The influence of genotype on the growth performance parameters that were studied are presented in Table 2.
Table 2
Effect of genotype on growth performance of broilers (4–8 weeks of age)
Trait/parameter
|
Cobb
|
Ross
|
SEM
|
p-value
|
Initial weight (g)
|
609.90
|
622.30
|
14.21
|
0.39
|
Final weight (g)
|
2674
|
2757
|
50.80
|
0.13
|
Weight gain (g)
|
2065
|
2135
|
49.40
|
0.18
|
Growth rate (g/day)
|
58.99
|
61.02
|
1.40
|
0.17
|
Total feed intake (g)
|
5711
|
5687
|
142.40
|
0.87
|
FCR/bird
|
2.77
|
2.68
|
0.04
|
0.07
|
Total water intake (g)
|
11186
|
10657
|
463.30
|
0.28
|
From Table 2, all growth performance parameters (final weight, weight gain, growth rate, FCR, feed intake and water intake) evaluated did not reveal any significant differences (p > 0.05) between the two genotypes, and this might be due to the fact that the two breeds have comparable genetic potential; as such any one of Cobb and Ross genotypes can serve as a farmer’s preference. The results of growth performance traits assessed in this study contradicted the findings of Sterling et al. (2006) who observed significant difference in body weight gain, feed intake and feed conversion ratio of Cobb and Ross 308 birds, with the former breed recording better performance than the latter. Similarly, Hristakieva et al. (2014) reported that Соbb 500 broiler genotypes attained a higher live weight, and were heavier than Ross 308 genotypes by about 6.29% at 49 days of age (7 weeks). Results from the current study also disagreed with those of Mmereole and Udeh (2009) who found that the local chicken cross with the Barred Plymouth Rock (G3) and Barred Plymouth Rock (G4) were significantly (p < 0.01) heavier than the local chicken (G1) and the Barred Plymouth Rock by local chicken (G2) groups, at the 1st, 4th and 8th weeks of age, respectively. Mmereole and Udeh (2009) concluded that the G4 and G3 genotypes had superior genetic potential for body weight gain than the G1 and G2 genotypes. The results of the current study again contradicted the findings of Olawumi et al. (2012) who reported that both sexes of Marshal Broilers recorded the highest live weight at 56 days of age (8 weeks) when compared with Arbor Acre and Hubbard chickens, and described the former (Marshal) as having superior genetic potential for meat yield than the latter.
The effect of dietary treatments on growth performance of Cobb and Ross broiler chickens in this study is presented in the Table 3.
Table 3
Dietary treatment effect on growth performance parameters of broiler chickens (4–8 weeks of age)
Parameter
|
0%
PKOR
|
10%
PKOR
|
20%
PKOR
|
SED
|
p-value
|
Initial weight (g)/bird
|
612.60
|
616.40
|
618.90
|
17.40
|
0.935
|
Final weight (g)/bird
|
2849a
|
2654b
|
2644b
|
62.30
|
0.010
|
Weight gain (g)/bird
|
2236a
|
2037b
|
2025b
|
60.50
|
0.007
|
Growth rate (g/day)/bird
|
65.13a
|
59.93b
|
58.00b
|
1.72
|
0.007
|
Total feed intake (g)/bird
|
5984a
|
5698ab
|
5416b
|
174.4
|
0.022
|
FCR/bird
|
2.68a
|
2.80b
|
2.68a
|
0.04
|
0.022
|
Total water intake (g)/bird
|
11715a
|
10862ab
|
10186b
|
567.4
|
0.040
|
Feeding cost (GH¢)/bird/5wks
|
5.82
|
4.97
|
4.76
|
-
|
-
|
Feeding cost/kg weight gain in GH¢
|
15.60
|
13.92
|
12.76
|
-
|
-
|
Savings on feed cost (GH¢)/kg weight gain/bird
|
0.00
|
1.68
|
2.82
|
-
|
-
|
Means in a row with same letter superscripts are not significantly different (p > 0.05)
|
Birds on 0% PKOR had significantly (p < 0.05) higher final live weight, weight gain and growth rate than birds on diets with 10% and 20% PKOR (Table 3); indicating that these traits were negatively related to the levels of PKOR. The trend may be attributed to lower nutrient digestibility as PKOR levels increased. This explanation is supported by Sundu and Dingle (2003) who reported that heating agro-industrial by-products at high temperatures during processing may cause feed products such as PKC (and its variants, PKM and PKOR) to undergo Maillard reaction (the reaction of reducing sugar with amino groups leading to the formation of a characteristic brown complex); a high level of heat is applied before and during oil extraction which may adversely affect nutrient digestibility. Confirming this explanation, McDonald et al. (2002) reported that Maillard reaction occurring as a result of prolonged heating of feed products leads to formation of complex linkages within and between peptide chains, some of which are resistant to hydrolysis by proteases enzyme, thereby reducing the solubility, digestibility and utilisability of proteins in such feed products. Another feed factor which might have contributed to the lower live weight and correlated traits in birds on the 20% compared with the 0% PKOR ration is the higher fibre content in the former, a trait which is known to reduce digestibility of feeds (McDonald et al. 2002). The results obtained in this study are also in agreement with those of Ojewola and Ozuo (2006) who reported that birds fed diets containing 10%, 15% and 20% of PKC, instead of soybean meal, had depressed body weight compared with the control (0% PKC).
