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Thursday, December 10, 2009

Performance of cattle grazing endophyte infected tall fescue compared novel endophyte or endophyte free tall fescue

This is a paper I wrote covering the effects of grazing tall fescue on cattle. I learned a lot on the topic and I hope you will too! Enjoy!

Performance of cattle grazing endophyte infected tall fescue compared novel endophyte or endophyte free tall fescue

ABSTRACT

Tall fescue (Festuca arudinacea) is a cool-season forage used by many cattle producers for grazing cattle. Unfortunately, a large proportion of tall fescue stands in the United States are infected with an endophyte fungus that produces toxins called ergot alkaloids. Consumption of these ergot alkaloids provides negative side effects in cattle and other livestock species, collectively referred to as “fescue toxicosis.” A review of recent literature compared the impacts of growing cattle grazing endophyte-infected fescues to novel endophyte and non-infected tall fescue stands. The results from this show that cattle performance is reduced from grazing endophyte-infected tall fescue stands with results being reduced body weight gains, serum prolactin levels, DMI, and an increase in rectal temperatures. These side effects can be avoided by grazing stockpiled forages during the late fall and winter, when ergot alkaloid concentrations are at the lowest levels, or by replacing endophyte-infected tall fescue stands with novel endophyte or non-infected tall fescues stands.

INTRODUCTION

Tall fescue (Festuca arudinacea) is one of the leading perennial cool-season forages for a large portion of the United States. This cool-season forage is optimal for cattle production because of its stand persistence. The plant is very tolerant of minor flooding, moderate drought, intensive grazing, poor fertility, and heavy traffic. The majority of the plant’s growth occurs during the spring season and often comes close to dormancy during summer months (Curtis, 2007). As optimal as this forage may appear, cattle usually exhibit lower productivity when grazing tall fescue due to toxins found in the mature plant.

A small fungus, known as an endophyte (Neotyphodium coenophialum), grows between the cells of the plant and produces a toxin. This toxin is the cause of lowered productivity for cattle grazing endophyte infected (E+) tall fescue. The toxins, ergot alkaloids, are present in the seed when planted. After germination of the plant, the endophyte lives at the base of the plant, but does not grow into the leaves. During the reproductive stages, the endophyte grows between the cells of the stem and the toxins become concentrated in the seeds of the plant (Bacon, 1993). Collectively, the symptoms from consumption of the ergot alkaloids are known as “fescue toxicosis.” Previous research has shown that cattle with fescue toxicosis often exhibit rough hair coat, reduced feed intake, high respiration rate, elevated body temperature, reduced milk production because of lowered prolactin levels, reduced body weight gain, lower conception rates, excessive salivation, and an overall unthrifty appearance (Brown, 2009; Curtis, 2007). Recent research has focused on the development of tall fescue stands that are endophyte-free (E-) or stands that contain a novel endophyte (NE). This lower level is less toxic to cattle grazing tall fescue. The reviewed studies compare cattle performance and stand persistence of E- and NE tall fescue stands to that of E+ tall fescue stands. The purpose of this paper is to review the findings of recent studies to understand the effects of grazing E+ tall fescue compared to E- and NE tall fescue stands on beef cattle productivity.

RESULTS

Animal Performance

The four studies included in this review examined the performance of beef cattle grazing tall fescue with varying levels of endophyte infection. Performance data collected include measurements on body weight gain, serum prolactin levels, pasture utilization, and rectal temperature. The studies also measured differences in performance during grazing between seasonal changes.

Body Weight Gain. The given studies evaluated difference in body weight gain between cattle grazing tall fescue forages with varying endophyte status. Cattle grazing E+ tall fescue stands generally had lowered body weight gains than those of cattle grazing E- and NE tall fescue forages (Drewnoski, 2009). Hopkins stated that during the spring grazing season, cattle grazing E+ tall fescue stands consistently had decreased body weight gains up to half of that from cattle grazing E- or NE tall fescue stands (2006). In a study evaluating the performance of lactating cows and their calves on varying levels of endophyte infection, Curtis found that lactating cows on the low treatment (0% endophyte infection) had less loss of BW and greater BCS than cows on medium (51%) or high (89%) treatments (2007). There were no residual effects on body weight gain in the nursing calves in this study. Beck found that during warm growing seasons for every percent increase in endophyte infection there was a corresponding decrease in ADG by five grams (2008). The general consensus from these studies is that endophyte infection does decrease body weight gain during the warm seasons, but has little to no effect on body weight gain during the late fall to winter season.

