Potencial forrageiro de gliricídia (Gliricidia sepium (Jacq.) Steud.) sob diferentes intervalos de corte e sua inclusão em dietas para frangos de corte

Abstract

This research was conducted in two complementary trials. In the first trial, the objective was to evaluate the productivity and bromatological composition of gliricidia as a function of different cutting intervals, as well as to characterize its amino acid profile. Initially, the soil was previously prepared with a leveling harrow to uniform the terrain, and samples from the 0-20 cm depth layer were collected for chemical analysis before and after the crop cycle. The gliricidia crop was established from seedlings produced in a greenhouse, which, after sixty days under regular irrigation and subsequent acclimation to sunlight, were transplanted to the field. Planting was carried out in a dense regime, with a spacing of 1.0 m between rows and 0.5 m between plants, totaling 20,000 plants per hectare. At 150 days after planting, a uniformity cut was performed at 50 cm above the ground to standardize the stand, from which subsequent cuts, maintaining the same height, were carried out according to the intervals defined for each treatment. The research was conducted in a Completely Randomized Design (CRD). The treatments consisted of four cutting intervals (45, 60, 75, and 90 days), with seven replications each, totaling 28 experimental units. The experimental unit was the plot, composed of three crop rows with 135 plants each. For the analyses, data from the three rows were summarized by the mean to represent the value of each plot, ensuring data independence for statistical analysis. The data were subjected to analysis of variance (ANOVA), and when significant differences were detected (p<0.05), the treatment means were compared by Tukey's test. Polynomial regression analysis was also performed to evaluate the behavior of the variables as a function of the cutting intervals, selecting the best-fit model based on the coefficient of determination and the significance of the parameters. The trial on the impact of different cutting intervals (45, 60, 75, and 90 days) on the yield and nutritional quality of gliricidia revealed differences. In annual dry matter production, the 60-day interval recorded 233.34 kg, a value 14.6% higher than the 45-day interval (203.62 kg) and 18.3% higher than the 75-day interval (197.25 kg). Compared to the 60-day interval, the 90-day interval (184.40 kg) showed a reduction of 21.0%. Regarding the bromatological composition, the crude protein content decreased with increasing cutting interval: the 32.45% at 45 days reduced to 31.41% (-3.2%) at 60 days, 30.37% (-3.3% compared to the previous) at 75 days, and 28.60% (-5.8%) at 90 days, totaling an 11.9% reduction between the extremes. The total dry matter/crude protein ratio (kg/ha) at the 60-day interval (122.18 kg/ha) was 27.5% higher than the 45-day interval (95.85 kg/ha) and 28.1% higher than the 90-day interval (87.88 kg/ha). The analysis of total crude protein production per hectare (CP/ha), which synthesizes dry matter productivity and its protein content, confirms the superiority of the 60-day cutting interval. It is concluded, therefore, that the 60-day cutting interval was the most balanced, providing the highest dry matter yield and the best dry matter/total protein ratio per hectare. Although the crude protein content is maximized at shorter intervals (45 days), the sharp drop in overall productivity makes management at 60 days more advantageous when the goal is to optimize the joint production of matter and nutrients. In the second trial, the objective was to evaluate the effects of including gliricidia leaf meal in broiler diets on zootechnical performance, carcass characteristics, jejunal morphometry, short-chain fatty acids, and biochemical parameters. The gliricidia meal and flour were produced from leaves and tender stems harvested at four different cutting intervals (45, 60, 75, and 90 days), originating from the first trial of this thesis. For this trial, the cutting intervals did not influence the production of the two derivatives, since all material, after harvest and weighing, was homogenized before processing both products. The material was dried in a forced ventilation oven at 55°C for 72 hours and, in order to increase the protein content, the petioles were manually separated from the leaf blades during the production of the meal, since a previous analysis had proven that the petioles have a lower protein content compared to the leaf blades. Then, the meal was ground in a Willey-type mill with a 2 mm mesh sieve to produce the flour, intended for bird feed and to be subjected to chemical-bromatological and amino acid analysis. The research was conducted with 480 male broiler chickens, Ross lineage, in a completely randomized design, consisting of five levels of gliricidia meal inclusion (0%, 0.75%, 1.5%, 3%, and 4.5%), six replications, and 16 birds per experimental unit. Zootechnical performance parameters (weight gain, feed intake, and feed conversion ratio) were evaluated at 21 and 42 days of age. At the end of the experimental period (42 days), biological samples were collected for specific analyses: jejunal fragments for intestinal histomorphometry (villus height, crypt depth, and absorption area); cecal content for quantification of short-chain fatty acids; and blood for serum biochemical profile (metabolites and liver enzymes), analyzed by automatic spectrophotometry. At 42 days, carcass and cut yields were evaluated, as well as meat quality parameters pH (at 15 minutes and 24 hours post mortem), color (at 15 minutes and 24 hours post mortem), water holding capacity, cooking loss, shear force, and lipid oxidation by thiobarbituric acid reactive substances (0, 30, and 90 days). The collected data were subjected to analysis of variance, with mean comparisons by Dunnett's test and polynomial regression analysis, adopting a significance level of 5%. The inclusion of gliricidia meal in broiler feed presents a dual dose-dependent effect, acting as a pharma-nutrient agent. In the initial phase (1 to 21 days), a reduction in feed intake was observed in treatments with 1.5%, 3%, and 4.5% inclusion, with a minimum value of 863.04 g at the 4.5% level compared to 1182.80 g for the control. The 0.75% level (1142.17 g) did not differ from the control. Regarding weight gain, all inclusion levels resulted in values lower than the control (909.55 g), with the lowest value recorded at the 4.5% level (623.00 g). Feed conversion was worse at the 3% (1.376) and 4.5% (1.386) levels, while the other treatments remained equivalent to the control (1.301). In the total phase (1 to 42 days), a difference in feed intake was found at all experimental levels, including 0.75% (4383 g versus 4614 g for the control). Weight gain was lower in the group with 4.5% inclusion (2466 g versus 3127 g). Feed conversion was worse at the 1.5% level (1.501 versus 1.476 for the control). The productive efficiency index was lower in treatments with 1.5%, 3%, and 4.5% (479, 436, and 404, respectively) compared to the control (524). Carcass yield was lower at the 3% (68.91%) and 4.5% (68.17%) levels, with no differences in the other evaluated parameters. No changes were observed in the values of thiobarbituric acid reactive substances, cooking loss, shear force, water holding capacity, pH, meat color, or cecal short-chain fatty acid concentration. A reduction in serum concentrations of uric acid (up to 3.11 mg/dL) and cholesterol (up to 100.83 mg/dL) was recorded in treatments with 3% and 4.5% inclusion, with no differences at the other levels compared to the control. At doses above 0.75%, its bioactive compounds impair zootechnical performance, although they promote metabolic benefits at higher levels (3% to 4.5%), without affecting meat quality or intestinal integrity. However, for commercial poultry farming, the production losses outweigh any metabolic advantages, making its use unfeasible at the tested levels.