Livestock Research for Rural Development 22 (12) 2010 Notes to Authors LRRD Newsletter

Citation of this paper

Egg production performance of first and second filial generation naked neck (NaNa, Nana) and normal feathered (nana) birds of a cross between indigenous naked neck (NaNa, Nana) males and exotic commercial females (nana)

K Adomako, J K Hagan* and O S Olympio

Department of Animal Science, P.M.B., KNUST, Kumasi, Ghana
* Department of Animal Science, P.M.B, UCC, Cape Coast, Ghana


An experiment was conducted to compare the laying performance of first and second filial generation birds (naked neck, Nana and NaNa and normal feathered, nana) of a cross between indigenous naked neck males (Nana) and exotic commercial females (nana) under semi-intensive system. The crossing produced offspring in the proportion of 48.7% Nana (390 birds) to 51.3% nana (410 birds) in the F1 generation. The two genotypes (Nana, nana) were compared in a Randomized Complete Block Design (RCBD) experiment, with the three villages, where the birds were raised, as blocks and the two genotypes (Nana, nana) as treatments. Each block had 240 birds, 120 each of Nana and nana layers.


Nana birds were significantly (P<0.05) higher in number of eggs per clutch,  hen-housed and hen-day rates of lay, egg size and survivability, than their nana counterparts. However, age at first egg and egg size to body weight ratio were significantly better in the nana birds compared to the Nana ones. In the second mating, males and females of F1 Nana birds were selected and mated inter se. This produced 16.8% NaNa (202 birds), 54.5% Nana (654 birds) and 28.7% nana (344 birds) offspring in the F2 generation and these were compared in a Randomized Complete Block Design (RCBD) experiment, with the three villages, where the birds were raised, as blocks and the three genotypes (NaNa, Nana and nana) as treatments. Each block had 270 birds, 90 each of NaNa, Nana and nana layers. It was observed that Nana and NaNa birds were significantly (P<0.05) higher in number of eggs per clutch, hen-housed and hen-day rates of lay, egg size and survivability.


Using birds that show the naked neck phenotype in local chicken production will enhance egg production performance significantly.

Key words: chicken, clutch-size, crossing, hen-day, hen-housed


In Ghana, the total poultry population is estimated to be over 33 million with 60-80% of this being rural scavenging chickens (LPIU 2006; Gyening 2006). Rural poultry production is an important agricultural activity of almost all rural communities in Africa, providing scarce animal protein in the form of meat and eggs as well as being a reliable source of petty cash. However, indigenous chicken production in Ghana is greatly hampered by genetic and management problems. Pertinent among these problems are smaller sizes of birds and eggs, diseases and predators.


Naked neck (Na) and frizzle (F) genes have been found to improve meat and egg production in birds under high ambient temperatures (Merat 1986). Crossbreeding improves economic traits which have low heritabilities such as egg production through heterosis; and the improvement is even higher when the two breeds involved in the crossing differ widely in performance in terms of economic traits. The objective of this study therefore was to produce naked neck birds (NaNa, Nana) from a cross between local naked neck males (Nana) and exotic females (nana), and compare their egg production performance with that of their contemporary normal feathered (nana) ones.  


Materials and methods 

Location and duration of experiment


The experiment was carried out at the Department of Animal Science, Kwame Nkrumah University of Science and Technology (KNUST), Kumasi (Altitude 261.4MSL, Latitude 06o 41’N and Longitude 01o 33’W); and three selected villages/towns within the Asante-Akim South District of Ashanti Region, Ghana, namely, Yawkwei, Juaso and Nkwanta. The average rainfall, temperature and relative humidity of the KNUST experimental station during the experimental months were 126.06mm, 28.50 oC and 72.40% respectively. The experiment extended from May 2006 to December 2007.


Experimental birds


Sixty (60) exotic females and six (6) indigenous naked neck (Nana) males were used in the initial crossing. The exotic females were received from Akate Farms Limited, Kumasi, Ghana. The local naked neck males were bought from Yawkwei, Juaso, and Nkwanta within the Asante-Akim South District in the Ashanti Region of Ghana. The indigenous naked neck males were mated to the exotic females in a ratio of 1:10.




