Dairy producers recognized early that cattle grazing E+ tall fescue had reduced growth and milk production and exhibited other signs of toxicosis. Most dairy managers in the mid-southern United States use E+ tall fescue as exercise lots and do not depend on the forage to supply a significant portion of the nutrient needs of the cows. Many managers also use E+ fescue pastures for raising dairy heifers, where performance demands are similar to those of beef replacement heifers and stocker steers. However, the advent of novel endophytes may allow dairy producers in the future to use tall fescue as a valuable forage for heifers and milking cows.
The U.S. tall fescue growing region supports about 1.4% of the U.S. sheep population (West and Waller, 2007). Most of the sheep in the region are in small flocks, and few graze monocultural pastures of tall fescue. Sheep have been used in tall fescue toxicosis research as the species of interest and as model animals to represent larger ruminants such as beef cattle. Ingestion of E+ tall fescue by ewes resulted in reduced milk production (Stidham et al., 1982), decreased serum prolactin (Bond et al., 1988), and lower cholesterol (Bond et al., 1988; Stuedemann et al., 1985). In three out of four studies, there was no difference between highly infected tall fescue and orchardgrass for ewe productivity, ADG, gestation length, average number of lambs born, lamb birth weight, lamb survival, and lamb ADG to weaning (Bond et al., 1988).
Ewes experienced problems such as delayed onset of estrus and increased embryonic mortality rather than oocyte fertilization failure due to E+ grazing (Bond et al., 1982, 1988). Yearling cross-bred ewes had more reproductive problems than mature ewes (Burke et al., 2002). These results have led to the recommendation of providing paddocks of E- or novel endophyte tall fescue when breeding yearling ewes.
Sheep have been used in tall fescue toxicosis research to represent cattle because they would require fewer resources. Chestnut et al. (1992) used sheep in a digestibility trial to evaluate responses to E+ and E- tall fescue hays with similar organic matter and N digestibilities. In a similar study, Burns and Fisher (2006) reported no difference in DMD or CP digestibility when sheep were fed hays varying in endophyte status. Hannah et al. (1990) fed tall fescue seed to lambs to determine the effects of increasing levels of ergovaline on digestibility and ruminal kinetics. When ergovaline levels were greater than 1.5 mg/kg and temperatures were at 34°C, ruminal and total tract OM, NDF, and cellulose digestibility decreased. These results support numerous studies in cattle in which elevated ergovaline levels and temperature have been associated with poor animal performance. McLeay and Smith (2006) investigated the effects of ergotamine and ergovaline on the smooth muscle of the reticulorumen. They reported an immediate decrease in the frequency of cyclical reticulum and rumen contractions compared to recordings made before administration of ergot alkaloids. Reticulorumen motility alterations may explain, in part, the variation in digestibility reported for ruminants consuming highly infected tall fescue.
Growing lambs have been used as a less expensive animal than cattle in safety grazing trials to evaluate elite tall fescue cultivars infected with novel endophytes not producing ergovaline. Lambs grazing E+ tall fescue had reduced ADG and lower prolactin levels than lambs fed E- or tall fescue containing a novel endophyte (Parish et al., 2003a). Similar observations were reported by Emile et al. (2000) for lambs even though ambient temperatures were lower than those reported by Parish et al. (2003a). These results indicate that sheep can serve as an excellent model for selecting tall fescue cultivars and endophyte combination when seed availability would limit grazing trials using cattle.
Limited information exists on the effects of N. coenophialum on goats. This probably is due to the limited exposure goats have to tall fescue because of their preference for forbs and browse. However, with the increasing numbers of goats in the mid-southern United States, more research will be needed if goat production on tall fescue-based pasture systems becomes more popular.
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