Abstract
A study was carried out to determine the efficiency of soybean oil meal replacement with increasing amount of peas (from 10% to 40%) in the diets for turkeys on anatomic carcass dissection and chemical indicators of breast, shoulder, thigh and shin muscles, physical indicators of breast muscles and the content of tryptophan and oxyprolin. The anatomic dissection of carcasses indicated that male turkeys fed peas had from 0.28% to 0.61% (P > 0.05–P < 0.05) less shoulder muscles, whereas female turkeys of the same groups had from 0.09 to 0.31% (P > 0.05–P < 0.05) more abdominal fat compared with the turkeys the diets of which did not contain any peas. The chemical analysis of meat showed that feeding the diets with the increasing amount of peas resulted in 0.69–0.82% lower amount of fat in female shoulder muscle (P > 0.05–P < 0.05). Soybean oil meal replacement with field peas in broiler turkey diets had no significant influence on the other anatomic indicators of the carcass and the other physicochemical indicators of meat as well as the content of trypthophan and oxyprolin in the muscles. Our study indicated that soybean oil meal replacement with peas up to 20% from 0 to 4 weeks, 25% from 5 to 8 weeks, 30% from 9 to 12 weeks and 40% from 13 to 16 weeks, and with 100% soybean oil meal replacement at the final stage had no negative influence on the carcass qualities of broiler turkeys.
1. Introduction
Soya is the main protein source in poultry diets. By its protein content (38–48.5%), biological value and indispensable amino acids, soya is considered as one of the best feeds, but the increasing price of this raw material continues to be a concern (Nalle Citation2009). However, soybean is largely imported and, besides, its widespread diffusion as genetically modified organism has in recent times produced a feeling of mistrust (Lanza et al. Citation2003). It is known that raw soybeans induce pancreatic hyperplasia and hypertrophy, causing pancreatic enlargement in various animal and bird species (Grant Citation1989). Moreover, it is also known for allergenicity soybean in humans and for the immune-mediated gut disorders that it induces in piglets and calves (Lalles & Peltre Citation1996).
Data on immune responses to legume seeds, other than soybean, are scarce (Lalles et al. Citation2004). As a result, it has become necessary to evaluate alternative protein sources, for example, leguminous feeds which can fully or partially substitute conventional protein sources in poultry feed formulations (Nalle Citation2009).
Out of legume–grain crops, field peas are considered as one of the most suitable for soybean oil meal replacement in poultry diets as their protein is better assimilated (Jeroch Citation1998; Morkunas Citation2002). Despite the lower protein content in peas in comparison with soybeans, the protein composition is more diverse (Bennett Citation2002). Jeroch (Citation1998) indicates that peas could provide adult birds with all the necessary protein matter. Their lysine content is relatively high, but there is a relative deficiency in sulphur amino acids and tryptophan compared to soybean meal (Gatel Citation1994). Therefore, peas are not suitable for young birds as the only protein source (Bennett Citation2002).
The areas under peas in Lithuania are considerably high. In the last five years, the areas under sown peas increased from 15,900 ha in 2010 to 24,500 ha in 2013 (Department of Statistics Citation2014). In Lithuania a study was carried out to determine the efficiency of partial soybean oil meal replacement with home-grown peas (8%, 12% and 16%) in broiler chicken diets and to evaluate the carcass qualities of broilers. This study indicated that breast muscles of male chickens fed peas were more developed and the dressing percentage was respectively by 2.25%, 1.49% and 1.73% higher than that of control birds fed soybean oil meal. The chemical composition of broiler chicken meat in relation with the pea content in the diet was not detected (Morkunas et al. Citation1999; Vaitiekunas & Моrkunas Citation1999; Morkunas Citation2002).
In the study by Savage et al. (Citation1986), soya was replaced with 25% peas in the feeds for turkeys till 16 weeks of age. For older turkeys, the amount of peas was gradually increased and accounted for 55% in the finishing period.
The difference between the dressing percentage of the female turkeys fed either soybean feeds or soybean–pea feeds was 0.36%, whereas for male turkeys it was only 0.09%, but in all cases the difference was statistically insignificant (P > 0.05). The difference in the content of abdominal fat for female and male turkeys was 0.23% and 0.21%, respectively, but the difference between the groups was insignificant (P > 0.05; Savage et al. Citation1986). There were also no significant differences between the groups for the physical indicators of meat when feeding turkeys either soybean or soybean–pea diets (Savage et al. Citation1986).
