Effects of abomasal slaframine infusion on ruminal digesta passage and digestion in steers

Slaframine was infused intra-abomasally once daily 3 h after feeding to four ruminally and abomasally cannulated Jersey steers (586 ± 88.6 kg) at 0 (saline control), 10, 20, or 30 μg kg−1 BW in a 4 × 4 Latin square design experiment. Periods were 14 d in length. On a DM basis, diets were a 38:62, sorghum silage: concentrate offered at 125% of the net energy required for maintenance. Ruminal, abomasal, and fecal samples were collected at 2-h intervals on days 10–12, and ruminal contents were completely evacuated and sampled at 3, 6, 12, and 24 h after feeding on days 13 and 14. Ruminal volume and pH increased (linear; P < 0.05) from 1.6 to 8.9% and from 0.10 to 0.22 units, respectively, with SF. Total ruminal VFA and ammonia concentrations decreased (linear; P < 0.05) with SF from 4.1 to 9.4% and from 5.3 to 10.2%, respectively. Apparent ruminal DM and starch digestion increased at the lowest dosage and decreased at higher dosages of SF (quadratic; P < 0.05). Ruminal NDF digestion decreased with SF (linear; P < 0.1). Totat tract DM digestion was not affected by SF. Fractional turnover rate of ruminal DM increased (linear; P < 0.05) from 1.6 to 11.3% with SF. During the first 8 h after SF administration, liquid dilution rate increased as much as 18.5% with the highest dosage of SF (linear; P < 0.05). During the 10– to 21-h period after SF administration, dilution rate decreased with the 10– to 20-μg kg−1 BW dosages of SF (quadratic, P < 0.05). Outflow of AA tended to decrease at 10 and 20 and increased at the 30 μg kg−1 BW dosages of SF (quadratic, P < 0.05). Abomasal infusion of SF alters digesta passage and the site of digestion of nutrients between the rumen and the lower digestive tract. The highest level shifted the site of digestion to the lower tract while lower dosages enhanced ruminal digestion. Key words: Rumen fermentation, digestion, passage, muscarinic, cholinergic