Furthermore, Soltan (2009) as well as Ezieshi and Olomu (2008) indicated that feeding PKM (mechanically extracted) depressed broiler chick weights, while PKM types (solvent extracted) highly depressed final body weight of broiler birds. In contrast with these, Okeudo et al. (2006) reported that average body weight of broilers was approximately 2 kg in each dietary group at the 8th week of age, and was not significantly affected by inclusion of PKC up to levels of 30% in the diets. Egenuka et al. (2013) who studied the effect of different dietary levels (0%, 20% and 40%) of PKC on the growth of chickens indicated that there were significant (p < 0.05) increases in the final live weight of the growers with increase in the level of palm kernel cake included in the rations. These differences in the findings reported from feeding trials using PKOR and PKC/PKM may be related to the different levels of fibre in the rations fed and the varying degrees of Maillard reaction that had occurred in these products used. It is known for example that all reactions up to the formation of Amadori compounds at the initial stage of Maillard reactions, are reversible, to release amino acids for utilisation (van Rooijen et al. 2013; Lund and Ray 2017). It is advisable for agro-processing industries that produce PKC/PKM/PKOR used as feed to reduce the amount and duration of heat applied during processing in order to minimize the degree of Maillard reaction that occurs in the by-products. Also, farmers and feed manufacturing companies may use PKOR/PKC/PKM in combination with feedstuffs high in essential amino acids, or incorporate industrially manufactured amino acids such as lysine (the main essential amino acid most affected by Maillard reaction), and/or enzymes to improve the overall utilisation of heat treated agro-industrial by-products.
Birds on rations with 20% PKOR consumed significantly (p < 0.05) lower amount of feed than birds on 0% PKOR rations; intakes on 20% rations were not different however from those on 10% PKOR rations (Table 3). The lower feed intake by birds on rations with 20% PKOR compared with those on 0% PKOR, may be due to the higher energy content in the 20% PKOR (Table 1); birds will generally consume feed at levels to meet their energy requirements (McDonald et al. 2002). Thus, the higher the amount of energy in the feed, the lower the amount of feed needed to meet the energy requirements, and vice versa. The lower feed intake observed with increasing levels of PKOR agree with work by Soltan (2009) and Onuh et al. (2010) who worked with palm kernel cake in diets for broiler chickens.
Feed conversion ratio (FCR) of birds on rations with 0% and 20% PKOR (Table 3) were significantly lower (p < 0.05) than for birds on 10% PKOR; implying that the ration without PKOR and ration with 20% PKOR had similar and better utilisation levels than on 10% PKOR. Feed conversion ratio (FCR) is a measure of the animal’s efficiency in converting feed mass into body mass. Some feed factors that influence utilisation are digestibility and nutrient or energy content. The better utilisation of the ration without the PKOR and the ration with the 20% PKOR may have resulted from combined effects of higher digestibility, higher nutrient absorption and higher energy content; this may be so, even though the ration with 20% PKOR might have had a lower digestibility. In effect, the higher energy content of the ration with 20% PKOR might compensate for any nutrient losses to chickens due to lower digestibility, giving it a favourable feed conversion ratio. The FCR results from this study agree with those from Egenuka et al. (2013) who reported no significant differences in FCR of broilers fed 0% PKC and 40% PKC diets. This work however, conflicts with the report of Okeudo et al. (2006) who observed that broilers fed 0% PKC diet had significantly lower FCR than those fed 45% PKC diet.
