Nutritional Influences on Reproduction: Effects of Endophyte-infected Tall Fescue on Beef Cattle Performance

Introduction

Tall fescue, a cool-season perennial grass, is one of the most commonly grown forages for over 8.5 million cattle in the United States. Cattle suffering from fescue toxicosis experience decreased feed intake and performance, elevated respiration rate and body temperature, rough hair coats and necrosis of the extremities (tail, hooves, and ears) due to loss of circulation. Endocrine and reproductive effects of fescue toxicosis in cattle include decreased calving rate and pregnancy rates, reduced circulating concentrations of hormones such as cortisol, prolactin (PRL), progesterone (P4) and LH. This toxicosis results in estimated losses to the United States beef industry of $609 million annually due to lowered conception rates and depressed body weight gains.

We have made considerable progress in “identifying the window” in timing of reproductive loss associated with grazing infected tall fescue. We also know that addition of clover to our pastures will help reproductive performance in cattle, as does the addition of supplemental feeding of grain (etc.). This supplementation with clovers and grain is thought to have a “diluting” effect on the toxic component of tall fescue grass. In technical terms, the assumed “bad” component of tall fescue infected with the endophyte, Neotyphodium coenophialum, is an alkaloid known as “ergovaline” (produce by the endophyte) that negatively affects performance of the animal but plays a beneficial role on the hardiness of the grass. However, recent research by Hill et al. indicates that transport of the ergopeptine alkaloid “ergovaline” across ruminal gastric tissue is low as compared to the simple ergoline alkaloids such as lysergic acid; thus, suggesting other alkaloids may play a larger role in tall fescue toxicosis. 

So with all this said, the tall fescue research team at the University of Tennessee has focused their research attention on determining “how” and “when” the grazing of endophyte-infected tall fescue (E+) affects reproduction in cows and bulls. We performed these studies by either grazing tall fescue pastures (E+ or MaxQ, non-toxic endophyte, NTE) or by using a synthetic compound called ergotamine tartrate (referred to as ERGOT) to simulate the negative effects of ergovaline since ERGOT was commercially available, presented the same signs of tall fescue toxicosis, and we could control the nutritional status of the animal (thus removing nutrition from the equation as it relates to reproduction). Now to the reproduction part, we first wanted to know when consumption of endophyte-infected tall fescue had a negative effect on reproduction. There are several different periods of concern when looking at reproduction in a beef cattle setting, so we broke these time periods into different stages beginning with (1) the effect on the bull, (2) late pregnancy losses in the cow, (3) losses due to hormonal changes before estrus (heat), and (4) embryonic or uterine losses immediately following estrus. [...]