Work

In situ ruminal degradation kinetics of tropical Urochloa genotypes under shade and full sun in Yucatán, Mexico

Year: 2026

Type: preprint

Abstract: Silvopastoral systems can modify forage nutritive value through changes in light availability; however, information on their effects on ruminal degradation kinetics of tropical Urochloa grasses remains limited. This study evaluated the influence of light environment and season on forage chemical composition and in situ ruminal dry matter degradability of five tropical Urochloa genotypes grown in Yucatán, Mexico. Forages were harvested under full sun and shade generated by scattered trees during the rainy, nortes (regional cool season), and dry seasons. Ruminal dry matter degradability was determined using the nylon bag technique in three rumen-cannulated cattle, and degradation kinetics were estimated using the Ørskov and McDonald model. Shaded conditions significantly increased crude protein concentration across genotypes and seasons. The soluble fraction ( a ) was the degradation parameter most responsive to environmental conditions, showing significant effects of genotype ( p = 0.002), light environment ( p < 0.001), season ( p < 0.001), as well as genotype × season ( p < 0.001) and genotype × light × season ( p = 0.034) interactions. In contrast, the potentially degradable fraction ( b ) and the fractional degradation rate ( c ) showed fewer and less consistent responses. Potential degradability ( a + b ) remained relatively stable across genotypes, light environments, and seasons. These results indicate that shade modified nutrient availability and ruminal degradation kinetics without affecting overall degradability potential. Moderate shade improved forage nutritional quality through increased crude protein concentration and changes in soluble fraction dynamics. The contrasting responses observed for the soluble fraction ( a ) among genotypes highlight the importance of genotype × environment interactions and support the selection of adapted Urochloa genotypes for tropical silvopastoral systems under seasonally variable conditions.

Source: Research Square

DOI: 10.21203/rs.3.rs-10122211/v1