Avaliação agronômica e do valor nutritivo do terço superior da rama em diferentes variedades de mandioca

Abstract

The aerial part of cassava is a product of superior quality to many tropical forages used in animal feed. The objective of this study was to evaluate the productivity and nutritive value of the aerial part of 18 cassava varieties. The plants were harvested at eighteen months of age. The statistic used was the multiple factorial analysis. It was observed that the 18 varieties studied were grouped into three types, which were mainly discriminated by the variability observed in the ruminal degradation characteristic of dry matter (DM) and neutral detergent fiber (NDF). The varieties grouped in type 2 showed the highest protein content (20.70%), followed by the varieties present in type 3 (20.45%) and the lowest value was found in type 1 (19.09%) varieties. Varieties present in type 2 varieties also had the lowest content of acid detergent fiber free of ash and protein (ADFap) and lignin (LIG) (34.15 and 15.30%, respectively), type 1 had a higher content of ADFap ( 36.14%) and type 3 had a higher LIG content (19.63%). In the protein fractionation, the type 2 varieties had a higher fraction of non-protein nitrogen and a lower fraction of the undegradable fraction, type 3 showed a higher fraction of true protein of rapid and intermediate degradation and lower of the slow degradation protein. The varieties grouped in type 3 presented a higher fraction of the soluble carbohydrate and of rapid and intermediate value of the undegradable fraction. The potential degradation (PD) of DM was higher in type 3 (74.44%), followed by type 2 (74.16%) and the lowest value in type 1 (69.43%). The effective degradability (ED) of DM was higher in type 2 (52.87%), followed by type 3 (52.43%) and the lowest value was found in type 1 (49.61%). PD of NDF was higher in type 2 (59.54%) and lower in type 1 (54.67%). The highest ED of NDF value was obtained in type 2 (22.18%) and the lowest in the varieties grouped in type 3 (19.84%). The varieties grouped in type 2 were those with the highest root yield (10.01 t of DM.ha-1) and higher productivity of the upper third of the cassava branch (1.41 t of DM.ha-1). Based on the productivity and nutritional aspects, the varieties grouped in type 2 are more proper for use in ruminant feeding.