Effects of endophyte-infected tall fescue on animal performance

Agriculture, Ecosystems and Environment, 44 ( 1993 ) 233-262

233

Elsevier Science Publishers B.V., Amsterdam

Effects of endophyte-infected tall fescue on animal performance S.P. Schmidt and T.G. Osborn Department of Animal and Dairy Sciences, Auburn University, AL 36849-5415, USA

ABSTRACT Schmidt, S.P. and Osborn, T.G., 1993. Effects of endophyte-infected tall fescue on animal performance. Agric. Ecosystems Environ., 44: 233-262. Cattle grazing tall fescue (Festuca arundinacea Schreb. ) infected ( E + ) with the fungal endophyte Acremonium coenophialum (Morgan-Jones and Gams) or fed diets containing E + hay and seed exhibit signs of toxicosis. These signs are intensified by a hot environment and include hyperthermia, poor appetite, rough hair coat, reduced gains, lowered conception rates, suppressed milk production and hypoprolactinemia. As a result of the hyperthermia, cattle seek shade and stand in water. Grazing times for cattle on E+ fescue change to the cooler evening and night hours compared with grazing times on endophyte-free ( E - ) fescue. Cattle switched from E - to E+ fescue exhibit changes in grazing times and decreased forage intake within days, whereas cattle switched from E+ to E - continue to exhibit signs of toxicosis for several weeks. In most fescue grazing studies where several levels of infestation were present, steer average daily gains (ADG) decreased linearly by approximately 0.045 kg for each 10% increase in E + level. The decrease in ADG due to E+ was numerically greater for British-bred (Bos taurus) steers than for Brahman-cross (Bos indicus) steers although statistical significance has not been consistent. Differences in ADG are associated more with decreased intake than other factors such as decreased digestibility, although in hay and seed feeding trials the decreased gain was greater than could be accounted for by the decreased energy consumption. Steers that graze E + fescue prior to entering a feedlot for finishing probably will exhibit compensatory, gains unless they enter the feedlot during a period of heat stress. Lactating beef cows grazing E + pastures often will be in negative energy balance, have reduced pregnancy rates and have decreased milk production compared with those grazing E - . Calf weaning weights also will be reduced. For replacement heifers continually consuming fescue pasture or hay varying from 0 to 99% infested, milk production decreased 0.15 kg, pregnancy rate decreased 3.5% and ADG decreased 0.04 kg for each 10% increase in infestation level. Pregnant mares grazing E+ fescue have a prolonged gestation of approximately 1 month, fail to exhibit normal signs of approaching parturition, have a high incidence of dystocia, retained and thickened placentas, weak or stillborn foals, and agalactia, and decreased pregnancy rates. Energy supplementation of mares grazing E+ fescue has not been effective in ameliorating these reproductive problems. Removal of mares from E + fescue 1 month prior to anticipated parturition results in normal parturition and mammary development. Removal of mares 10 days post-term results in signs of impending parturition within 48 h. Fescue toxicosis signs have been observed in all species studied, and all have had some measure of animal performance adversely affected.

('orrespondence to: S.P. Schmidt, Department of Animal and Dairy Sciences, Auburn University, AL 36849-5415, USA.

© 1993 Elsevier Science Publishers B.V. All rights reserved 0167-8809/93/$06.00

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INTRODUCTION

Tall fescue is a cool-season, perennial bunch-grass (Buckner, 1985 ) which has enjoyed much popularity over the past 50 years. Today it is estimated that tall fescue is grown on over 14 million hectares in the US (Stuedemann and Hoveland, 1988 ), and it is the most widely grown pasture grass in the humid areas of the eastern US (Buckner et al., 1979). Most of the tall fescue grown in the southeastern US is of one cultivar, 'Kentucky 31' ('KY-31'). Fescue has been popular as a pasture grass because of its wide range of adaptation, ease of establishment, persistency under a wide variety of management regimes, tolerance of poor soil and climatic conditions and long grazing season with good winter growth (Siegel et al., 1984; Ball et al., 1987; Stuedemann and Hoveland, 1988 ). Indices of forage quality such as digestible dry matter, crude protein, cell wall content, and minerals suggest that tall fescue is of high quality and should give good animal performance. Instead, tall fescue has gained a reputation for causing reproductive problems in farm livestock, reduced calf weaning weights, and reduced gains with grazing steers. The production problems associated with consumption of tall fescue generally have been categorized as one of three disorders: fescue foot, bovine fat necrosis, and 'summer slump' or 'summer syndrome'. The latter disorder has come to be known by the collective term 'fescue toxicosis'.

Fescuefoot The most dramatic visible disorder of cattle grazing fescue is 'fescue foot' which is a dry, gangrenous condition most often associated with lameness and the loss of ear tips, tail tip and in acute situations feet and hooves or the entire limb (Garner and Cornell, 1978; Yates, 1963, 1983). Not only are the animars extremities affected but, animal performance is also reduced in affected animals (Jacobson et al., 1970). Fescue foot usually occurs in cattle grazing tall fescue in the cool seasons of the year, namely winter, and therefore seems to be associated with lower ambient temperature (Garner and Cornell, 1978; Yates et al., 1979). Yates (1963) stated in his review of fescue foot that the first reports of fescue foot were made by Cunningham in Australia in 1949, Pulsford in New Zealand in 1950 and Goodman in the US in 1952. It has been speculated by many investigators that the toxic principle in tall fescue responsible for fescue foot has vasoconstrictive properties (Jensen et al., 1956; Yates et al., 1979 ). Jensen et al. (1956) reported that post-mortem dissection of the vasculature of an affected foot showed thrombosis of the arteries. They concluded that the toxic principle causes vasoconstriction in the extremities which results in thrombosis. Lower ambient temperature, which is associated with the development of this syndrome, would normally result in vasoconstriction to con-

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serve body heat (Curtis, 1983 ). If this vasoconstriction associated with normal thermoregulation in cold environments was further exacerbated by the consumption of a vasoconstrictive substance, then it is logical to hypothesize that blood flow to the extremities could be reduced to the point of gangrene (Woods et al., 1966). Even though many scientists have speculated that a relationship exists between the fungal endophyte, Acremonium coenophialum (Morgan-Jones and Gams, 1982), and fescue foot, no conclusive evidence exists that this is the case. Hoveland et al. (1983b) observed no evidence of fescue foot in longterm grazing studies comparing E + with E - rescue. Stuedemann et al. (1985c) and Pedersen et al. (1986) observed findings similar to those of Hoveland et al. (1983b). In contrast, steers and heifers grazing E + rescue in late winter in Texas developed signs of fescue foot (Read and Camp, 1986 ). Therefore, it appears that even though a casual relationship between the consumption of E + fescue and fescue foot has been observed, adequate evidence is lacking to conclusively prove that this fungus is responsible for fescue foot.

