Additive, heterosis and reciprocal effects on egg production and quality of exotic x indigenous crossbred chickens 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 assess egg production and quality performance, additive breed, heterosis and reciprocal effects for genetic stocks arising from 4x4 diallel crosses from four parental stocks (two exotic and two indigenous chickens). The data on egg production and quality were recorded on individual bird basis and were analyzed using general linear models procedures.

The results revealed that the differences between genetic stocks were significant for age at sexual maturity (ASM), first egg weight (FEW), average egg weight at 48 weeks of age (EWT48), egg shell thickness at 48 weeks of age (EST48) and number of eggs in 90 days of laying after attainment of sexual maturity (EN90). No significant differences were observed between genetic stocks for number of eggs in180 days of laying after attainment of sexual maturity (EN180) and egg shape index at 48 weeks of age (ESI48).Indigenous chickens from the warm ecological zone (WW) laid eggs with thicker shells at 48 weeks of age (EST48) and matured earlier (140 days) than other genetic stocks. The highest EWT48 was observed in broiler stock (56.3g), followed by the cross between Broiler and Black Australorp (54.1g) while indigenous chickens from the warm zone (WW) had the lowest (42.5g).The cross between indigenous chickens from the warm ecological zone and broiler (WB) had more eggs at 90 days post sexual maturity than other genetic stocks. There were no statistical differences between genetic stocks in EN180 but the cross between broiler stocks and indigenous chickens from the cool ecological zone (BC) followed by the cross between broiler and Black Australorp chickens (BA) showed better performance in this trait. Additive breed constant estimates for the broiler stocks were higher than those of other stocks with respect to FEW and EWT48 while the Black Australorp stocks had slightly higher additive constant estimates for EN90 and EN180. The cross between indigenous chickens from the cool zone and broiler (CB) as well as the cross between indigenous chickens from the warm ecological zone and broiler (WB) exhibited positive heterosis in EN90 and EN180. Reciprocal effects were observed for the cross between Black Australorp and indigenous chickens from the cool ecological zone in FEW as well as the cross between Black Australorp and Broiler stock (AB) in EST48. It is concluded that the use of broiler as sires and either indigenous chickens or Black Australorp as dams produced crossbreds that were good in FEW, EWT48 and EN180 while the use of broiler as dams and indigenous chickens from the warm ecological zone as sires favored EN90.

Key words: dam parent, diallel crossing, genetic stock, parental stock, sire parent

Introduction

Indigenous chickens kept in rural areas are characterized by low productivity (Dessie et al 2011) due to their low genetic potential for growth and egg production which is compounded by poor management conditions (Minga et al 1989; Katule 1992; Kitalyi 1998). Recently, Guni et al (2013) estimated the total annual egg number per hen per year for indigenous chickens in Tanzania to be about 45, while egg weight ranges from 20.8g to 55g.  Variability in performance within and between different indigenous chicken ecotypes notably on egg production have been reported suggesting that selection between and within indigenous chicken populations for egg production could lead to some improvement in this trait (Msoffe et al 2001; Msoffe 2004; Guni and Katule 2013; Guni et al 2013). It is however, well acknowledged that genetic improvement of poultry through selection may take a very long time, thus crossbreeding coupled with selection can speed up genetic gain by utilizing heterotic effects.

However, conflicting reports exist for production traits such as body weight and egg production (Nwosu and Omeje 1985). This could be attributed to existing genetic diversity of both the indigenous and exotic chicken breeds. Moreover, the existing diversity offers an opportunity to test which combination(s) perform best for traits of economic interest. Key to this is to establish which breed/strain should be on the paternal and which one should be on the maternal side in the crossing. In this regard, diallel crossing has been commonly used to test and evaluate the combining ability of different parental populations hence, enabling to identify best lines, estimate additive breed, heterosis and reciprocal effects in crossbred animals (Jakubec et al 1987).The present study therefore was designed to compare the performance of the parental and crosses from indigenous chickens designated as cool (CC) and warm (WW) with, exotic broiler (BB) and Black Australop (AA) on egg production and quality under sub-humid zone of central Tanzania.

