Resumen:
Environmental impact of livestock production has received a considerable public scrutiny because of the adverse effects of
nutrient run-offs, primarily N and P, from agricultural land harboring intensive energy livestock operations. Hence, this study was
designed to determine the efficacy of dietary phytase supplementation on fermentation of a sorghum grain–based total mixed
ration (TMR) using a ruminal in vitro digestion approach. Phytase was supplemented at three doses: 0 (control), 540 (P540), and
720 (P720) g/t dry matter, equivalent to 0, 2.7 × 10
CFU/t DM, respectively. Compared to P720 and the control,
gas production was higher for P540 after 12 h (P = 0.02) and 24 h (P = 0.03) of fermentation suggesting a higher microbial
activity in response to phytase supplementation at lower phytase levels. Correspondingly, dry matter degradability was found to
have improved in P540 and P720 compared to the control by 13 and 11% after 24 h of incubation (P = 0.05). For ammonia
nitrogen (NH3-N), a tendency towards lower values was only observed for P540 at 24 h of fermentation (P = 0.07), while minimal
treatment effects were observed at other fermentation times. The concentrations of total volatile fatty acids (VFA) were higher
(P < 0.05) after 48 h of fermentation for P540 and P720 compared to the control (P = 0.03) by 10% and 14%, respectively.
Ruminal acetate tended towards higher values in the presence of phytase after 12 h of fermentation (P = 0.10), but towards lower
values after 24 h of fermentation (P = 0.02), irrespective of the phytase dose applied. A trend towards lower ruminal propionate
levels was observed in the presence of phytase after 6 h (P = 0.10) and 12 h (P = 0.06) of fermentation, while no effects were
found at other fermentation times. In conclusion, phytase supplementation has the potential to improve metabolic energy activity
of rumen microorganisms and the use of feed constituents. Thus, phytase supplementation could help to reduce environmental
contamination in areas of ruminant production.