Bovine fat necrosis Another disorder which has been shown to occur in cattle grazing fescue is "bovine fat necrosis' which is sometimes referred to as liptomatosis (Wilkinson et al., 1983 ). Fat necrosis is characterized by the presence of masses of hard or necrotic fat, primarily in the adipose tissue of the abdominal cavity. The manifestations of fat necrosis usually result in inadequate physical space within the abdominal cavity and regions of the reproductive tract due to these large masses of fat. Therefore, dystocia and digestive disturbances are a common sign (Wilkinson et al., 1983 ). Even though fat necrosis is not usually of great economic concern to the cattle industry as a whole, it can be of great concern for an individual producer. In acute situations death of an animal may occur due to intestinal strangulation. Necrotic fat contains more crude protein and ash, with less ether-extractable material, than does normal fat, and the cholesterol content of the etherextracted fraction is three to four times greater in necrotic than in normal fat with no differences in long-chain fatty acid content (Rumsey et al., 1979 ). Fat necrosis is likely to occur where the pasture sward is essentially pure fescue, and these pastures have received relatively high levels of nitrogen fertilization (Williams et al., 1969; Wilkinson et al., 1983; Stuedemann et al., 1985a). The source of this nitrogen fertilizer can vary from a commercial fertilizer product to organic sources such as broiler litter. It has been shown that cattle grazing pastures fertilized with either type of nitrogen have developed fat necrosis (Hemken et al., 1984; Stuedemann et al., 1985a). Stuedemann et al. (1985a) also noted that the incidence of fat necrosis increased with increasing nitrogen fertilization and that plasma cholesterol concentra-

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tion was lowest in cows grazing E + fescue which received the high level of nitrogen fertilization. Steers grazing an experimental line of fescue known to be E + and to produce signs of fescue toxicosis also had lowered plasma cholesterol concentration (Stuedemann et al., 1985a). Stuedemann and Hoveland (1988) speculated that E + fescue and the resulting poor animal performance may be related to fat necrosis; however, the mechanism(s) responsible for this relationship has not been established.

Fescue toxicosis This disorder often is referred to as 'summer slump' or 'summer syndrome' because of the unthrifty animal appearance and poor performance during the summer. Fescue toxicosis is of great economic concern to the cattle industry because it has caused large economic losses to beef producers in the US. Even though fescue foot and fat necrosis are of concern to the beef producer, they are not nearly as common as fescue toxicosis nor do they result in the tremendous economic losses to the beef industry as does fescue toxicosis. The signs of fescue toxicosis are reduced animal gains, reduced feed intake, intolerance to high environmental temperature, excessive salivation, rough hair coat which the animal fails to shed in the spring, elevated body temperature, and endocrine imbalance (Bush et al., 1979, Hemken et al., 1979; Schmidt et al., 1982; Hoveland et al., 1983a; Stuedemann and Hoveland, 1988 ). Additionally, animal behavior is altered in that the animals seek shade, stand in the water and consequently spend less time grazing during the hot part of the day (Bond et al., 1984; Stuedemann et al., 1985b, 1989a). These signs have become the focal point of much research over the past two decades. In 1973, J.D. Robbins, C.W. Bacon and J.K. Porter visited the A.E. Hays farm near Mansfield Georgia where one herd of Angus cattle grazing fescue exhibited virtually all the signs of fescue toxicosis while another herd exhibited none of the signs (Robbins, 1983 ). Based on work in New Zealand which showed that tall fescue was susceptible to infection by an endophytic fungus, these scientists hypothesized that the toxic syndrome might involve a fungus (Bacon et al., 1977). Bacon sampled the pastures and noted that the pasture which produced the toxicosis in the cattle was 100% infested with a fungal endophyte while in the other pasture only 10% of the plants were infected (Robbins, 1983 ). Following analysis of additional forage samples from the states of Georgia, Kentucky, Maryland, Missouri and Virginia the researchers hypothesized that the endophytic fungus Epichlo~ typhina was associated with the observed fescue toxicosis in cattle (Bacon et al., 1977 ). This fungus was later reclassified by Morgan-Jones and Gams ( 1982 ) as Acremon-

ium coenophialum. During the time these discoveries were being made in Georgia, a grazing study was being conducted by Hoveland et al. (1980b) at the Blackbelt Sub-

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237

station in west-central Alabama. The objective of this study was to compare steer performance on pastures of'KY-31" fescue and a phalaris grass in westcentral Alabama. Beef steer average daily gains (ADG) on the 'KY-31' fescue were similar to those recorded from cattle grazing the phalaris, averaging 0.78 kg day-~. It was noted that these gains were comparable to beef gains obtained in cattle grazing a high-quality small grain pasture (Hoveland et al., 1980b). Because these ADG were superior to those reported from previous studies of cattle grazing fescue (0.4-0.5 kg day -I ) (Blaser et al., 1956; Mott et al., 1971 ), the pastures were sampled for the presence of the endophytic fungus. The fungus was not present in the tall fescue pastures in this study but was found to be present in adjacent tall fescue pastures (Hoveland et al., 1980b). In a second grazing study being conducted simultaneously at the same location, it was observed that the ADG of steers in two of three fescue paddocks averaged 0.68 kg day- I over a 3-year period, while steers grazing the other tall fescue paddock gained only 0.45 kg day- ~. It was found that the two paddocks supporting the fastest ADG had a low frequency of the fungus (20%) while the paddock which resulted in the slow ADG had a heavier infestation ofAcremonium coenophialum (60%) (Hoveland et al., 1980a ). These observations were consistent with those of Bacon et al. ( 1977 ). Based on these observations, a 4 year grazing study (Hoveland et al., 1983b ) was conducted at the same substation. Steers were assigned to paddocks that were either infested with the fungus (94% of the plants or greater infected) or were relatively free of the fungus (less than 5% of the plants infected ). The 4-year mean ADG of cattle on the pastures with the low infection rate was 0.83 kg day- t compared with only 0.50 kg day- t for the cattle grazing the E + pastures. Other signs of fescue toxicosis, including elevated body temperatures, rough hair coats and excessive salivation, were noted in the cattle grazing the E + pastures. Also, animal behavior was altered in that the cattle on the E + pastures spent less time grazing during the daytime and more time in the shade. Even though none of these grazing trials demonstrated a cause and effect relationship, they did confirm the hypothesis of Bacon et al. (1977) that the fungal endophyte Acremonium coenophialum was associated with the fescue toxicosis syndrome. Furthermore, they demonstrated that excellent cattle performance could be obtained on tall fescue in which a low percentage of the plants were infected with the endophytic fungus. The remainder of this review focuses on the effects of endophyte-infected fescue on animal performance. EFFECT OF THE ENDOPHYTE ON G R A Z I N G / G R O W I N G ANIMALS

Steer grazing trials Since early reports of the association of the fungal endophyte with fescue toxicosis, many grazing and feeding trials have been conducted, mainly at

