Effects of monensin on ruminal fluid viscosity, pH, volatile fatty acids and ammonia levels, and microbial activity and population in healthy and bloated feedlot steers

Pharmaceuticals, direct-fed microbials, and enzymes for enhancing growth and feed efficiency of beef cattle

This article provides a brief review of the types of products commonly used in one or more countries of North America to enhance the performance of growing beef cattle. Performance-enhancing products primarily target metabolism (e.g., anabolic implants, zilpaterol, and melengestrol acetate) or gut function (e.g., ionophores, low-level antibiotics, direct-fed microbials, and enzymes). Using currently available performance-enhancing products, rate and efficiency of growth typically are improved from 5% to 20% and 3% to 10%, respectively.

Monensin controlled-release intraruminal capsule for control of bloat in pastured dairy cows

Monensin, a polyether ionophore antibiotic, is potentially an important agent for bloat relief in dairy cows grazing temperate legume-based pasture. A series of studies was undertaken to determine the effect of monensin, when delivered continuously in the rumen of lactating dairy cows by means of controlled-release capsules (monensin CRC). Such devices release approximately 300 mg/head/day for 100 d. A short-term pilot study made at Ruakura, New Zealand, tested monensin CRC in cows selected for high susceptibility to bloat and grazing lucerne (Medicago sativa) or red clover (Trifolium pratense). Treatment significantly reduced the incidence of bloat, while milk yield and protein yield were increased. There was no effect on fat yield. Following the pilot study, 6 large-scale field experiments involving a total of 368 lactating dairy cows, were made in Australia and New Zealand to confirm the effectiveness of monensin CRC for bloat control and to measure the effect of such treatment on milk production and composition. A severe bloat problem occurred in 2 experiments, mild bloat occurred in 2 others, while no visual signs of bloat were observed in the remaining 2 experiments. Bloat was significantly (P less than 0.05) reduced by monensin CRC treatment when data was pooled over the 4 experiments in which bloat occurred. Daily milk yield was increased in all experiments from a mean of 17.7 in untreated groups to 18.8 kg/head/day (P less than 0.05) in monensin CRC-treated cows. Protein percentage was not affected by treatment, while there was a decrease from 4.29 to 4.10% fat, although total fat yield was not affected.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynamics of ruminal ciliated protozoa in feedlot cattle

Fluctuations in ciliated protozoan concentrations were monitored in 40 individually fed crossbred heifers that were stepped up to an 85% concentrate diet either slowly (12 days) or rapidly (3 days), with or without monensin (30 ppm). Ruminal fluid was withdrawn from all animals by stomach tube at the start of the study, after each group reached full feed, and at 14-day intervals thereafter throughout the finishing period until termination (day 119). Neither monensin nor speed of step-up affected (P greater than 0.10) total protozoan concentrations, ruminal pH, or lactic acid concentrations. Average protozoan concentrations peaked on day 5, progressively declined until day 56, and then increased (P less than 0.05), suggesting an adaptation to ruminal conditions. Concentrations of Isotricha spp. were higher (P less than 0.05) on the final two sampling dates than at any other time. After day 28, Entodinium, Isotricha, and Polyplastron were the only surviving genera. Protozoa were not detected in 11 heifers on day 42 and day 56, but only two animals were defaunated on day 119, indicating either exogenous or endogenous refaunation. Average protozoan concentrations were not different (P greater than 0.25) between ruminal samples collected by stomach tube the day before slaughter (2.8 x 10(5)/g) and digesta samples collected the next day (1.6 x 10(5)/g). In feedlot cattle, defaunation apparently is transitory and individual animals harbor a dynamic protozoan population that fluctuates in response to changing ruminal conditions.

Effect of monensin on rumen ciliate protozoa in sheep

In a first experiment 4 rams consumed over a period of 70 days 0; 82; 208 and 345 mg of monensin daily, respectively. All doses of monensin caused a marked decrease in total numbers of rumen protozoa in samples taken after this period. More than 90% of total protozoal numbers belonged to the genus Entodinium. The sensitivity of the genus Entodinium to monensin was found to be lower than that of genera Dasytricha and Isotricha. In the second experiment 24 lambs were fed hay and concentrates in the ratio 60:40% (groups 1 and 2) and 40:60% (groups 3 and 4). Groups 2 and 4 received 40 mg monensin per animal daily during 16 weeks. The decrease in protozoal numbers due to monensin in samples taken after this period was significant (P less than 0.001) in lambs fed the concentrate diet (groups 3 and 4) and also in lambs from groups 1 and 2 fed the roughage diet (P less than 0.05). The statistical evaluation of the inhibition of total protozoal numbers by monensin (%) in lambs fed both diets has shown that the antiprotozoal effect of monensin was significantly more intensive with the concentrate diet (P less than 0.025) than with the roughage diet.