MATERIALS AND METHODS

This study was conducted at the University of Limpopo Animal Unit, South Africa. The mean temperatures in winter range between 10.1 and 28.4°C and in summer between 18 and 36°C. The mean annual rainfall ranges from 446.8-468.4 mm. A total of 40 chickens were used in a complete randomized design having two treatments (Broiler and indigenous Venda chickens) with each breed replicated five times. The chickens were both raised under the same management system and fed a commercial starter mash from day-old until 35 days old, grower mash from Day 36 until Day 70, before commencement of the experiment. Feed and water were supplied ad libitum. At the age of 70 days the chickens from both breeds were killed by cervical dislocation according to the standard and ethic recommendations of the University of Limpopo.

Data collection: On Day 70, all the chickens were fasted for 24 h and weighed individually, killed and the feathers were removed manually. The average weight at slaughter of the Ross 308 broiler and indigenous Venda chickens were 1485.4±4 and 1269.8±5 g, respectively. The GIT lengths were measured using a five metre WEBCO tape measure. The individual parts were separated; the length and weights were taken using a power tape and RADWAG digital scale (model PS 750/C/2), respectively. The pH of the separate parts of the gastrointestinal tracts were measured after slaughtering using a pH meter by inserting a glass electrode directly in the opening made in the organs with digesta.

Statistical analysis: Data on weight, length and pH of the GIT of both the Ross 308 broiler and Venda chickens were analyzed using the General Linear Model (GML) procedure of the statistical analysis of variance (SAS, 2008). A T-test was used to test the significance of difference between treatment means (p<0.05) (SAS, 2008). Differences were considered significant at p<0.05.

RESULTS

The results of the comparison between live weight and internal organ weights of Ross 308 broiler and indigenous Venda chickens fed the same diet are presented in Table 1. The live weight was significantly higher (p<0.05) in broiler chickens compared to indigenous Venda chickens. Indigenous chicken crop, gizzard and large intestines were heavier (p<0.05) than those of Ross 308 broiler chickens. There were no differences (p>0.05) between proventriculus, small intestine and caecum weights of Ross 308 broiler and indigenous Venda chickens fed the same diet.

Ross 308 broiler chickens had longer (p<0.05) GIT than the indigenous Venda chickens (Table 2). Indigenous Venda chickens had shorter (p<0.05) small intestines than Ross 308 broiler chickens.

Table 1:	Comparison between live weight (g) and internal organ weight (g) of broiler and indigenous chickens fed the same diet
*Significant (p<0.05)

Table 2:	Comparison between internal organ length (cm) of broiler and indigenous chickens fed the same diet
*Significant (p<0.05), GIT: Gastrointestinal tract

Table 3:	Comparison between digestive organ pH of broiler and indigenous chickens fed the same diet
*Significant (p<0.05)

Ross 308 broiler and indigenous Venda chickens had similar (p>0.05) large intestine and caeca lengths. The small intestine segments (duodenum, jejunum and ileum) were longer (p<0.05) in broiler chickens than in indigenous chickens (Table 2).

The results on the comparison of the pH of digestive organs of Ross 308 broiler and indigenous Venda chickens are presented in Table 3. The pH of the crop, gizzard and the small intestine were lower (p<0.05) in indigenous Venda chickens than in Ross 308 broiler chickens. Ross 308 broiler chickens and indigenous Venda chickens had similar (p>0.05) pH values of the proventriculus, large intestine and the caecum.

