TALL FESCUE/ENDOPHYTE/ANIMAL RELATIONSHIPS

ENDOPHYTE EFFECTS ON ANIMALS

Grazing Time

Several studies have shown that animals on EI pastures spend less time grazing during the day and more time grazing at night.  In Maryland, grazing time was reduced by approximately 20% as compared to steers gazing EF fescue. (Table 1).

In a Georgia study in which steers were switched from EI (>95% infected) to EF (<1% infected) fescue steers on EF fescue spent 60% of the time between noon and 6:00 p.m. grazing, as compared to only 4 to 6% by steers on EI fescue.  Steers switched to EI fescue showed a reduction in grazing time within two days, and intake for this group was depressed within one week.  Forage intake for the group switched to EF fescue remained lower for at least 10 days following the switch, but was normal after 28 days.  However, grazing time for those switched to EF was still reduced one month later.

Intake and Digestibility

Both on-farm observations and research have provided evidence that cattle prefer EF fescue.  In Tennessee, steers had a preference for clover in EI pastures, but there were indications that they preferred fescue to clover in EF pastures.  When heifers in Missouri were offered diets containing 60% fescue seed, either EF or 75% EI, 11 of 12 heifers avoided the EI diets.  Much, but not all, of the reduction in livestock average daily gain (ADG) or gain per unit area of land on EI fescue is due to reduced intake.

Normally, physical factors such as high fiber content are associated with poor intake, but they do not explain intake differences between EI and EF fescue.  Further, the toxicants do not appear to have a major effect on ruminal microbial digestion. Digestibility and crude protein content are small in EI and EF fescue.

EFFECTS ON BEEF YEARLING GAINS

Since the early reports of the association of the endophyte with fescue toxicosis, many grazing and feeding trials with EI and EF fescue have been conducted.  A summary of data (Table 2) illustrate, that decreased gains of steers grazing EI forage are widespread, quite uniform and not limited to certain geographic areas or management conditions.

Fescue toxicosis is commonly referred to us "summer syndrome” or "summer slump" because visible signs are most pronounced during hot weather.  However, poor weight gains on EI pastures can occur throughout the grazing season (Table 3).  During November, December and March there was a 50% decrease in ADG of steers grazing EI fescue, as compared to EF fescue.  During the warmer months of April, May and June, the decrease was 59%.

Though air temperature, humidity, presence of other forages and animal management are known to have an influence, steer ADG has been shown to decrease approximately 0.1 lb for each 10% increase in infection rate.

Increased nitrogen (N) fertilization increases the incidence of bovine fat necrosis, but investigations have revealed that N fertilization does not affect steer ADG on EI fescue.  However, N fertilization of EI fescue can increase gain per acre because of higher stocking rates.

EFFECTS ON BEEF COWS AND CALVES

Most of the fescue in the Untied States is used in commercial beef cow-calf operations.  In several studies (Table 4), cows grazing EI fescue lost weight and had lower pregnancy rates, and their nursing calves had slower gain, and reduced weaning weights compared to those grazing EF pastures.

It is known that a decline in body condition can affect reproduction, and cows that are thin before and at calving have a long interval between calving and first estrus.  Therefore, cows entering the breeding season in a poor or negative gaining condition because of EI fescue probably will have a prolonged post-partum interval regardless of late, endophyte effects.

In Kentucky and Missouri, supplementary feed (in the form of either, clover or grain) for cattle on EI fescue improved pregnancy rates, but not up to economically acceptable levels.  Thus, it appears that factors other than nutrition are involved in the reduced pregnancy rates associated with EI fescue.

EFFECTS ON BEEF HEIFERS

In an Alabama study, weaned beef heifers were assigned to pastures having low, medium or high levels of infection (Table 5), and received hay of similar infection levels during winter.  Heifer ADG decreased as infection level increased.  However, the later ADG of cattle led hay was the opposite, with the high infection group having the fastest gains.  All heifers were observed in estrus prior to their first breeding, but pregnancy rates decreased as infection level increased.  Following first calf births, pregnancy rates were further reduced in heifers grazing pastures with medium and high infection level, but not in those grazing low-endophyte pastures.  Initiation of the estrus cycle to heifers grazing EI fescue is not delayed, and cessation of the estrus cycle in animals already cycling does not occur.  Research in Alabama indicates that conception is not affected by the endophyte.  Reduced calving percentages of cattle on EI fescue appear to be due to early embryonic death.  Experiments to date have not made clear whether the endophyte affects calf birth weights.