Serum Prolactin Levels. Endophyte infection has been correlated with decreased serum prolactin levels in cattle grazing E+ tall fescue stands. Drewnoski found that growing heifers grazing tall fescue stands had depressed levels of prolactin despite lowered levels of ergot alkaloids during the fall and winter seasons (2009). However, Hopkins found that there were no significant differences in prolactin levels for cattle grazing fall stockpiled tall fescue stands (2006). During the spring grazing season when forages are in the growing stages, ergot alkaloid levels are rising and seem to have a greater effect on prolactin levels. Hopkins found that cattle on E+ stands consistently showed lower serum prolactin levels than those grazing E- or NE tall fescue stands (2006).

Rectal Temperatures. Only one study in this review observed measurements of rectal temperatures in cattle grazing different tall fescue stands. These observations showed that rectal temperatures did not vary between treatments during the fall season. However, temperatures observed were elevated in the spring with cattle grazing E+ tall fescue stands corresponding to increased ergot alkaloid concentrations (Hopkins, 2006).

Pasture Utilization. Cattle grazing during the spring season grazed more heavily on E- or NE stands than E+ stands, showing preference for tall fescue stands with lower levels of endophyte infection (Hopkins, 2006). However, during the fall season there seemed to be no difference in pasture utilization between treatments (Curtis, 2007). During the fall grazing season, cattle did not exhibit any differences in DMI between treatments (Drewnoski, 2009; Hopkins, 2006). Hopkins did observe that due to elevated rectal temperatures and increased water consumption during the spring season, cattle did have lower DMI levels on E+ tall fescue stands (2006).

Seasonal Grazing. Overall, the review of these studies finds that cattle perform better with E+ tall fescue stands when grazing stockpiled forage during the late fall and winter season versus grazing these E+ stands during the spring season. Beck showed that cattle grazing E+ tall fescue stands had greater ADG during the fall compared to the spring season (0.62 vs. 0.31, kg, 2008) Gains were lower for cattle grazing E+ than NE, but gains for NE (0.85) did not differ between seasons (Beck, 2008). Beck also found that net returns were greater for cattle grazing NE compared to E+ tall fescue stands (219.09 vs. -170.14, $/ha; 2008).

Tall Fescue Forage

Measurements in forage composition for the four studies included varying levels of wild-type endophyte infection (E+), novel endophyte infection (NE), and endophyte free (E-) tall fescue stands. These studies also evaluated differences in endophyte characteristics during seasonal changes.

Endophyte Levels. Several previous studies have shown that animal performance with varying endophyte status in tall fescue differs. In addition, stand persistence becomes a factor with increase grazing pressure, drought, and harsh environmental conditions. Beck found that E- tall fescue stands had decreased stand persistence and do not tolerate drought or intensive grazing well; resulting in a stand loss within four years (2008). NE tall fescue stands have the attributes of stronger persistence than E+ tall fescue stands without the decrease in animal performance (Beck, 2008). Hopkins found that there is a greater ratio of forage cover to bare soil with E+ tall fescue stands (2006).

Seasonal Changes. Endophyte levels change with the growing seasons. There tends to be greater ergot alkaloid concentrations in tall fescue stands during the spring, summer, and fall growing seasons as compared to levels during the late fall and winter seasons (Drewnoski, 2009; Hopkins, 2006). Drewnoski noted that ergot alkaloid levels dropped as much as 80% during late fall to winter seasons (2009). This would suggest that grazing stockpiled E+ tall fescue stands is most beneficial for animal performance from mid-December thru mid-March (Drewnoski, 2009).