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universities in the southern region of the US, to study and more clearly define the problem. The majority of the research reported in the literature has dealt with cattle, particularly steers, grazing fescue in a pasture situation. Table 1 summarizes data from several states which illustrate that decreased gains by steers grazing infected fescue are widespread, quite uniform, and not limited to certain geographical areas or management conditions. Fescue toxicosis originally was commonly referred to as 'summer syndrome' or 'summer slump' because signs were most pronounced during hot weather. However, Hoveland et al. (1984) showed that poor weight gains on endophyte-infected pastures occur throughout the grazing season (Table 2 ), being reduced almost as much during the cool-season months as during the warm-season months. TABLE I Daily gains of steers as affected by low or high incidence of endophyte infection of fescue Location

Alabama

Arkansas Georgia Kentucky Mississippi Missouri Oklahoma Tennessee Texas Virginia

Endophyte ~

Daily gain

Low E (%)

High E (%)

Low E (kg day -~ )

High E (kg day -~ )

2 0 0 0 0 < I NR 2 3 < I 2 8 0

> 90 > 90 100 81 76 61 NR 83 76 71 91 77

0.83 0.66 0.96 0.71 0.59 0.70 0.68 0.62 0.85 0.67 0.97 0.65

0.45 0.28 0.20 0.51 0.46 0.45 0.46 0.21 0.62 0.48 0.46 0.41

Feed

Reference

Pasture Hay Seed Pasture Pasture Pasture Pasture Pasture Pasture Pasture Pasture Pasture

Hoveland et al., 1983b Schmidt et al., t 982 Schmidt et al., 1982 Goetsch et al., 1988 Stuedemann et al., 1986 Boling, 1985 Evans et al., 1989 Crawford et al., 1989 McMurphy et al., 1990 Chestnut et al., 1991 Read and Camp, 1986 Tulley et al., 1989

~Number of infected tillers per 100 tillers. 2Not reported. TABLE 2 Seasonal daily gains (kg) of steers grazing E + and E - fescue ( 3-year average )

Months

November, December, March April, May, June

Endophyte

ADG decrease

< 50/o

> 94%

0.72 0.78

0.36 0.32

IAdapted from Hoveland et al., 1984.

50% 59%

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The relationship between levels of nitrogen fertilization, either from an organic or an inorganic source, and increased incidence of bovine fat necrosis (Stuedemann et al., 1985a) caused speculation that there might be a relationship between nitrogen fertilization rate and fescue toxicosis. Stuedemann et al. ( 1986 ) reported that a high rate of nitrogen fertilization (336 versus 134 kg N ha- ~year- ~) did not affect steer ADG, but it did increase gain per hectare because of higher stocking rates necessary to maintain constant forage availability. Most of the early grazing trials which were performed to investigate the association between the endophyte, fescue toxicosis, and animal gains were conducted on pastures having either very high or very low levels of infestation. A negative linear relationship between steer gain and level of endophyte was proposed by investigators where intermediate levels of endophyte infection existed, and it was suggested by some that ADG decreased approximately 0.045 kg for each 10% increase in infection rate (Garner et al., 1984; Williams et al., 1984; Stuedemann et al., 1985c; Pedersen et al., 1986 ). Crawford et al. (1989), utilizing fescue pastures having endophyte infection frequencies ranging from 3 to 83%, reported that season-long steer ADG fit the following relationship: ADG (kg d a y - ~ ) = 0 . 6 6 - ( 0 . 0 0 4 5 × % E + ) , (R2=0.51). Seasonal variation existed whereby spring-summer ADG was decreased 0.068 kg day- ~for each 10% increase in E +, while no relationship existed for autumn grazing. Williams et al. (1984) and Stuedemann et al. (1985c) also reported that a relationship existed for spring-summer grazing but not for autumn. Not all researchers have shown a linear relationship. Fribourg et al. ( 1991 ) reported that the effect of the endophyte on animal performance was not linear. They observed a greater depression per unit of infestation at lower levels (approximately 20% E + ) than at higher levels (35% E + or greater). Their fescue pastures contained clover, whereas those used by investigators cited previously were essentially pure stands of fescue. Fribourg et al. ( 1991 ) reported that fescue-clover pastures in which the fescue ranged from 0 to 80% infestation were similar in composition and quality at the initiation of grazing, but under grazing pressure, the proportion of clover tended to decrease as percent endophyte increased. In the E - pastures, cattle preferred the fescue; thus, the proportion of clover increased and fescue decreased over the grazing season. Knowledge of the relationships among endophyte infection frequency in fescue, animal selectivity when other forage species are present, and animal performance is important and helpful when making management and economic decisions.

Behavioral changes associated with endophyte-infectedfescue Long before the discovery of the endophyte, it was known that cattle grazing fescue spent more time in the shade compared with cattle grazing other

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forages, and they also would get into ponds or watering troughs and wallow in the mud. Bond et al. (1984) reported that steers grazing a high-endophyte experimental fescue line spent less time grazing during the day and more time grazing at night (Table 3 ); they spent more time standing or lying in the shade, and had a reduced total grazing time compared with steers grazing a lowendophyte fescue. Paterson et al. (1987) reported a similar shift from daylight to night grazing. In a study designed to determine carry-over effects when steers are switched from E+ fescue to E - fescue, Stuedemann et al. (1985b) noted that steers on the E - fescue spent 60% of the time between 12:00 and 18:00 h grazing, whereas steers on the E + fescue spent only 4-6% of that time grazing (Table 4). In contrast to Bond et al. (1984), they did not observe a difference in total grazing time between the E+ and E - fescue. After grazing the E + and TABLE 3

Percentage of total daylight or dark hours steers spent in various activities"2 Activity

Grazing Lying in field I n shade

Daylight

Dark

E-

E+

E-

E+

(%)

(%)

(%)

(%)

52 14 15

34 2 51

8 81 0

22 50 3

'Adapted from Bond et al., 1984. 2Activities such as time at water trough, consuming salt and standing in water not included. TABLE 4

Effect of change-over on percentage of time steers spent grazing between 12: 00 and 18: 00 h t Date

Endophyte < 1%

(%)

High 2 to >95%

(%)

low

Low 3 to high

(%)

(%)

10 33 6

40 28 25

Beforeexchange May 14 and 15

60

6

604 65 44

44 21 14

After exchange 2 days 1 week 1 month

'Stuedemann et al., 1985b. ZExchanged from high to low-endophyte fescue. 3Exchanged from low to high-endophyte fescue. 4percentage grazing time for steers not exchanged.

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E - fescue for approximately 6 weeks, half the steers in each group were switched from E + to E - and E - to E + (Table 4). Steers switched to E + showed a reduction in grazing time between 12: 00 and 18: 00 h within 2 days, whereas those switched to E - still had reduced grazing times 1 month later. Forage intake for the group switched to E - remained reduced for at least 10 days following the switch but was normal by 28 days; they also showed compensatory gains during the 112 day post-exchange period (Stuedemann et al., 1989a). Forage intake for the group switched to E + was depressed within l week after the exchange, and gains during the post-exchange period were slower. Very little research has been conducted to measure animal selectivity responses to E - and E + fescue. Fribourg et al. ( 1991 ) indicated that steers seemed to have a preference for clover in E + fescue pastures, but preferred fescue to clover in E - fescue pastures. When heifers were offered diets in selffeeders containing 60% fescue seed, either E - or 75% infested, l 1 or 12 heifers avoided the diets with E + seed (Garner and Cornell, 1987 ). The feeders were switched daily so the heifers would not learn which to avoid. Likewise, when 12 bulls with no prior exposure to fescue were switched from these same E - seed diets to the E + seed diets, three refused to eat for 48 h, seven ate only small amounts (0.9 to 1.8 kg daily), and two ate approximately 5 kg daily compared with intakes of the E - seed diets ranging from 6.3 to 9.1 kg daily.