The comparison of the chemical composition of meat of turkeys fed either organic home-made feeds or ordinary feeds composed of imported protein components indicated that there were no differences regarding the protein and ash content in meat but the fat content was 0.73% lower and, in the authors' viewpoint, this had improved the carcass quality (Vitina Citation2002).
The purpose of our study was to determine the efficiency of the increasing amounts of peas in the diets for hybrid turkeys cross BIG-6 and to analyse the effects of the pea contents on the anatomic carcass dissection data and the chemical indicators of breast, shoulder, thigh and shin muscles, the physical indicators of breast muscles and to determine the contents of tryptophan and oxyprolin in the above muscles.
2. Material and methods
2.1. Animals and sampling
The study was carried out in 2011–2012 on a turkey farm belonging to farmer Tamosiunas, district of Anyksciai. Male and female turkeys were grown separately; turkeys were assigned to two control groups (one male and one female) and six experimental groups (three male and three female) of 12 one-day-old turkeys each ().
Table 1. Experimental design.
The diet of control group turkeys contained soybean oil meal which was replaced by 10%, 15% and 20% Eiffel variety peas in the diets for turkeys of Trial group 1 up to four weeks of age, Trial group 2 and Trial group 3, respectively. In later growth periods, pea contents in the diets were increased. In the finishing growth period, the content of peas in the diet accounted for 40%, and genetically modified soybean oil meal was completely replaced. At the age of 16 weeks, three male and three females of average weight were chosen from each group for control slaughtering. Prior to slaughter, the birds had not been fed for 12 h. Carcasses were anatomically dissected according to the methodological recommendation of anatomic carcass dissection and organoleptic evaluation of poultry (Lukashenko et al. Citation1984).
The chemical composition of meat was analysed by standard AOAC methods (AOAC Citation1990). The contents of tryptophan and oxyprolin in meat were determined by the methods of Marina and Schut (Citation1970) and Neiman and Logan (Drozdenko Citation1977). The pH value of meat was determined by laboratory pH meter with a glass electrode, colour intensity by the methods of Fewson and Kirsammer, water binding capacity by the method of Grau and Hamm modified by Volovinskaya and Kelman and cooking losses by the method of Schilling (Levantin Citation1977). All analytical studies were carried out the Analytical Laboratory of the LHSU Institute of Animal Science.
2.2. Statistical analyses
Processing of the data was performed using software Statistica (Data Analysis Software System, Version 7.0; StatSoft, Inc., Tulsa, OK, USA). The statistical evaluation of the results was performed using descriptive statistics and Student's t test for independent samples. In the tables, all of the data are displayed as mean () ± standard error (SE) of mean. The probability level of P 0.05 was considered to be statistically significant.
3. Results and discussion
The dressing percentage differences between the control and three trial groups of male and female turkeys that were offered the increasing amount of peas in the diet were from +0.41% to −0.84% and from +0.45% to –0.72% (P > 0.05) ().
Table 2. Anatomic carcass dissection data (%).
These findings are in agreement with the results of Savage et al. (Citation1986) who indicated that the carcass dressing difference between male turkeys fed compound feeds containing from 20% to 55% of peas and pea-free diets (control group) was only 0.09%, whereas correspondingly between female turkeys 0.36%, and the differences were statistically insignificant (P > 0.05; Savage et al. Citation1986). Furthermore, Nalle (Citation2009) and Laudadio and Tufarelli (Citation2010) also found that the dressing percentage of broiler chickens were not affected (P > 0.05) by 20% and 40% pea treatments during the 35-day and 49-day grow-out period. The anatomic carcass dissection indicated that the content of shoulder muscles in the males of the control group was from 0.28% to 0.61% (P > 0.05–P < 0.05) higher than that of the trial groups (Groups 1–3) and conversely than was the case with females from Groups 2 and 3. There was no data found in scientific literature regarding the effects of peas used in turkey feeds on the content of shoulder muscles.
