Why do Angora goats seem to die more from cold during summer than winter?

Thursday, 26th April 2018

Angora goats are known to be vulnerable to cold stress, especially for the first 6 weeks after shearing and so losses through hypothermia are not uncommon.

Why do these catastrophic Angora goat mortalities occur after shearing if unseasonal cold spells occur in the summer, since those summer cold spells are milder than normal winter cold?

 

Research was carried out on Arthur Rudman’s farm Blaauwkrantz to determine the thermoregulatory responses to shearing. (2009  Hetem, de Witt,Fick, Fuller, Kerley, Maloney, Meyer and  Mitchell).

 

What happens to the Angora goat’s body temperature after shearing?

The trials showed that after shearing the abdominal and subcutaneous (skin) temperatures of the goats decreased.

During the Day: After shearing the blood vessels in the skin of the goats remained vasodilated (dissipating heat) during the day, as indicated by small differences between core (abdominal) and subcutaneous (skin) temperatures.

During the night Night: The difference between abdominal and subcutaneous temperature of the gloat doubled at night after shearing in September (winter) and nearly trebled in March (summer).

It was strange that the changes in temperature with shearing was greater in summer than in winter, despite ambient temperatures being significantly lower in September than in March.

 

How do the goats try maintain their body temperatures after shearing?

  1. Vasoconstriction leads to a reduction in heat delivery to the skin, so reduce heat loss from the body.
  2. The goats look for shelter - selection of warm microclimates.
  3. Increase their metabolic rate (heat production)

 

Adaption to temperatures after shearing

In summer, the goats lose some capacity for thermoregulation in the cold, because they had been chronically heat-stressed before shearing, and had adapted to that stress. The blood vessels under the skin in unshorn goats are constantly dilated.

Similarly, sheep are less able to adapt to exposure to cold stress after summer shearing than after winter shearing (Glass and Jacob, 1992). The resilience of sheep after shearing in winter may be the result of cold adaptation in winter (Sykes and Slee, 1969a; Slee, 1972; Young, 1981).

The Angora goats are slow to adapt. Abdominal temperatures remained lower than pre-shearing temperatures for weeks, even up to 3 months after shearing, only gradually returning to pre-shearing values.

If fleeced goats are not acclimatized to cold, they may actually become more susceptible to cold stress after shearing.

Why are the goats slow to adapt after the summer shearing?

In summer the predominant demands on the goats’ thermoregulatory system were heat dissipation, even at night, before shearing. The chronic heat stress imposed on fleeced goats in summer results in a reduction in the competence of their autonomic responses necessary for heat conservation. Consequently, the goats were less well equipped in the late summer than in the late winter to cope with the loss of the insulating fleece.  So the reason is poor seasonal acclimation

In Merino sheep, the body temperatures both before and after shearing were lower than the maximum body temperature that we observed in our goats. We suspect that the Merino sheep, in spite of their full fleece, never were as heat-stressed as our goats were. Angora goats, exposed to full sun, have been shown previously to have higher, and more variable, body temperatures than Merino sheep do (McGregor, 1985 and 1998), suggesting that solar radiation provides a greater heat load on Angora goats than on Merino sheep.

 

Effect of shearing on water loss through skin - reduces body temperature

Although shearing impairs heat conservation, it facilitates radiant heat gain during the day.

When goats are hot evaporative water loss, both cutaneous and respiratory, is high.

It has been shown in Merino sheep water intake nearly doubled after shearing.

The water turnover rates of Angora goats also increased significantly after shearing, though they did not double in this trial.

The impairment of cutaneous water loss due to the fleece cover is one factor that contributed to the relatively high body temperature of our Angora goats before shearing and the significant drop in temperature post shearing.

 

Effect of shearing on the metabolic rate of Angora goats

Cold exposure (after shearing) increases the metabolic rate of Angora goats (Wentzel et al., 1979; Fourie, 1984.) This increased metabolic rate contributes to the increased energy requirements of Angora goats after shearing.

 

Effect of shearing on goat activity

The trial showed an increase in daily activity from pre- to post-shearing during March.

Similarly, the foraging time for shorn Merino sheep is higher than for unshorn Merino sheep (Hutchinson and McRae, 1969; Birrell, 1989).

The activity pattern of our goats, which presumably was foraging activity, took place after sunrise and in the late afternoon.

Daily activity increased nearly two-fold after summer (March) shearing, but not winter (September) shearing. This increased activity after March shearing was likely the result of an increased foraging time, food intake and metabolic rate.

Similar results were found for sheep in colder weather, in that daily movement patterns remained unaltered or even decreased after winter shearing (Webster and Lynch, 1966). These results are likely to correspond to the depression in food consumption reported for newly shorn sheep exposed to extreme cold (Webster and Lynch, 1966; Panaretto and Vickery, 1971; Donnelly et al., 1974

 

Conclusion

The slow adaption from seasonal heat stress in summer to a cold snap post shearing is the reason for increased mortalities in summer despite the fact that it is colder in winter.

 

Also see the SAMGA website article on ‘Cold (Hypothermia) and the Angora goat.

https://www.angoras.co.za/article/cold-hypothermia-and-the-angora-goat#244

 

References/Extracted from:

 

Shearing at the end of summer affects body temperature of free-living Angora goats (Capra aegagrus) more than does shearing at the end of winter

  1. S. Hetem1- , B. A. de Witt1 , L. G. Fick1 , A. Fuller1 , G. I. H. Kerley2 , S. K. Maloney3,1, L. C. R. Meyer1 and D. Mitchell1

 1 Brain Function Research Group, School of Physiology, University of the Witwatersrand Medical School, 7 York Road, Parktown 2193, South Africa;

2 Department of Zoology, Centre for African Conservation Ecology, Nelson Mandela Metropolitan University, PO Box 77000, Port Elizabeth 6031, South Africa;

 3 Physiology, School of Biomedical, Biomolecular, and Chemical Science, University of Western Australia, 35 Stirling Highway, Crawley 6009, Australia

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