Comparative growth and livability performance of exotic, indigenous chickens and their crosses in Tanzania

W G Munisi, A M Katule¹ and S H Mbaga¹

Tanzania Livestock Research Institute - Mpwapwa, P.O.Box 202 Dodoma, Tanzania
wilfredmunisi@yahoo.com
¹ Department of Animal Science and Production, Sokoine University of Agriculture,
P. O. Box 3014, Morogoro, Tanzania

Abstract

A study was conducted in central Tanzania to compare growth performance and livability of two exotic stocks namely Broiler (B) and Black Australorp (A), and two indigenous chickens sourced from warm (W) and cool(C) ecological zones and their crossbreds. The four parental stocks were used in 4x4 diallel crossing to produce 16 genetic stocks totaling 1256 experimental chicks. Birds were fed on nutritionally balanced diets to meet their requirements as per age and physiological stage. Variables studied were livability from day old to 48 weeks of age and body weights at day old, 4, 8 and 12 weeks of age. The data on growth traits were recorded on individual bird basis and analyzed using the General Linear Models procedure of SAS (2003), while frequency procedure of SAS (2003) was used for livability analysis.

 

Results revealed that genetic stocks differed in body weight at various ages. The broiler genetic stock (BB) was the heaviest at all ages. Among the indigenous ecotypes, the genetic stock from cool ecological zone (CC) was heavier than that from warm ecological zone (WW). However, at 12 weeks of age, the cross between the indigenous chickens from warm ecological zone and broiler (WB) in female birds as well as the cross between the broiler and indigenous chickens from the warm ecological zone (BW) in male birds had body weights which were close to that of straight broiler stocks (BB). The mean body weights of 12 weeks of age of the crosses ranged from 625g in the cross between indigenous chickens from the warm ecological zone and the indigenous chickens from the cool ecological zone (WC) to 1537g in the cross between the warm ecological zone and the broiler stocks (WB) for female birds. Similarly at 12 weeks of age, the mean body weights for male birds ranged from 894g in the cross between the indigenous chickens from the warm ecological zone and Black Australorp (WA) to 1833g in the cross between the broiler and indigenous chickens from the warm ecological zone (BW). Livability also differed significantly (p< 0.001) among genetic stocks in favor of the cross between Black Australorp and broiler (AB) females and its reciprocal (BA). The survival rate for female birds ranged from 32.3% in the indigenous chickens from the warm ecological zone (WW) to 72.3% in the cross between the broiler and the Black Australorp stocks (BA).The additive genetic contribution from the broiler stocks (BB) was higher than those of other stocks with respect to body weights. It is concluded that if is aimed at improving body weight and overall survival rate, then both broiler and Black Australorp crosses would offer the best option under moderate input production conditions.

Key words: additive breed effects, body weight, diallel crossing, dual purpose chickens, genetic stock, heterosis, reciprocal effects, synthetic breeding

Introduction

Indigenous chickens of developing countries are characterized by low productivity. However they possess other important merits like scavenging behavior and ability to survive in harsh environmental conditions and poor management systems (Yakubu et al 2008). Furthermore, these chickens are able to tolerate various diseases (Minga et al 2004; Ajayi, 2010). There are many factors contributing to low productivity of the birds, but the most fundamental is their low genetic potential (Katule 1992, Kitalyi 1998).  Nonetheless, genetic variability exists in productive and disease resistance traits (Msoffe et al 2004, 2006). The variability, if fully exploited, can provide the basis for genetic improvement (Adebambo et al 2010).

 

Genetic improvement of indigenous chickens may be achieved through either selection or crossbreeding using improved breeds or through employment of both approaches. Selection captures the benefits associated with additive gene action. However, simulation studies by (Lwelamira et al 2008) revealed that Kuchi, a large indigenous chicken ecotype in Tanzania, would require between three to six years of selection to attain 1300 g body weight at 16 weeks of age under intensive management system. This implies that a lot of time and resources would be needed to arrive at intended genetic improvement of indigenous chickens when selection within breed is opted for.

