Cross and reciprocal effects on growth traits in a diallel mating involving four selected genetic groups of native chickens

This study was conducted to estimate the specific cross and reciprocal effects on body weight traits in a diallel mating involving four selected genetic groups of native chickens. Experimental stocks were four genetic groups of native chicken, i.e. Paraokan (A), Banaba (B), Camarines (C), and Bolinao (D. Each cross per genetic group consisted of 3 roosters and 9 hens with 25 and 26 months old as parental stocks. A total of 362 F1 hybrids were used in this study. Observation on the growth traits were carried out for 16 weeks. A full diallel cross design were used in this study. Results of cross which were estimated with specific combining ability (SCA) showed varying magnitudes in the estimates of all ages considered. The BC cross consistently showed the highest SCA effect at 4,8,12, and 16 weeks of age. The reciprocal effects of DB and DC showed positive estimates at all ages studied, indicated that they may have higher potential than the original cross in term of improving the body weight traits.


Introduction
Diallel mating is a method in crossbreeding where the performance of a breed, strain or line in cross combination can be evaluated in term of general and specific combining abilities.Most research on diallel mating focuses on the phenomenon of heterosis, while the effect of reciprocal is very few, even though in crosses, the use of male or female line is very important to obtain optimal results.Hence, diallel mating perform to seek a particular combination do relatively better or worse than would be expected on the basis of the average performance of the lines involved.
Several authors [1,2,3] have attempted to ascertain the relative importance of the general and specific combining abilities in determining the genetic variance in traits of economic importance in poultry.However, most of these studies involved only commercial hybrid stock and very limited on genetic group belonging to the indigenous type of chickens.
The common genetic design for estimating component of genetic variance in an inbreeding population is diallel mating, which is the set of all possible mating among a given number of genotypes [4].The diallel set may or may not included reciprocal and parents.There are four methods of diallel cross [5] i.e. parents + F1s + reciprocal, parents + one set of F1s (without reciprocal), F1s + reciprocal (without parents), and one set of F 1 s (no parent and reciprocal).Furthermore, there is a full diallel set where reciprocal crosses are included and half diallel one where only one set of F1s is included.
The term of diallel mating were used to describe a procedure which is a set of p inbreed lines are chosen and crosses among these lines are made [5].There are a maximum of p 2 possible crosses, which can be represented by pxp matrix with elements xij such that xii represents the i th inbred, xij(i±j) represents F1 between i th and j th inbred, and xji represents its reciprocal.Through diallel mating, it can be seen which combination of cross is the best to use in an effort to increase the growth performance of native chickens.Reciprocal effects are the result of sex-linked (gene on the Z chromosome) and maternal effects (confounded by effects of genes on the W chromosome in female and effects of mitochondrial genes) effects [6].

Materials and Methods
Four groups of Philippine native chickens, i.e.Paraoakan (A), Banaba (B), Camarines (C), and Bolinao (D) were used in this study.Each cross per genetic group consisted of 3 roosters and 9 hens with 25 to 26 months old as parental stocks.Mating of the hens and roosters was done using artificial insemination (AI) teqnique.Hatching eggs were collected and store under ordinary room temperature.One week-egg collected were incubated using electrically operated four draft types of incubator.Pedigree baskets were used to prevent mixing of chicks at hatching time.A total of 362 F1 hybrids of crosses and reciprocals were used in this study.Observation on the growth trais were carried out for  A full diallel cross design were used in this study, whereas parents, F1's, and their reciprocals are included according to Griffing method 1 [5] so the mathematical model is:

