Three trials were conducted to evaluate the efficacy of laidlomycin pr
opionate (LP) to reduce the incidence and severity of ruminal acidosis
in cattle fed high-grain finishing diets. In each trial, LP was fed a
t 0, 6, or 12 mg/kg of diet DM. In two acidosis-challenge trials, rumi
nally fistulated steers were fed (DM basis) a 50% concentrate diet and
then fed a 95% concentrate diet at a specific intake (2.75% BW) or st
eers were dosed intraruminally with a 100% concentrate diet. Laidlomyc
in propionate did not alter ruminal pH or total acid concentrations, b
ut in Trial 1 the 6 mg/kg level altered (P <.10) the molar proportions
of the acids, increasing total ruminal VFA and decreasing ruminal lac
tate. In Trial 3, a finishing trial, LP reduced(P <.10) intake day-to-
day variation of individually fed steers during a 13-d adaptation peri
od from a 65 to a 100% concentrate diet, suggesting reduced incidence
of subacute acidosis. Feed intake was lower (P <.05) during the first
13 d of the trial due to LP but was not affected over the entire trial
. Laidlomycin propionate improved feed efficiency (gain/feed) when cal
culated on a live weight basis (linear, P =.05) or carcass weight basi
s (linear, P = .20). Laidlomycin propionate does not prevent ruminal a
cidosis, but it may reduce the severity of ruminal acidosis during ada
ptation to a 100% concentrate diet.