data loggers over the entire two-month period was analysed, but for ease of interpretation, only temperature recordings over certain periods will be presented in Figures 4 to 7. As the data loggers that recorded the body temperature were implanted just underneath the skin (subcutaneous), this temperature would be lower than core body temperature, as measured with a rectal thermometer. When ambient temperature was relatively warm, subcutaneous temperature was similar to rectal temperature. However, during colder ambient temperatures, subcutaneous temperature was lower than rectal temperature, sometimes up to a 3.5 °C difference. During the cold stress trial when the goats were subjected to cold, wet and windy conditions, subcutaneous temperature was up to 6 °C lower than rectal temperature.

 

Figure 4 illustrates the daily fluctuation in subcutaneous temperature of the groups from 16 June 2010 to 19 June 2010. This was a relatively cold five-day period, and the animals had been shorn four days previously. Minimum ambient temperature ranged from –8.45 °C on 18 June 2010 to 0.11 °C on 19 June 2010. Maximum daily ambient temperature ranged from 10.16 °C on 16 June 2010 to 17.18 °C on 19 June 2010. On the coldest night, subcutaneous temperature, measured with data loggers, of the Control group animals averaged 33.31 °C and the Coats group animals 36.8 °C. This difference in subcutaneous temperature between the Coats and Control group animals was also evident on the other nights.

 


Figure 4. Subcutaneous and ambient temperatures recorded from 16 June 2010 to 19 June 2010

 

Figure 5 depicts the daily fluctuation in subcutaneous temperature of the groups from 25 June 2010 to 30 June 2010. This was a relatively warmer period, and the animals had two weeks’ hair growth. Differences in subcutaneous temperature between the Coats and Control group animals were still evident, although not as pronounced as in Figure 4.

 


Figure 5. Subcutaneous and ambient temperatures recorded from 25 June 2010 to 30 June 2010

 

 

Figure 6 depicts the daily fluctuation in subcutaneous temperature of the groups from 15 July 2010 to 21 July 2010. This period had relatively cold nights (ranging from –1.4 °C to –5.43 °C), and the animals had four weeks’ hair growth. Differences in subcutaneous temperature between the two groups were less evident than in the previous figures. From this stage onwards until the end of the trial period, with the exception of the cold stress trial on 10 August 2010, no significant differences in subcutaneous temperature were observed between the Coats and Control group animals.

 

Figure 7 depicts the daily fluctuation in subcutaneous temperature of the groups from 09 August 2010 to 11 August 2010 and includes the 2010 cold stress trial on 10 August 2010. The ambient temperature was 2.6 °C at the start of the trial at 08:00, and increased to 12.6 °C at 14:00 when the trial ended. Significant differences in subcutaneous temperature were recorded between the groups. The lowest average subcutaneous temperature recorded for the Coats group animals during the cold stress trial was 35.7 °C, while a corresponding value of 31.3 °C was recorded for the Control group animals.

 


Figure 6. Subcutaneous and ambient temperatures recorded from 15 July 2010 to 21 July 2010

 


Figure 7. Subcutaneous and ambient temperatures recorded from 09 August 2010 to 11 August 2010

 

 

DISCUSSION

It is interesting to note that Angora goat producers struggled with the same cold-related problems in the 1920s as they do today. On 15 September 1925, H.W. Rieck registered a patent for a goat coat in the United States of America (Rieck, 1925) to protect Angora goats against cold, wet spells. He stated in his application: “It seems to be the nature of the animal that it will stand shivering in the cold and rain, to the detriment of its health”.  

 

Goats are homeothermic animals and are able to maintain a balance between heat metabolism and environmental temperature to avoid either hyper- or hypothermia within the thermoneutral zone (Lu, 1989). To achieve thermoregulation, the body alters three main factors to achieve a constant, normal body temperature. These factors are heat transfer to the epidermis, rate of evaporation and rate of heat production.

 

Hypothermia is a condition marked by an abnormally low internal or core body temperature. It develops when body heat is lost to a cool or cold environment faster than it can be replaced. At a rectal temperature of less than 28 °C, the ability to regain normal temperature is lost, but the animal will survive if external heat is applied and the temperature returns to normal (Tuli & Gilbert, 2008).

 

When the body is unable to warm itself, cold-related stress results. Three factors that contribute to cold stress are cold air temperatures, high velocity air movement and contact with cold water or surfaces. A cold environment forces the body to work harder to maintain its temperature. Cold air, water and snow all draw heat from the body. Wind chill is the combination of air temperature and wind speed, and could enhance cold stress. Although it is obvious that below freezing conditions could cause cold stress, temperatures above 20 °C can also bring it about, especially when these are accompanied by rain and wind. A sharp temperature drop in summer can cause severe cold stress with heavy losses.

 

When exposed to cold conditions, the body loses heat through the skin at a more rapid rate than under higher ambient temperature conditions (McCullough & Arora, 2004). This increased heat loss causes the hypothalamus to activate the temperature regulation mechanisms (Kaiser, 2010). Blood vessels in the skin constrict to prevent excessive heat loss and muscles shiver to produce heat. The primary objective of the hypothalamus is to keep the vital organs (heart, lungs, liver, kidneys and the brain) at an acceptable temperature; all the thermoregulation mechanisms are designed to protect the core.