In our study, the analysis of the carcass dissection data indicated that the content of abdominal fat in female turkeys increased from 0.09% to 0.31% (P > 0.05–P < 0.05) with the increase of the pea content in the diet. Savage et al.(1986) have reported that the differences for the content of abdominal fat between the male and female turkeys fed from 20% to 55% peas and the turkeys of the control groups were respectively 0.46–0.67% and 1.13–1.36%, but this difference was insignificant (P > 0.05). This, regarding the abdominal fats, is in agreement with the findings of Bekric et al. (Citation1990) and Laudadio and Tufarelli (Citation2010) in their trials with chicken broilers fed, respectively, 27% and 40% peas. The breast muscle content of males in the trial groups was from 0.44% to 1.83% lower in comparison with the control group, but this difference was insignificant.
There was no significant difference between the groups for the breast, thigh, shin muscles, internal edible parts and dressing percentage of the turkeys of both genders and also for the female shoulder muscles and male abdominal fat content irrespective of the diet formulation. This is in agreement with the studies of Savage et al. (Citation1986), who conducted a similar trial with peas and obtained the same results, with the study of Christodoulou et al. (Citation2006) where turkeys were fed from 20% to 80% of chickpeas (Cicer arietinum L.) and also with the studies of Laudadio and Tufarelli (Citation2010) and Nalle (Citation2009), who conducted trials with chicken broilers (20–40% peas) and found no relationship between the breast and thigh muscle percentage and weight of internal organs in relation to the feed composition. Conversely to the studies of Savage et al. (Citation1986) and Christodoulou et al. (Citation2006) who found no correlation between the content of female abdominal fat and the content of peas or chickpeas in the diet or gender difference, in our study, there was a significant difference for the content of abdominal fat in female turkeys.
Breast and shoulder muscles of males fed peas contained respectively from 0.59% to 1.00% and from 0.20% to1.09% more dry matter, whereas the dry matter content in shoulder muscles of female turkeys was from 0.25% to 0.49% lower (P > 0.05; –).
Table 3. Chemical composition and physical parameters of breast muscles.
Table 4. Chemical composition of shoulder muscles.
The dry matter content in the thigh muscles () of both males and females was, respectively, from 0.20% to 0.48% and from 0.46% to 0.71% lower, whereas the same content in shin muscles was, respectively, from 0.02% to 0.74% and from 0.05% to 0.15% higher in comparison with the control birds (P > 0.05; ). Higher protein content was found in the breast muscles of males under trial – it was from 0.58% to 0.94%, and the protein content in shoulder muscles of females was from 0.26 to 0.44% higher compared with the respective control groups (P > 0.05). Female turkeys under trial were distinguished by a higher protein content in thigh (Groups 1–3) and shin muscles (Groups 2–3) that was, respectively, by 0.27–0.62% and 0.53–0.73% higher compared with the control birds (P > 0.05).
Table 5. Chemical composition of thigh muscles.
Table 6. Chemical composition of shin muscles.
The fat content was from 0.05% to 0.20% and from 0.15% to 0.49% higher in, respectively, breast and shoulder muscles of the treated males, whereas it was lower from 0.69% to 0.82% in the shoulder muscles of the treated females (P > 0.05–P < 0.05). These findings are in agreement with the results of Nalle (Citation2009) who has reported that the sex of birds could affect digestion and absorption of nutrients due to their differences in biochemical and physiological functions. The content of fat in the thigh muscles of the treated females was from 1.06% to 1.34% lower, whereas the same content in the shin muscles of males was from 0.37% to 0.94% higher in comparison with the control birds (P > 0.05).
The fat content differences in the shoulder muscles of females found in our study are in partial disagreement with the findings of Ratnayake et al. (Citation1989) who have reported that there are no differences for the fat content in muscles when birds are fed different feeds. On the other hand, our results agree with those of Laudadio and Tufarelli (Citation2010) who found that 40% peas in the diets of broiler chickens had significantly reduced the fat content in the muscles.
It might be concluded that there was no significant difference for the chemical composition of turkey meat between the control and trial groups, except for the difference in fat content of female shoulder muscles. This is in agreement with the findings of Leskanich and Noble (Citation1997) who reported that there were no differences in protein content in breast muscles in their trial. The feed composition had no influence on the chemical composition of breast muscles in the study by Yau et al. (Citation1991). Similar results were reported by Bampidis and Christodoulou (Citation2011) in the trial with heavy-type BUT-9 cross turkeys fed from 20% to 80% chickpea (Cicer arietinum L.), when no differences for the chemical composition of different muscles were found in comparison with the soybean oil meal control group. The tryptophan:oxyprolin ratio, which characterizes protein quality, in the breast muscles of the treated females was lower from 0.08 to 1.35 units, whereas in shoulder muscles it was higher from 0.37 to 0.71 units compared with the control group. The content of tryptophan in the thigh muscles of treated females was higher from 12.79 to 36.67 mg/100 g of muscles.
