Fertilizer sulphur as a factor affecting voluntary intake, digestibility and retention time of pangola grass (Digitaria decumbens) by sheep

1. Pangola grass (Digitaria decumbens) was grown with or without sulphur fertilizer, cut at seven stages of growth, dried and given to sheep with or without a supplement of 0.6 g S as sodium sulphate/d. Voluntary intake and digestibility of dry matter (dm) and retention time in the reticulo-rumen, of various components of the grasses were determined. 2. Grass grown on the S-fertilized plots had a mean S content of 1.57 g/kg dm compared with 1.03 g/kg dm for the control but there was no difference in the level of other elements. S fertilizer increased the level of acid-detergent fibre and lignin. 3. In the absence of a S supplement, fertilizer S increased voluntary intake by 10.5%, dm digestibility by 0.008 and reduced the period food dm was retained in the reticulo-rumen by 18.5%. Fertilizer S had no effect on rumen pH or volatile fatty acid concentration in rumen fluid, but decreased the molar proportions of propionic and butyric acids and increased those of acetic, isobutyric, isovaleric and caproic acids. 4. Supplementary S had little effect on the voluntary intake and dm digestibility of the S-fertilized grass but increased the voluntary intake and dm digestibility of the control grass by 22% and 0.036 respectively (P < 0.01). Thus the voluntary intake and dm digestibility of S-fertilized grass was lower than that of the control grass when the determinations were made with sheep supplemented with S. 5. It was concluded that S fertilizer increased nutritive value by overcoming a simple S deficiency in the diet when diets contained less than 1.7 to 1.8 g S/kg dm but this benefit was offset by a decrease in the content of digestible neutral-detergent solubles and an increase in the lignin content of the food.