 

Surrounding the core is the periphery, which includes the skin, muscles and legs. The body will begin to shift blood flow from the extremities and skin to the core. This allows exposed skin and the extremities to cool rapidly until the periphery reaches the same temperature as the surrounding environment, and then the heat flow stops and body heat is preserved.

 

Additional energy is required to maintain core body temperature under extreme environmental temperatures. This additional energy expenditure causes physiological and behavioural adaptations under thermal stress, and can lead to impaired production or even death. Physiological and endocrinological reactions to cold stress of animals are discussed in detail in other studies (Thompson & Thomson, 1977; Bianca & Kunz, 1978; Fregly, 1982; Feistkorn et al., 1983; Fregly, 1989; Oda et al., 1995; Sano et al., 1997; Al-Tamimi, 2006; Al-Tamimi, 2007; Marai et al., 2007).

 

Wentzel et al. (1979), Al-Tamimi (2006) and Al-Tamimi (2007) reported a lowering in core body temperature, as well as in subcutaneous (Al-Tamimi, 2006) and skin temperatures (Bianca & Kunz, 1978) in goats exposed to cold conditions. Similar results were obtained for various sheep breeds (Slee & Sykes, 1967; Panaretto & Vickery, 1971; Bennett, 1972; Ellis et al., 1985).

 

Abdominal and subcutaneous temperatures of Angora goats in the Eastern Cape province were recorded for 10 days pre-shearing and post-shearing during March and September (Hetem et al., 2007). Shearing resulted in decreased mean, minimum and maximum daily abdominal temperatures, while mean daily subcutaneous temperatures also decreased post-shearing. It was suggested that the thermoregulatory system of goats was more labile after shearing and that shearing had greater thermoregulatory consequences in March than in September. This may provide an explanation for the vulnerability of Angora goats to cold in summer.

 

Rectal temperature of animals in both the Coats and Control groups in this study also decreased during both the 2009 and 2010 cold stress trial periods. However, rectal temperature of the Coats group was 2.21 °C higher than that of the Control group in 2009 at the end of the stress period. A similar trend was observed in 2010, although rectal temperature of the Coats group animals was 0.87 °C higher than the Control group animals. In both years, rectal temperature of many of the Control group animals dropped to below 34 °C, while only one Coat group animal in 2009 dropped below 34 °C.

 

Differences were also obtained in skin temperature between the two groups, especially on the ear and hind leg. Temperatures recorded on the extremities were much lower than those recorded on the shoulder or britch, or the rectal temperature, confirming restricted blood flow to the extremities. The most pronounced difference was between skin temperature recorded on the shoulder and britch. This is the area directly covered by the coats. The hair beneath the coat was not entirely dry, but it felt warm, humid and steamy under the coats, compared to the skin surfaces of the extremities, which felt cold and wet.

 

The relatively high amplitude of the daily subcutaneous temperature graphs indicates that the goats were subjected to large diurnal variation in ambient temperature. Thermoregulatory measures had to be activated, which the relatively lower subcutaneous temperatures confirm. The animals protected with coats had much lower daily amplitudes than the Control group animals during the earlier days of the trial, when they were just shorn. As the hair length increased, the differences in daily amplitude between the groups diminished. After four weeks’ hair growth, there were no significant differences in subcutaneous temperatures of Coats and Control group animals when they were subjected to normal winter temperatures. However, at eight weeks’ hair growth, both Coats group and Control group animals subjected to cold, wet and windy conditions, showed a drop in subcutaneous and rectal temperature, although not to the same level of newly shorn goats.

 

Animals in both the Coats and Control groups showed an increased heart rate over the first two hours of the trial, after which it decreased to below the initial values at the end of the trial period. The same tendency was observed by Wentzel et al. (1979), where animals subjected to a cold treatment initially showed an elevated heart rate. At the stage where some animals started to collapse, the heart rate was subnormal. The elevated heart rate is positively related to increased heat production (Brosh, 2007).

 

Whole-body blood glucose turnover rate was also found to be lower during mild cold exposure (Sano et al., 1997). In another cold stress trial (Wentzel et al., 1979), blood glucose concentration of cold stressed goats showed an initial increase from 4.7 ng/ml to 8.2 ng/ml, after which it decreased rapidly to a minimum of 2.2 ng/ml at the point of collapse. In this study, serum glucose levels of animals in both groups showed a marked drop towards the end of the trial period to 1.33 ng/ml and 1.66 ng/ml in the Coats and Control groups respectively.

 

CONCLUSIONS

Judging from the relative drop in rectal and skin temperature and other physiological parameters recorded, the animals in the Coats group were more able to withstand cold, wet and windy conditions than animals without protection. The coated goats have an advantage over the unprotected goats up to four weeks after shearing when exposed to normal winter temperatures. Even with eight weeks’ hair growth, animals wearing coats had a lower drop in rectal and subcutaneous temperature than unprotected goats when subjected to cold, wet and windy conditions.

 

The fact that animals in both groups shivered to the same extent at the end of the trial period, and experienced a drop in skin temperature on the extremities and periphery, indicates that the coats were not entirely able to provide absolute protection against cold, wet and windy conditions to the extent that prevent all the thermoregulatory measures of the body to be activated. It could, however, be concluded that the coats provide sufficient protection to newly shorn Angora goats during adverse weather conditions for it to be implemented in practice.

 

ACKNOWLEDGEMENTS

The following people and institution are acknowledged for their contribution to this project:

 

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Published

Grootfontein Agric 11 (2): 1-18