| Ruminal protozoa (RP) are the main contributors to bacterial turnover in the rumen; therefore, we hypothesize that suppression of RP would improve N utilization in the rumen. In the first experiment, lauric acid (LA, C12:0), showed strong anti-ruminai protozoal activity when a single dose of 160 g/d was given via ruminal cannula, reducing RP by 90%. In the second experiment, intakes of 164 and 243 g/d of LA reduced the RP by only 25 and 30% respectively, showing that these levels in the TMR were not sufficient to suppress RP effectively. In a third study, cows consumed four levels of LA in the TMR (0, 129, 270, and 438g/d) to determine the dietary level that would effectively suppress RP. Consuming 270, and 438 g/d of LA reduced RP by 67, and 80%, respectively. Intake of 270 g/d of LA reduced ruminal ammonia and total free amino acid concentrations by, respectively; 48 and 51%, and increased ruminal propionate concentration by 55%. After LA was removed from the diet, RP returned to pre-dosing numbers within 12 days. A fourth trial with 48 lactating cows was conducted to evaluate higher levels of LA in the TMR. LA intakes of 220, 404, and 543 g/d reduced RP by 28, 50, and 64% respectively; however, the two higher levels also reduced DMI and consequently milk production. In a fifth experiment, dietary coconut oil, in which LA comprises about 45% of the fatty acid composition, was evaluated as a practical defaunating agent. Intakes of 288 and 687 g/d of LA and CO respectively; reduced RP numbers by about 40%. LA reduced yields of milk and milk components and CO reduced MUN. Surprisingly, no significant effect on ruminal ammonia and total free AA was observed in this study, suggesting that this level of suppression of RP may be insufficient to improve N utilization in the rumen. It is still a challenge to reduce RP population, in a practical way, to levels that could potentially improve N utilization in dairy cows without negatively affecting DMI, ruminal fermentation, and NDF digestibility. |