Intake and digestibility of endophyte-infected fescue Much of the reduction in animal performance, measured as either ADG or gain per unit area of land, is the result of reduction in feed intake (Hemken et al, 1979; Schmidt et al., 1982; Jackson et al., 1984a,b; Bolt and Bond, 1989; Stuedemann et al., 1989a); however, this reduction in feed intake does not completely account for the reduction in body-weight gain (Schmidt et al., 1982; Osborn, 1988 ). In addition, Mizinga et al. (1990) observed decreased ADG in lactating Angus cows pair-fed diets containing 20% fescue seed (91% infested) compared with cows fed E - seed diets. This is indicative that the toxic substance (s) in the E + fescue are causing physiological modifications and stresses on the animal on a more intricate physiological basis than is observed superficially. Decreased digestibility of the forage could be responsible for a portion of the reduced performance when cattle consume E + fescue. However, Schmidt et al. (1982) showed that in vitro dry matter digestibility was superior for E + hay when compared with E - hay, indicating that forage digestibility is not the cause of the reduced ADG on E + fescue. Goetsch et al. (1987b,c) suggested that the reduced intake of E + fescue is not limited by physical factors which usually are associated with feed intake control of forage diets. These

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factors include amount or bulkiness of the digesta and the presence of forage residue in the rumen. In fact, Goetsch (1987b) stated that the toxicants do not have a major effect on ruminal microbial digestion. Additionally, when a number of additives were added to the diets of cattle consuming E + fescue, no effect was seen on feed intake and digestion of dry matter or organic matter (Goetsch et al., 1987a ). Therefore, it appears that digestibility and quality of E + fescue are not inferior to that of E - fescue, and the reduction of feed intake associated with E + fescue consumption is not a function of the feed itself. Results of digestibility trials have not been consistent with other species. E + seed was shown to have increased crude fiber, nitrogen free extract and dry matter digestibilities in diets fed to laboratory rats (Neal and Schmidt, 1985 ). Digestibility of fescue hay fed to horses was not affected by presence of the endophyte (Redmond et al., 1991b). Barth et al. (1989) observed no differences in digestibility of dry matter, organic matter, crude fiber, nitrogen-free extract, acid detergent fiber or cellulose when sheep were fed E - or E + fescue hay; however, crude protein digestibility was decreased by E + even though the hays were isonitrogenous. Ruminal and total tract digestibilities of organic matter, neutral detergent fiber and cellulose in fescue seedbased diets fed to sheep were decreased by the presence of the endophyte (Hannah et al., 1990). Rumen fluid dilution rates also were greater in sheep fed E + diets. Although the results reported by Hannah et al. (1990) appear to contradict those reported by Goetsch et al. (1987c), intakes relative to animal size were not the same in these two experiments. Intake can affect rate of passage as well as rumen fluid dilution rate, and both can affect digestibility. Thus, because of the effect that presence of the endophyte has on intake, accurate measurements of digestibility are difficult to obtain.

Effect of the endophyte on thermoregulation Cattle consuming E + fescue often exhibit hyperthermia as shown by increased rectal temperature (Hemken et al., 1979; Hoveland et al., 1983b; Goetsch et al., 1987c; Strahan et al, 1987). Hemken et al. ( 1981 ) showed that consumption of infected rescue has the most detrimental effect on the animal when the ambient temperature exceeds 31 oC. Even though reports in the literature are fairly conclusive with respect to the effect of E + rescue on hyperthermia in cattle, not all species respond the same. Rectal temperature was not affected in sheep (Bond et al., 1980) or horses (Monroe et al., 1988) consuming E + rescue and was reduced in rats (Neal and Schmidt, 1985). Osborn (1988) fed steers diets composed of E - or E + hay and seed in controlled environments at 21 °C (cool) and 32°C (hot) (Table 5). In general, the main effects of endophyte presence showed that feed intake was depressed, rectal temperature and respiration rate were elevated, heart rate was

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243

TABLE 5 Effect of consuming E - or E + fescuC seed and hay diets in a 21 °C or 32°C environment on certain physiological variables and peripheral temperatures2 Item

Feed intake (kg day- ~) Rectal temperature ( ° C ) Respiration rate (cpm) Heart rate (cpm) Ear canal ( ° C ) Ear tip ( ° C ) Pastern ( ° C ) Coronary band ( ° C ) Tail tip ( ° C )

21 °C

32 °C

E-

E+

E-

E+

6.7" 39.0 46 70" 35.4" 35.0 ~ 30.4 30.1 33.4"

4.3 b 39.0 45 53 b 34.1b 33.2 b 29.4 29.5 32.1 b

5.4* 39.9" 78" 65" 38.3 37.8 36.8 36.0" 37.9"

2.2 b 40.4 b 95 b 49 b 38.1 36.4 36.1 35.2 b 37.2 b

Means within environment with different superscripts differ ( P < 0.05 ). ~Endophyte-free or 95% endophyte-infected. 2Osborn, 1988.

reduced, and all measured peripheral temperatures were reduced; however, statistical significance varied between environments. Feed intake was reduced 36% in the cool environment, but rectal temperature and respiration rate were not affected by consumption of the E + diet. In the hot environment, feed intake was reduced 60% in steers fed the E + diet, and rectal temperature and respiration rate were increased due to the endophyte. These resuits agree with those of Hemken et al. ( 1981 ) where differences due to E + were observed above 31 °C but not below. Heart rate was reduced approximately the same in both environments in response to E + . Peripheral temperatures were decreased in the cool environment, but the effect of endophyte presence in the hot environment was not clearly delineated (Table 5). The normal vasodilation response to elevated temperatures (for body heat dissipation) was probably confounded by the vasoconstrictive properties associated with the endophyte which resulted in an inconsistent change in peripheral temperatures. The observed hyperthermia has been suggested to be a result of peripheral vasoconstriction which is caused by the toxicants (Walls and Jacobson, 1970; Bush et al., 1979; Bacon et al., 1986; Lyons et al., 1986 ). The vasoconstriction would decrease the animal's ability to dissipate body heat through evaporative and non-evaporative mechanisms. Elevated ambient temperature further compounds the problem. The consumption of ergot-infected rye by cattle has also been shown to cause vasoconstriction (Woods et al., 1966). This ergot which infects rye contains chemical compounds similar to those found in E + tall fescue (Yates et al., 1985 ). The increased respiration rate which has also

