The influence of dry matter percentage and bulk density of grass and clover on short-term intake rate in Friesian cattle

Abstract

Bite dimensions (bite depth, area and volume) and herbage intake parameters (bite weight, biting rate and intake rate) were measured indoors on grass and pure clover swards across a range of dry matter percentages (DM%) and sward bulk densities (BD). In the first trial, three rising two year Friesian heifers (mean liveweight = 362 kg) were offered daily, three pure clover turfs (35 cm x 42.5 cm) of a similar height (11.3 cm mean height) but varying in DM% (29.5 to 40.8%) and BD (13.6 to 19.0 g/ cm³) for three periods according to a modified latin square over three days. Turfs were cut from a vegetative Huia white clover (Trifolium repens) seed crop in January. In the second trial in May, three rising 2 year Friesian heifers (mean liveweight 372 kg) were fed Nui rye grass (Lolium perenne) turfs of mean pre-grazing height 19 cm, varying in DM% and BD from 23.8 to 49.3% and 4.9 to 6.6 g/ cm³ respectively. DM bite weight (DMBW) of grass increased with DM% (0.77 to 1.81 g/bite), due to an increase in BD caused by drying (5.4 to 7.2 g/ cm³) as bite volume was not affected. Rate of biting remained constant across treatments so that DM intake rate of grass also increased with rising DM%. Although BD treatments had no effect on intake variables, the range of BD produced had the major over-riding effect on DMBW (a 1 g/cm³ (18%) increase in BD induced a 0.2 g (26%) increase in DMBW). DM% and BD had little effect on intake variables of clover suggesting that maximum rate of intake was maintained within the range of sward conditions produced. It appears in this instance that DM% does not influence DM intake rate of grass through water content per se, but rather, indirectly through increasing sward BD. Intake rate of clover was less affected by changes in sward structure and DM% than for grass.