The objective of this work was the

measure the in situ and ruminal degradability and dry matter

digestibility of three fattening diets for lambs, used by lamb

producers in the central area of Tamaulipas, México. The

nylon bag technique was used to determine in situ dry matter

digestibility, using three lambs with cannulas in the rumen,

distributed in a Latin Square design. The ruminal incubation

times were 0, 4, 8, 12, 24 and 48 h. All treatment diets (T)

used ground sorghum grain (Sorghum vulgare) as a base.

T1 included rice (Oryza sativa) polishing with 7.53% on a

dry matter basis (DM) of sorghum straw as forage; T2 had

5% DM of sorghum straw as forage; and T3 had 5% DM of

buffel grass (Cenchrus ciliaris) hay plus 3% DM of alfalfa

hay (Medicago sativa). In T1, the highest (P<0.05) value of

digestibility at 0 and 4 h was observed. For 24 h, the highest

(P<0.50) digestible fraction was obtained with T2. At 48 h,

no difference (P>0.05) was observed between treatments.

The washing loss and the degradation constant were higher

(P<0.05) for T1 than T2 and T3. The diet of T1, containing

rice polishing, produced the highest digestible fraction at

the fi rst hours of incubation in rumen (0 and 4 h). T3 was

digested in smaller proportion, although it could be the best

diet for feedlots of lambs because of the lower acidosis risk.

Keywords: Ruminal digestion, rations, sheep.