Comparing the results of the ration with 0% PKOR with that of the 10% PKOR in the current study, the higher FCR of the latter may be attributed to poorer digestibility and lower nutrient utilisation relative to the former. However, comparing the FCR of the 10% and 20% rations, the higher value for the former could be due to its lower energy content relative to the latter; though both may have similar lower digestibility. Consequently, in spite of the apparent poorer digestibility of the 20% PKOR ration, its higher energy content might have compensated for nutrient losses, resulting in better feed conversion ability. Farmers may be able to reduce feed intake and therefore feeding cost with 20% PKOR inclusion in rations, and yet still achieve good feed conversion ratios.
The important economic motivation for the use of PKOR in poultry rations is its potential to minimize feed cost when it replaces a conventional feed ingredient of relatively higher price. The results from this study revealed that the inclusion of PKOR at 10% and 20% (with PKOR directly replacing wheat bran) led to a reduction in feeding cost/kg weight gain of GH¢1.68 and GH¢2.84 respectively; this confirmed work by Odoi et al. (2007) who also reported significant reduction in feed cost when up to 15% of PKOR were fed to broiler finisher chickens. These reductions in feed cost per kilogram weight gain translates into potentially huge savings and therefore increased profit margins. The results are also similar to those of Ezieshi and Olomu (2008) and Egenuka et al. (2013), who reported significant reductions in feed cost per weight gain with increasing PKC inclusion rates. The results of this work suggest that farmers can make substantial savings on feed costs, which translates into increased profit margins, when they replace wheat bran with PKOR up to 20% rate in broiler finisher rations.
The effect of genotype x ration interaction on some growth parameters is presented in Table 4
Table 4
Effect of genotype x ration interaction on growth parameters in broiler chickens
Traits
|
Breeds
|
SED
|
P-value
|
Cobb
|
Ross
|
Rations
|
0% PKOR
|
10% PKOR
|
20% PKOR
|
0% PKOR
|
10% PKOR
|
20% PKOR
|
Initial weight (g)/bird
|
590.00
|
628.50
|
610.40
|
635.1
|
604.40
|
627.40
|
24.61
|
0.18
|
Final weight (g)/bird
|
2783
|
2607
|
2633
|
2915
|
2701
|
2656
|
88.00
|
0.68
|
Total weight gain (g)/bird
|
2193
|
1978
|
2022
|
2280
|
2096
|
2028
|
85.60
|
0.64
|
Growth rate (g/day)/bird
|
62.68
|
56.51
|
57.77
|
65.13
|
59.93
|
58.00
|
0.02
|
0.65
|
Total feed intake (g)/bird
|
5948
|
5700
|
5484
|
6019
|
5695
|
5348
|
246.60
|
0.84
|
Total water intake (g)/bird
|
11683
|
11082
|
10792
|
11747
|
10643
|
9580
|
802.40
|
0.54
|
FCR
|
2.71
|
2.88
|
2.71
|
2.64
|
2.71
|
2.64
|
0.06
|
0.49
|
There were no significant (p > 0.05) genotype x ration (environment) interaction effects on growth parameters studied in broilers. This work implied that there were no joint effects of breed and ration on birds’ performance; that is, the two factors acted autonomously of each other as explained by Olawumi et al. (2012). The results of the current investigation are also in consonance with work by Mmereole and Udeh (2009) who reported no significant genotype by diet interactions on body weight and weight gain of the Nigerian local chicken, and its crosses with the Barred Plymouth Rock. The absence of genotype x ration interactions in the present study indicates that the nutritional environment of birds on the three rations (0%, 10% and 20% PKOR) similarly favoured gene expression and regulation of traits. Hence, the two genotypes could be said not to have differed in ranking. The implication is that farmers may keep any of the two genotypes, on any of the three rations fed, without any detrimental effect on growth performance or production; this is provided that nutritional composition of diets fed are adequate to meet requirements of broiler birds in that category.
The influence of genotype on the carcass parameters that were studied are presented in Table 5.
