Energetic values of animal by-products for broiler chickens of different ages

The objective of this study was to determine the chemical composition and apparent metabolizable energy (AME), AME corrected for nitrogen balance (AMEn) and its respective metabolizable coefficients of animal byproducts for broiler chickens with different ages. Meat and bone meal, poultry by-product meal, tilapia processing residue and poultry fat were evaluated. A total of 760 male broiler chickens were used and evaluated and the phases: pre-starter (1 to 8 d of age); starter (11 to18 d); grower 1 (21 to 28 d); grower 2 (31 to 38 d), and finisher (41 to 48 d). Total excreta collection method was performed in five metabolism assays. The experimental design was completely randomized, and data were submitted to analysis of variance, posteriorly, the four feeds were compared by Tukey test and a regression analysis was performed with broiler chickens age. The significance was considered at 5% probability. The values of AME and AMEn were higher in older birds for all ingredients. The lesser CAME and CAMEn were obtained for meat and bone meal, for the regression analysis poultry by-product meal, tilapia processing residue and poultry fat had an increased linear effect with birds age and there was no adjust for meat and bone meal for regression analysis. Research, Society and Development, v. 10, n. 6, e37110615639, 2021 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v10i6.15639 2


Introduction
The dependence of the poultry sector on corn and soybean meal generates demand for alternative products, as lowcost feed sources (Dalólio et al., 2019), in this context, the use of by-products from animal origin is an important strategy to reduce production costs, besides, it can provide an appropriate destination for the waste generated by the industries and slaughterhouses (Eyng et al., 2011).
The use of by-products in poultry diets makes necessary precise knowledge of its chemical composition and metabolizable energy, providing a formulation with lower cost and efficient use of energy by birds (Mariano et al., 2012;Vieira et al., 2015). Protein by-products of animal origin are important sources of energy, amino acids, calcium and phosphorus, however, the lack of standardization in the production process leads to variations in the levels of nutrients and energy (Troni et al., 2016). These variations in the nutrient profile occur due to the addition of bones, blood, heads, lean tissues, viscera, hooves, hide, feathers, and fat besides the differences in processing methods and conditions (Adeola et al., 2018).
Broiler chickens need a high-energy diet to support its rapid growth and metabolism (Cao & Adeola, 2016), so fat sources are also important ingredients to increase dietary energy levels and are becoming an essential component in the formulation of high energy broiler diets. Besides other benefits of adding fats include improved feed texture, reduced dustiness, and increased palatability (Tancharoenrat et al., 2013;Rodriguez-Sanchez et al., 2019).
The ability of animals to extract nutrients from feeds most likely increases with age with the most drastic changes in the first few weeks of life, and such age-related increases could be substrate-associated and therefore dependent on feed ingredient (Adeola et al., 2018). It demonstrates the importance of determining the metabolizable energy of feeds at different broiler chickens ages (Schneiders et al., 2017).
The objective of this study was to determine the values of apparent metabolizable energy and apparent metabolizable energy corrected for the nitrogen balance and its respective coefficients of metabolizability for different by-products of animal origin, with broiler chickens at different ages.

Methodology
The experiment was carried out at the Poultry Research Center of Western Paraná State University (Marechal Cândido Rondon, PR, Brazil) and the experimental procedures were approved by the Animal Ethics Committee of the University under number 026/09.
A total of 760 male, one-day-old (Cobb 500) broiler chickens were obtained from a commercial hatchery and raised on a concrete floor covered with pine wood shavings, receiving a diet based on corn and soybean meal, and water ad libitum.
When the broiler chickens reached to the respective ages, they were transferred to the metabolic cages, which were equipped with trough type feeders and drinkers. The room temperature was kept within the ideal thermal comfort zone indicated for each phase, according to the strain recommendations (Cobb-Vantress, 2008).
Broiler chickens were distributed in a completely randomized design with four treatments (feeds) and five replications (the cages were considered the experimental units -EU). Each assay lasted eight days consisting in three days for adaptation and five for collections, which were performed according to Sibbald & Slinger (1963), in intervals of 12 hours to avoid possible fermentations (Rodrigues et al., 2005).
The MBM, PBM and TPR replaced the RR at 200 g kg -1 and PF replaced the RR at 100 g kg -1 . For determining the feeds chemical composition, analyzes of dry matter (DM), crude protein (CP), ether extract (EE), ash and the minerals: calcium (Ca), phosphorus (P), magnesium (Mg), sodium (Na) and potassium (K), were performed according to the methodologies described by Silva and Queiroz (2002). Gross energy (GE) analysis was performed with an oxygen calorimetric bomb (IKA C200), and AME was corrected to zero N retention (AMEn) using the factor of 8.22 kcal g -1 (Hill & Anderson, 1958). Geometric mean diameter (GMD) of the MBM, PBM and TPR were determined according to the methodologies of Zanotto and Bellaver (1996).
Based on the analyzes of the chemical composition of feeds and excreta, the AME and AMEn values were obtained by the equations proposed by Matterson et al., (1965) and posteriorly it was obtained the energy metabolizable coefficient.
Data were submitted to analysis of variance (ANOVA) and regression procedure to verify the effects of different ages on the metabolizable coefficients for each feed. The comparison between feeds within the same period was obtained by Tukey's test at 5% probability using the software SAS version 9. .

