PSXII-15 Fiber content in diets for feedlot lambs: ruminal and cecal pH and short chain fatty acids

Abstract

Fifty-eight Dorper x Santa Inês ram lambs (initial BW 20.7 ± 1.19 kg and 75 ± 10.83 d old) were assigned to a randomized complete block design to evaluate the effects of fiber content on ruminal and cecal pH and SCFA. The treatments were defined by the fiber (“Coastcross” hay) content in diets (CP: 16,12% ± 0.92): 0F: no forage diet (NDF: 10.4%); 5F: 5% of forage (NDF: 12.1%); 10F: 10% of forage (NDF: 15%); 15F: 15% of forage (NDF: 15.5%); 20F: 20% of forage (NDF: 20.8%) and 25F: 25% of forage (NDF: 23.5%). The experiment lasted 89 days, at the end of the experiment the lambs were slaughtered without fasting. The forage inclusion linear decreased ruminal concentration of propionate (0F: 45.4; 5F: 39.7; 10F: 41.5; 15F: 39.4; 20F: 35.3; 25F: 30.5 mM/100mM; P < 0.01) and total SCFA (0F: 106.6; 5F: 96.4; 10F: 84.2; 15F: 90.6; 20F: 63.0; 25F: 71.2 mM; P = 0.01) and increased the ruminal concentration of acetate (0F: 43.4; 5F: 45.3; 10F: 47.8; 15F: 49.8: 20F: 51.8; 25F: 57.2 mM/100mM; P < 0.01). However, there was a quadratic effect on ruminal pH (0F: 5.61; 5F: 5.66; 10F: 5.98; 15F: 6.27; 20F: 6.05; 25F: 5.74; P = 0.01). There was no effect of fiber levels on cecal concentration of acetate, propionate, butyrate and acetate:propionate ratio. Nevertheless, there was a linear decrease in cecal concentration of valerate (0F: 3.28; 5F: 2.35; 10F: 2.39; 15F: 2.64: 20F: 2.12; 25F: 1.80 mM/100mM; P < 0.01) and total SCFA (0F: 173.9; 5F: 165.7; 10F: 153.2; 15F: 155.2; 20F: 139.9; 25F: 128.9 mM; P < 0.01). Similarly to rumen, cecal pH presented a quadratic response (0F: 5.92; 5F: 6.12; 10F: 6.15; 15F: 6.23; 20F: 6.30; 25F: 5.83; P < 0.01). In conclusion, cecal fermentation was different from rumen fermentation. However, pH variation was similar, with higher values for 15F diet.