 

On the other hand crossbreeding between indigenous stock and exotic commercial chickens, would take advantage of productive merits which have already been accumulated through selection in the exotic chickens as well as merits for hardiness which have been endowed in indigenous chickens through decades of natural selection (Rajkumar et al 2011). Furthermore, crosses will have advantage emanating from the phenomenon of heterosis (Katule 1990; Guéye 1998). In recent time crossbreeding through provision of exotic cocks has been the main approach to improve indigenous chickens in Tanzania (Massawe 2009). However, the major setback in the crossbreeding program has been the need for repeated provision of exotic birds for crossing. This has been hampered by unreliable supply and high costs of acquiring and maintaining exotic breeding cocks. In other countries, reduction in fitness in imported breeding cocks due to genotype x environment interaction obstructed optimum utilization of this genetic improvement approach (Ndofor-Foleng et al 2006).

 

An alternative improvement approach would be to carry out crossing between two or more populations to create a single population of chickens followed by selection within the crossbred population, a method which is popularly known as synthetic breeding (Aggarwal et al 1979). With synthetic breeding, only one population with all desirable traits has to be maintained instead of two or more parental populations needed in regular crossing programs. Depending on the genetic diversity between the parental breeds, various levels of heterosis would be expected. However, before adopting any breeding strategy, adequate information on qualities and capabilities of different breeds of chickens is required. The information is important in order to select the right type of breeds/genetic stocks to cross so as to blend desirable qualities of the original parental stocks in one stock.

 

The current work focused on evaluating the performance of various parental breeds and crossbred genetic stocks and assessing the relative importance of additive breed effects, heterosis and reciprocal effects as determinants of growth and livability performance of chickens.   

Material and methods

Experimental site

 

The study was carried out at the Tanzania Livestock Research Institute (TALIRI) – Mpwapwa, located in central Tanzania. The area receives on average 660 mm of rainfall annually, falling mainly from November to April, with a dry spell in February and a long dry season from May to November. The Institute is at an elevation of around 1100 m above sea level with mean temperature ranging between 24⁰C to 29 ⁰C.

 

Study layout and procedure

 

Four stocks (two exotic and two indigenous) of chickens were used in a 4 x 4 diallel crossing to produce sixteen different genetic stocks. A total of 1256 experimental chicks were produced in three hatches. The exotic stocks used were the meat type (Broiler) chickens (B) used in Tanzania and an egg type Black Australorp (A) from the TALIRI farm. The indigenous stocks consisted of one stock collected from a warm ecological zone of central Tanzania (W) and another stock which was obtained from a cool highland zone of Tanzania (C). The mating arrangement and the resultant progeny genetic stocks were as shown in Table 1. The obtained progeny genetic stocks were compared for growth and livability performance.

Management of experimental birds

 

Chicks were wing banded at day old and brooded separately by genetic stocks for four weeks. The composition of the diets offered was as shown in Table 2. The chicks were vaccinated against Newcastle disease when they were 10 days old and then every after three month’s interval. They were also vaccinated against gumboro disease at day 14^th and 28^th. At 10 weeks of age they were vaccinated against fowl pox disease. The chickens were transferred to floor rearing pens after two months of age where female chickens were raised until they reached 48 weeks of age.

Data collection

 

Individual birds were weighed at day old and thereafter, at four week intervals up to the age of 12 weeks using an electronic balance. Data on livability were obtained from the record book maintained on daily basis. The average number of birds of each genetic stock alive in a given period was obtained by summing up the number of birds alive each day during the respective period and dividing by the number of days in that period. The livability was recorded from day old to 48 weeks of age.

 

Statistical data analysis and merit component estimation

 

The data on weights of birds were analyzed using the SAS General Linear Models (GLM) procedure using statistical model 1.

 

Y_ijk = µ + G_i + P(G) _ik + e_{ijk   …………………………………………………………………………………………………………(1)}

 

Where:

 

Y_ijk is an observation from the k^th bird in the j^th pen of the i^th genetic stock,

µ = general mean common to all birds in the experiment,

G_i= the fixed effect of the i^th genetic stock

P (G)_ij = effect of the j^th pen within the genetic stock,

e_ijk = random effects peculiar to each individual bird.  

