Grazing Novel Endophyte-infected Fescue Following Grazing Endophyte-infected Fescue to Alleviate Fescue Toxicosis in Beef Calves

Abstract Text: The objective was to investigate the efficacy of grazing novel endophyte-infected fescue following grazing endophyte-infected fescue as a means to alleviate fescue toxicosis; exhibited as poor ADG, BCS, hair coat score (HCS; 1-5), increased respiration rate, and decreased serum prolactin (PRL). Fall-born, Simmental×Angus calves (yr 1: n = 36 steers, average BW = 182±28 kg; yr 2: n = 36 heifers, average BW = 240±16 kg) were stratified by BW and randomly allotted into 6 groups within each yr. In yr 1, grazing (139 d) initiated May 2, 2012; in yr 2, grazing (121 d) initiated May 5, 2013. Groups were randomly assigned to 3 treatments: 1) endophyte-infected fescue (KY-31; whole grazing season), 2) novel endophyte-infected fescue (MaxQ; whole grazing season), and 3) KY-31 (early half of season, period 1) followed by MaxQ (late half of season, period 2; KY-31/MaxQ). Groups were rotated every 5 d through 3.24 ha pastures that were subdivided into six 0.54 ha paddocks. Put-and-take cattle were used to ensure forage availability was not different (P = 0.73) between treatments. Period 1 ADG, BCS, HCS and respiration rate were analyzed using a contrast of MaxQ vs. KY-31 and KY-31/MaxQ as both treatments grazed KY-31 pastures during this time. Period 1 respiration rate was not different (P = 0.26); yet, ADG was greater (P < 0.01) for cattle grazed on MaxQ than KY-31. Period 2 respiration rate was greater (P = 0.01) for KY-31 than MaxQ, with KY-31/MaxQ being intermediate. Period 2 ADG and final BCS were greater (P ≤ 0.04) for MaxQ and KY-31/MaxQ than KY-31. There was a year×treatment interaction (P = 0.02) for final HCS. In yr 1, MaxQ and KY-31/MaxQ had improved (P ≤ 0.01) final HCS than KY-31. In yr 2, MaxQ had improved (P ≤ 0.04) final HCS, with no difference (P = 0.10) between KY-31 and KY-31/MaxQ. There was a treatment×time interaction (P < 0.01) for PRL. Mid- and end of period 1 PRL for MaxQ were greater (P ≤ 0.01) than KY-31 and KY-31/MaxQ; however, mid- and end of period 2 PRL for MaxQ and KY-31/MaxQ were greater (P ≤ 0.01) than KY-31. Overall ADG was greater (P< 0.01) for MaxQ and KY-31/MaxQ than KY-31. Grazing MaxQ following grazing KY-31 alleviated fescue toxicosis symptoms; thus, cattle experienced compensatory gain resulting in similar overall performance to cattle that grazed MaxQ continuously. 

Keywords: beef cattle endophyte fescue grazing