An experiment using 40 Angus or Brahman X Angus preconditioned feeder calves was conducted to evaluate the influence of shipping on cellular immune reactivity. Steers were allotted on the basis of weight and breed to a control or shipped group. Shipped steers were trucked 700 km to a feedlot; control steers remained at the ranch of origin. Total and differential leukocyte counts, phytohemagglutinin skin-test responses, lymphocyte blastogenic responses, monocyte phagocytic function, packed cell volumes and concentrations of plasma cortisol were determined before, immediately after and 1 wk after shipment. At unloading, total leukocytes were increased (P less than .05) in shipped Angus steers. Shipped steers also had higher (P less than .01) numbers of neutrophils. Skin-test responses to phytohemagglutinin were higher (P less than .05) in Angus than in Brahman X Angus steers, but shipping did not influence the reaction. Lymphocyte blastogenic responses were lower (P less than .05) in shipped steers; however, cortisol levels in plasma were not elevated (P greater than .10) in shipped calves. Monocyte phagocytosis and packed cell volume were not influenced by shipping. These data suggest that shipped steers have suppressed lymphocyte blastogenic responses.

No abstract

One thousand twenty steers and heifers were used in six feeding trials to examine the influence of laidlomycin propionate on feedlot performance and to determine the most efficacious dietary concentrations of that ionophore. Cattle were fed diets ranging in energy content from 1.08 to 1.49 Mcal NEg/kg of DM. Laidlomycin propionate improved rate of gain and feed conversion in both steers and heifers. Improvements in performance were not evident when laidlomycin propionate was fed at only 3 mg/kg. However, both average daily gain and feed conversion were improved by laidlomycin propionate within the range of 6 to 12 mg/kg of DM (P less than .001). Feed consumption was not substantially affected by inclusion of laidlomycin propionate in the diet. Improvements in ADG and feed conversion were greater on lower-energy diets than on higher-energy diets, but both these performance characteristics were improved regardless of the type of diet fed. Average daily gain was maximized with laidlomycin propionate at 6 mg/kg, whereas improvements in feed conversion were sustained through 12 mg/kg. Carcasses of cattle fed diets containing 6 to 12 mg/kg of laidlomycin propionate weighed 7.3 kg more (P less than .001) than carcasses of cattle fed the control diets. Yield grade and quality grade were not affected by laidlomycin propionate (P greater than .05).

The successful use of ionophores under extensive grazing conditions requires self‐administration systems. This study was conducted to evaluate the efficacy of monensin administration via a monensin ruminal delivery device (MRDD) for beef cattle grazing early‐summer bluestem range. Performance trials were conducted in 1986 and 1987 (76 and 75 d, respectively) with beef steers managed under three stocking rates (SR). Treatment groups within each pasture were (i) control (forage only = FO); (ii) MRDD; (iii) estradiol 17β implant (E); and (iv) MRDD + E for the 1986 trial and E and MRDD + E for the 1987 trial. Concurrent with the 1987 trial, eight beef heifers with ruminal and esophageal fistulas were assigned to the FO and MRDD treatments to determine effects of monensin administration via an MRDD on forage use characteristics. In 1986, a treatment × SR interaction was observed (P < 0.05) for average daily gain (ADG). Within the 1.75 and 1.5 SR, ADG with MRDD was similar (P > 0.10) to that with FO. In contrast, within the 1.25 SR the MRDD, E and MRDD + E groups gained more (P < 0.05) than the FO group. The E and MRDD + E treatment groups consistently displayed higher (P < 0.05) ADG than the MRDD or FO groups, regardless of stocking rate. In 1987, no treatment × SR interaction was observed for ADG. The MRDD + E steers tended (P= 0.09) to gain more than E steers; however, SR did not influence ADG. Forage organic matter intake, digestibility, liquid flow, and most fermentation characteristics were not different (P > 0.10) for heifers receiving an MRDD compared with nontreated (FO) heifers. Use of an MRDD to administer monensin to grazing cattle tended to promote increased ADG when cattle were managed under the highest SR; however, response was not consistent across years for the two lowest SR. The MRDD treatment resulted in only minor alterations of measured forage use characteristics.