Immunity in Angora goats
By Dr Hobson

Friday, 12th March 2021

Immunity in Angora goats

 

Why do Mohair producers struggle with the control of parasites in Angora goats more so than in sheep, particularly in weaned kids?

 

It is well known and proved that the Angora goat has a poorer ability to resist certain internal parasites compared to sheep.

Goats historically evolved as browsers and so have been less exposed to infective larvae and oocytes which are rarely found more than 20cm above the ground.

 

Even when comparisons between Angora goat kids and other goats are made the acquired immunity is poorer. This can be demonstrated in the development of Antibodies against roundworms between Cashmere and Angora goats compared over 3 years of data. (Ref: Breeding Fibre Goats for Resistance to Worm Infections Gastrointestinal, nematode or helminth By S. Walkden-Brown, B. Sunduimijid, M. Olayemi, J. Van Der Werf and A. Ruvinsky)

 

This is one of the reasons that when treating kids for parasites (roundworms, coccidiosis) the levels of parasites appear to quickly climb to previous levels after repeated exposure. The graph is consistent with the greater ability of Cashmere goats compared to angora goats to limit infections following a challenge.

antibody_ig_levels.png

What is this immunity?

There are 2 types of immunity:

  • Innate immunity is the general non-specific responses without prior exposure to the pathogen (genetic inherited response)
  • Acquired (adaptive) immunity is the immune response when recognising specific antigens with the development of a very specific immune response (antibody-mediated, cell-mediated, or both) and with the development of memory cells. (T and B lymphocytes).

 

How does immunity work against intestinal parasites?

It is believed that intestinal parasites stimulate a Type 2 antibody-dependant response while with intracellular parasites a Type 1 response is stimulated. The Type 2 response involves the flooding of the local mucosa with inflammatory cells (mast cells, eosinophils) and the development of immunoglobulins (IgE). Initially cytokines including interleukins. The first line of defence is the gut-associated lymphoid tissue which responds to the antigens released by the parasite. (See the enlarged mesenteric lymph nodes of the Angora kid stimulated by a severe chronic coccidiosis infection in the photo below)

antibody_2.jpg

Immunity results in:

  1. Expulsion of the adult parasite by damaging its cells or by the stress to resist the attack from the host.
  2. Reduced fecundity and delayed development of the adults in its effort to survive
  3. Reduced establishment of larvae

 

A number of factors have an impact on the immune system resulting in the poor and delayed response by Angora goat kids.

 

  1. AGE

The immune response of goats against H. contortus (wireworm) has been reported to be lower and develop later in age as compared to sheep (Hoste et al. 2008).

 

The age of the development of acquired immunity in Angora goats may vary but studies suggest that some  resistance to roundworms is established by 12 months of age and that there is no marked increase in resistance beyond that age, although if adjusted for infecting dose size suggested an increase in acquired resistance may occur up to 18 months of age.

 

Studies supporting this:

  • Adult goats develop at least some host resistance to gastrointestinal nematodes but it occurred later than 12 months of age. (Vlassoff et al. 1999)
  • In Angora goats, there is less development of resistance with age and exposure so there is less divergence in the level of infection between young and adult animals. ( Le Jambre and Royal -1976)
  • Kids acquired their first nematode infections between 2 and 3 months of age and the intensity of infection increased erratically thereafter to reach a plateau once the kids were 14 months of age. (Helminth and arthropod parasites of Angora goats in the southern Karoo I G Horak 1, KM Macivor, C J Greeff)
  • 2 Angora goat kids worm population was evaluated monthly for 2 consecutive years from the time they were 1 week old until they reached 12 months of age. Nematode burdens increased erratically in the kids reaching the greatest numbers when they were 1 year old and were generally low in adults ( I G Horak 1, M M Knight, E J Williams)

 

Goat kids can develop resistance to infection provided that they have sufficient challenge beforehand. This suggests that parasite control methods that rely on maintaining some parasite burden in the host are more likely to be successful than those that suppress worm infections totally.

 

Roundworm management based upon close monitoring of worm egg counts (WEC) and treatment intervention only when the WEC exceeds a given threshold based on worm species involved, animal condition, nutrition, and climatic conditions is likely to maintain immunity in the population and help regulate infections. (Kahn et al., 2006; Scrivener et al., 2006).

 

Also, see Target selective treatment and Roundworm management on the website

https://www.angoras.co.za/article/targeted-selective-treatment-ts

https://www.angoras.co.za/article/roundworm-management-strategies-in-angora-goats

 

 

 

REPRODUCTIVE STATUS

Pregnancy (a month before kidding) and lactation (2 months) result in a weakened immune system with the result that when usually 5% of stage L3 wireworm larvae picked up off the pasture develop into adults this can rise to 25-30%.

This is also reflected in the study where ewes that had given birth and were lactating had significantly higher FECs than 'dry' does in the flock, suggesting that like sheep, goats exhibit a post-parturient relaxation of immunity.(.A Vlassoff 1, S A Bisset, L W McMurtry)_

 

SEX

Adult ewes (dry) have better immunity than ‘kapaters’ and rams. The susceptibility of male animals to infections may be due to sex steroids (androgens), which modulate several aspects of host immunity (Klein 2000), and hence, these are often more susceptible to infection and carry higher parasite burdens.

 

NUTRITION

Nutrition is vital to the goat’s immune response effecting both the goat’s resistance and resilience as supported by studies:

  • Deficiencies in trace elements such as selenium, molybdenum, copper, zinc have been associated with higher worm counts.
  • Protein supplementation can increase the rate of acquisition of immunity and resistance to reinfection (Coop and Holmes, 1996).
  • Goats receiving a high protein diet had decreased faecal egg counts compared with those with a normal protein diet during lactation (Hoste et al., 2005). This trial also showed that the response of goats to supplementary feeding was characterized by an improvement in resilience, while effects on host resistance were less evident. (Resilience is the ability of the host to maintain production in the face of infection with parasites while resistance is the ability to resist or throw off infection).
  • It has been reported that goats infected with contortus and given extra protein in their diet had higher eosinophil counts (Torres-Acosta et al. 2004; Marume et al. 2011; Pathak & Tiwari 2013), decreased FEC and worm burdens (Knox et al. 2006), compared to goats given lower protein intake.

 

Therefore supplementary feeding, in particular provision of extra protein, can assist resilience to infection especially during times when metabolic resources are being directed to overcome the pathophysiological effects of infection (Knox et al. 2006).

 

GENETICS

Heritability to worm resistance although lower than sheep is a selection trait that can significantly impact roundworms as demonstrated in studies:

  • Genetic resistant animals had a lower FEC and had higher antibody levels (IgG) and mucosal eosinophilia in response to a secondary challenge infection than the non-resistant line. (Gill 1991)
  • The genetic resistance resulted from the expression of acquired immune responses rather than innate responses. FEC and PCV are two important parameters as an indicator for resistance as they are heritable with the range from 0.1 to 0.35 (Bishop 2012).

The selection for worm resistance is very achievable, see the website https://www.angoras.co.za/article/breeding-worm-resistant-angora-goats

 

STRESS

Weaned Angora kids were monitored for antibody levels, weight gain to demonstrated the effect of weaning stress on decreasing the ability of kids to amount an effective immune response. (H. Imik M. Aytaç).

 

See the impact of weaning stress on Angora goat kids on the website https://www.angoras.co.za/article/weaning-shock-in-angora-goat-kids

 

This will explain why Angora goat kids are so susceptible to parasites and why good management is required when raising Angora kids

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