CHAPTER 2: REVIEW OF LITERATURE
2.3 S LOW - GROWING CHICKEN STRAINS
Indigenous chickens are invaluable reservoirs of genes for adaptive and economic traits that provide a diversified genetic pool (Muchadeyi et al., 2007). Six major categories are recognized namely; normal feathered, Naked Neck, frizzle, silky, dwarf and the feathered feet (Mtileni et al., 2012). Most indigenous chicken populations arise from the uncontrolled crossbreeding of various local and imported strains. As a result, the chickens are viewed as indescript strains. Most of them, therefore, have no identified description and are generally unimproved (Pedersen, 2002).
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Common strains of chickens in SSA, include the Naked Neck, Ovambo, Potchefstroom Koekoek and Venda chickens (Grobbelaar et al., 2010; Packard, 2014; Nthimo et al., 2004).
Less popular strains, particularly in South Africa, are the Nguni, Natal Game and the Zulu (Grobbelaar et al., 2010). These birds show small genetic distances to justify population substructuring (Muchadeyi et al., 2007). Slow-growing strains are inseparable from the rural scenario due to their adaptability under harsh environmental conditions (Miao et al., 2005).
Adaptability of indigenous chickens in the tropical environment has been through reduction in body sizes as a means of reducing maintenance feed requirement and increasing feed efficiency (Rashid et al., 2005). Their small body sizes reduce maintenance feed requirements and make survival on a low plane of nutrition possible. Apart from their low egg production potential and growth rates, there is a good market for both meat and eggs from slow-growing strains in both the European Union (EU) and Asia (Miao et al., 2005) presenting opportunities for commercialisation and export.
2.3.1 Naked Neck
The Naked neck (NN) chickens are thought to originate from Malaysia from where they spread to all parts of the world. The chickens are a widely distributed, multi-coloured, relatively light- weight strain kept for meat and eggs for household consumption. White, red and black feather combinations are common and the strain is adapted to hot environments. The NN is an adaptable strain and can be found in all diverse climates of Southern Africa. They have a more efficient heat dissipation mechanism due to the absence of feathers in the neck region resulting from reduced plumage cover which is an advantage when temperatures are high and birds have to dissipate excess heat (Deeb and Cahaner, 2001). The reduced feather cover aids in thermoregulation at high ambient temperature (Eberhart and Washburn, 1993) by increasing sensible heat loss. The Naked Neck gene (Na) is an autosomal, incompletely dominant gene
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(Raju et al., 2004) which causes bare skin on the neck which becomes reddish towards sexual maturity. The Na allele is associated with increased tolerance to heat, which is probably due to the 30 % reduction in overall plumage for heterozygotes and 40 % for homozygotes (Raju et al., 2004; Rajkumar et al., 2010, Fathi et al., 2013).
Naked Neck chickens reach sexual maturity at 155 d of age, with males weighing about 1.95 kg and females 1.4 kg (Chikumba and Chimonyo, 2014). Naked Neck chickens possess better post weaning (>12 weeks of age) heat tolerance than OV and PK chickens owing to the presence of the major gene that causes reduced plumage cover (Cahaner et al., 1993; Fathi et al., 2013).
2.3.2 Ovambo (OV)
The OV are predominantly dark-coloured birds that are thought to have originated in the Ovamboland rural areas of Namibia (van Marle-Koster and Nel, 2000). The birds are capable of flying and roosting in trees to avoid predators (Grobbelaar et al., 2010; Nthimo, 2004). They are quite aggressive and can kill mice and small rats (Grobbelaar et al., 2010; Nthimo, 2004).
They attain sexual maturity at average weights of 2.16 kg for males and 1.54 kg for females at 20 weeks of age (Nthimo et al., 2004). Ovambo chickens are a dual-purpose strain (van Marle- Koster and Nel, 2000) that can be used for both egg and meat production.
2.3.3 Potchefstroom Koekoek
Named in relation to its colour pattern, this strain is a composite dual purpose strain that was developed in the 1950s’. It is characterised by a barred colour pattern that is similar between males and females though the females tend to be darker than the males. The feature is, thus, used for colour sexing (Grobbelaar et al., 2010). The strain was developed by the crossing of
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Black Australorp cockerels with White Leghorn hens and the Plymouth Rock (Grobbelaar et al., 2010; Packard, 2014). The PK is popular among rural farmers in SSA for egg and meat production as well as their ability to hatch their own offspring (Grobbelaar, 2008). The meat of this strain is still popular among local communities and is preferred to that of commercial broiler hybrids (Grobbelaar et al., 2010).
2.3.4 Venda
The strain was first identified in Venda, Limpompo Province (Grobbelaar et al., 2010) and later discovered in other parts of South Africa. Venda chickens reach sexual maturity at the age of 143 days with an average body weight of 2.1 kg in males and 1.4 kg in females at 20 weeks old. The average egg weight for the strain is 52.7 g. These chickens have white and black or white and brown plumage with shades of dark green on the feather tips (Joubert, 1996). They are characterized by lower egg production, instinct to broodiness and adaptability for household production. A description of some common local strains of chickens is shown in Table 2.1.
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Table 2.1. Description of the some of slow-growing chicken strains common to Southern Africa
Strain Origin Phenotypic
appearance
Average weight (kg) Source Male Female
Naked Neck Introduced to Africa by traders from Malaysia
Very colourful, Naked Neck major gene
2.0 1.6 Van Marle Köster &
Casey (2001)
Ovambo Namibia, Ovambo land
Brown & black plumage, aggressive birds
2.2 1.9 Van Marle Köster &
Casey (2001)
Potchefstroom Koekoek
Cross between Black Australorp and White Leghorn
Black & white speckles
3 - 4 2.1 Viljoen (1986); Van Marle Köster &
Casey (2001)
Venda First official
recording in 1979
in Venda, Northern
Province, SA
White & black /white & brown plumage, green on feather tips
2.0 1.9 Van Marle Köster &
Casey (2001)
Source: Van Marle Köster et al. (2008)
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