Rg. Warren et al., Utilising temperate and tropical pastures and compensatory growth during winter to maximise growth in cattle, TROP GRASSL, 32(4), 1998, pp. 264-269
The effect of combinations of temperate and tropical pastures, and of inter
actions with compensatory growth, on liveweight gain in steers was investig
ated over the winter-spring period in the subtropics. Sixteen Brahman cross
bred steers (294 +/- 4.4 kg; +/- s.e.) were either not supplemented (low gr
owth rate; L) or supplemented with silage and with a mixed sorghum-barley g
rain-based ration (2 kg/hd/d) (high growth rate; H) in autumn. Growth rates
over ca. 100 d (hereafter autumn) for L and H groups were -0.21 and 0.71 k
g/d, and liveweights at the end of autumn were 270 +/- 5.4 and 365 +/- 8.2
kg, respectively. Steers were re-allocated within original groups so that h
alf grazed ryegrass (Lolium multiflorum) cv. Aristocrat alone (LR, HR) and
half grazed ryegrass (3 d/week) and carryover pangola grass (Digitaria eria
ntha) (4 d/week) (LRP, HRP). Liveweight gains over the next 88 d (winter-sp
ring) were 1.17 +/- 0.056, 1.05 +/- 0.055, 0.86 +/- 0.057 and 0.67 +/- 0.03
7 kg/d, and final liveweights were 373, 362, 441 and 423 kg for LR, LRP, HR
and HRP, respectively. Growth rates over winter-spring were higher (P<0.05
) for steers grazing ryegrass alone than for the combined grazing treatment
, and were higher (P<0.05) for unsupplemented steers than for those supplem
ented in autumn, but there was no interaction between winter-spring and aut
umn treatments. Over the winter-spring grazing period, herbage mass on offe
r averaged 2725 and 4280 kg/ha dry matter (DM) for the ryegrass and pangola
grass pastures, respectively. Average green leaf percentages were 43 and 2
2%, and within this component crude protein (CP) concentration was 24-29% a
nd 11-14% and in vitro DM digestibility (IVDMD) was 75-78% and 56-62%, resp
ectively. The concentrations of ammonia-nitrogen in rumen fluid from steers
grazing ryegrass or pangola ranged from 93-126 mg/L, with no treatment eff
ects.
The results indicate that carryover tropical pasture can be used in practic
al feed plans to augment the limited supply of temperate pasture, thereby r
educing costs with only small reductions in animal performance. They also i
ndicate that severe restrictions in growth rate during the autumn period wi
ll result in compensatory growth later on, but may jeopardise attainment of
market specifications for heavy carcases at a young age.