An updated meta-analysis of the anti-methanogenic effects of monensin in beef cattle

Meta-analyses were performed to quantitatively summarize the effects of monensin on in vivo methane (CH4) production in beef cattle, and differentiate these outcomes according to dietary management, dose of monensin, and length of monensin supplementation. Data from 11 manuscripts describing 20 individual studies were used, and CH4 was converted to g/d when required. Studies were classified according to dose of monensin (mg/kg of diet dry matter), length of monensin supplementation prior to the last CH4 measurement, feeding management (ad libitum vs. limited-fed), and diet profile (high-forage or high-concentrate diets). Variance among studies were assessed using a χ² test of heterogeneity and calculated using I² statistics. The inclusion of monensin decreased (P < 0.01) CH4 production by 17.5 g/d when all studies were analyzed together. A moderate (P < 0.01) heterogeneity (I² = 55%) was detected for CH4 production estimates between studies; thus, meta-analyses were performed within classes. The reduction in CH4 differed (P < 0.01) according to dose of monensin, as it decreased (P < 0.01) by 25.6 g/d when the high recommended dose range was used (32 to 44 mg/kg), and tended to decrease (P ≤ 0.07) by 9.7 and 13.5 g/d when the moderate (≤31 mg/kg) and above recommended (≥45 mg/kg) doses were used, respectively. The reduction in CH4 also differed (P < 0.01) according to the length of monensin supplementation. Monensin decreased (P ≤ 0.05) CH4 production by 24.3 g/d when supplemented for <15 d, by 15.4 g/d when supplemented from 23 to 33 d, by 24.3 g/d when supplemented from 52 to 79 d, and tended to decrease (P = 0.06) CH4 production by 3.21 g/d when supplemented from 94 to 161 d. The reduction in CH4 did not differ (P = 0.37) according to diet profile, despite a 30% difference in reduction when monensin was added to high-forage (20.89 g/d) compared with high-concentrate diets (14.6 g/d). The reduction in CH4 tended to differ according to feeding management (P = 0.08), decreasing by 22.9 g/d (P < 0.01) when monensin was added to diets offered ad libitum, and by 11.5 g/d (P = 0.05) in limit-fed diets. Collectively, this study provides novel insights and further corroborates monensin as CH4 mitigation strategy in beef cattle operations. The most effective responses were observed during the first 79 d of monensin supplementation, and when monensin was included between 32 to 44 mg/kg of diet, was added to high-forage diets, and added to diets fed ad libitum.

Amiodarone does not affect the distribution and fractional turnover of triiodothyronine from the plasma pool, but only its generation from thyroxine in extrathyroidal tissues

The peripheral metabolism of T3 has been studied in 10 hypothyroid patients receiving daily oral replacement doses of 200 micrograms T4 or 60 micrograms T3, in divided doses, before and during treatment with 400 mg amiodarone (AMD) daily for 3 weeks. Each patient received 1 microCi/kg BW [125I]T3, iv. Blood samples were drawn at 10, 20, 30, and 60 min and 2, 4, 6, 8, 12, 24, 36, 48, 60, and 72 h, followed by trichloroacetic acid precipitation and ethanol extraction of the serum samples. The parameters of T3 kinetics were obtained from the area under the disappearance curve of [125I]T3 from serum using a noncompartmental analysis. In five T4-treated patients, AMD induced a significant increase in serum T4 (P less than 0.02), serum free T4 (P less than 0.01), and serum TSH (P less than 0.02) and a marked decrease in serum T3 (P less than 0.005). Fractional turnover and MCRs were not affected by the drug. However, the extrathyroidal pool of T3 (P less than 0.02) and its degradation rate (P less than 0.001) were both significantly diminished. In the five T3-treated patients, AMD did not induce alterations in the parameters of T3 kinetics or in serum T3 and TSH concentrations. The data clearly establish that AMD does not affect the distribution and fractional removal of T3 from the plasma pool, but only its generation from T4 in extrathyroidal tissues. This conclusion does not rule out the possibility that the drug may interfere with a number of intracellular events dependent on T3 action which may be independent of T3 deiodination.