Behaviour 2019
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No positive effect of dietary mixing for howler monkeys on available nitrogen when diet contain tannins
Fabiola Carolina Espinosa-Gómez1, Laura Teresa Hernández-Salazar2, Ian R. Wallis3, Sergio Gómez-Rosales4. 1Facultad de Medicina Veterinaria y Zootecnia, Universidad Popular Autónoma del Estado de Puebla, Puebla, Puebla, Mexico; 2Instituto de Neuroetología, Universidad Veracruzana, Xalapa, Veracruz, Mexico; 3Evolution, Ecology, and Genetics. Research School of Biology, The Australian National University, Canberra, ACT, Australia; 4Centro Nacional de Investigación Disciplinaria en Fisiología y Mejoramiento Animal, Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias, Ajuchitlán, Querétaro, Mexico

Leaf-fruits diet of Mantled howler monkeys (Alouatta palliata) often contains low nutrients but high fiber and tannins. It has been hypothesized that howlers prefer mixed diets for nutrient complementation or toxin dilution, which may improve digestibility. The aim of this study was to evaluate the concentration of available nitrogen (AN), condensed tannins (CT) and dry matter digestibility (DMD) of six plant species part of howler monkey´s natural diet (fruits and leaves), mixed diets (N=19) with different percentage inclusion of leaves, and diets consisting of plant mixtures selected by monkeys. We determined in vitro AN and DMD using the method of DeGabriel et al. (2008). We also measured the effects of tannins in AN by adding polyethylene glycol (PEG). Ficus aurea leaves that was the second preferred food by monkeys, had the highest level of DMD, AN and low CT. There were no differences in DMD among all plant mixtures (p=0.46) but there were by plant species (p=0.04). AN was not different between mixed diets but when we added PEG for inactivating tannins, the concentrations of AN were much higher (p< 0.0001), showing the negative effects of tannins on protein digestibility.