Table 5
Effect of genotype on carcass traits of broilers
Parameter
|
Cobb
|
Ross
|
SED
|
p-value
|
Live weight (g)
Warm carcass weight (g)
|
2674
2070
|
2757
2126
|
50.80
56.20
|
0.13
0.34
|
Warm dressing percentage (%)
|
77.41
|
77.11
|
1.04
|
0.70
|
Chilled carcass weight (g)
|
2010
|
2074
|
57.60
|
0.34
|
Chilled dressing percentage (%)
|
76.98
|
76.85
|
1.04
|
0.67
|
Weight of cut parts (g)
|
|
|
|
|
Breast (g)
|
643.00
|
710.00
|
34.80
|
0.14
|
Thigh (g)
|
321.90
|
322.30
|
14.87
|
0.66
|
Drumstick (g)
|
282.50
|
278.70
|
12.95
|
0.66
|
Back (g)
|
519.00
|
516.00
|
27.80
|
0.51
|
Wing (g)
|
243.60
|
249.40
|
15.25
|
0.83
|
Weight of organs (g)
|
|
|
|
|
Heart (g)
|
11.92
|
12.41
|
0.309
|
0.14
|
Liver (g)
|
55.60
|
56.10
|
3.73
|
0.89
|
Kidney (g)
|
13.94
|
15.02
|
0.62
|
0.11
|
Spleen (g)
|
1.96
|
2.05
|
0.21
|
0.15
|
Gizzard (g)
|
56.19
|
59.55
|
1.48
|
0.09
|
Abdominal fat pad (g)
|
18.45
|
18.79
|
0.24
|
0.18
|
SED: standard error of difference of means
|
The carcass weights, dressing percentages, weights of primal cuts, weights of viscera organs and abdominal fat pad did not vary significantly (p > 0.05) between Cobb and Ross genotypes (Table 5). This implies that the two genotypes had similar genetic potential for carcass yield. The productive performance of three commercial broiler genotypes (Marshall, Arbor Acres and Hubbard) reared in the savannah zone of Nigeria was assessed by Olawumi and Fagbuaro (2011) and in contrast to the results of this study reported that, as regards the carcass traits, Marshall genotype had superior (p < 0.05) and higher mean values in dressing out weight, eviscerated weight, carcass weight, carcass percentage, breast muscle weight, back muscle weight, thigh muscle weight, drumstick weight, neck weight and wing weight when compared with Arbor Acres and Hubbard, supporting Musa et al. (2006) and Ojedapo et al. (2008) who also reported significant effect of breed in all the carcass traits evaluated including abdominal fat weight.
However, the three genotypes studied by Olawumi and Fagbuaro (2011) recorded similar values in dressing out percentage and abdominal fat, similar to the findings of the present study. Moreover, there was no significant difference between the Arbor Acres and Hubbard genotypes for the carcass traits evaluated, indicating that these two genotypes probably shared common genetic composition (Olawumi and Fagbuaro 2011), which is in consonance with the outcome of the current study. The weight of visceral organs were also similar for both Cobb and Ross genotypes in this study which agrees with the report of Olawumi and Fagbuaro (2011) but contrary to the result of Taha et al. (2010) who reported significant effect of breed on these traits. The non-significant difference in the weight of visceral organs in the present study indicates that Cobb and Ross broiler genotypes shared comparable genetic composition in respect of these organs and hence had similar organ functions. Consequently, farmers can choose to buy either Cobb or Ross and raise them for the market as whole carcass or cut carcass parts.
The effect of dietary treatments on carcass performance of Cobb and Ross broiler chickens in this study is presented in Table 6.
