Why is intake reduced when cattle are fed tall fescue?

Authors: Klotz, James

Submitted to: Proceedings of the Kentucky Alfalfa Conference
Publication Type: Proceedings
Publication Acceptance Date: 2/21/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: A major problem for the cattle producer that utilizes tall fescue forage is the unrealized or reduced gains in body weight in growing animals. Is the problem of reduced growth solely a consequence of reduced intake in affected animals? Other factors that could be contributing to the reduced growth besides intake are effects ergot alkaloids have on the digesta and absorption of nutrients. A series of studies were conducted that separated intake of ergot alkaloids from intake of feed. These studies led to the overall conclusion that the decrease in weight gain associated with fescue toxicosis is driven by the corresponding decrease in feed intake. This has led to the framing of a new question, what is driving the decline in intake?

Technical Abstract: Previous research that has evaluated the reduced body weight gains of cattle grazing endophyte-infected tall fescue pastures have been confounded by the concomitant reduction in dry matter intake caused by exposure to ergot alkaloids. Research using pair-fed rumianlly cannulated steers has permitted the dosing of ergot alkaloids independent of feeding. These studies determined that consumption of ergot alkaloids caused decreased metabolism, did not negatively effect the overall energy balance or digestion of feed, cause a large reduction in blood flow to the stomachs of steers, and decreased particulate passage of gut contents. Additionally, in all of these studies a consistent observation that was made was the increased percentage of rumen dry matter contents observed in steers receiving ergot alkaloids. Based on this observation and the previously mentioned findings, it was concluded that cattle gain less on toxic endophyte-infected tall fescue pastures because they eat less. Although simple sounding, this conclusion has resulted in a shift in the focus of current research to better understand the decrease in intake in animals suffering from fescue toxicosis. Currently research is focusing on the effects ergot alkaloids have on gut motility and the rumen microbial populations associated with fermentation of forages to possibly explain the reduced intake associated with fescue toxicosis.