Differences in Forage Quality When Comparing Novel and Endophyte-infected Fescue Over the Grazing Season

Abstract Text: Objectives were to compare forage characteristics and in situ digestibility of novel and endophyte-infected tall fescue over the growing season. Tall fescue is widely used for grazing beef cattle predominantly in the Southeastern United States. Endophyte-infected tall fescue (KY-31) possesses many positive agronomic qualities, but can depress cattle growth due to ergot alkaloid-producing endophytes. Novel endophyte-infected tall fescue (MaxQ) combines the agronomic advantages of KY-31 with improved cattle performance. However, comparison of forage quality between MaxQ and KY-31 is lacking. We hypothesized MaxQ would have greater in situ digestibility than KY-31, in part due to decreased ADF and NDF concentrations when compared to KY-31. Samples were taken at 10 d intervals over 70 d, beginning May 28. Clipped samples were collected from randomly selected locations in 4 different paddocks per cultivar at each time point. Forages were analyzed for DM, NDF, and ADF. Composite samples were incubated in ruminally fistulated steers (n = 2) for 12 and 24 h to determine in situ DM disappearance (DMD) and NDF disappearance (NDFD). Data were analyzed using the MIXED procedures in SAS (SAS Inst. Inc., Cary, NC) with repeated measures. There were interactions of cultivar by d collected for ADF (P = 0.03) and NDF (P < 0.01). On d 20, 30, 50, and 60 of collection, paddocks of KY-31 had 2.5 to 7.8 percentage units greater NDF than paddocks of MaxQ. Similarly, on d 20, 30, 50, 60, and 70 of collection, paddocks of KY-31 had 3.0 to 6.2 percentage units greater ADF than paddocks of MaxQ. There were no interactions (P ≥ 0.16) of cultivar, incubation time, or week sampled for DMD. As expected, the 24-h in situ DMD was greater (P < 0.01) than the 12-h in situ DMD. Over the course of the growing season, DMD of both MaxQ and KY-31 decreased (P < 0.01). There was an interaction (P= 0.05) of incubation time and sampling d on NDFD. From d 10 through d 40, 24-h NDF digestibility was greater than 12-h NDF digestibility; however, from d 50 through d 70, there was no difference in 12 versus 24-h in situ NDF digestibility. Although forage quality differed over the growing season, lack of difference in in situ DMD and NDFD between MaxQ and KY-31 suggest that improved forage quality is not the mechanism for increased performance of cattle grazing MaxQ compared to those grazing KY-31.

Keywords: cattle, forage quality, fescue