PS10-9. Nutrient Return and Animal Performance from Dairy Heifers Raised in Contrasting Meadow Fescue Grazing Systems.

Abstract Pasture-based systems can be a win-win strategy for developing dairy heifers. This two-year study (2023–2024) evaluated Holstein heifers grazing meadow fescue (Schedonorus pratensis) pastures under three systems: Meadow Fescue+N fertilizer (MF+N; 157 kg N/ha/yr), Meadow Fescue+Clover (MF+Clover), and non-N fertilized Meadow Fescue (MF). Heifers were managed using rotational stocking. The MF+N pastures had the greatest herbage mass (1,780 kg DM/ha), followed by MF+Clover (1,580 kg DM/ha) and MF (1,430 kg DM/ha; P < 0.001). Forage nutritive value followed a similar trend, with MF+N maintaining the greatest crude protein (CP; 19.1%) and in vitro organic matter digestibility (IVOMD; 65.1%) throughout the season. Heifers grazing MF+N had greater average daily gain (ADG; 0.67 kg/day) than those on MF+Clover (0.56 kg/day) and MF (0.54 kg/day; P = 0.012). Stocking rate (SR) was also greatest in MF+N (4.80 AU/ha; [1 animal unit = 300 kg]), resulting in greater gain per area (GPA; 364 kg/ha) compared to MF+Clover (268 kg/ha) and MF (249 kg/ha; P = 0.001). Dry matter intake (DMI) ranged from 7.3–7.7 kg/day across treatments (P = 0.85), but nitrogen intake and urinary excretion were significantly greater in MF+N due to greater forage CP (P < 0.0001). Enteric methane production did not differ among treatments, averaging 180–183 g CH4/day (P = 0.91). Methane yield per unit of intake was similar (23 g CH4/kg DMI), but MF+N had lower enteric methane production per unit of gain (267 g CH4/kg ADG; P = 0.01), indicating improved methane production efficiency. Overall, MF+N systems enhanced productivity, nutrient cycling, and methane efficiency, while MF+Clover offered moderate improvements over unfertilized pasture. Clover establishment was challenging in MF+Clover, therefore improved clover establishment strategies for grass-legume systems are warranted.