The subject of this study is the validation of a high-performance liquid chromatography method for the analysis of amino acids in feed. The contents of amino acids were determined in maize, soybean, soybean meal, as well as in their mixtures enriched with different amounts of methionine, threonine and lysine. The method involves the acid hydrolysis of the sample (6 h at 150ºC), automated derivatisation of amino acids with the aid of o-phthaldialdehyde and 9-fluorenylmethyl chloroformate reagents, separation on the ZORBAX Eclipse-AAA column, and detection using a diode-array detector. The method is characterized by high specificity (the difference between the retention times of the feed samples and standard mixtures are below 1.7 %), wide linear range (from 10 to 1000 nmol cm-3, r2 = 0.9999), high accuracy (recovery 93.3-109.4 %), and the precision of the results (RSD below 4.14 % in case of repeatability and below 4.57 % in the case of intermediate precision). The limit of detection and the limit of quantification are in the range 0.004-1.258 μg cm-3 and 0.011-5.272 μg cm-3, respectively. The results demonstrate that the procedure can be used as a method for the determination of the composition of primary amino acids of feed proteins. [Projekat Ministarstva nauke Republike Srbije, br. 31081
Enzyme supplementation of diets enhances broiler performance by improving some of the basic production parameters such as average feed intake, feed conversion ratio, or average weight gain. The enzyme NSPase is commonly used in broiler diets containing high levels of viscous cereals such as barley, oat, wheat, or sorghum. The use of NSPase in diets with different levels of sunflower meal has been not been extensively explored. The experiment was carried out to evaluate the effects of the inclusion of sunflower meal levels in grower and finisher broiler diets supplemented or not with enzymes (cellulase, β-glucanase, and xylanase) on broiler performance, intestinal function, and carcass traits. A completely randomized experimental design, with 3*2 factorial arrangement with five replicates, was applied (1200 Ross 308 broilers). Sunflower meal inclusion and enzyme supplementation started in grower phase. Broiler performance significantly improved in grower phase (weight gain and feed conversion ratio) by enzyme supplementation, while the effect of sunflower meal was evident in finisher phase, when it significantly reduced weight gain. Sunflower meal increased ileal viscosity, and the interaction between diet and enzyme supplementation was statistically significant. Maltase activity was reduced with sunflower meal dietary inclusion, while enzyme supplementation had no effect either on maltase or sucrase activity. There were no any effects of sunflower meal inclusion with or without enzyme supplementation on carcass characteristics. It can be concluded that high inclusion of sunflower meal in broiler diets may impair broiler performance, but this may be overcome by enzyme supplementation. The effect of enzyme supplementation more evident in the grower phase than in the finisher phase.
The determinations of nutrient costs and breakeven prices of feedstuffs are important activities in the field of nutritional economics. Current methods are either extensions of the Petersen method, which dates back to 1932, or mathematical programming methods generally set as linear programming problems. Both sets of methods have severe limitations that make them unsuitable or biased for deriving unit costs of nutrients and aggregate breakeven costs of feedstuffs in a given market. We propose a least-squares method that, under verifiable conditions, yields maximum likelihood estimates of unit costs of nutrients and breakeven prices of feedstuffs. Assumptions to the maximum likelihood estimates are verified with studentized residuals, leverage values, and variance inflation factors. The method has been programmed into a Windows application and can be used by those with little formal training in statistics.
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