The birds were kept under the deep litter system with wood shavings for three months. They were fed layer mash ad-libitum (17.5% CP and 2700 Kcal ME/Kg) and were also provided with fresh water ad libitum. Each of the six pens used for keeping the parents had two laying boxes measuring 30 cm x 30 cm. Eggs were collected twice daily, labelled and stored for not more than 7 days at room temperature (25oC) before incubation.


The birds were dusted with Malathion poultry dust against lice, soft ticks and mites. They were also dewormed and given Pen Strip, which is a source of antibiotic and vitamins.




The eggs were selected for artificial incubation by discarding very small eggs or very large eggs, broken shells, blood stained or dirty eggs. The eggs were incubated and hatched at the hatchery of Akropong Farms, a commercial hatchery based in Kumasi, Ghana. The incubation was done weekly for ten consecutive weeks.


Chick rearing


After hatching, each batch of chicks was brooded in one unit of the brooder house. Electric bulbs (100watts) were used to provide light and the required heat for the chicks.  The chicks were wing-tagged and weighed individually. Glucose was administered via the drinking water. Commercial chick mash (19.5%CP and 2800Kcal ME /Kg) and fresh drinking water were given ad libitum. The chicks were vaccinated against Newcastle and gumboro diseases. Coccidiostat, antibiotics and vitamins were also given through their drinking water during the first month. The growth rates of chicks were recorded weekly up to the sixth-week.


Parents for the second generation birds


During the sixth week, twenty (20) heterozygous naked neck males and one-hundred and twenty (120) heterozygous naked neck females were selected to be mated inter se to produce the second generation. The males were kept separately from the females. The birds were fed commercial grower mash (15%CP and 2650Kcal ME/Kg) at six weeks of age and layer mash at seventeen weeks of age (17.5%CP and 2700Kcal ME/Kg). Feed and fresh water were given ad libitum. They were vaccinated against fowl pox and Newcastle (Newcavac) diseases. Deworming took place after every three months via their drinking water. Birds were sometimes stressed due to weighing and transfers, therefore vitamins were administered intermittently. Four weeks after the first egg has been laid, the males were introduced to the females in a ratio of 1:10; and collection of eggs for incubation took place two weeks thereafter. Details on laying boxes, egg collection, selecting eggs for incubation and chick rearing up to six weeks have already been covered. After the sixth week, these second filial generation (F2) birds were transferred to the three villages mentioned earlier.


Mating involving indigenous naked neck and commercial layers


There were two crosses. The first cross was between normal feathered exotic layers (nana) and indigenous heterozygous naked neck males (Nana), producing offspring that were 48.7% heterozygous naked neck (Nana) and 51.3% normal feathered birds (nana) in the first filial generation (F1). The second cross was an inter se mating of the heterozygous naked necks (Nana) from the F1 generation. The second cross produced offspring that were 16.8% homozygous naked neck (NaNa), 54.5% heterozygous naked neck (Nana) and 28.7% normal feathered (nana/ff) birds. The two crosses are diagrammatically shown below:

Selection and training of chicken keepers


The chicken keepers used for the study were selected prior to the experiment. The selection was done during an earlier survey to assess the performance of local chickens in Ghana. Three keepers were selected from each of the three villages/town (Yawkwei, Juaso and Nkwanta). The selection was based on educational level and the interest in keeping local birds. Each keeper made a hen-coop or prepared a place for the birds and these were inspected prior to the transfer of the birds.


A top-loader weighing scale was given to each keeper. They were trained on simple poultry management practices such as feeding and giving water under sanitary conditions, culling, litter changing, maintaining clean coop, recording age at first egg and counting of the number of eggs per clutch. To quantify the amount of feed given daily, each keeper was made to use a single container filled to the brim for giving feed all the time.


Chick transfer and rearing at the villages


After six weeks, the chicks were transferred to the villages for rearing under, semi-intensive system. Each keeper was first given 80 F1 female birds, which were made up of 40 heterozygous naked neck (Nana) and 40 normal feathered (nana) birds. For the second generation birds (F2) each keeper was given 90 birds, 30 from each of the three genotypes (homozygous naked neck-NaNa, heterozygous naked neck-Nana and normal feathered-nana). The keepers kept the birds either in a locally designed hen-coop or in an uncompleted building that is roofed, in which case the cemented floor was covered with wood shavings. Each keeper was guided to prepare a mash to supplement scavenging feeds. The mash was prepared from milled-maize or milling waste mixed with smoked fish waste, palm kernel cake and wheat bran. The mash was given to the birds thrice daily. Fresh water was provided ad libitum either in a plastic bowl or an earthen ware pot. Figures 1 and 2 show the transferred birds being introduced into their new pen and a locally prepared feed supplement.