Material and methods

Study layout and management of birds

The mating plan and management of experimental birds were as described by Munisi et al (2015).

Data collection

The variables recorded included age at sexual maturity (ASM), egg weight at sexual maturity or first egg weight (FEW), average egg weight at 48 weeks of age (EWT48), egg shell thickness at 48 weeks of age (EST48), egg shape index at 48 weeks of age, number of eggs in 90 days of laying after attainment of sexual maturity (EN90) and number of eggs in180 days of laying after attainment of sexual maturity (EN180). All studied variables were recorded on individual bird basis.

Age at sexual maturity (ASM) was considered as the age at which the first egg was laid. Egg weight at sexual maturity or first egg weight (FEW) and average egg weight at 48 weeks of age (EWT48) were weighed by an electronic balance which could weigh to the nearest 0.1g. Egg shell thickness at 48 weeks of age (EST48) was recorded as the average of three readings taken from different sides of an egg shell, the equator (middle), narrow and broad end using a digital caliper. Egg shape index at 48 weeks of age (ESI48) was recorded by taking the ratio of distance across (width) to length of an egg and multiplying by 100.

Data analysis and merit component estimation

Data on egg production, egg quality traits and 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 as described by Munisi et al (2015). Means for components of merit were compared using t-test, while, least squares means for recorded traits were computed and compared between the genetic stocks.

Results and discussions

Performance of genetic stocks with respect to age at sexual maturity and egg weights

The least squares means for ASM, FEW and EWT48 are summarized by genetic stocks in Table 1.The general trend was for genetic stocks derived from a cross between broilers and indigenous chickens from warm ecological zone to have relatively lower age at sexual maturity compared to those from Black Australorp.  Likewise, among parental stocks, indigenous chickens from the warm ecological zone (WW) had much lower ASM (171 days) than indigenous chickens from cool ecological zone (188 days) followed by Black Australorp (187 days) and BB had the longest ASM (209 days).  This trend was expected since indigenous chickens from warm ecological zone (WW) was much lighter than other parental stocks and broilers were the heaviest (Munisi et al 2015). This observation is consistent with the findings of Yeasmin et al (2003), Zaman et al (2004) and Katule (1990), who reported that sexual maturity is often attained later in heavier stocks than in light birds. The ages at sexual maturity for indigenous chickens in this study were slight lower than values of 195 days reported by Katule (1992). Much lower values (155-165 days) have been observed in Nigeria indigenous chickens (Mary, 2006). This variation is largely attributed to genetic differences between indigenous chickens used in the two studies.

It is further observed that reciprocal crosses between broilers and indigenous chickens from warm areas (BW and WB) matured much earlier than crosses between Black Australorp and indigenous chicken from cool ecological zone. Other combinations were at intermediary levels. Females from BW and WB crosses were also heavier at 12 weeks (Munisi et al 2015), contradicting the fact that heavier birds tend to mature later. In this regard, the early sexual maturity was to a large extent seems to have been influenced by the indigenous birds from warm ecological zone. According to Dunnington and Siegel (1991) crossing tends to improve some measures of reproductive fitness including age at sexual maturity, which was observed among the BW and WB reciprocals.