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S.P. SCHMIDT AND T.G. OSBORN

been associated with fescue toxicosis is generally associated with increased rectal temperature (Hemken et al., 1981 ). In fact, some animals actually pant (Hemken et al., 1981; Osborn, 1988 ), most likely in an attempt to cool themselves and dissipate the increased heat load. Panting is a normal method of evaporative heat loss for many species of animals (Curtis, 1983 ). The copious salivation which is another sign of fescue toxicosis may be due to the panting. During times when ambient temperature is high and the signs of fescue toxicosis are more intense (Hemken et al., 1981; Osborn, 1988 ), animal performance may be affected not only by consumption of E + fescue, but also by improper functioning of the animal's thermoregulatory mechanisms. Thermoregulation is a very complex physical, behavioral and neuroendocrinological process. Core body temperature remains almost constant within _+ 1°C in a normal animal (Guyton, 1986). Maintenance of this core body temperature is paramount to the normal function of the animal for all metabolic processes. The thermoregulatory center located in the hypothalamus receives impulses from thermosensitive cells throughout the body (Curtis, 1983; Guyton, 1986 ) and integrates this information to serve as a thermostatic body temperature control center. If the toxic agent(s) in E + fescue are resulting in neurotransmitter and endocrine imbalances within the brain, especially those areas associated with thermoregulation (Marple et al., 1988; Schillo et al., 1988 ), then it is conceivable that this neural dysfunction could result in abnormal function of the thermoregulatory center and contribute to the hyperthermia observed in cattle consuming E + fescue. When the animal begins suffering from hypothermia, the hypothalamus induces heat-producing reactions. The first of these is vasoconstriction to decrease evaporative and non-evaporative heat loss. This is followed by heatproducing reactions for body warmth. Conversely, when body temperature becomes too great, the animal must decrease heat production and dissipate the excess heat. Vasodilation is the first result of increased core body temperature followed by sweating. The output of the thermoregulatory center also affects the function of the respiratory centers in the ports and medulla oblongata which in turn control breathing (Chatonnet, 1983; Curtis, 1983). Respiration rate is related to effective environmental temperature and, in general, it remains at a minimal level until a threshold temperature is reached (Curtis, 1983). In cattle, the respiratory reaction to warming the hypothalamus is directly proportional to environmental temperature and presumably skin temperature, resulting in an increase in respiration rate (Curtis, 1983 ). Finch ( 1986 ) has stated that 15% of the metabolic heat produced in cattle is lost via the respiratory tract; the remainder must be transported to the skin where it is dissipated via evaporative or non-evaporative methods.

ENDOPHYTE-INFECTED TALL FESCUEAND ANIMALPERFORMANCE

245

Cattle consuming E + fescue exhibit elevated respiration rates (Hemken et al., 1981; Schmidt et al., 1982; Hoveland et al., 1983b; Osborn, 1988), indicating that these animals are suffering from heat stress. Furthermore, since these respiration rates seem to remain high for extended periods of time, it is very possible that these cattle are having difficulty adapting to the high environmental temperature. It has been hypothesized that prolactin (PRL) plays an important role in water and electrolyte balance (Nicoll, 1981; Faichney and Barry, 1986), and thus may be intimately involved in thermoregulation (evaporative heat loss). Cattle consuming E + fescue have been shown to have decreased PRL concentrations in the plasma (Hurley et at., 1981; Bolt et at., 1983; Daniels et at., 1984; Thompson et al., 1987; Lipham et at., 1989), and if PRL plays a role in thermoregulation then this also could be responsible for the observed hyperthermia. Brahman versus British breeds of cattle Brahman cattle are known for their heat tolerance and may be better adapted to resist or tolerate the hyperthermia observed during hot weather. In a breed comparison of steers grazing E - and E + fescue pastures, McMurphy et al. (1990) showed that Angus and Brahman-Angus crosses both exhibited decreased gains as the result of endophyte presence (Table 6). However, the magnitude of the decrease (14 versus 38%) was less for the Brahman-cross steers. In a comparable trial (Goetsch et al., 1988 ) with Brahman-cross and British-cross steers, the results were quantitatively similar (Table 6 ). However, the breed X fescue type interaction was not significant, indicating that both breeds were affected similarly. Stuedemann et al. (1989b) also reported that Angus and Brahman-cross steers were affected equally when grazing E + fescue. In all three of these experiments the Brahman-cross breeds out-gained TABLE 6 Daily gains of British and Brahman cross-bred steers grazing E - or E + rescue Breed

Endophyte

ADG decrease

Reference

(%)

< 1%

76-81%

(kg)

(kg)

Angus Brahman-Angus

0.85 ~ 0.93

0.52 0.80

38 14

McMurphy et al., 1990

British cross Brahman cross

0.552 0.87

0.34 0.68

39 21

Goetsch et al., 1988

t Breed × fescue type interaction, P < 0.01. 2Breed × fescue type interaction, P > 0.05.

246

S.P. SCHMIDT AND T.G. OSBORN

the British breeds. This is not unexpected because of the greater heterosis normally exhibited when Bos indicus cattle are crossed with Bos taurus cattle.

Feedlot gains of steers that previously grazed infected fescue Because of the rough hair coats and unthrifty appearance of steers that have grazed E + fescue and carry-over effects lasting several weeks when cattle are removed from infected to non-infected pastures, cattle from the southern region of the US often are discriminated against at the market place and bring reduced prices. Thus, it is important to determine carry-over effects of the endophyte on subsequent feedlot performance (Table 7 ). Cole et al. ( 1987 ) grazed steers in Georgia and shipped them to a feedlot in the Texas panhandle either during the summer or in early autumn. Steers arriving during cooler weather, that previously had grazed E+ fescue, exhibited compensatory gains, especially during the first 28 days in the feedlot, and gained faster than steers that previously had grazed E - fescue. Steers arriving during hot weather did not show compensatory gains, but their feedlot gains were not reduced as a result of the previous exposure to the endophyte. Piper et al. ( 1987 ) moved steers from fescue pastures to feedlot pens in Arkansas. Steers that had previously grazed E + pastures gained more than steers from E - pastures when they were moved to the feedlot in October but not in July. These two studies suggest that ambient temperature at the time cattle are moved to finishing programs can affect subsequent feedlot gains and prolong any carry-over effects of endophyte exposure. Lusby et al. (1990) and McDonald et al. ( 1988 ) also reported compensatory feedlot gains by cattle that previously had grazed E + fescue. Lusby et al. (1990) reported that even though rectal temperatures TABLE 7 Feed-lot daily gains of steers that had previously grazed low or high-endophyte fescue Arrival date

Daily gain

Reference

Low E (kg day- J )

High E (kg d a y - t )

October July

1.41 a 1.77

1.68 b 1.77

Cole et al., 1987

October July

1.05" 0.91

1.26 b 1.00

Piper et al., 1987

June Autumn September

!.58" 0.75" 1.09

1.84 b 1.04 b 1.18

Lusby et al., 1990 McDonald et al., 1988 Smith et al., 1986 ~

•.bp< 0.05 between fescue types. 'High E group had better feed efficiency ( P < 0.05 ).

