|JOHNSON, J - University Of Kentucky|
|PHILLIPS, T - University Of Kentucky|
|BARRETT, M - University Of Kentucky|
|SCHRICK, F - University Of Kentucky|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/29/2011
Publication Date: 7/1/2012
Citation: Johnson, J.M., Aiken, G.E., Phillips, T.D., Barrett, M., Klotz, J.L., Schrick, F.N. 2012. Steer and pasture responses for a novel endophyte tall fescue developed for the upper transition zone. Journal of Animal Science. 90:2402-2409.
Interpretive Summary: Tall fescue is a productive and persistent cool-season perennial grass that is the predominant grass utilized for forage in the transition zone between the temperate northeast and subtropical southeast. Unfortunately, ergot alkaloids produced by a fungal that infects most tall fescue plants can cause toxicosis in cattle. Fescue toxicosis annually costs the U.S. beef cattle industry just under 1 billion dollars. Symptoms of ‘fescue toxicosis’ include reduced conception rates, retention of rough hair coats, elevated core body temperatures, and reduced DM intakes and weight gains. Endophytes were identified by AgResearch Ltd. that do not produce ergot alkaloids; thereby, alleviating toxicosis while maintaining plant tolerances to grazing, heat, and drought stresses. A tall fescue cultivar, ‘Jesup’, adapted to the southern transition zone was infected with a novel endophyte, AR542, and commercially released as Jesup-MaxQTM (MaxQ). A University of Kentucky geneticist, Dr. Tim Phillips, developed a late maturing tall fescue genotype, KYFA9301, that is adapted to the US northern transition zone and, once artificially infected with a novel endophyte, could serve as an option to Jesup-MaxQ for cattle producers in the northern transition zone. A 2-yr grazing experiment was conducted to evaluate steer performance and forage quality and productivity of KYFA9301 infected with AR584 novel endophyte in comparison to Kentucky 31 infected with the toxic common endophyte, MaxQ, and endophyte-free KYFA9301. Toxicosis was alleviated in steers grazing AR584-KYFA9301 and steer weight gain was similar between the three nontoxic tall fescues. Pasture carrying capacities were greater for AR584-KYFA9301 than for MaxQ in late June and early July. Once commercially released, novel endophyte infected KYFA9301 will serve as the productive and nontoxic cultivar option for livestock producers in the upper transition zone.
Technical Abstract: A 2-yr grazing experiment was conducted with crossbred steers (8 to 10 mo and with initial BW of 304 kg ± 34 kg in 2008 and 277 kg ± 24 in 2009) to evaluate animal performance and pasture responses of a late maturing tall fescue [Lolium arundinaceum (Schreb.) Darbysh] population (KYFA9301) infected with the AR584 novel endophyte (Neotyphodium coenophialum) (NE9301) as compared with Kentucky 31 fescue infected with the common toxic endophyte strain (KY31), ‘Jesup MaxQ’ fescue infected with the AR542 endophyte (MaxQ), and endophyte-free KYFA9301 (EF9301). Endophyte-fescue treatments were assigned for seeding in 1.0-ha pastures in a randomized complete block design with three replications. Pastures were grazed from 6 May to 23 July in 2008 (76 d) and 2 April to 25 June in 2009 (84 d). Each pasture was grazed with 4 tester steers and put-and-take steers were used to maintain forage mass at 2,500 ± 250 kg DM/ha. Shrunk BW was taken at initiation and termination of grazing each year. Rectal and skin temperatures were recorded and jugular blood was collected each year at approximately days 28, 56, and study completion. Responses were analyzed with mixed models and preplanned orthogonal contrasts were used to compare KY31 with nontoxic fescues, EF9301 vs. novel endophyte fescues, and NE9301 vs. MaxQ. All steer responses were similar (P > 0.10) among the non-toxic fescues. Average daily gains and total BW gain per ha for the 3 nontoxic fescues were greater (P < 0.001) than for KY31. Rectal/skin temperatures for the 3 nontoxic fescues were less (P < 0.001) and serum prolactin concentrations were greater (P < 0.01) than for KY-31. Pasture carrying capacity was greater (P = 0.003) for KY31 than the 3 nontoxic fescues, and was greater for EF9301 (P = 0.017) than the 2 novel endophyte fescues. However, stocking rates (kg BW/ha) at the initial and midpoint days of grazing were similar (P > 0.40) among endophyte-fescue combinations, but by the final day of grazing stocking rate was greater (P < 0.001) for KY31 than for the nontoxic fescues and was greater (P = 0.053) for NE9301 than for MaxQ. Results indicated that NE9301 is as effective as EF9301 and MaxQ in improving weight gain and alleviating fescue toxicosis, and that NE9301 can provide higher carrying capacities than MaxQ in the late spring and early summer in the northern transition zone.