For mares grazing E+ fescue, Monroe et al. (1988) observed a high percentage of still-born foals. Surviving foals were large-framed, dysmature, and emaciated looking (poor muscle mass), with overgrown hooves. When the foals survived the birthing process, the mares had an average gestation length 27 d past the expected foaling date (Fig. 17-1). These foals appeared weak and many times were not alert, exhibiting a nonresponsive type of behavior and appearing lethargic. Later, with proper care, the foals appeared normal (Monroe et al., 1988; Earle et al., 1990). In addition, septicemia (bacterial infection at or near birth) is a frequent problem and is likely a result of the low level of passive immunity. Putnam et al. (1991) reported that of 11 mares grazing E+ fescue, only three foals were alive at birth and only one of the three survived the first month. In that study, dysmaturity or neonatal death of foals was not observed in 11 mares grazing E- pastures.

Taylor et al. (1985) and Kosanke et al. (1989) observed lack of lung maturation in stillborn foals born to E+ mares. Amniotic fluid from E+ mares lacked pulmonary phospholipids, and phosphatidylethanolamine was present in only 12% of those E+ mares (Clare et al., 1994). These data suggest that lack of lung maturation may be a contributing factor to the high rate of foal death observed from mares on E+ fescue. Boosinger et al. (1994) examined several organs and tissues from foals of E+ and E- mares. Histologic studies of thyroid glands from foals exposed to E+ continuously or after gestation Day 300 revealed numerous distended colloid-filled thyroid follicles lined by flattened cuboidal epithelial cells. Mean plasma T3 concentrations were reduced in these foals. Foals from mares exposed to E+ continuously or from Day 300 to foaling demonstrated a response to thyroid stimulating hormone by showing improved mental alertness, desire to stand, and good suckle reflex.

Brendemuehl (1995) collected colostrum from normal mares and tested it for immunoglobulin G (IgG) concentration. Foals from mares exposed to E+ fescue continuously or from gestation Day 300 were administered 1.0 L of the pooled, collected colostrum collections by nasogastric tube within 1 h of birth. Compared to control foals not from E+ or E- fescue mares, these foals had decreased serum IgG concentrations. These data suggest that foals from E+ mares receive less IgGs from the milk produced by the mares, and their absorption rate was lower even if the milk IgG levels were at or near normal levels. These factors, combined with the lower level of colostrum production in E+ mares, explain why many foals from E+ mares quickly become septic. The lower colostrum and nutrient intake from milk, especially IgG, probably accounts for many foal deaths from E+ mares that have live foals at birth. Brendemuehl et al. (1994c) observed lower serum T3, adrenocorticotrophic hormone (ACTH), cortisol, and total progestogen levels in foals from E+ mares compared to foals from E- mares.


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