Furthermore, values in Table 1 show greater variability among genetic stocks with respect to FEW. For the parental stocks, broiler stock (BB) had the heaviest first eggs (53.2g), followed by Black Australorp (43.4g), whilst indigenous chickens from the cool ecological zone (CC) and indigenous chickens from the warm ecological zone (WW) had the smallest eggs (39.7 and 35.5 g respectively). Among the crosses, the cross between broiler and the indigenous chickens from cool ecological zone (BC) had the heaviest eggs (44.7 g) followed by the cross between Black Australorp and broiler stock (42.8g).The pattern was similar for EWT48 whereby, the broiler stocks (BB) had the heaviest eggs at 48 weeks of age (56.3g) followed by the cross between broiler and Black Australorp (54.1g). As expected, indigenous chickens from warm ecological zone (WW) had smallest egg weight at 48 weeks of age (42.5g). Similar results were observed by Katule (1990) who reported heavier eggs from the meat breed than other breeds. The observed mean egg weight for the broiler stocks and its crossbreds in the current study falls within the range of 50 to 56g described by (FAO, 2003). Furthermore, the egg weights of 51 to 53g for broiler crossbreds have been reported by Niranjan et al (2008). Egg weights for indigenous chickens from cool ecological zone (CC) reported in the present study lie within the range of 37.4 and 49.5g reported by Katule (1998) and slightly higher than the weight of 36.8g reported in Nigerian indigenous chickens (Adedokun and Sonaiya 2001) and 42.5g for Tanzania indigenous chickens (Msoffe et al 2004).Eggs weights of Black Australorp (AA) were within values reported by Singh et al (2009) for the same breed. These differences are largely explained by the difference in body weights among genetic stocks similar to what was earlier reported by Monira et al (2003) and Bharambe and Garud (2012).

Performances of genetic stocks with respect to egg production and quality traits

The performances of different genetic stocks with regard to EST48, indicates that among the parental stocks, Black Australorp stock (AA) had thinner egg shell while indigenous chickens from the warm ecological zone (WW) had much thicker eggs shell, indigenous chickens from the cool ecological zone (CC) and broiler stock (BB) being intermediary (Table 2). Across all genetic stocks, EST48 was statistically significant. Among the crosses, the cross between indigenous chickens from the cool ecological zone and indigenous chickens from the warm ecological zone (CW) exhibited thicker egg shells value that was comparable to that of indigenous chickens from the warm ecological zone (0.34 mm). Studies have shown that shell thickness and egg production are negatively correlated (Kumar et al 1971; Singh1990 cited by Agaviezor et al 2011).  However, the similarity in egg shell thickness between the parental stocks other than Black Australorp (AA) could be explained by low level of egg outputs among the genetic groups as depicted in Table 2 at 90 days after maturity.  Across genetic groups there were significant variations in EST48. Similar observations were made by other workers (Niranjan et al 2008; Bharambe and Garud 2012).  Whilst these reports indicated variation also in egg shape index, in the current study such differences were not clear, which is consistent with report by Rajkumar et al (2009) and Ralcheva et al (2009).The broiler crossbreds (CB and WB) as well as the cross between indigenous chickens (CW) tended to produced egg with slightly higher egg shape index values, though the difference were not statistical significant.

With regard to average egg number laid in 90 days, the cross between the indigenous chickens from the warm ecological zone and broiler stocks (WB) had  more eggs than other genetic stocks (P<0.05).This result could be attributed to the large positive heterosis observed for EN90 (Table 4).The findings agree with those of Onwurah and Nodu (2006) who also reported high number of eggs for the cross between local chickens and Anak broiler stocks. Contrary to expectation, indigenous chickens from the cool ecological zone (CC) laid more eggs than broiler stocks (BB).

Despite the observed differences at 90 days, the performances of all genetic stocks were similar at 180 days post sexual maturity for egg number, although there was a tendency for slight higher egg number in the BC (28) followed by BA (27). Katule (1992) reported similarity in egg production between parental exotic and indigenous chickens as well as their crossbreds. In the current study egg numbers were generally lower than that reported for similar stocks by Lwelamira et al (2008). In Ethiopia lower egg number at 12 weeks post sexual maturity were reported between Fayoumi x Local Naked neck (29.5 eggs) and that between Rhodes Island Red x Local Netch  (29.1 eggs) (Bekele et al 2010).Similar lower values were observed between main crosses and their reciprocals when Normal local, Naked neck and frizzle chickens were crossed with exotic broiler breeder stock (Nwachukwu et al 2006). In the study conducted in Nigeria, egg number ranged from 25 to 41 at 90 days. The lower egg number in the current study compared to these two studies could in part be attributed by stress related to feeding, space and lower acclimatization of indigenous chickens or their crosses to fully confinement.

