The effect of spring turnout date on weight gain by cattle on native pasture

Abstract

The effect of early turnout on pasture quality and weight gain by beef cattle was assessed with 32 Hereford feeder cattle which were turned out on pasture on four separate dates in each of 2 yr in a randomized complete block design with two replications. In 1998, steers were allocated to four treatments numbered consecutively T1 to T4 according to turnout date: 6 May [110 growing degree days above 5°C (GDD)], 13 May (152 GDD), 20 May (195 GDD) and 27 May (255 GDD). Steers grazed separate 0.4-ha paddocks continuously for 28 d. In 1999, turnout dates were 11 May (124 GDD), 18 May (156 GDD), 26 May (226 GDD) and 2 June (304 GDD), with 0.6, 0.5, 0.4 and 0.3 ha of pasture allocated to each treatment (two steers, two heifers), respectively. Soil resistance to penetration, sward height, herbage mass and chemical composition, and animal liveweight gain were recorded. Early turnout did not increase soil compaction. Herbage mass at turnout for T1 to T4 was 532, 780, 1370 and 1299 kg dry matter (DM) ha-1, respectively, in 1998, and 901, 983, 1324 and 1719 kg ha-1, respectively, in 1999. Herbage mass increased by 273 kg ha-1per week as turnout was delayed in 1998 and 256 kg ha-1in 1999. Crude protein concentration declined from approximately 200 g kg-1 DM at T1 to less than 175 g kg-1 DM at T4 in both years. Fibre concentration, as indicated by ADF and NDF, increased 1 wk after turnout. Forage quality declined as turnout was delayed, but grazing did not improve forage quality relative to ungrazed swards. In 1998, cattle in T1 to T4 lost 4.7, 4.0, 1.2 and 4.2% of BW, respectively, in the week after turnout, whereas in 1999, T1 to T4 lost 1.2, 4, 0.5 and 1.5% of BW, respectively. In 1998 over the 28-d period, steers in T1 and T2 lost 0.52 and 0.21 kg d-1, respectively, whereas steers in T3 and T4 gained 0.60 and 0.51 kg d-1. In 1999, over the 28-d period, cattle in T1 to T4 gained 1.1, 0.64, 1.1 and 0.61 kg d-1, respectively, with cattle in T1 gaining significantly more weight (P < 0.014) than those in T4. The results suggest a weight gain of 0.5 to 1.0 kg d-1 can be achieved in a 28 day grazing period with early turnout on native pasture provided herbage mass ranges between 900 and 1300 kg DM ha-1 and approximately 130 kg forage DM head-1 is initially on offer. Key words: Native pasture, grazing, steer performance