 

On the basis of this statistical model, least squares means for weights at various ages were computed and compared between the genetic stocks. In addition, constant estimates for various components of merit (additive, heterosis and reciprocal effects) were derived using the SAS (2003) General Linear Models procedure with the solution option. The analysis was based on the following mathematical model:-

Means for components of merit were compared using t-test.

 

X_αβ= p₁G₁  + p₂G₂ +...+ p_nG_n+c₁₁H₁₁+ c₁₂H₁₂+c₂₁H₂₁  +c₂₂H₂₂+ c₁₃H₁₃ +c₃₁H₃₁ +c₃₃H₃₃+…+ c_inH_in +c_niH_ni +…+c_nnH_nn+ k₁₁R₁₁ …+ k_nnR_nn ……...............................................................................(2)

 

Where:

 

X_αβ = performance of the _β^th bird from the _α^th genetic stock,

p₁,p₂,…,p_n= p_i = proportion of inheritance from the _i^th breed in a given genetic stock,

G₁,G₂,…G_n= G_i = additive effect of the _i^th breed,

c_11, c₁₂,...c_in= c_ij =constant representing level of heterozygosity emanating from the i^th and j^th parental breeds in a given genetic stock

H₁₁,H₁₂,…,H_nn= H_ij= magnitude of heterosis in the cross between the i^th and j^th parental breeds

k₁,k₂,…k_n= k_i = constant representing the presence or absence of reciprocal effects in a given genetic stock

R₁₁,R₁₂,…,R_nn= R_ij = magnitude of reciprocal effects expressed when the i^th and j^th parental breeds are interchanged as sire and dam breeds.

 

The constants p, c and k were fitted in the above equation in accordance with the following procedure:

The proportion of inheritance from a given breed (p) was coded 1.0 if the genetic stock under consideration was a parental breed, ½ or 0.5 for F₁ cross with another breed and 0.0 if the breed’s germplasm was not represented in the genetic stock being considered. For heterosis, the coding was either 1.0 or 0.0 depending on the expected level of heterozygosity (c) in the progeny resulting from a given pair of parental breeds. The constants for reciprocal effects (k) were coded 1.0 for genetic stocks arising from dissimilar parental breeds with the breed of interest being on the paternal side and -1.0 for genetic stocks from dissimilar parental breeds with the breed of interest being on the maternal side, as summarized in the design matrix in Table 3 below.  However, except for reciprocals, the constant estimates for additive and heterosis were biased, the bias being imposed by the procedure used to compute the constant estimates. To obtain unbiased constant estimates for additive genetic and reciprocal effects the procedure used by Katule (1990) was adopted.

The data on livability were analysed using the frequency procedure of SAS (2003). Chi-square tests were applied to test associations between genetic stocks and livability.

Results and discussions

Variation among genetic stocks with respect to juvenile body weights

 

Table 4.1 shows least squares means for body weights of female birds summarized by genetic stocks. The genetic stocks were significantly (p < 0.001) different in body weights at all stages of growth. With the exception of the cross between the indigenous chickens from the warm ecological zone and the broiler (WB) at hatching time, broiler stocks (BB) were consistently heavier than other genetic stocks. The broiler stocks grew more quickly than other genetic stocks due to the fact that they have been intensively selected for rapid growth and heavy body weights. This conforms to Katule’s (1992) observations that the highest performance is expected in the breed which had been developed purposely for higher performance in that trait. Olawumi and Fagbuaro (2011) reported higher body weights at eight weeks of age for broiler chickens than the values obtained in the current study. The difference in the results of these studies may be due to broiler strains or environment differences. Similarly, Binda et al (2012) observed that meat breeds were heavier than native chickens from hatching to week 8 of age.  However, at 12 weeks of age, the cross between the indigenous stock from the warm ecological zone and broiler (WB) did not differ significantly in weight (P>0.05) from broiler stock (BB).This indicates that crossing indigenous chickens from warm ecological zone (W) and broiler (B) stocks produced crossbreds that close the gap due to broiler breed additive effects and heterosis effects. The results are comparable with the study carried out by Momoh et al (2010) who showed that crossing heavy ecotypes with light ecotype tend to produce crossbreds with body weights close to that of heavy ecotypes.