Variation in additive breed effects with respect to age at sexual maturity, egg weight, egg production and quality characters

The additive breed constant estimates show significant differences for ASM, FEW as well as EWT48 but not for EST48, ESI48, EN90 and EN180 (Table 3). Generally, positive additive breed constant estimates values were observed for all traits considered in the current study. It is also observed that the additive breed constant estimates for broiler stock were higher than other genetic stocks for ASM, FEW and EW48 only. This observation could be explained by the fact that broiler stocks have been selected for high growth rate and large live weight. According to Joseph and Moran (2005), selection for live body weight of chickens can result in increased egg size. Thus, the use of broiler stocks as one of the parental stocks in any crossing can improve egg weight since the F₁ progeny would inherit half of their genes from each of the parents. The current results however, are in contrast with the findings by Katule (1990) who did not observe additive genetic difference between breeds in egg size. This might probably be due to differences in genetic materials used in the two studies. Higher additive breed constant estimates for the broiler germplasm than other genetic stocks was expected because sexual maturity is attained later in heavier stocks than in light birds (Yeasmin et al 2003 and Zaman et al 2004).

Variation in heterosis effects with respect to age at sexual maturity, egg weight, egg production and quality characters

The constant estimates for heterosis in crosses involving parental genetic stocks are shown in Table 4. With the exception of the AC   and AW, all other crosses showed negative heterosis with respect to age at sexual maturity. The results in other words showed that crossbreds resulting from Black Australorp and indigenous chickens (AC and AW) had positive heterosis, while those indigenous chickens and broilers had negative heterosis with respect to age at sexual maturity. It is worth noting that the negative heterosis for age at sexual maturity observed for the cross between indigenous chickens and broiler (CB and WB) was in the desirable direction. With negative heterosis, it implies that the crossbreds had lower values of age at sexual maturity than the mid parents. Nonetheless, statistical difference with respect to this trait was observed only between WB and AC. In the case of FEW negative heterosis was evident for all crosses indicating that this trait was less influenced by dominance effects. Nonetheless, positive heterosis was revealed in the WB crosses for ESI48, EN90 and EN180 and AW for EWT48. These observations are in agreement with dominance and overdominance theories. According to the theories, crossbred animals are expected to supercede at least the mid-parent due to the fact that they will be much more buffered against unfavorable conditions than one or both of their parents (Falconer 1960 and Sheridan 1982 cited by Katule 1990).In this regard, the cross between indigenous chickens from the cool ecological zone and broiler (CB) as well as indigenous chickens from the warm ecological zone and broilers (WB) seem to be advantageous in EN90 and EN180. The observed results are in agreement with those of Katule (1990) who observed positive heterosis in EN90 for the cross between meat type breed and indigenous chickens. Similarly, Waleed and Sajida (2011) observed positive heterosis for egg number at 100 days for the cross between Iraq local line (Brown line) and Exotic breed (New Hampshire). Furthermore, the findings are also in accordance with those of Saadey et al (2008) who obtained positive heterosis in egg number at 105 days for the cross between Sinai (Egyptian local chickens) and Rhode Island Red as well as in the cross between Sinai and White leghorn chickens. Positive heterosis for the cross between Black Australorp and indigenous chickens from warm ecological zone (AW) in EWT48 in the current study was in agreement with the findings of Katule (1990) who observed positive heterosis in egg weight for the cross between egg type and indigenous chickens. However, the results of current study are in contrast with negative heterosis observed by Waleed and Sajida (2011) for the cross between White leghorn and Iraq local chickens in egg weight.