Xijkl = µ + gi + gj + sij + rij + bk + eijkl
where: i,j = 1,2,3,4 (i ≠ j), and µ = population means gi = general combining ability for the first parent gj = general combining ability for the second parent sij = specific combining ability effect parents i and j rij = reciprocal effect for parent i and j bk = replication effect eijkl = error The error effects are assumed to be not correlated with each other nor with the various genotypic effect and they are normally distributed with mean zero and variance σe 2 .σe 2 is pooled error mean square obtained from the replicated experiment and has n degree of freedom.This article is only focuses on the effects of specific cross and reciprocals, while inter-se mating is not discussed.The specific cross was calculated: SCAij = cross effect-(GCAi + GCAj), where the cross effect = certain trait mean of given cross overall mean of certain trait, GCAj = the GCA for breed j (the AA, BB, CC, and DD genotype) [6].Reciprocal effect (rij) for the combination i x j was calculated as rij = (yij-yji)/2.Data gathered was analyzed using SAS GLM following a one way ANOVA in a complete randomized design.The general and specific combining abilities were analyzed using the diallel analysis [7].Data of the progenies were analyzed using completely randomized design (CRD) and the differences among treatment means were compared using Duncan multiple range test (DMRT).

Body Weight
The means for body weight for crosses and reciprocals are presented on Table 1.The result of Duncan's test performed for making pair-wise comparison of the means of F1's crosses and reciprocals are also presented in the same table.At day old, the hight initial chicks weight was observed in the AB cross while the lowest was noted in CD cross.However, statistical analysis showed not significant effect.The average initial body weight in this study slightly higher than [8], where DOC weight was 29.22g.
Significant differences among progeny means were noted at 4, 8, 12, and 16 week of age.At 4week of age, the highest was observed in the AB cross with 230.34g and the lowest was noted in DC cross (177g).Duncan's test found that AB, AC, and BC were significantly difference than DD, CD, DB, and DC.Similarly, DC cross was found to be significantly lower than CB and BA.This finding was lower than that reported by [9] where native chicken fed with commercial ration had body weight 331.33g.At 8 weeks old, BC cross was the highest while the lowest was noted in CD cross.The results obtained were higher than those found by [10] where the body weight of native chickens at 8 weeks of age was 433±85g.
The highest 12-week body weight was revealed in BC hybrid (1078.25g)and the lowest in DC hybrid (946.75g).Futher test showed that BC hybrid is significantly higher than DD, AD, and CD crosses.At 12 weeks of age, most F1's hybrid result from diallel mating both crosses and reciprocals were higher than that found by [11 and 12].At 16 weeks of age, most progeny already had body weight higher than 1 kg in liveweight.This indicaed that diallel mating had significant effect on produce high body weight.The progeny of BC cross was consistently showed significantly improve body weight 4-week of age until 16-week of age.This indicated that body weight of this study has been improved already as a result of selecting parental stock and the effect of diallel mating.

Cross effects
Cross effects is estimated using specific combining ability.Estimated of cross effect constants for body weight traits in a diallel mating involving four genetic groups of native chickens are presented in Table 2.  1 Means in the same column with common superscript are not significantly different (P>0.05) 2 First letter indicates genetic group of male parents 3 Figure in parentheses indicates contribution to the total variance Table 2 showed varying magnitude of differences in the estimates at all ages considered.The differences among genetic groups within day-old, 4 and 12 weeks of age were found to be insignificant.These non-significant differences effects at these ages indicated that the amount of nonadditive genetic variance influecing the expression of these traits are more or less similar.
The non-additive genetic variance accounted for a greater portion of total variancethan did additive genetic variance for day-old age, 8, 12 and 16 weeks of age.The BC cross consistently showed the highest positive effects at 4,8, 12, and 16 weeks of age so does the BD cross, even though it is lower than the BC cross.This result tends to suggest that the cross of Banaba male x Camarines female has promising result in improving body weight through genetic group crossing.On the contrary, the CD cross showed zero estimates in body weight at all ages considered, indicating very limited potential for improving growth rate using this specific mating scheme.This finding is in accordace with [13,14] that this represents of non additive gene action.Several previous studies also found the significant effects of crosses for body weight traits [11][12][13][14] The cross between the Banaba and the Bolinao female was not significantly different from AB, AC, AD, and BC crosses.On the other hand, cross effect of the CD cross was significantly lower than BD, BC, and AD crosses.Since the effect of cross (SCA) refers to the average inferiority or superiority of a cross relative to the average performance of the lines involved in that cross [15], then the CB cross was considered inferior than the BD, BC, and AD cross in this study.
Estimate of cross effect on body weight at 16 weeks of age showed that the BC cross was highest (53.87) and significantly different from those of the AD and CD crosses.This finding is in agreement with the finding of [14] that SCA is a greater importance than GCA in body weight.The proportion of non-additive variance in the total genetic variance (77%) was found to be higher than additive variance (23%).This would mean that there was a strong effect of crossing on body weight at 16 weeks of age, suggesting that if selection is applied to the crosses, the improvement would be expected to come from cross effect than inter se mating.Specific combining ability (SCA) defined as a numerical value that expresses the deviation of a specific cross compared to what would be expected from the average performance of the lines involved in that cross [15].

