Several signs of tall fescue toxicosis have been reported in beef cows and heifers. These signs include decreased milk production, reduced body weight, rough haircoat, reduced pregnancy rates, and reduced serum prolactin. Decreased milk production of cows grazing E+ tall fescue has been associated with lower weaning weights of calves (Keltner et al., 1988; Peters et al., 1992).
Watson et al. (2004) compared beef cow-calf performance of animals grazing either E+ fescue or tall fescue infected with the novel endophyte AR542, which is nontoxic (see Chapter 20). Cows grazing tall fescue with AR542 (trademarked as MaxQ in the United States [Pennington Seed Co., Madison, GA] and MaxP in New Zealand and Australia [Grasslanz Technology Ltd., Palmerston North, New Zealand]) had higher body condition scores and average daily gain (ADG) than those consuming wild-endophyte E+ tall fescue. No difference in calving rate or calving interval was observed. Birth weights of calves from dams grazing E+ tall fescue were lower than those of calves from dams grazing tall fescue with MaxQ. Calves raised on tall fescue containing MaxQ had higher ADG than those grazing tall fescue with naturally occurring wild E+. These results were similar to those reported by Smith et al. (1975) for cows grazing E- fescue or orchardgrass (Dactylis glomerata L.) pastures. Both cows and calves grazing E+ pastures had reduced serum prolactin levels. Lower birth weights for calves born to first-calf heifers grazing E+ pastures were reported by Bolt and Bond (1989) and Waller et al. (2001) when compared with heifers grazing E- tall fescue pastures. The lower birth weights may be linked to reduced uterine blood flow in animals consuming ergot alkaloids present in E+ tall fescue (Porter and Thompson, 1992) or to reduced nutrient intake associated with decreased dry matter intake (DMI) commonly reported for cattle grazing E+ tall fescue.
Brown et al. (1992) reported that Angus cows (Bos taurus) grazing E+ tall fescue had more of a decrease in milk production than Brahman cows (B. indicus). Browning (2004) evaluated growth and tolerance to E+ using Hereford and Senepol steers. Hereford steers had reduced growth, increased respiration rates, and increased shade use compared with Senepol steers consuming E+ in summer (Fig. 16-4 and 16-5). Similar differences between Brahman and Hereford steers were reported also (Browning, 2000). Collectively, these studies demonstrate the possibility of a genotype X environment interaction for beef cattle grazing E+ tall fescue. However, it should be noted that the differences observed between B. indicus and B. taurus cattle grazing E+ tall fescue may be related to the differences in heat tolerance of the animals and not only exposure to the alkaloids. Research on mice indicated there is a possibility that animals can be selected for tolerance or resistance to toxins in E+ fescue (Wagner et al., 2000), possibly providing an explanation for some of the variability that has been seen among cattle grazing E+ tall fescue.
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Fig. 16-4. Angus steers on E+ tall fescue wallowing under shade rather than grazing during the day at Knoxville, TN, in July 2003.
Fig. 16-5. Angus steers grazing E- tall fescue rather than seeking shade, Knoxville, TN, in July 2003.
A factor that greatly influences economic returns in cow-calf enterprises is the percentage of cows that deliver a live calf each year. Pregnancy rates of cows grazing E+ tall fescue were 55% while those grazing E- tall fescue were 96% (Schmidt et al., 1986). More recent investigations on reduced pregnancy rates have focused on determining the time when, during the reproductive cycle, ergot alkaloids have the greatest detrimental effects. Burke and Rorie (2002) investigated follicular and luteal development and function in mature lactating beef cows grazing E- or E+ tall fescue during the early postpartum period. Follicular dynamics were altered in cows grazing E+ tall fescue, but apparently were not affected by ergot alkaloids. Seals et al. (2005) reported that age and size of ovulatory follicles were not altered when heifers were administered ergotamine tartrate to simulate the effects of ergot alkaloids found in E+ tall fescue. In another study, pregnancy rates and embryonic losses tended to be different among cows between 30 and 60 d of gestation after environmental temperatures were high for 3 wk when grazing E- or E+ tall fescue (Burke et al., 2001). Waller et al. (2001) used pregnant (30-45 d) beef heifers to graze either E+ or E- tall fescue pastures until full term. Calving began in early October, and the numbers of calves born were not different between the E+ or E- groups. They concluded that problems in conception and pregnancy were occurring before the first 30 d of gestation. Schuenemann et al. (2005c) implanted 7-d embryos in control heifers and in heifers fed ergotamine tartrate for 30 d. Survival rates of these embryos were not different, thus indicating that loss in pregnancy occurred within the first 7 d following conception, or that there was a failure at the time of conception. The period of concern has been narrowed to release of the mature follicle and the first 6 d of embryo development, rather than the approximately 9 mo of gestation.
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