Table 6
Effect of ration on carcass parameters of broiler chickens
Trait/parameter
|
0% PKOR
|
10% PKOR
|
20% PKOR
|
SED
|
P-Value
|
Feed cost/kg gain in GH¢
Savings on feed cost in GH¢
Live weight (g)
Warm carcass weight (g)
|
15.60
0.00
2894a
2254a
|
13.92
1.68
2654b
2027b
|
12.76
2.84
2644b
2012b
|
62.30
68.8
|
0.010
0.007
|
Warm dressing percentage (%)
|
79.14a
|
76.38b
|
75.99b
|
1.27
|
0.040
|
Chilled carcass weight (g)
|
2130
|
1994
|
1989
|
70.50
|
0.072
|
Chilled dressing percentage (%)
|
77.73
|
75.62
|
75.48
|
1.28
|
0.184
|
Weights of cut parts (g)
|
|
|
|
|
|
Breast (g)
|
716.80
|
683.20
|
667.90
|
42.60
|
0.121
|
Thigh (g)
|
327.60
|
306.50
|
318.70
|
18.22
|
0.289
|
Drumstick (g)
|
285.50
|
269.3
|
279.90
|
15.86
|
0.290
|
Back (g)
|
553.20
|
497.50
|
475.30
|
38.10
|
0.060
|
Wing (g)
|
246.90
|
227.50
|
247.20
|
26.41
|
0.609
|
Weight of organs (g)
|
|
|
|
|
|
Heart (g)
|
12.02
|
12.37
|
12.10
|
0.38
|
0.639
|
Liver (g)
|
53.80
|
58.30
|
55.60
|
4.56
|
0.626
|
Kidney (g)
|
14.35
|
14.24
|
14.84
|
0.76
|
0.708
|
Spleen (g)
|
1.81
|
1.96
|
1.90
|
0.25
|
0.851
|
Gizzard (g)
|
59.63
|
57.24
|
57.71
|
1.81
|
0.403
|
Abdominal fat pad (g)
|
18.38
|
18.66
|
18.82
|
0.29
|
0.341
|
Means in a row with same letter superscripts are not significantly different (p > 0.05)
|
From Table 6, birds on 0% PKOR recorded significantly (p < 0.05) higher warm carcass weight than birds fed rations with 10% and 20% PKOR. The warm dressing percentage of birds on 10% and 20% PKOR ration was significantly lower (p < 0.05) than those on 0% PKOR ration. The differences could be attributed to the fact that birds on the 0% PKOR ration had significantly higher weight gain than those on the 10% and 20%; implying that body weight gain and warm carcass traits are correlated. The warm dressing percentage measures the yield of the body muscle of the chicken, made ready to be cooked or frozen. The values obtained were 79.14%, 76.38% and 75.99% for the 0%, 10% and 20% PKOR rations respectively. These values are slightly above reported average of 70–75% (Lessler et al. 2007), due possibly to the fact that more of the nutrients derived from the rations fed to the broilers were used to synthesize muscles rather than to develop such unwanted parts as feathers, offal and viscera. The significant reduction in the dressing percentage with increasing level of PKOR observed in this study disagrees with work of Soltan (2009) who revealed that PKC dietary inclusion at different levels had no effect on dressing percentage when compared with the control, similar to what has been reported by Shakila et al. (2012). Though the warm carcass weight and warm dressing percentage of the 0% were significantly higher (p < 0.05) than the 10% and 20% PKOR rations in the current study, the values obtained for the PKOR-based diets were slightly above reported values of 70–75%; implying that PKOR inclusion up 20% in broiler finisher ration supports good carcass traits. Hence, farmers who wish to slaughter and sell their broilers on warm carcass weight can make considerable financial gains by using up to 20% of PKOR in their broiler finisher ration.
The chilled carcass weight and chilled dressing percentage were similar for all the treatment groups even though the trend in values for the control ration was numerically higher than the rations with the PKOR. Fresh meat is approximately 70 to 75percent water, making carcasses very susceptible to evaporative cooling loss in the first 24 hours of chilling, with the losses ranging from 3 to 5 percent of the hot carcass weight (Rentfrow 2010). Carcasses with moderate fat cover will have good water-holding capacity and less liable to cooler shrink. Knowing the effect of chilling on the carcass is necessary to avoid misunderstandings between meat processors and consumers, in terms of the price difference between warm and chilled carcasses or the possible reduction in weight of paid hot carcass which has to be chilled by the processor and later collected by the consumer/buyer. From Table 6 the warm carcass weight of the control ration lost about 5.5% weight after chilling for 24 hours whereas the 10% and 20% lost 1.63% and 1.14% weight respectively within the same chilling period; indicating that the carcass of birds fed PKOR rations was more resistant to evaporative cooling losses due probably to moderate intramuscular fat content of the meat. Consequently, farmers and companies who wish to process live birds and add value to the meat by chilling and selling chilled broiler meat would find PKOR inclusion in the broiler rations profitable.
