The feeding value of five varieties of whole-plant cassava (SC5, SC7, SC9, SC14, and SC205) was assessed through analysis of the nutritional composition and in situ ruminal degradability. The results showed abundant nutrients in whole-plant cassava, and the means of starch and crude protein (CP) were 267.7 and 176.8 (g kg−1), and ranged from 223.7 g kg−1 (SC9) to 296.4 g kg−1 (SC14) and from 142.4 g kg−1 (SC5) to 195.8 g kg−1 (SC9) (p < 0.05), respectively. Meanwhile, the moderate neutral detergent fiber (NDF) of whole-plant cassava was also observed and ranged from 266.2 g kg−1 in SC9 to 286.6 g kg−1 in SC14 (p < 0.05). In addition, the trace elements, such as Fe, Mn, Cu, and Zn, in whole-plant cassava were relatively enriched, and their mean concentrations were 135.8, 1225.2, 5.8, and 105.3 mg kg−1 (p < 0.05), respectively. Both the highest essential amino acid and total amino acid concentrations were obtained in SC7 (p < 0.01). The hydrogen cyanide (HCN) content of fresh and dried whole-plant cassava ranged from 76.5 to 131.6 and from 36.0 to 56.7 mg kg−1 (p < 0.05), respectively. The in situ dry matter ruminal degradability and metabolizable energy (ME) varied significantly (p < 0.05) and were consistently lowest and highest in SC9 and SC14, ranging from 50.9% to 80.0% and from 7.5 to 12.3 MJ kg−1, respectively. Collectively, all varieties of whole-plant cassava had a high feeding value, as reflected by abundant starch, minerals, amino acid, and water-soluble carbohydrates, while having a low fiber content and HCN toxicity, as well as excellent ruminal digestibility characteristics, and they could be used as a potential feed resource for ruminants.