The objective of this study was to find out the effect of high concentrations of total salts (ST) and sulphates (Sulf) in drinking water on the degradability of tall wheatgrass (Thinopyrum ponticum). Six trials repeated at different moments using rumen fluid from a steer fed on either alfalfa hay (diet A) or alfalfa hay plus grass pasture (diet 13) were performed. Drinking water was obtained from a watering place located in the same paddock of the pasture. Rumen fluid and tall wheatgrass were incubated at 39 degrees C in artificial saliva prepared with drinking water. Six treatments were evaluated in flasks fitted with graduated syringes. The flasks contained 60 ml of ruminal inoculum and I g of tall wheatgrass except in treatment I (TI). Treatments were T1: without forage; T2: control; T3: ST (3,000 mg/l); T4: ST (7,000 mg/l); T5: Sulf (1,500 mg/l) y T6: Sulf (7,000 mg/1). Salts used were: sulphates and chlorides of sodium, potassium, calcium and magnesium. To estimate the ruminal degradability of tall wheatgrass, gas production as a function of incubation time was evaluated by measuring the gas accumulated in the syringes during 50 h. The pH of the incubates of each treatment at the beginning and at the end of the trials was also recorded. Data were analysed using ANOVA and means were compared using Dunnett's test. Effects of block (diet), treatment, hour, and interactions of hour x block and hour x treatment on gas production were detected (P < 0.05). In both diets, A and B, ST7.000 was the treatment that most affected the degradative activity of rumen microorganisms, followed in diet A by Suit(7,000) and in diet B by ST1,500. Some significant differences of pH were found between treatments, and between initial and final values. It was concluded that high concentrations of salts, particularly of ST, decrease the degradative activity of rumen microbes after 50 h of digestion.