 

With regard to males, the results presented in Table 4.2 indicate that at 12 weeks of age, the cross between broiler and indigenous chickens from warm ecological zone chickens (BW) did not differ significantly in weight from broiler stocks (BB). The results reveal that crossing broiler chickens (B) with indigenous chickens from warm ecological zones (W) resulted into crossbreds with body weights close to that of broiler chickens. The result were in conformity with the findings of Gnakari (2007) who reported comparable body weights between pure bred broiler and broiler crossbred after eight weeks of age in Côte d'Ivoire.

 

Overall, the results of the study showed that the crossbreds with inheritance from broiler stocks were generally heavier than other crossbreds at all ages. This was expected because of the fact that body size is influenced by additive genetic effects as well as heterotic effects. The obtained result also conforms to what has been reported by other investigators (Katule 1990; Sunett 2013).

 

 The results also revealed that the cross between the indigenous chickens from the warm ecological zone and Black Australorp (WA) in both sexes were significantly (P<0.001) heavier than the indigenous chickens from the warm ecological zone (WW) at eight weeks of age (Tables 4.1 and 4.2). The observed higher body weights of the crossbreds (WA) than those of indigenous birds (WW) were probably due to breed complementarity and the fact that heritability for body weight is moderately high (Kadigi et al 1998). The results also conform to what was reported by Adedokun and Sonaiya (2002) who observed that crossbred males derived from Dahlem red x Nigerian native chicken were heavier than straight bred native males.  

 

It is also interesting to note that the body weights results of the Black Australorp crossbreds (AW and AC) as well as those of indigenous chickens from two ecological zones (WW and CC) in the present study were lower than those of Tswana crossbreds and Tswana straightbreds reported by Patrick and Phakedi (2013). The differences observed in the performances of genetic stocks with regard to body weights for the two studies could be attributed to genetic and nutritional background of both the exotic and indigenous breeds used in the respective studies.

Variation among genetic stocks with respect to livability

 

Livability differed significantly (P<0.001) among genetic stocks in females (Table 5). The reciprocal crosses between broiler and Black Australorp stocks (BA and AB) in both sexes survived better than other genetic stocks. The improved performance in livability of the broiler and Black Australorp crossbreds might be due to inheritance from broiler line. The broiler stock (BB) appeared to survive better when compared to Black Australorp stock (AA). The broiler stock (BB) had a 63% survival rate while the WW stock had 32% survival rate. The results from the present study are in agreement with those of Iraq et al (2005) who found improvement in livability for crossbreds than purebreds. The poor livability of indigenous chickens observed in the current study was probably due to the fact that indigenous chickens are used to the free range environment and the confinement might impose a stress which could render them susceptible to disease ailment. During feeding indigenous chickens, unlike exotic chickens, displayed feed ingredient selectivity. This resulted to body weakness, signs of drooping wings and finally death. Some of birds developed habit of cannibalism which caused death to cannibalized individuals. The observed poor livability of indigenous chickens under intensive management corresponds to other investigators reports. Petrus et al (2012) reported cannibalism being among the causes of mortality in indigenous chickens kept under intensive management system. Tadelle and Ogle (1996), cited by Petrus (2012), showed that diseases and nutritional deficiencies caused more problems to local chickens than exotic stocks in intensive management system. Several other workers (Demeke 2003, Demeke 2004; Halima et al (2006) revealed the inferiority of indigenous chickens under intensive system with respect to livability. Nonetheless, the mortality observed in the current study in indigenous chickens is slightly higher than those reported in other studies (Tadelle et al 2003; Demeke 2004; Halima et al 2006). However there were no significant differences (P>0.05) among genetic stocks in males with respect to livability.