Resumen

REYES-ESTRADA, Osvaldo et al. Seasonal changes in intake, chemical composition and ruminal degradability of the diet selected by grazing steers. Ecosistemas y recur. agropecuarios [online]. 2014, vol.1, n.2, pp.97-106. ISSN 2007-901X.

Seasonal changes in intake, chemical composition and ruminal degradability of the diet selected by steers in a medium-sized grassland in northern Mexico were evaluated. Samples were obtained from four rumen-fistulated steers (350 ± 3 kg BW). The data were analysed with an analysis of variance (ANOVA) and a completely randomised block design. The smallest intakes of dry matter (DM) were recorded in winter (4.43 kg d^-1) and spring (4.54 kg d^-1) (p > 0.05). The greatest content of crude protein (CP) (10.49 %) and the greatest in vitro digestibility of the organic matter (IVDOM) (67.34 %) were recorded in summer (p < 0.05). The greatest concentrations of neutral detergent fiber (NDF) and of acid detergent fiber (ADF) were observed in winter (p < 0.05). The smallest "a" soluble fraction of DM (16.38 %) was recorded in spring and the greatest effective degradability (ED) was recorded in summer (55.34 %) (p < 0.05). The A+B potential degradability (PD) of the NDF and the "c" degradation constant rate were different between seasons (p < 0.05). The greatest CP degradability parameters were recorded in summer and the smallest ED value of the CP was observed in winter (46.04 %; p < 0.05). It is concluded that the intake, chemical composition and ruminal degradability of the DM, NDF and CP of the diet selected by grazing steers changed throughout the year.

Palabras llave : Bovines; diet; grazing; in situ; nutritive value.