Latin square trial reveals distinct rumen protein degradabilities across supplements in cannulated steers, indicating varied nitrogen flow to the lower digestive tract.
Key Points
To evaluate the rumen degradation of single-cell protein, maize-gluten meal, rapeseed meal, and urea, and to determine their effects on carbohydrate digestion and microbial nitrogen synthesis in steers.
Four steers fitted with rumen and abomasal cannulas were fed four isoenergetic diets containing urea, single-cell protein, maize-gluten meal, or rapeseed meal in a 4 x 4 Latin square design.
Digesta flows to the abomasum were measured using chromic oxide and polyethylene glycol markers.
Microbial nitrogen synthesis was quantified using RNA, 35S, and diaminopimelic acid as microbial markers.
Rumen ammonia concentrations were approximately 9 mmol/l across all protein supplement diets, significantly lower than the 16 mmol/l observed with the urea diet (P < 0.05).
Rumen liquid outflow rate was significantly faster on the rapeseed meal diet (0.160/h) compared to the urea diet (0.099/h; P < 0.05), whereas particulate marker outflow rates did not differ significantly (0.027 to 0.032/h).
True rumen protein supplement degradability was 0.51 for maize-gluten meal, 0.73 for single-cell protein, and 0.98 for rapeseed meal, corresponding to dietary nitrogen degradabilities of 0.69, 0.79, and 0.90, respectively.