Intake and digestibility in heifers grazing a Dichanthium spp. dominated pasture, at 14 and 28 days of regrowth

The effect of two stages of regrowth (14 days versus 28 days) on the organic matter digestibility (OMD) and organic matter intake (OMI) of a native sward comprising mainly Dichanthium spp. was assessed at equal total herbage allowances when grazed by tethered Creole heifers. Ingestive behaviour (bite rate, bite mass, grazing and ruminating time) of the heifers and the herbage morphology and chemical composition were also measured in response to the two regrowth treatments. Chemical and morphological characteristics of the Dichanthium spp. varied significantly with days of regrowth. Total herbage allowance was 14 kg DM/day for both treatments, but leaf allowance was greater after 14 than after 28 days of regrowth (5.8 kg DM/day versus 3.9 kg DM/day). At 14 days of regrowth, OMD was greater (0.70 versus 0.67, P<0.01), whereas OMI was lower (57.5 g/kg LW0.75 versus 65.9 g/kg LW0.75, P<0.01) than that at 28 days. Consequently, digestible OMI (DOMI) at 14 days was less than at 28 days of regrowth (40 g/kg LW0.75 versus 44 g/kg LW0.75, P<0.05). Similar rates of biting were measured on both swards (64 bites/min versus 60 bites/min, P>0.05), although bite mass (161 mg OM versus 226 mg OM, P<0.001), intake rate (10.3 g OM/min versus 13.5 g OM/min, P<0.01) and bite depth (6 cm versus 14 cm, P<0.001) were lower on the 14-day sward. The heifers spent more time grazing on the 14-day sward compared with the 28-day sward (417 min/day versus 360 min/day P<0.05). However, this did not allow them to compensate the lower bite mass, and a 9.5% greater DOMI, was achieved on the 28-day sward, even though the leaf fraction and crude protein contents were less in this sward.