BRAHMAN VS BRITISH BREEDS OF CATTLE

Brahman cattle are known for their heat tolerance and may be better adapted to resist or tolerate the hyperthermia (high body temperature) observed during hot weather.  In breed comparison, Angus and Brahman-Angus cross steers have exhibited decreased gains when grazing EI fescue, but the magnitude of the decrease was less for the Brahman-cross steers.  Brahma-cross animals frequently gain better due to greater heterosis, thus reduced endophyte effects, if any, are difficult to detect.

FEEDLOT GAINS OF STEERS THAT PREVIOUSLY GRAZED FESCUE

Because of their unthrifty appearance, steers, that have grazed EI fescue often bring reduced prices, making it important to determine whether there are carryover effect, on feedlot performance.  Studies in Georgia, Arkansas, Oklahoma and Tennessee indicate that when steers grazed on EI fescue arrived at a feedlot during cooler weather, they gained faster than steers which had grazed EF fescue, especially during the first 28 days.  Steer, arriving during hot weather did not show increased gains, but their gains were not reduced as a result of previous exposure to EI fescue.

EFFECTS ON MILK PRODUCT ION

Consumption of EI fescue reduced milk production to as much as 45% in beef cows and 50% in beef heifers in Alabama, and by 60% in dairy cows in Kentucky.  Milk production of lactating dairy cows can be sharply reduced even when fescue has low infection levels, but EF provides excellent nutrition for lactating animals.  Milk production by dairy cow, consuming EF fescue was similar to those grazing alfalfa-orchardgrass in Kentucky, and annual ryegrass in Alabama.  Differences in milk production appear to be primarily due to differences in intake.

EFFECTS ON HORSES

Several studies have provided evidence that the fungus is associated with horse reproductive problems.  Clemson University scientists found that mares grazing EF pastures produced more live foals, and had less agalactia, fewer retained placentas and greater conception rates than mares on EI fescue.  In Kentucky, 40 % of the mares grazing EI fescue, had reproductive abnormalities.  In Georgia, prolactin levels in the blood (associated with milk production) were depressed when mares grazed EI, but not EF, fescue.

In a classic study in Auburn University, pregnant mares of various breeds were placed on adjacent EI and EF pastures, where they remained until foaling.  The dramatic increase in foaling problems, foal deaths, gestation lengths and foal weights, and the reduction in numbers of mares lactating, foals surviving and mares surviving (Figure 1 and Figure 2) provide convincing evidence of the dangers associated with grazing pregnant mares on EI fescue.

A striking difference between horses and cattle is the luck of carryover effects when mares are removed from EI pastures.  Test results show that horses respond rapidly to EF fescue and have a rapid turnover of toxicants, allowing them to quickly overcome the negative effects.  Conversely, lactating mares moved onto EI fescue will cease lactating within a few days.

Mares removed from EI fescue one month before foaling can often recover from fescue toxicosis and have normal foals.  The prevalent recommendation to producers, however, is that mares be removed from EI fescue 60 to 90 days before anticipated foaling.  Grain supplementation to mares grazing EI fescue has no benefit with regard to endophyte effects.

EFFECTS ON THERMOGREGULATION

Cattle consuming EI fescue typically exhibit hyperthermia (abnormally high body temperature) as shown by increased rectal temperature.  Studies in Kentucky have shown that EI fescue has the most detrimental effect on cattle when the ambient temperature exceeds 88F.

In Alabama, steers were fed non-infected or infected hay and seed in controlled environments at 70F (cool) and 90F (hot).  Feed intake was reduced 36% by steers fed the EI diets in the cool environment, but rectal temperatures and respiration rates were not affected.  In the hot environment feed intake was reduced 60% in steers fed the EI diet, and rectal temperatures and respiration rates increased.

In the cool environment steers fed the EI diet exhibited reduced temperatures at the extremities (ear tips, tail tip, hooves).  This hypothermia (reduced temperature) in animals consuming EI fescue is most likely a result of vasoconstriction caused by the toxicants.  The vasoconstriction (constriction of the blood vessels) would decrease the animals ability to dissipate this increased heat load, and is further confounded by high air temperature.  Reduced blood flow in the extremities due to vasoconstriction causal by fungus toxins could also he associated wish the fescue foot syndrome.

It now appears that the toxicants in El fescue result in abnormal function of the thermoregulatory center many animals.  This, coupled with high environmental temperature, could lead to the hyperthermia observed in cattle consuming infected fescue.  Increased respiration rates (often evidenced by panting) probably helps animals to cool themselves and dissipate the increased heat load.  Excessive salivation, also a sign of fescue toxicosis, may be due to the panting.