Variation in reciprocal effects with respect to age at sexual maturity, egg weight, egg production and egg quality characters

The constant estimates for reciprocal effects of genetic stocks are shown in Table 5. It should be noted that the negative or positive sign associated with a constant estimate is merely the consequence of coding procedure applied to isolate these effects whereby the contribution of reciprocal effects from the dam was coded -1 and that from sire +1. Generally, the position of a breed in a particular cross influences the performance of resulting progenies for a trait under consideration. The crosses which had negative signs indicated that higher performance for a particular trait could be reached if the first listed breed could be on the dam side. The crosses with positive signs gave an indication that higher performance could be obtained for a particular trait if the first listed breed in the resultant cross could be used as sire parent.

From the current results, significant difference was observed between Black Australorp and indigenous chickens from the cool ecological zone (AC) and indigenous chickens from the cool ecological zone and Black Australorp (CA) reciprocal crosses for FEW. The positive constant estimates observed in FEW for AC indicate that higher performance in first egg weight could be obtained if the indigenous chickens from the cool ecological zone are used as dam parent and Black Australorp as sire parent. This is supported by the results in Table 1which reveal that AC had relatively heavier first eggs than its reciprocals (CA). The findings corroborates with those Sola-Ojo (2011) who observed reciprocal effects in egg weight for the cross between exotic egg type strain Dominant Black (DB) and Fulani Ecotype chickens. Likewise, there was a significant difference between AB (The cross between Black Australorp and broiler) and its reciprocal BA (The cross between broiler and Black Australorp) for EST48with positive constant estimates implying that thicker eggs shell could be obtained if Black Australorp is used as sires and broilers as dams. Results in Table 2 confirm this observation whereby the cross between Black Australorp and broiler stock (AB) had eggs with thicker shells than the eggs of the cross between broiler and Black Australorp (BA). Reciprocal effects in egg shell thickness were reported for the cross between Delham Red and Giriraja chickens (Bharambe and Garud 2012). Although  the cross between Black Australorp and broiler stock (AB) and its reciprocal (BA) did not differ significantly in EWT48 EN90 and EN180, the  negative constant estimates for  these traits denote  that higher performance  for these traits could be obtained when Black Australorp are used as dams and broilers as sires. Likewise, reciprocals involving indigenous chickens, gave a negative constant estimates in the cross between indigenous chickens from the cool ecological zone and broiler (CB) for EN90 and EN180 which signify the potentials for indigenous chickens from cool ecological zone (CC) as dams and broiler as sires. This is confirmed by higher number of eggs for the cross between broiler and indigenous chickens from the cool ecological zone (BC) than its reciprocal CB (Table 2).

Conclusions

• Genetic stocks derived from the cross between broiler and indigenous chickens from the warm ecological zone had relatively lower age at sexual maturity compared to those from Black Australorp.

  
  

• All crosses involving broilers showed better performance in egg weights at 48 weeks of age than other crossbreds.

  
  

• Crossing indigenous chickens from warm ecological zone and broiler produced crossbred (WB) with better performance than other genetic stocks in egg production at 90 days after attaining sexual maturity.

  
  

• Broiler stocks showed higher additive breed constant estimates than other parental stocks.

  
  

• Crossing broiler with either indigenous chickens from the cool ecological zone or indigenous chickens from the warm ecological zone exhibited positive heterosis in EN90 and EN180 days after attaining sexual maturity.

  
  

• Reciprocal effects were observed in EST48 and FEW for the cross between broiler and Black Australorp stocks as well as the cross between Black Australorp and indigenous chickens from the cool ecological zone respectively.

  
  

• Thus the use of broiler as sires and indigenous chickens or Black Australorp as dams could produce crossbreds with better performance in FEW, EWT48 and EN180 while the use of broiler as dams and indigenous chickens from the warm ecological zone as sires could favor EN90.

Acknowledgements

The authors acknowledge the Commission of Science and Technology (COSTECH) for the financial support and National Livestock Research Institute (TALIRI-Mpwapwa) for providing infrastructures.

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Received 16 April 2015; Accepted 9 May 2015; Published 1 August 2015

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