Agronomic responses and cattle performance in cultivars of tall fescue and orchardgrass under continuous stocking.

Abstract

Tall fescue [Schedonorus arundinaceus (Shreb.) Dumort.; (TF)] is the primary forage species used by cow-calf producers in grazing systems in Tennessee. It is an excellent cool-season perennial grass due to its great forage mass (FM), nutritive value, and extensive growing season. Orchardgrass [Dactylis glomerata L.; (OG)] is also a widely used cool-season grass in the U.S. This study compared TF and OG cultivars under continuous stocking in terms of FM, nutritive value, and animal performance over two grazing seasons (2022 to 2023) in Spring Hill, Tennessee, U.S. Treatments were: 1) OG cv. Persist I (OG-P1), 2) OG cv. Persist II (OG-P2), 3) TF cv. Kentucky 31' (TF-K31), and 4) a novel endophyte TF cv. Max Q (TF-NE). Forage mass was not affected by treatments (P = 0.0519), with an average of 2979 kg DM ha^-1. Crude protein (CP) and neutral detergent fiber (NDF) concentrations were also unaffected by treatments (P = 0.6728, P = 0.1300), averaging 106 and 687 g kg^-1, respectively. However, TF-NE had the lowest acid detergent fiber (ADF) (P = 0.0258; 380 g kg^-1) and the greatest in vitro dry matter digestibility in 48 hours (INVDMD48) (P < 0.0001; 680 g kg^-1), while OG-P2 had the greatest ADF (400 g kg^-1) and the lowest INVDMD48 (661 g kg^-1). Total gain and average daily gain (ADG) were affected by treatment × year interaction (P = 0.0314 and P = 0.0161, respectively). In 2022, TF-NE, TF-K31, and OG-P1 outperformed OG-P2, but no differences were observed in 2023 (total gain: 78.6 kg animal^-1; ADG: 0.78 kg animal^-1 day^-1). Ergovaline concentrations in TF-K31 were low, which likely minimized its negative effects. These findings indicate that both TF and OG can sustain beef cattle production under continuous stocking, with TF offering potential advantages in botanical composition and forage nutritive value over time.