Comparison of feed additive technologies for preconditioning of weaned beef calves

Our objective was to evaluate the response of weaned calves to different supplemental feed additives in a supplement to affect calf performance and mitigate stress response observed during weaning and preconditioning. At weaning in each of 2 yr, 160 Angus and Brangus calves (203 and 227 ± 2.3 and 2.5 kg) were stratified by BW, sex, and breed and were randomly allotted to 1 of 4 treatments ( = 40 calves/treatment): 1) supplement without feed additives (control, CON), 2) supplemented with chlortetracycline, 350 mg/d (CTC), 3) supplemented with monensin, 175 mg/d (RUM), and 4) supplemented with rumen modifier, 5 g/d (ACT). Calves were held by treatment in 1 of 4 drylot pens for 7 d after weaning and were offered ad libitum access to hay and 2.27 kg/d of supplement before placement in one of thirty-two 0.8-ha pastures (5 calves/pasture). On pasture calves were supplemented with 2.27 kg/d (yr 1) or supplemented at 1.0% BW (yr 2). Calf BW and blood samples were collected following weaning (d 0, 1, 4, 7, 11 in yr 1; d 0, 1, 3, 7, 14 in yr 2), at the conclusion of the preconditioning period (d 50, 51 in yr 2), and after transportation (d 52, 55, 59, 65 in yr 2) for analysis of acute phase protein (APP) concentrations. In yr 2, after 44 d on pasture, calves were loaded on 2 semitrucks and transported for 24 h. On return, calves were placed in 4 pastures with hay and fed their respective supplements for 14 d. For each year, data were analyzed with the MIXED procedure of SAS. The model included the main effect of treatment, and pasture was the experimental unit. All variables quantified by day were analyzed using repeated measures. In yr 1, ACT and CTC had greater (P <0.05) 52-d ADG than RUM, whereas CON was intermediate. However, in yr 2, over the 50-d postweaning period there was no difference (P = 0.20; 0.52 kg/d) in ADG response among treatments. After transportation, 7- and 14-d ADG were improved (P < 0.05) for ACT and CTC compared with CON and RUM. In both years, postweaning plasma concentrations of haptoglobin were similar (P > 0.05) among treatments; however an effect of day after transport (P < 0.001) was observed. Feed cost of gain and income over production cost (P ≥ 0.15; mean = $0.51/kg and $73.51, respectively) were not different among treatments. Use of supplemental additives may improve calf performance during a preconditioning period of this duration, but no additive was effective at mitigating stress postweaning. Additives were equally effective in supporting calf growth performance during a posttransportation period.

Comparison of the oral bioavailability and tissue disposition of monensin and salinomycin in chickens and turkeys

The current study describes the pharmacokinetic parameters of two carboxylic polyether ionophores: monensin in turkeys and salinomycin in chickens. These data can be used to understand and predict the occurrence of undesirable residues of coccidiostats in edible tissues of these animal species. Special attention is paid to the distribution of residues between the different edible tissues during and at the end of the treatment period. For the bioavailability studies, monensin was administered to turkeys intravenously, in the left wing vein, at a dose of 0.4 mg /kg and orally at a dose of 20 mg /kg. Salinomycin was administered to chickens intravenously, in the left wing vein, at a dose of 0.25 mg /kg and orally at a dose of 2.5 mg /kg. Residue studies were carried out with supplemented feed at the rate of 100 mg /kg of feed for monensin in turkeys and 70 mg /kg for salinomycin in chickens, respectively. Coccidiostats had a low bioavailability in poultry (around 30% for monensin in chickens, around 1% for monensin in turkeys and around 15% for salinomycin in chickens). Monensin in chickens had a longer terminal half-life (between 3.07 and 5.55 h) than both monensin in turkeys (between 1.36 and 1.55 h) and salinomycin in chickens (between 1.33 and 1.79 h). The tissue /plasma partition coefficients showed a higher affinity of both monensin and salinomycin for fat, followed by liver and muscle tissue. The depletion data showed a fairly rapid elimination of coccidiostats in all the tissues after cessation of treatment. According to the results of depletion studies, a withdrawal period of 1 day seems sufficient to avoid undesirable exposure of consumers.