Proportion and digestibility of tree legumes in diets of grazing cattle in a tropical silvopastoral system

• Published in: Livestock science 2021-10, Vol.252, p.104689, Article 104689
• Main Authors: Costa, Suellen Brandão de Miranda, de Mello, Alexandre Carneiro Leão, Dubeux, José Carlos Batista, Ferreira dos Santos, Mércia Virginia, da Cunha, Márcio Vieira, Coelho, Janerson José
• Format: Article
• Language: English
• Subjects: Arboreal legumes; fecal δ13C; Legume digestion; Mixed pastures; Ruminant diet
• ISSN: 1871-1413; 1878-0490
• DOI: 10.1016/j.livsci.2021.104689

•δ13C isotope is useful for tracking grass/legume proportion in grazing cattle diets.•Grazing cattle in silvopastoral system prefer grass than tree legumes.•Gliricidia sepium increased forage digestibility in diets composed of grass.•Mimosa caesalpiniifolia reduced forage digestibility in diets composed of grass. In Silvopastoral Systems (SPS) the dynamics and complexity of the combination between grasses and legume trees can significantly impact forage intake and digestibility, affecting livestock performance. This research was composed of two parallel studies. The first one consisted of a field trial assessing three grazing systems: signalgrass (Urochloa decumbens Stapf.) monoculture, and two SPS, one composed of signalgrass + gliricidia [Gliricidia sepium (Jacq.) Kunth.], and another by signalgrass + mimosa (Mimosa caesalpiniifolia Benth), in a randomized complete block design with three replications. Yearling crossbred 5/8 (Holstein/Zebu) steers (175 ± 29 kg initial body weight) were used as experimental animals. Response variables included δ13C in diet and the proportion of C3 species in the feces. The second study was an in situ dry matter digestibility (ISDMD) assay using fistulated male buffalos, and it was evaluated the increasing levels of each legume from the SPS (0, 25%, 50%, 75%, and 100%) in replacement to signalgrass, under different incubation period (24, 48, and 96 h). The range of the carbon isotope (δ13C) found in the cattle's feces (-14.2 to -16.4 ‰), in both signalgrass monoculture pastures and SPS, evidenced the preference of the cattle under SPS for consuming grasses (C4) instead of tree legumes (C3), as both were available. The carbon isotope (δ13C) in plants with C4 metabolism ranges between -9 and -16‰, and in C3 from -22 to -34‰. Increases in the intake of legumes during the dry period might have occurred due to lesser herbage mass and nutritive value of the grass. The ISDMD reached its greater values (>80%) in the inclusion levels of 75 and 100% of gliricidia, at 48- and 96-h incubation (P