Reciprocal effect
Reciprocal effects are the result of sex-linked and maternal effects.Sex linkage probably accounts for the most important reciprocal effects, as the Z chromosome is known to have an effect on some traits in chickens [16].The estimates of reciprocal effects on four selected genetic groups of native chicken are presented in Table 3.The reciprocal cross of BA and DB showed positive estimates at all ages studied, indicating that they may have higher potential than the original cross in terms of improving the body weight traits.The reciprocal constants for body weight at 4 weeks of age were all positive, in contrast with constants derived at other ages.However, since the differences in were found to be insignificant, the result tends to suggest sex-linked and maternal effect on the four genetic groups are similar.Reciprocal effect in this study was greater than that found by [16] that worked crosses between Iraqi brown lines with two exotic breed of laying chickens but lower than [3] that study in crosses between local strains with exotic meat type chickens.
At8 week of ages, the DC cross showed the highest reciprocal constant whiles the DA cross was the lowest.Even though, no significance differences were found in this age period, but the presence of negative value at CA and DA crosses indicated that there was no sex-linked gene effect on body weight at particularly crosses.Similarly trends were noted at 12 weeks of age with the CA and DA crosses showing poorer performance as compared to CB and DB crosses.The value of reciprocal constants in this study were lower than [3] but higher than [16].The differences perhaps due to the differences in model and chickens used, where the two previous study using the exotic breeds.The previous study [3] usedThai indigenous chickens, also found similar trend of reciprocal effect.Reciprocal effect for body weight in this study was lower than that cross between local and commercial chickens [17].
Significant differences (P<0.05) were observed among reciprocal crosses for body weight at 16 weeks of age.Significant differences were observed between the CB, DB, and DC crosses versus CA cross.Other reciprocal crosses showed insignificant effect on body weight at this age.These results suggest that the DB and DC crosses were superior to the BD and CD crosses probably due to sexlinked effect.However, sex-linked effect was not in evidence for AB and BC.The significance reciprocal effect accounted for 8.54% of the total variance tend to indicate the presence of maternal effect and/or sex linkage for this trait.The important of reciprocal effect on body weight was reported by [12,18,19] especially in crosses between different breeds of chickens.Since the reciprocal effect as the average difference between a lines used as a sire versus the same line uses as a dam, so the cross of Bolinao female with Banaba and Camarines females was better than using Bolinao as the male line.

Conclusion
The cross of Banaba male x Camarinesfemale (BC cross) has promising result in improving body weight through genetic group crossing.On the contrary, the CD cross showed zero estimates in body weight at all ages considered, indicating very limited potential for improving growth rate using this specific mating scheme.For reciprocal, DB and DC crosses were superior to the BD and CD crosses probably due to sex-linked effect.However, sex-linked effect was not in evidence for AB and BC.The significance reciprocal effect accounted for 8.54% of the total variance tend to indicate the presence of maternal effect and/or sex linkage for this trait.Since the reciprocal effect as the average difference between a lines used as a sire versus the same line uses as a dam, so the cross of Bolinao female with Banaba and Camarines males was better than using Bolinao as the male line.

Table 1 .
Average body weight (g) of the progenies of crosses and reciprocals1Means in the same column with common superscripts are not significantly different (P.0.05)2First letter indicates the geneticgroup of male parents.

Table 2 .
Estimates of cross effects for some body weight traits of F1's in a diallel mating1

Table 3 .
Estimates of reciprocal effects on body weight traits in a diallel mating1Means in the same column with common superscript are not significantly different (P>0.05)2Firstletterindicatesgenetic group of female parents3Figures in parentheses indicate the percent contribution to the total variance 1