Evaluating the effects of acidosis and bacterial inoculum concentrations on the development of liver abscesses in beef × dairy steers

Abstract

Objective

We evaluated the association of diet type, ruminal acidosis bout frequency, and intraruminal bacterial inoculum concentration on liver abscess (LA) development in steers.

Materials and Methods

Beef × dairy steers (n = 40, initial BW = 107 ± 11 kg) were assigned randomly to 1 of 5 treatments that included intraruminal inoculation of either a high dose (HD; 100 mL of 1 × 10⁸ and 100 mL of 1 × 10⁹ cfu per steer) or a low dose (LD; 100 mL of 1 × 10⁶ and 100 mL of 1 × 10⁷ cfu per steer) of Fusobacterium necrophorum ssp. necrophorum and Salmonella enterica serovar Lubbock, respectively. Treatments included the following: NCON = high-forage diet with no bacterial inoculation; CON+HD = high-forage diet with a single HD inoculation; 2AD+HD = 2 acidotic diet cycles with a single HD inoculation; 4AD+3LD = 4 acidotic diet cycles with a series of 3 LD inoculations; and 4AD+HD = 4 acidotic diet cycles with a single HD inoculation. Steers were slaughtered 21 d after the last bacterial inoculation. Animal was the experimental unit. Continuous data were analyzed using mixed models, and categorical data were analyzed as binomial proportions with treatment, time, and their interactions as the fixed effects.

Results and Discussion

Incidence of LA were 0%, 37.5%, 37.5%, 50%, and 12.5% for NCON, CON+HD, 2AD+HD, 4AD+3LD, and 4AD+HD, respectively, but the difference among treatments was not significant. Although no difference was observed in rumenitis among treatments, steers with LA presented rumenitis scores that were 8 percentage points greater than steers without LA. Steers consuming the high-forage diet also were presented with rumenitis. Hematocrit values were greater in NCON, 2AD+HD, and 4AD+HD than CON+HD or 4AD+3 LD. Similarly, neutrophil:lymphocyte ratio differed among treatments, with a greater ratio for CON+HD and 2AD+HD than for NCON, 4AD+3LD, and 4AD+HD.

Implications and Applications

A key finding of this study was that steers fed a high-forage diet given a high dose of F. necrophorum and S. enterica, even in the absence of the acidotic diet, developed LA.