Figure 1.  Arrival of birds at a village

Figure 2.  a locally prepared mash

Data collection


Egg production parameters measured included age at first egg, rate of lay (hen-housed and hen-day), egg weight, clutch size, egg and body weight ratio,


Egg production


The age (days) at which each of the genotypes laid their first egg, was taken as the age at first egg. The number of eggs per clutch was estimated by counting the number of consecutive eggs laid by individual layers before a brief pause in laying. An average value from five layers for each phenotype within each sire’s offspring from each village was used. All the eggs laid were recorded daily for six months period. Egg production was calculated in terms of rate of lay i.e. percentage of the total number of eggs produced divided by the total number of hens alive per day (hen-day), or divided by the total number of hens housed (hen-housed).


Egg and body weight ratio


This was determined as the ratio of egg weight to the body weight of the layer. Three eggs each collected from five layers selected from each phenotype from each village were used in calculating the ratio. The average values were calculated by dividing the total body weight by the total egg weight for each phenotype from each of the villages.




Mortality was calculated as the percentage of birds that died between day-old and the end of the experiment.


Statistical analysis


The experimental design was Randomized Complete Block Design (RCBD) with the three villages as blocks and the two (Nana, nana) or three (NaNa, Nana and nana) genotypes as treatments. The data was analyzed using the following linear model:


Yij = μ +Vi + Gj + E ij


Yij = Observation for a given variable

μ = Overall general mean common to all observations

Vi = Environmental effect due ith location (i= 1, 2, 3)

Gi = Genetic effect due to jth phenotype (i=1, 2 or 1, 2, 3)

Eij = random error effects peculiar to each observation.


Analysis of Variance was performed using Genstat Software (Discovery Edition 3). Where the differences between means were significant, the Least Significant Difference (LSD) test was used to separate them.



Laying performance of F1 birds


Number of eggs per clutch, egg size, hen-housed and hen-day egg production rates were significantly (P<0.05) better in the Nana layers compared to the nana ones (Table 1). However, age at first egg and egg size to body weight ratio were significantly (P<0.05) superior in nana layers than Nana ones (Table 1). Mortality was significantly higher (P<0.05) in nana birds compared to their Nana counterparts.

Table 1.  The effect of the naked neck gene on laying performance of f1    birds

Parameters/ F1 birds





Average age at first egg                      





Average eggs per clutch





Average egg size, g





Average egg size-body weight ratio





Rate of lay (hen-housed), %





Rate of lay (hen-day), %





Mortality, %





Means followed by different superscripts are significantly different at 5% level of significance; LSD=Least Significant Difference; and SEM= Standard Error of the Mean;

Laying Performance of F2 Birds


Number of eggs per clutch, egg size, egg size to body weight ratio, hen-housed rate of lay and hen-day rate of lay were significantly (P<0.05) lower in the F2 nana layers compared to those of NaNa and Nana F2 birds. F2 nana layers laid their first eggs significantly (P<0.05) earlier than NaNa and Nana F2 layers.  Age at first egg was significantly (P<0.05) better in Nana F2 layers than NaNa ones whilst the value for hen-day rate of lay was significantly (P<0.05) higher in NaNa F2 layers than Nana ones (Table 2).

Table 2.   Laying Performance of NaNa, Nana and nana F2 Birds                   

Parameter/ Phenotype






Average age at first egg, days






Average eggs per clutch






Average egg size, g






Average egg size to body weight ratio






Rate of lay-hen-housed, %






Rate of lay-hen-day, %






Mortality, %






Means followed by different superscripts are significantly (P<0.05) different at 5% level of significance; LSD=Least Significant Difference; SEM=Standard Error of the Mean

During the experimental period, birds carrying the naked neck gene (NaNa and Nana) survived significantly (P<0.05) than their normal feathered contemporaries (Table 2).