DISCUSSION AND CONCLUSION

This review of recent literature on the topic of endophyte infection of tall fescue stands concludes that endophyte infection levels do affect animal performance. These negative effects are greatly reduced by grazing stockpiled forage during the late fall and winter seasons or by replacing E+ tall fescue stands with either E- or NE tall fescue. Performance of cattle is greater, and health problems can be minimized when grazing stockpiled tall fescue stands in the fall compared to grazing during the spring growing season (Hopkins, 2006). The negative impacts of ergot alkaloids can be avoided by using E- or NE tall fescue stands for grazing and are more beneficial to use in seasons with warmer ambient temperatures (Drewnoski, 2009; Beck, 2008; Hopkins, 2006).

Cattle grazing E+ tall fescue will exhibit decreased performance due to the presence of ergot alkaloids. Effects on cattle performance include reduced body weight gains, decreased serum prolactin levels, increased rectal temperatures, and decreased DMI and pasture utilization. Cattle exhibit these symptoms most during warmer growing seasons with higher ambient temperatures and an increased presence of ergot alkaloids. Effects are not as significant, even negligible, during cool seasons when ambient temperatures are cooler, and there is a decreased presence of ergot alkaloids.

There are a few considerations to make when replacing a native E+ tall fescue stand. E+ tall fescue stands exhibit the greatest stand persistence of the three types of endophyte status. Performance of cattle grazing NE tall fescue is comparable to that on E- tall fescue, and NE takes advantage of the stand persistence from a non-toxic endophyte (Beck, 2008). Beck found that a period of three to seven years is required to recover the costs of replacing an E+ tall fescue stand with a NE tall fescue (2008).

There is value in replacing E+ tall fescue stands with NE tall fescue for grazing during warmer growing seasons; however, animal performance is not greatly impacted by ergot alkaloids when grazing stockpiled tall fescue forages during the late fall and winter seasons. NE tall fescue stands offer greater animal performance, longer growing seasons, and a decreased risk of stand persistence when utilized as a forage source for grazing cattle (Hopkins, 2009). Hopkins recognizes that NE tall fescue stands with greater stand persistence will be needed for successful application in cattle grazing programs. Although, it may be more economical for producers to utilize stockpiled E+ tall fescue forages for late fall and winter grazing to avoid the negative impacts of ergot alkaloids found in the forage.

Literature Cited

Bacon, C.W. 1993. Abiotic stress tolerances (moisture, nutrients) and photosynthesis in endophyte-infected tall fescue. Agric., Ecosystems, and Environ. 44:123-141.

Beck, P.A., S.A. Gunter, K.S. Lusby, C.P. West, K.B. Watkins, and D.S. Hubbell, III. 2008. Animal performance and economic comparison of novel and toxic endophyte tall fescues to cool-season annuals. J. Anim. Sci. 86:2043-2055.

Brown, K.R., G.A. Anderson, K. Son, G. Rentfrow, L.P. Bush, J.L. Klotz, J.R. Strickland, J.A. Boling, and J.C. Matthews. 2009. Growing steers grazing high versus low endophyte (Neotyphodium coenophialum)-infected tall fescue have reduced serum enzymes, increased hepatic glucogenic enzymes, and reduced liver and carcass mass. J. Anim. Sci. 87:748-760.

Curtis, L.E., and R.L. Kallenbach. 2007. Endophyte infection level of tall fescue stockpiled for winter grazing does not alter gain of calves nursing lactating beef cows. J. Anim. Sci. 85:2346-2353.

Drewnoski, M.E., E.J. Oliphant, B.T. Marshall, M.H. Poore, J.T. Green, and M.E. Hockett. 2009. Performance of growing cattle grazing stockpiled Jesup tall fescue with varying endophyte status. J. Anim. Sci. 87:1034-1041.

Hopkins, A.A., and M.W. Alison. 2006. Stand persistence and animal performance for tall fescue endophyte combinations in the south central USA. Agron. J. 98:1221-1226.