Results and Discussion
Chemical composition of MBM in this study showed variations (Table 2)   and obtained lesser content of CP (337 g kg -1 ) and ash (215 g kg -1 ), and a greater fat content (374 g kg -1 ) compared to the present study, which had CP, ash and EE contents of 512.5; 253.7 and 146.8 g kg -1 , respectively. Eyng et al. (2013) used TPR in broiler chicken diets with 452.5 g kg -1 of CP, demonstrating the broad variation of CP content of this by-product.
The composition of PBM was similar to the obtained by Troni et al. (2016) for CP and EE contents, the authors obtained average values of 582.4 and 121.5 g kg -1 respectively, however, the authors obtained lower values for Ca (57.4 g kg -1 ) and P (32.9 g kg -1 ). Silva et al. (2014) obtained values for CP, fat, and Ca of 569.1; 138.4 and 53.2 g kg -1 respectively, and the greater difference occurred in the Ca contents compared to this experiment, which agrees with the revision of Silva et al.
(2010) who found the higher variation for PBM in mineral content, Ca and P.
In the particle size evaluation, considering the classification of Zanotto and Bellaver (1996), MBM was classified as fine granulometry (GMD less than 600 µm) while PBM and TPR, as medium granulometry (GMD from 600 to 2000 µm), in this classification, feeds with GMD higher than 2,000 µm are considered coarse. The GMD of MBM (581 µm and 723 µm. Smaller particle size increases the relative surface area of feed and can expose the nutrients to digestive enzymes (Xu et al., 2015), however, very fine particle size may increase passage rate and reduce feed digestibility. On the other hand, birds demonstrate a certain preference for coarser feed particles, which can stimulate the gizzard development and increase digesta retention time, improving feed digestibility (Amerah et al., 2007;Amerah et al., 2008). However, birds may encounter difficulties when consuming very coarse or fine particle sizes (Amerah et al., 2007).
Regarding the AME values (Table 3)   For the TPR the AME values from d 41 to 48 (3,705 g kg -1 ) were similar to those described by Eyng et al. (2013) of 3,733 kcal kg -1 , however, in the present study, lesser values were obtained for younger broiler chickens.
The AMEn values of PBM at grower 1, grower 2, and finisher phases are similar to those published by Rostagno et al. There were greater values of AME and AMEn in older birds; this increase in AMEn values with the advancing age of birds is caused by the improvement in the nutrient's utilization. This effect is related to digestive enzyme production and absorptive capacity, where increases with age and such age-related increases could be substrate-associated and, therefore dependent on feed ingredient (Adeola et al., 2018). In the present study, all the feeds showed higher AMEn values after 11 days of age, according to Adeola et al. (2018) studies have shown that ME value of a diet is lowest between day 4 and 7 posthatching in broiler chicks followed by an increase with post-hatching age.
The AME values of PF increased with bird's age, where the values in the starter phase (8,135 kcal kg -1 ) were greater than those of Tancharoenrat et al. (2013) who evaluated different fat sources and obtained AME values for PF of 4,311; 8,066; 8,379 and 8,159 kcal kg -1 for birds with one, two, three and four weeks of age, respectively, being lowest in the first week of birds' age. The authors indicated that the lower fat digestibility and AME value could be explained by the poor physiological capacity to absorb dietary fats in newly hatched chicks, however, in this study lesser AME occurred in both pre-starter (1-8 d) and starter phase (11-18) when compared to the other phases evaluated. The mean values of AME were higher than AMEn in the phases pre-starter (1-8 d), grower 1 (21-28 d), and finisher (41-48 d) for all the feeds evaluated, indicating a positive nitrogen retention, a common effect in birds in ad libitum intake (Kato et al., 2011). The values of CAME and CAMEn (Table   4) were higher for PF compared to other sources, which was expected, since lipids are widely used in broiler diets to increase the dietary energy density, due to its higher apparent metabolizable energy (AME) content in relation to other feedstuffs and is often used to improve dietary energy density to meet the requirements of fast-growing broiler chickens (Skřivan et al., 2018). Among the three protein sources, MBM showed the lowest values of CAME (P<0.05) for all ages evaluated, which may be related to its processing and composition, since the contents of EE, GE and CP of MBM were lesser than TPR and PBM. In addition, MBM had the highest ash values (406.9 g kg -1 ), compared to TPR (253.7 g kg -1 ) and PBM (181.2 g kg -1 ). In a study for prediction of metabolizable energy with PBM, Silva et al. (2010) highlighted that by-product meals with higher contents of mineral matter showed lower values of metabolizable energy, showing an antagonistic correlation, where higher contents of mineral matter, had lesser metabolizable energy values. The higher mineral contents with calcium and sodium ions, can also cause the saponification of fats present in animal flours, reducing their use by birds (Troni et al., 2016;Eyng et al., 2011).
Regarding the regression analysis (Table 5), there was a linear increase (P<0.05) for the CAME of TPR, PBM and PF with the birds age, however, there was no adjustment (P>0.05) in the regression for MBM. When corrected for nitrogen (CAMEn), there was a linear increase with birds age (P<0.05) only in TPR and PF while no effect (P>0.05) was found for PBM and MBM. Adeola et al. (2018) found quadratic effects in AME and AMEn in relation to the ages 0-7, 6-11, 10-16, and 15-21, wherein the day 0 to 7 energy values were lower than subsequent ages. There was a linear increasing effect (P<0.05) for CAME and CAMEn with the advancing age of birds fed PF; this occurs due to increased ability of broiler chickens to use nutrients with age, since the most drastic changes occurs in the first weeks of life, being more pronounced with young birds fed sources rich in saturated fatty acids (Aardsma et al., 2017). Tancharoenrat et al. (2013) evaluated different fat sources including PF and found an improvement in AME with advancing birds age, the authors also highlighted the occurrence of lower AME values in birds from 0-7 d, which occurred in this study for CAMEn values.

Conclusion
Meat and bone meal energetic value was not influenced by age and showed the lesser energetic values. The CAME values of tilapia processing residue, poultry by-product meal and poultry fat increased with broiler chicken's age.