247

ENDOPHYTE-INFECTED TALL FESCUE AND ANIMAL PERFORMANCE

were elevated in steers grazing E + fescue at the end of the grazing trial where ambient temperatures were 27-32 °C, they were normal 1 week later during processing at the feedlot 725 km away where the ambient temperatures were 14-18°C. In agreement with the results of Cole et al. (1987), Lusby et al. (1990) reported that compensatory gains were most rapid during the first 7 weeks indicating that the effects of the endophyte are not permanent and that compensatory gain or fill began almost immediately. Smith et al. ( 1986 ) did not observe compensatory gains by cattle that previously had grazed E + fescue, but they did report improved feed efficiency. Lusby et al. (1990) suggested that retained ownership through the feedlot should be considered by producers whose stocker cattle graze E + fescue because of the anticipated compensatory gains. EFFECT OF THE ENDOPHYTE ON PERFORMANCE AND REPRODUCTION OF COWS, N U R S I N G CALVES, A N D D E V E L O P I N G R E P L A C E M E N T HEIFERS

Cows and calves Most of the tall fescue in the US is consumed on commercial cow-calf operations. These producers also most likely raise their replacement heifers on fescue pastures. Although several experiments involving the cow herd have been conducted with fescue as a forage system, there is a limited amount of data in which E + rescue was compared with E - fescue. In several studies involving cows with nursing calves (Table 8), cows grazing E + fescue lost weight, and their calves had slower gains and reduced weaning weights compared with those grazing E - or low-endophyte fescue. Pregnancy rates for TABLE 8 Effect of endophyte-infected fescue on the performance of cows and nursing calves Calves

Cows

Reference

Daily gain (kg day -j )

Pregnancy rate (%)

Daily gain (kg day-~ )

205 day wean weight (kg)

E-

E+

E-

E+

E-

E+

E-

E+

0.46 0.21 0.19 0.04 0.36

-0.23 -0.05 0.27 -0.11 0.21

-~ 95 87 892 78

55 58 74 49

1.16 0.78 0.74 0.73 1.02

0.85 0.62 0.59 0.58 0.86

236 215 222 240

197 186 190 209

tNot determined or not reported. 2 E - fescue was 21% infested versus 77% for E + .

Schmidt et al., 1983 Gay et al., 1988 Essig et al., 1989 Tucker et al., 1989b McDonald, 1989

248

s.P. SCHMIDT AND T.G. OSBORN

cows grazing E + fescue were also reduced. The economic implications of reduced pregnancy rates are obvious. It is known that a decline in body condition can affect reproduction, and cows that are thin before and at calving have a prolonged interval between calving and first estrus (Wiltbank et at., 1964; Hansen et al., 1982). Therefore, cows entering the breeding season losing weight or in poor body condition because of E + fescue will probably have a prolonged post-partum interval regardless of the effects of the endophyte. Gay et al. ( 1988 ) showed that clover interseeded with E + fescue improved pregnancy rates compared with E + fescue only (68% versus 55%), but these pregnancy rates were not equal to the E - group. Cows grazing E + fescue (77% infested) and supplemented with a grain mixture had pregnancy rates equal (82% versus 82%) to those grazing low-endophyte fescue but not receiving supplemental feed (Tucker et al., 1989b), whereas pregnancy rate for a high-endophyte group receiving only hay was 66%. Because supplementary feed, either clover or grain, improved pregnancy rates but not up to levels acceptable to the cattle industry, it appears that factors other than nutrition are involved in the reduced pregnancy rates associated with E + fescue.

Replacement heifers Heifers raised on E + fescue beginning as young calves had delayed puberty and decreased first-service pregnancy rates (Washburn et al., 1989). Daniison et al. (1986) assigned weaned beef heifers to pastures having low (0-20% infested ), medium (25-60% infested), and high (80-99% infested ) levels of infection (Table 9). The heifers were maintained on their respective E + treatments for 2 years until they were re-bred following birth of their first calf. During winter, they received hay harvested from fields having E + levels similar to their respective pasture treatments. Breeding was done during the spring. Heifer ADG while grazing decreased linearly with increasing infestaTABLE 9 Effect of endophyte-infected fescue on gains, pregnancy rates and milk yield of heifers ~ Endophyte level (%)

0-5 25-60 80-99

Initial weight (kg)

255 254 268

Dailygains ( k g d a y - ~ ) Grazing

Winter

Total

0.75 0.57 0.34

0.08 0.16 0.54

0.54 0.44 0.39

Danilson et al., 1986. 2Schmidt et al., 1986. 3S.p. Schmidt et al., unpublished data, 1986.

Pregnant (%)

Postcalving pregnant 2

Milk produced 3 (kg per 12 h)

93 45 33

3.7 3.2 1.8

(%)

96 82 55

ENDOPHYTE-INFECTED TALL FESCUE AND ANIMALPERFORMANCE

249

tion level; however, winter ADG while fed hay was just the opposite with the high-infestation group having the fastest grains. All heifers were observed in estrus prior to their first breeding; however, pregnancy rate decreased linearly as E + level increased. Bond and Bolt (1986) demonstrated that the initiation of estrous cycle activity in heifers grazing E + fescue was not delayed; furthermore, cessation of the estrous cycle in heifers already cycling did not occur. Following birth of their first calf, pregnancy rates were further reduced in heifers grazing the medium and high-endophyte pastures but not in those grazing the low-endophyte pastures (Schmidt et al., 1986 ). A subsequent study (Ahmed et al., 1990) with similar heifers showed that the heifers apparently were cycling and ovulating normally, but cellularity changes in the corpus luteum (CL) of heifers grazing E + fescue may have altered CL function such that pregnancy could not be maintained. Bond et al. (1988) hypothesized that reduced fertility in ewes was more likely the result of embryonic mortality than failure of ovum fertilization. It was demonstrated that more ewes returned to estrus when grazing E + fescue than when grazing orchard-grass pasture. The effect of the endophyte on calf birth weight is not clear. Beers and Piper (1987) and Bolt and Bond (1989) reported lighter birth weights of calves from heifers exposed to E + fescue (Table 10); however, Schmidt et al. ( 1986 ) indicated that birth weights were not different among progeny of heifers grazing E - compared with E + treatments. Interestingly, these latter heifers were the only ones grazing E + fescue from breeding through calving. Heifers used by Beers and Piper ( 1987 ) were removed from fescue at approximately 3-4 months of gestation and were maintained on wheat/bermuda-grass pastures through calving. Bolt and Bond (1989) introduced pregnant heifers to E + fescue at about Day 155 of gestation where they remained until they calved at which time they were removed to a dry lot and fed corn silage. The approximately 130 day exposure to the E + fescue did not affect milk production by the heifers or weight gain by their calves. Reproduction in laboratory animals also has been shown to be altered when they consume E+ fescue diets. Zavos et al. (1986) demonstrated that male TABLE 10 Effect of E + fescue on calf birth weights of 2-year-old heifers ABW ~ (kg)

Probability (e<)

Reference

3.7 4.9 1.8

0.02 0.05 0.27

Bolt and Bond, 1989 Beers and Piper, 1987 S.P. Schmidt, unpublished data, 1986

~Binh weight of calves from heifers grazing E - fescue minus birth weights from E + fescue.

