General Combining Ability for Growth Traits in F 1 Crosses of Native Chickens of Nigeria in the Savanna Region

Nine genetic groups of native chickens of Nigeria were generated from a 3 x 3 diallel mating involving the normal feathered (NF), frizzle feathered (FF) and naked neck (Na) local birds. A total of 97, 75 and 73 straight bred chicks were hatched for the respective genetic groups. Correspondingly, 132,151 and 153 chicks resulted from various crosses (normal and reciprocal) of the parental birds. Body weights were taken at hatch and subsequently at 4, 8, 12, 16 and 20 weeks of age. Heterosis were calculated and general combining ability (GCA) were computed based on the pedigree of the birds. Body weight varied significantly (p<0.05) among the genetic groups at the various ages of measurement. Crossbreeding improved body weight in the crossbred over the parental genotypes. Heterosis for body weight at 20 weeks of age were positive and ranged from 1.93 in the Na birds to 12.18 in the NF birds. General combining ability (GCA) were 1058.97, 1044.01 and 1123.04 in the NF, FF and Na genotypes respectively. Consequently, variability was least in the Na genetic group signifying a higher selection pressure on these birds in the savanna region of Nigeria. The FF birds had a good hybrid ability and a greater gene variation for BW than the NF and Na genotypes. The study noted that that using the Na males against the FF females will give a greater advantage for body weight at 20 weeks of age in the savanna region of Nigeria. It is therefore recommended that Na males be crossed with FF females in developing table birds for this region from the available local stock.

additive variations were generally more important than dominance in determining body weight at different ages [4,[6][7][8]. It is common knowledge in animal breeding that the phenotypic value of an animal is the sum of its genetic makeup and the environmental effect. While many researchers have reported on the performance of the Nigerian local chickens in hybrid combinations elsewhere, there is a dearth of information on this performance in the savanna region of Nigeria. The current study is therefore designed to provide baseline information on the GCA of three genetic groups of the Nigerian local chickens in the savanna ecology with the aim of identifying desirable combiners for choice of meat type chickens in this region.

Materials and Methods
The experiment was carried in Makurdi -Nigeria. Makuirdi is located within the savanna region of the country. The experimental birds were generated from a controlled breeding population of parent stock involving three genetic groups of Nigeria local chickens in a diallel mating arrangement as shown in (Table 1).
The parent stock were sourced from local markets within and around Makurdi. They were kept for an adaptation period of four weeks. Birds with signs of ill health were isolated and treated.
All birds were vaccinated against the common endemic diseases in the region. At the end of the adaptation period, the birds were distributed randomly into breeding pens with a mating ratio of 1:10 male to female respectively. Eggs were collected and identified according to sire lines, incubated and hatched artificially using the electric incubator. The day-old chicks were properly identified by colour marking, using indelible dyes and brooded under standard conditions on deep litter for eight weeks. Compounded chick and grower mash containing 18% crude protein and 2800Kcal/kg metabolizable energy, and 15% crude protein and 2670Kcal/kg metabolizable energy were feed ad libitum during the brooding and rearing phases respectively. There was no restriction to water intake throughout the experimental period. Routine vaccination was carried out as recommended for the environment. Progressive increase in body weight in the genetic group was evaluated 4-weekly to 20 weeks of age of the birds using a digital weigh scale.
Daily weight gain was calculated using the procedure described by Msofffe et al. [9].

Statistical Analysis
The general linear model procedure of SAS [10] statistical analysis software was used to evaluate the effect of genetic group on body weight gain. Paired comparison was carried out using the Duncan's multiple range test [11]. The model used was used: Heterosis for body weight in the genetic groups was computed as described by Fairll [12]. The general combining ability (GCA) for body weight in the genetic groups was calculated using [13] procedure body weight when compared to its contemporaries. This is suggestive that full plumage cover and the associated stressing factors characteristic of the tropical environment could have set in between the 8 th and 12 th week of age. The naked neck birds tend to cope better with this challenge than the other two genotypes of the native chickens of the savanna region of Nigeria. In all the genetic groups, cross breeding resulted in significant (p<0.05) improvement in body weight over the straight bred genotypes.  Note: NF = Normal feathered, FF = Frizzle feathered genotype, Na = Naked neck genotype