DISCUSSION

In the present study there were significant differences in live weights between the two breeds, with Ross 308 broiler chickens having higher weights compared to indigenous Venda chickens. This result was expected as broiler chickens are known to be fast growing breeds as compared to the indigenous chickens (Musa et al., 2006; Kamali et al., 2007; Nguyen et al., 2010). Gizzard weights of broiler and indigenous Venda chickens were 38.42 and 55.81 g, respectively. Thus, indigenous Venda chickens had heavier gizzard weights than those of Ross 308 broiler chickens. These findings are supported by Jamroz (2005) who observed that gizzard weights of broiler chickens were lower than those of slow growing strains of chickens. Similarly, Taha et al. (2011) reported differences in gizzard weights of five different strains of chickens. However, Olawumi and Fagbuaro (2011) reported similar gizzard weights in different strains of chickens. Larger gizzards are more efficient in grinding feed particles of various sizes into smaller particles (Musa et al., 2006; Taylor and Jones, 2004). It is possible that indigenous Venda chickens have adapted through breeding to have larger gizzards due to high fibrous feeds they depend on. In the present study, crop and large intestine weights of 54.80 and 3.41 g, respectively, of indigenous Venda chickens were higher than 9.47 and 3.09 g, respectively, of broiler chickens. No work was found on the comparison of the weights of crop and large intestines between broiler and indigenous chickens. Taylor and Jones (2004) reported a link between the enlargement of the gizzard and a decline in the small intestine weight. The current study recorded that proventriculus, small intestine and ceca weights of broiler and indigenous Venda chickens were similar.

The results of the present study show that the gastrointestinal tract (GIT) and small intestine lengths of 182.4 and 163.1 cm, respectively, in broiler chickens, were longer than 132.0 and 128.0 cm, respectively, of indigenous Venda chickens. These findings are supported by Jamroz (2005) who reported that GIT of broiler chickens were longer compared to other slow growing chicken breeds. Contrary to the current findings, Khalid et al. (2010) reported that the GITs of the Malaysian village fowls were longer than those of broiler chickens. However, a study conducted by Dror et al. (1977) who compared light breeds and heavy breeds reported no differences between breeds in the lengths of the GIT and small intestine. In the present study, the three segments of the small intestines (duodenum, jejunum and the ileum) were longer in broiler chickens than in Venda chickens. Dror et al. (1977) reported that duodenum and jejunum were longer and heavier in lighter chicken breeds compared to heavy ones. However, in their study heavy chicken breeds had a longer and heavier ileum. GIT develops faster and early in broiler chickens compared to slow growing indigenous chickens. Yamauchi and Isshiki (1991) found that broiler chickens which are bred for rapid growth have a higher rate of small intestine development. Longer intestines are assumed to digest feed efficiently and provide a greater surface area for nutrient absorption. The increase in small intestine weight allows broiler chickens to reach a heavier body weight faster compared to indigenous chickens (Jamroz, 2005).

In the present study, the crop pH level of 4.896 in Venda chickens was more acidic compared to 6.084 of the broiler chickens. These findings are in agreement with the work reported by Hinton et al. (2000) that the pH values or levels in the crops of broiler chickens were not acidic. However, there was no literature available on the comparison of crop pH values of broiler and indigenous Venda chickens. The current study showed that gizzard pH values of broiler and indigenous Venda chickens were 3.470 and 2.970, respectively. Thus, indigenous Venda chickens had lower (acidic) gizzard pH values compared to broiler chickens. This might be the reason why indigenous chickens tend to digest fibre better than broiler chickens. According to Hetland et al. (2005) coarse feed particles, such as those provided by the fibrous feeds, remain longer in the upper part of the GIT. This stimulates gizzard activities, and hence increases the production of hydrochloric acid and refluxes between the proventriculus and gizzard (Duke, 1986; Hetland et al., 2005). A low gizzard pH improves pepsin activity and nitrogen retention and increases the solubility of the mineral fraction of the feed (Guinotte et al., 1995), which in turn might favour its absorption. The small intestine pH of 6.430 was higher in broiler chickens than 6.030 observed in Venda chickens. Nir et al. (1993) and Engberg et al. (2002) reported a negative relationship between gizzard pH and small intestine pH. Thus, a reduction in gizzard pH resulted in an increase in small intestinal pH.

CONCLUSION

It is concluded that differences exist in the body weight, GIT and pH values between the indigenous Venda and broiler chickens. The lower pH values and the larger crops and gizzards observed in the indigenous chickens might be the reasons why this breed has the ability to digest fibrous feed better than the broiler chickens.