The weight of visceral organs (heart, liver, spleen, kidney and gizzard) did not vary significantly (p > 0.05) across the dietary treatments; neither did the values indicate any particular trend. PKOR is high in oil; and oxidized oil raises the levels of aldehyde and other oxidized metabolites (Sottero et al. 2019). According to earlier work by Fellenberg and Speisky (2006), the accumulation of oxidative products may lead to increased weight of visceral organs, an indication of abnormality. However, none of the organs showed signs of abnormality in the present study as weight of organs were similar for all the dietary groups. The results are consistent with that of Chinajariyawong and Muangkeow (2011) who reported no significant difference in the relative weights of visceral organs of broiler chickens when fed palm kernel meal in rations up to 40%. Subsequently, feeding PKOR in broiler rations up to 20% will not cause organ abnormality and malfunction.
The results of this study showed that the inclusion of PKOR at 10% and 20% (with PKOR directly replacing wheat bran) led to a reduction in feeding cost/kg weight gain of GH¢1.68 and GH¢2.84 respectively, confirming work by Odoi et al. (2007) who also reported significant reduction in feed cost when up to 15% of PKOR were fed to broiler finisher chickens. The reductions in ration costs were due to the fact that PKOR, a low-cost feed ingredient replaced wheat bran, a conventional feed ingredient of relatively higher price. These reductions in ration cost per kilogram weight gain translate into huge savings and increased profit margin.
Influence of Genotype × Ration Interaction on Carcass Traits of Broilers
The effect of genotype x ration interaction on carcass parameters is presented in Table 7.
Table 7
Effect of genotype x ration interaction on carcass traits in broiler chickens
Traits
|
Breeds
|
SED
|
P-value
|
Cobb
|
Ross
|
Rations
|
0% PKOR
|
10% PKOR
|
20% PKOR
|
0% PKOR
|
10% PKOR
|
20% PKOR
|
Live weight (g)
Warm carcass weight (g)
|
2783
2213
|
2607
1981
|
2633
2015
|
2915
2294
|
2701
2073
|
2656
2009
|
88.00
97.30
|
0.68
0.74
|
Warm dressing percentage (%)
|
79.57
|
76.02
|
76.54
|
78.71
|
76.75
|
75.64
|
1.80
|
0.74
|
Chilled weight (g)
|
2121
|
1960
|
1983
|
2200
|
2045
|
1979
|
99.70
|
0.77
|
Chilled dressing percentage (%)
|
76.21
|
75.18
|
75.31
|
75.47
|
75.71
|
74.51
|
0.02
|
0.78
|
Breast weight (g)
|
735.30
|
653.80
|
688.30
|
742.20
|
637.60
|
661.50
|
28.15
|
0.88
|
Thigh weight (g)
|
319.70
|
310.80
|
307.30
|
343.50
|
336.20
|
311.90
|
25.76
|
0.52
|
Drumstick weight (g)
|
279.40
|
271.80
|
268.20
|
301.60
|
300.90
|
273.40
|
22.40
|
0.52
|
Back weight (g)
|
553.00
|
488.00
|
486.00
|
560.20
|
496.00
|
490.80
|
25.20
|
0.80
|
Wing weight (g)
|
233.60
|
235.60
|
233.70
|
252.80
|
274.30
|
242.40
|
26.41
|
0.54
|
Abdominal fat weight (g)
|
18.13
|
18.59
|
18.63
|
18.63
|
18.73
|
19.01
|
0.42
|
0.83
|
There was no significant (p > 0.05) genotype x ration interaction effect on carcass parameters in broilers (Table 7). The results of this work implied that there was absence of joint effect of breed and ration on birds’ carcass performance; that is, the two factors acted independently of each other as explained by Olawumi et al. (2012). The results of the current work contradicts the study by Toledo et al. (2004) who reported significant genotype × diet interaction effect on some carcass traits such as breast yield. The absence of genotype x ration interaction in the present study indicates that the nutritional environment of the three rations (0%, 10% and 20% PKOR) similarly favoured gene expression and regulation of carcass traits. Hence, the two genotypes did not differ in ranking. The implication is that farmers can raise any of the two genotypes on any of the three rations without detrimental effect on carcass yield; provided nutritional composition of rations fed are adequate for requirements of birds in that group.