Abstract:
Dietary treatments had a minimal effect on performance parameters in this study, with no response being observed for DM intake, body composition and lactational performance (P < 0.05). The only exception being milk protein content which was reduced (P = 0.04) by supplementation with MON. Ruminal pH and fermentation parameters were monitored at intervals over a 24 hour period. Treatment had no significant effect on ruminal acidity, however, both C and DFM tended (P = 0.07) to present with lower mean ruminal pH values than AB10. The AB10 treatment tended to reduce the time pH remained below 5.5, the threshold for sub-acute ruminal acidosis, as compared to C (AB10 = 6.1 hours versus C = 10.1 hours, P = 0.09) and was numerically less than DFM (9.3 hours) and MON (7.1 hours). Treatment had a minimal effect on the ruminal volatile fatty acids (VFA’s) and ammonia-nitrogen concentration. Treatment had no impact on microbial protein synthesis but MON tended (P = 0.07) to have a reduced MCP yield compared to AB10. Bacteria isolated from both the fluid and particulate phases of the rumen were found to differ in chemical and AA composition. Supplementation was shown to have an effect on the bacterial AA profile, with 9 and 10 of the 16 AA’s being either altered (P < 0.05) or tending to be altered (P ≤ 0.10), for the fluid-associated and particle-associated bacterial fractions, respectively. Of which the most limiting AA’s for dairy cows, lysine, methionine and histidine were affected by treatment (P < 0.05). This study demonstrates the potential of feed additives to alter the composition of the MCP following to the duodenum, however, no clear pattern of alteration in the AA profile was identified. Owing to the significant contribution of this protein source to meeting the AA requirement of ruminants’ further research on this topic is warranted.