250

S.P. SCHMIDT AND T.G. OSBORN

rats consuming E + fescue seed suffered from decreased feed intake and ADG as well as reduced testicular and total epididymal weights. Furthermore, it also was shown that sperm production was decreased even when corrected for testicular and epididymal weight; however, no effect was observed in sperm motility. Female mice also were studied by Zavos and coworkers in two studies. Only 79% of the mice consuming diets containing E + fescue seed gave birth, whereas, 100% of those on lab food diets gave birth (Zavos et al., 1987a). The interval between whelping and breeding was extended by 3 days in mice consuming the E + fescue diet and not only did these mice have fewer litters but also the number of pups per litter, litter weight and individual pup weight were reduced. In a second mouse study (Zavos et al., 1987b), pregnancy rate was once again reduced, and it was further reduced when both sexes consumed an E + fescue diet prior to conception. Animals which were pair-fed a control diet performed adequately in all three of these studies, suggesting that decreased feed intake or energy intake was not responsible for the altered reproduction.

Milk production Milk production was reduced by as much as 45% in beef cows (Schmidt et al., 1983), 50% in beef heifers (Table 9) and 60% in dairy cows (Hemken et al., 1979) consuming endophyte-infected fescue. In fact, Danilson et al. ( !986 ) showed a 0.15 kg day- ~ reduction in milk production for each 10% increase in pasture infestation level, and Hemken (1988) and Strahan et al. (1987) have suggested that there is no threshold level of infection for dairy cows. Strahan et al. ( 1987 ) showed that milk production by dairy cows consuming E- fescue was not different from those consuming alfalfa-orchard-grass forage (Table I l ) and that E + fescue resulted in reduced forage intake, reduced milk production, and a loss in body weight. The effects of E + fescue on milk T A B L E 11 Effect o f E + fescue on milk production by mid-lactation Holstein cows t Measurement

Alfalfa/orchardgrass control

"KY-31 ''2

"KY-31""

Infection level (%) Forage intake (kg) Daily milk (kg) ,J Body weight (kg)

0 10.9" 21.3" 14"

0 9. I b 19.6 a 12"

63 7. I c 15.6 b - 11.7 b

• .b.c( p < 0.05 ) a m o n g forage types. mAdapted from Strahan et al., 1987. 2"Kentucky-31" tall fescue.

ENDOPHYTE-INFECTED TALL FESCUE AND ANIMAL PERFORMANCE

2 51

production appear to be more detrimental for horses than for cattle. Monroe et al. (1988) showed that 88% of gravid mares grazing E + fescue suffered from agalactia after foaling. ALLEVIATING THE EFFECTS OF INFECTED FESCUE

Pasture management Several methods of pasture management have been suggested by researchers to ameliorate the effects of fescue toxicosis on grazing livestock. These include interseeding with clovers, preventing the formation of seed heads either by overstocking or clipping, pasture renovation, moving cattle to nonfescue pastures during hot weather, use of plant growth regulators, supplementing with grain or a 50:50 broiler litter/shelled corn mix, and use of creep feed or creep grazing with cow--calf pairs. Detailed discussion of these factors is beyond the scope of this review; a few comparisons will be made, however. Interseeding E + fescue pastures with clover has improved gains of grazing steers (McMurphy et al., 1990; Chestnut et al., 1991 ). However, even though presence of the clover prevented weight loss by cows with nursing calves, increased calf weaning weights and improved pregnancy rates of cows, the pregnancy rates were not improved to levels considered economical for the beef industry (Gay et al., 1988; Waller et al., 1989 ). Choice of grazing methods is important for those operators with E + fescue pastures. Heavy continuous grazing probably is best for E + fescue because the endophyte is concentrated in the seed heads, and heavy grazing tends to minimize seed-head production. In addition, at lower stocking rates, animals tend to selectively graze seed heads, even though the endophyte is concentrated there, and appear to have more severe toxicosis. When E + fescue pastures were grazed at three stocking rates, ADG either improved or did not change as stocking rate increased (Bransby et al., 1988 ), whereas ADG decreased as stocking rate increased on the low-endophyte pastures. At higher stocking rates, gain per hectare was also greater for E + fescue than for E - fescue. Rotational grazing is not recommended because it tends to allow seed-head formation. Creep grazing is one method of providing high-quality forage for calves at a time when forage quality and, therefore, milk production by the cow is declining. Tucker et al. (1989a) reported that addition of creep forages improved calf gain on highly infected tall fescue to a level equal to that of the calves on low-endophyte pastures without creep. Feed additives Several experiments have been reported in which nutrients, dietary ingredients, growth stimulants, anthelmintics, and other feed additives have been

252

S.P. SCHMIDT AND T.G. OSBORN

used in attempts to ameliorate the effects of fescue toxicosis (Table 12). In general, none of these factors have been effective either alone or in various combinations. There have been reports of success or promising results, but these have not been replicated at other locations. Some treatments have resulted in improved gains by grazing steers but not at a level that would be considered a 'cure'. The concept of using selenium, either injectable or in the feed, to overcome fescue toxicosis has persisted as a promising treatment among producers for several years. However, in several controlled experiments, selenium has had no beneficial effects for steers, sheep or horses.

TABLE 12 Dietary factors and other treatments that have been ineffective in alleviating fescue toxicosis Treatment

Species

Fescue diet

Reference

Sodium bentonite Fat Calcium carbonate Sodium bicarbonate Zeolite Activated carbon Fe Se Enzyme-culture product B-vitamins Vitamin E Yucca plant extract B-vitamins plus Se plus vitamin E Phenothiazine Activated carbon Ivomectin Panacur plus Warbex Ralgro Synovex Se Thiabendazole Se Ca aluminosilicate Acetylsalicylic acid Se plus Zn plus vitamin E Thiabendazole Lasalocid Phenothiazine

Steers

Hay

Goetsch et al., 1987a

Sheep Steers Steers

Hay Grazing Grazing

Goetsch et al., 1987d Boling et al., 1988 Goetsch et al., 1988

Horses Sheep Steers Sheep Steers

Grazing Hay Grazing Hay Hay

Monroe et al., 1988 Barlh et al., 1989 Evans et al., 1989 Anderson et al., 1990 Essig and Armstrong, 1990