The naked neck phenotype had positive effects on number of eggs per clutch, egg size and rate of lay than the normal feathered ones (Tables 1 and 2) because the Na gene which is located on the third chromosomes in chickens may have a linkage with some genes that control egg production which are located on the same chromosome. Secondly, part of dietary protein is used in feather formation and the reduction of feathers in naked neck birds releases more protein which can be used for egg formation. Furthermore, the average day temperatures during the experiment ranged from 25 to 28oC which could have caused heat stress in the layers. However, due to feather reduction in naked neck layers, they were able to dissipate heat properly which alleviated heat stress under the high ambient temperatures and therefore improved feed intake, feed utilization, egg formation and egg laying.


The results were similar to those of Somes (1988), Haaren-Kiso (1991) and Mathur (2003) who found that under constant heat stress, heterozygous naked neck birds perform significantly better than their normal feathered counterparts in terms of egg numbers. Rauen et al (1986) observed that the advantage of the Na gene at high temperatures for egg production mainly involves persistency of laying. Somes (1988), Hareen-Kiso (1991), Rauen et al (1986), Yoshimura et al (1997) and Mathur (2003) associated the naked neck genotype with bigger egg size compared to the normal feathered birds. Rauen et al (1986) reported that under high temperatures the heterozygous naked neck birds are superior in rate of lay compared to their normal feathered counterparts.


Age at first egg was better for the heterozygous naked neck birds than the homozygous ones because the former reached sexual maturity earlier than the latter. These F2 birds were hatched in the rainy season with average early morning (6-7am) ambient temperatures of 15-18oC which because of inadequate heating during brooding affected the growth of the homozygous naked neck birds and therefore resulted in a delay in sexual maturity. The usefulness of the naked neck genotype in stress management at higher ambient temperatures has already been explained in this section. Stress in birds during high ambient temperatures affects egg production markedly; therefore, the 1% higher production of the homozygous naked neck birds in hen-day egg production compared to the heterozygous naked neck genotype was due to the extensive feather mass reduction (40%) in the former compared to the latter (20% feather mass reduction).


The naked neck birds being inferior to the normal feathered (Tables 1 and 2) in age at first egg may be due to the fact that naked neck birds are associated with bigger egg sizes; because according to Oni et al (1991) breeds that attain sexual maturity early end up laying lighter eggs than late maturers. Egg size correlates positively with body size, therefore the naked neck birds that had much higher body weights compared to their normal feathered counterparts should have had higher egg size to body weight ratios than their normal feathered counterparts. So, the observation that the normal feathered birds were superior to the naked neck birds in terms of egg size to body weight ratio in this study might be due to the fact that average body weight of naked neck layers was higher than the body weight of the of the normal feathered phenotype raising the value for the egg weight to body weight ratio since the superiority of the naked neck birds over the normal feathered ones in egg weight was not to the same extent as that of the average body weight. In this study, local mash with much lower cost was used and therefore the inferior egg weight to body weight ratio of the naked necks did not affect the end profit for rearing them compared to the other phenotypes. However, if naked neck layers are to be kept in the tropics under commercial poultry conditions where because of the higher cost of feed, feed utilization would be a big issue, then feeding should be regulated to avoid unnecessary high body weight which might affect the end profit.


Mortality was lower in naked neck birds than the normals (nana), (Tables 1 and 2) because the presence of the Na gene in the birds might have increased their resistance against diseases. Additionally, the naked neck birds were very docile, which made them less prone to pecking despite their bare necks and this might have increased their survivability.    


It can therefore be concluded that using birds that show the naked neck phenotype in local chicken production will enhance egg production performance and survivability significantly.



We would like to thank the Kwame Nkrumah University of Science and Technology (KNUST), Kumasi, Ghana for supporting this work through a scholarship package given to Mr. Kwaku domako for his PhD programme. Our appreciation goes to Akate Farms and Trading Co. Ltd., Kumasi, Ghana for donating birds to support this work. We are also very grateful to the chiefs and people of the villages where the study took place especially Mr. Martin Addo Debrah, Mr. Eric Opoku-Mensah and Mr. Joseph Awunor for their immeasurable support during the study.



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Received 25 September 2010; Accepted 11 November 2010; Published 9 December 2010

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