August 20, 2020

Interpretive Summary: Effects of monensin inclusion and level of intake in limit-feeding strategies for beef cows

Interpretive Summary: Effects of monensin inclusion and level of intake in limit-feeding strategies for beef cows. 

By: Dr. Emily Taylor 

Competition for land resources and climatic variability have limited the forage available for grazing cattle. Thus, the expansion of primary production to meet the growing protein demand has been limited. Researchers are constantly looking at ways to optimize these systems to be economically and environmentally resilient to the changes. 

A recent article published in Translational Animal Science evaluated the effects of intake management and ionophore inclusion on diet utilization under managed in-take conditions in beef cattle. Specifically, their objective was to test the hypothesis that limit-feeding and use of an ionophore will improve diet utilization and reduce feed requirements for the maintenance of pregnant cows. 

Forty cows (diets at 120% (H) or 80% (L) of maintenance with either 0 or 200 mg/d monensin) were fed for 56d to evaluate effects on diet utilization and energy retention. Sixteen ruminally cannulated steers were also fed these diets to determine effects on digestion, energy value, and ruminal fermentation. 

Cows fed H had greater BW gain and retained energy, although heat production was also greater. Monensin had limited effects on overall BW gain, retained energy and calculated heat energy. In steers, L increased digestion of dry matter, organic matter, acid detergent fiber, and gross energy, while decreasing passage rate. Monensin lowered the acetate:propionate ratio and increased ruminal pH. Feed required for maintenance was not altered, however, limit-feeding reduced the apparent daily maintenance requirement 26% from the model-predicted values.  

These results suggest that limiting the intake of moderate energy density diets improves the efficiency of diet utilization of beef cows. The use of ionophores in conjunction with limit-feeding conferred expected outcomes for measures of ruminal fermentation and may have altered cow adaptation to restriction below targeted maintenance; however, these effects were not pronounced in the overall outcomes. the authors feel that further exploration of the role of ionophores, such as the timing of application, may be warranted.