Horses

Grazing

Redmond et al., 1991a

ENDOPHYTE-INFECTED TALL FESCUE AND ANIMAL PERFORMANCE

253

Pharmacological agents Abnormal hormone profiles have been shown to occur in cattle, sheep and horses consuming E + fescue. The majority of these responses are varied and inconclusive, except for the effect on circulating PRL concentrations. It has been demonstrated numerous times that plasma PRL concentrations are reduced in animals consuming E + fescue (Hurley et al., 1981; Bolt et al., 1982, 1983; Bond and Bolt, 1986; Thompson et al., 1987). The fact that PRL concentration in the plasma has consistently been shown to be reduced in animals consuming E + fescue, coupled with the fact that dopamine (DA) is a prolactin inhibitor, has lead to investigation of concentrations of DA and other neurotransmitters in both the peripheral circulation and the brain. Neurotransmitter concentrations were found to be altered peripherally, as well as in the controlling centers of the brain as a result of the ingestion of E + fescue (Porter et al., 1985; Robbins et al., 1985; Henson et al., 1987; Marple et al., 1988; Schillo et al., 1988). This has led some investigators to propose drugs which, when given to the animal, may result in more normal PRL concentration, improved animal performance and alleviate the signs of fescue toxicosis. Spiperone, a known DA antagonist, when administered intravenously was found to decrease DA concentration and increase PRL concentration in the plasma of wethers consuming E + fescue (Henson et al., 1987). Likewise, Lipham et al. ( 1989 ) orally administered the DA antagonist metoclopramide to steers grazing E + rescue pastures. Serum PRL and cholesterol concentrations increased in the metoclopramide-treated steers, and rectal temperatures were decreased. In addition, the metoclopramide-treated steers spent more time grazing and had faster daily gains on the high-endophyte but not the lowendophyte pastures. These studies further suggest that dopaminergic processes are involved in fescue toxicosis and that anti-fescue toxicosis drugs may have promise in overcoming the effects of the endophyte if certain criteria, such as route of administration, ease of delivery, long-term efficacy, and economic feasability are met. EFFECT OF THE ENDOPHYTE ON HORSES

The effects of E + rescue on mares and foals are more severe than in cattle or sheep. Pregnant mares that have grazed E + fescue show several of the following signs: prolonged gestation lengths; failure to exhibit signs of approaching parturition including lack of mammary development, 'hollowing' of the paralumbar fossa and softening of the gluteal muscles; severe dystocia; retained and thickened placentas; abnormal presentation of foals during delivery; increased maternal mortality; agalactia and rebreeding problems (Monroe et al., 1988; Earle et al., 1990; Putnam et al., 1990, 1991 ). In addition, the foals usually are stillborn or weak at birth and have a high incidence

254

S.P. SCHMIDT AND T.G. OSBORN

of irregular teeth eruption and overgrown hooves. Interestingly, horses grazing E+ fescue do not have elevated rectal temperatures (Table 13). Only about 10% of the mares grazing E+ fescue failed to shed their winter hair coats (J.P. Brendemuehl, personal communication, 1990). These mares appeared to have excessive sweating, but there was no apparent alteration of grazing behavior during the hot part of the day. Gestation length in mares grazing E+ fescue averages approximately 1 month longer than those grazing E - fescue (Tables 13 and 14). Some mares may carry foals for more than 370 days compared with the average of 336 days (Earle et al., 1990). Monroe et al. (1988) also reported (Table 13) a TABLE 13 Effect o f E + fescue on gravid mares, foals, parturition and re-breeding I Endophyte

Gestation length (days) Foal weight (kg) Rectal temp. ( ° C ) Placental weight (kg) Stillborn foals 2 Retained placentas 2 Agalactic mares 2 Mares re-bred 2

0%

94%

333" 44.5 38.2 3.7 c 0/8 1/8 I/ 8 6/8

360 b 48.6 38.2 4.9 4/8 5/8 7/ 8 3/7

• .bp< 0.01 ; cp= O. 12. tAdapted from Monroe et al., 1988. 2Number out o f eight mares. TABLE 14 Effect o f change-over at Day 300 o f gestation on mares grazing E - and E + ( > 80%) fescue a Treatment

EE+ EE+

to to to to

term term E+ E-

Gest. length ( days )

Foal score 2

335 a 358 b 345 b 334"

3.0" 1.7 b 1.7 b 3.0"

Udder score 3

Parlurition score 4

Placental weight

(kg) 3.01.0 b 1.2 b 3.0"

a.b.cp< 0.05 among fescue treatments within a column. ~Adapted from Putnam et al., 1990. 20, stillborn; 1, died; 2, weak; 3, normal. 3At Day 300; 0, no development; 4, good development and secretion. 40, normal; 2, dystocia, manual assist.; 4, fetotomy/cesarean section.

0.3 "'c 1.4 b'c 1.8 b 0.0-

4.5 6.0 5.9 4.1

ENDOPHYTE-INFECTEDTALLFESCUEAND ANIMALPERFORMANCE

2 55

greater incidence of stillborn foals, retained placentas and agalactic mares. A greater percentage of mares grazing E - fescue were re-bred following foaling than those grazing E + fescue. The re-breeding data are somewhat confounded by the fact that fixed breeding dates were set, and because the mares grazing E + fescue had longer gestation lengths, they had a corresponding shorter post-partum period for breeding. Another striking difference between horses and cattle is the lack of a carryover effect when mares are removed from E + fescue. When mares that were l 0 + days beyond their anticipated foaling date were removed from E + fescue to E - fescue, signs of impending parturition were observed within 48 h and the mares foaled normally (Earle et al., 1990; Redmond et al., 1991 ). Putnam et al. (1990) grazed pregnant mares on E + or E - fescue until Day 300 of gestation at which time half the mares in each group were switched from E + to E - fescue and vice versa (Table 14). Mares that had been on E + fescue just the last 4-6 weeks of gestation had gestation lengths, placental weights, and foal, udder and parturition scores that were similar to those of mares grazing E + fescue during the entire gestation. In contrast, mares switched from E + to E - fescue at Day 300 foaled normally and had normal foals. Results from these trials indicate that horses respond very rapidly to E + fescue and have a rapid turnover of the toxicants to quickly overcome the negative effects of the E + fescue. This also is borne out by the fact that lactating mares moved onto E + fescue will cease lactating within a few days (J.P. Brendemeuhl, personal communication, 1990). Injection and dietary treatments have been as ineffective in ameliorating the effects of the endophyte in horses as they have been in beef cattle. Neither selenium offered in a trace mineral salt and as an injectable (Monroe et al., 1988 ) nor phenothiazine offered in a supplement (Redmond et al., 1991 a) had a beneficial effect on mares grazing E + fescue or their foals. Similarly, corn fed to gravid mares grazing E + fescue to provide 50% of their energy requirements was not effective in ameliorating reproductive problems (Earle et al., 1990).. Research conducted with horses indicates that the endophytic fungus in fescue is highly toxic to gravid mares, but mares removed from E + fescue within a month of foaling appear to overcome the signs of fescue toxicosis and have normal foals. Until the mechanisms are more clearly understood and more data are obtained, researchers are recommending to producers that mares be removed from E + fescue 60-90 days before anticipated foaling. REFERENCES Ahmed, N.M., Schmidt, S.P., Arbona, J.R., Marple, D.N., Bransby, D.I., Carson, R.L., Coleman, D.A. and Rahe, C.H., 1990. Corpus luteum function in heifers grazing endophyte-free and endophyte-infected Kentucky-31 tall fescue. J. Anita. Sci., 68 (Suppl. l ): 468 (abstract).

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