Supplementing narasin or monensin to control coccidiosis in naturally infected calves.

This experiment compared narasin and monensin as anticoccidials for calves naturally infected with Eimeria spp. Twenty-four weaned, non-castrated male calves (Bos indicus × B. taurus cross) were assigned to this experiment (days -8 to 42). All calves were infected by Eimeria spp. according to oocyst count per gram (OPG) from fecal samples collected on days -8 and -7 (average 1,059 ±â€…101 oocysts/g). Calves were housed in individual pens, received corn silage, mineral mix, and water for ad libitum consumption, in addition to a grain-based supplement at 200 g/head daily. Fecal samples were collected on days -2 and -1 for OPG, and results averaged as initial OPG value. Calves were blocked according to initial OPG into eight blocks of three calves each, ranked within each block according to body weight (BW) recorded on day -1, and assigned to receive narasin (NAR; 0.8 mg/kg of BW), monensin (MON; 1 mg/kg of BW), or no ionophore (CON; negative control). Ionophores were added to the grain-based supplement, and offered from days 0 to 42 of the experiment. Calf BW was recorded on days 7, 14, 21, 28, 35, and 42. Fecal samples were collected on days 6 and 7, 13 and 14, 20 and 21, 26 and 27, 34 and 35, and 41 and 42 for OPG analysis, and results from samples collected on consecutive days were averaged. Aliquoted fecal samples were also pooled across calves from the same treatment and collection days, and used to determine the prevalence of individual species of Eimeria. No treatment effects were detected (P ≥ 0.51) for calf BW or growth rate. A treatment × day interaction was detected (P < 0.01) for OPG, as NAR and MON calves had less (P < 0.01) OPG compared with CON calves beginning on day 7. The OPG was also less (P ≤ 0.03) in MON compared with NAR calves on days 7, 14, and 28, but did not differ (P ≥ 0.48) on days 21, 35, and 42. The anticoccidial efficacy of NAR and MON did not differ (P ≥ 0.16) when calculated across all Eimeria spp., or according to prevalence of E. bovis and E. alabamensins. A treatment × day interaction was detected (P = 0.04) for anticoccidial efficacy to E. alabamensis, which was greater (P < 0.01) in MON calves on days 7 and 14 and did not differ (P ≥ 0.40) afterward. Collectively, both ionophores were similarly effective in controlling coccidiosis upon completion of the 42-d study, although the anticoccidial effects of monensin were noted earlier in the experiment. Nonetheless, these results corroborate narasin as an efficient anticoccidial ionophore for naturally infected calves.

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 (I²â€…= 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.