title: Effect of virginiamycin on ruminal fermentation in cattle during adaptation to a high concentrate diet and during an induced acidosis.
abstract: The objective of Exp. 1 was to compare the effects of virginiamycin (VM; 0, 175, or 250 mg x animal(-1) x d(-1)) and monensin/tylosin (MT; 250/ 90 mg x animal(-1) x d(-1)) on ruminal fermentation products and microbial populations in cattle during adaptation to an all-concentrate diet. Four ruminally cannulated, Holstein steers were used in a 4x4 Williams square design with 21-d periods. Steers were stepped up to an all-concentrate diet fed at 2.5% of BW once daily. Ruminal pH, protozoal counts, and NH3-N and VFA concentrations generally were unaffected by VM or MT. Mean counts of Lactobacillus and Streptococcus bovis were lower (P<.05) for VM-treated compared with control or MT-treated steers. Both VM and MT prevented the increase in Fusobacterium necrophorum counts associated with increasing intake of the high-concentrate diet observed in the control. The objective of Exp. 2 was to compare the effects of VM and MT on ruminal pH, L(+) lactate and VFA concentrations, and F. necrophorum numbers during carbohydrate overload. Six ruminally cannulated Holstein steers were assigned randomly to either the control, VM (175 mg/d), or MT (250 + 90 mg/d) treatments. Acidosis was induced with intraruminal administration of a slurry of ground corn and corn starch. The VM and MT premixes were added directly to the slurry before administration. Carbohydrate challenge induced acute ruminal acidosis (pH was 4.36 and L (+) lactate was 19.4 mM) in controls by 36 h. Compared with the controls, steers receiving VM or MT had higher (P<.05) ruminal pH, and the VM group had a lower (P<.05) L (+) lactate concentration. Fusobacterium necrophorum numbers initially increased in VM- and MT-administered steers. In the control steers, F. necrophorum was undetectable by 36 h. Virginiamycin seemed to control the growth of ruminal lactic acid-producing bacteria and, therefore, has the potential to moderate ruminal fermentation in situations that could lead to rapid production of lactic acid.
authors.affiliation: Department of Animal Sciences, Kansas State University, Manhattan 66506, USA.
authors.forename: M L
authors.initials: ML
authors.lastname: Coe
authors.forename: T G
authors.initials: TG
authors.lastname: Nagaraja
authors.forename: Y D
authors.initials: YD
authors.lastname: Sun
authors.forename: N
authors.initials: N
authors.lastname: Wallace
authors.forename: E G
authors.initials: EG
authors.lastname: Towne
authors.forename: K E
authors.initials: KE
authors.lastname: Kemp
authors.forename: J P
authors.initials: JP
authors.lastname: Hutcheson
mesh_terms: D000138:Acidosis / Q000662:veterinary*; D000222:Adaptation, Physiological; D000821:Animal Feed; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002417:Cattle / Q000378:metabolism*; D005285:Fermentation / Q000187:drug effects*; D005673:Fusobacterium / Q000302:isolation & purification; D006863:Hydrogen-Ion Concentration; D008297:Male; D012417:Rumen / Q000187:drug effects* / Q000382:microbiology; D016985:Streptococcus bovis / Q000302:isolation & purification; D014769:Virginiamycin / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D014769:Virginiamycin