Two hundred eighty-eight beef steers (British x Continental x Brahman) were fed a 90% concentrate diet containing either no ionophore (control), laidlomycin propionate at either 6 or 12 mg/kg of dietary DM, or monensin plus tylosin (31 and 12 mg/kg of DM, respectively). Neither of the two levels of laidlomycin propionate nor monensin plus tylosin affected (P greater than .10) ADG or feed:gain ratio. Monensin plus tylosin reduced (P less than .01) daily DMI for the 161-d trial period compared with the other three treatments. Laidlomycin propionate at 6 mg/kg increased (P less than .05) DMI relative to the control, laidlomycin propionate at 12 mg/kg, and monensin plus tylosin diets during the 2nd wk of the trial and from d 57 to 84. Treatments did not affect carcass measurements. In a second experiment, 12 ruminally cannulated steers were fed diets containing no ionophore or laidlomycin propionate at either 6 or 12 mg/kg of DM. Samples were obtained for two consecutive days while the dietary concentrate level was 75%, after which the diet was switched abruptly to 90% concentrate, and samples were collected on several days during a 21-d period. The rate at which steers consumed their daily allotment of feed was not altered markedly by laidlomycin propionate. Likewise, laidlomycin propionate did not affect total ruminal VFA concentrations or proportions. Ruminal concentrations of D-lactate were reduced (P less than .10) by 6 but not by 12 mg/kg of laidlomycin propionate.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of adding whole cottonseed (WCS) and live yeast culture (YC) to a diet of 60% alfalfa and 40% concentrate on ruminal fermentation and liquid dilution rate in steers were examined in two trials. Twelve ruminally cannulated Hereford steers (approximately 420 kg) were used. Concentrates were 1) a basal grain mix composed of ground corn, ground barley and rice bran, 2) basal mix with 10% WCS, 3) basal mix with 1.6% YC and 4) basal mix with 10% WCS and 1.6% YC. No differences were detected (P greater than .10) in ruminal pH of steers fed WCS or YC in either trial. Ruminal ammonia levels tended to be higher (P greater than .10) in steers fed WCS. Acetate was higher and butyrate was lower in steers receiving 10% WCS (P less than .10) compared with controls. Molar proportions of acetate and butyrate increased while propionate decreased (P less than .05) over time after feeding. Intake and apparent digestibility of dry matter was not influenced by treatments. Whole cottonseed and(or) YC appear to have minimal effects on ruminal fermentation, but they might alter ruminal liquid passage rate with diets containing 60% ground alfalfa and 40% concentrate.

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