The thigh muscles of treated turkeys contained less oxyprolin in comparison with the control groups, i.e. it was from 21.68 to 25.89 mg/100 g muscles in male turkeys and from 3.31 to 18.60 mg/100 g muscles in female turkeys. In male shin muscles, the content of oxyprolin was lower from 8.43 to 19.81 mg/100 g muscles (P > 0.05). The tryptophan:oxyprolin ratio was higher in male and female thigh muscles, respectively, by 0.68–0.87 and 0.28–0.72 units and in male shin muscles it was higher from 0.18 to 0.64 units in comparison with the control.
Morkunas (Citation2002) has indicated that peas and soybean oil meal contain, 1.21% and 1.13%, respectively, tryptophan calculated from total protein content in feeds. The results from our study indicated that the composition of feeds had no influence on the contents of tryptophan and oxyprolin in turkey muscles. Barroeta (Citation2007) has also concluded that the composition of amino acids in poultry meat is influenced by their genetic code and not by the composition of feeds.
There were no differences between the control and treated groups for the pH value of breast muscles. Also there was no significant difference between the treated and control groups for the cooking loss of breast muscles (from −2.34 to +1.48%), and this is in agreement with the findings of Savage et al. (Citation1986) who reported no significant differences for the cooking loss of breast muscles between the turkeys fed peas and only soybeans, respectively.
Water binding capacity in the breast muscles of the treated females was from 1.23% to 4.10% higher, but the difference was insignificant, what is contradictory to the findings of Laudadio and Tufarelli (Citation2010) who have reported that 40% of peas in the feed for broiler chickens significantly increased water binding capacity in breast muscles. Colour intensity of breast muscles differed from +9.57 to −3.86 unit between the control and treated groups of turkeys. However, this difference was insignificant and agrees with the conclusion of Christodoulou et al. (Citation2009) that even 80% chickpeas in the feed did not affect meat colour intensity. On the basis of the results from our study, it can be concluded that partial (10–40%) replacement of imported soybean oil meal with home-grown peas in the feeds for turkeys did not affect the quality of turkey meat. These results from our study confirm and broaden the findings of Mikulski et al. (Citation1997) that 20–24% of peas in the feed for turkeys have no negative influence on the turkey meat quality.
It would be highly advisable to use home-grown peas by the developing ecologic farming in Lithuania to produce quality poultry products.
One of the requirements for this production type is to feed birds with natural home-grown feeds.
4. Conclusion
Soybean oil meal replacement with an increasingly higher content of peas (from 10% to 40%) in the diets of turkeys resulted by 0.28–0.61% (P > 0.05–P < 0.05) lower content of shoulder muscles (% of carcass weight) in males and by 0.09–0.31% (P > 0.05–P < 0.05) higher content of abdominal fat in females.
The composition of the feed did not affect breast, thigh, shin muscles, internal edible body parts and the dressing percentage of both genders and also shoulder muscle content in females and abdominal fat content in males.
Higher percentage of peas in the feed did not influence the chemical composition of meat and physical indicators, except for a significantly lower fat content in the shoulder muscles of the treated females (from 0.69% to 0.82%; P > 0.05–P < 0.05).
The carcass and meat quality indicators of turkeys were not affected by soybean oil meal replacement with 20% peas from 0 to 4 weeks of age, up to 25% peas from 5 to 8 weeks of age, up to 30% peas from 9 to 12 weeks of age and 40% peas from 13 to 16 weeks of age when the use of genetically modified soybean meal was completely excluded.
For heavy-type turkeys at different growing periods 7.1% of soybean oil meal could be replaced by, respectively, 20%, 25% and 30% of peas from 0 to 4, from 5 to 8 and from 9 to 12 weeks of age. From 13 to 16 weeks of age it is recommended to fully replace soybean oil meal (26.5%) by 40% of peas.
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