Nine-year growth trial in NT finds interesting comparisons

The detailed research over nine-years, mid-2009 to mid-2018, was conducted at Douglas Daly Research Farm, 220km south of Darwin where average annual rainfall is 1209 millimetres usually falling between October and April. Growth of cattle was greater both per head and per hectare under continuous grazing (CG) compared to intensive rotational grazing (IRG).

Research was led by Tim Schatz Department of Primary Industry and Resources, Darwin, and colleagues, D. Foulkes, P. Shotton and M. Hearnden. Results are published in the CSIRO Animal Production Science Journal, Volume 60(15) 2020. A cell grazing expert consulted to help the stud's planning and design. Limited data indicated no evidence of grazing system effects on soil organic carbon in either grazing system.

Soil was sandy red earth. Buffel grass was the main pasture species with small amounts of a few other grasses, legumes and weeds. All paddocks had been continuously grazed and managed similarly for many years prior to the study. A new cohort of Brahman and Brahman-cross male weaners, six to nine months-of-age was used each year in both CG or IRG treatments. Typically their growth was measured from July to June the following year then replaced by next year's group.

In the IRG treatment 26 uniform 6ha paddocks were used in the first six years and from mid-2015 to mid-2018, 29 paddocks were used. Extra paddocks and longer recovery periods did not improve relative performance compared to CG. Paddocks in the IRG and CG treatments were the same size (a point of contention in some previous research).

Generally, the IRG group was moved to a new paddock every two to three days in the early wet season, daily during the mid-late wet season and every three days during the dry season. Rest period between grazes in the IRG treatment was around 60 days in the early wet season, 26 days in the mid-late wet season, and 78 days in the dry season. From mid-2015, after the extra paddocks were added, rest periods were around 70 days in the early wet season, 35 days in the mid-late wet season, and 105 days in the dry season.

In each year of this study, cattle growth was lower under IRG than CG. Liveweight gain was lower per head and per ha under IRG. The authors noted these results supported other research and research reviews. Wheeler (1962), Jones (1993), Briske et al. (2008), McIvor (2013), Hall et al. (2014) and Hawkins (2017) all found no conclusive experimental evidence of pasture production or livestock production advantages from IRG grazing compared with CG.

Average annual kg liveweight gain/ha was lower in IRG than CG in each year of the study. Averaged over the whole study, total growth per hectare was 43.8 kg/ha year higher in CG than IRG (233.6 vs 189.9 kg/ha year). Average difference in total-year weight gain per head between IRG and CG was 22.1 kg in the first six years and 44.0 kg in the last three years.

My comments to the summary is that it is important to appreciate that other research has shown that whatever the grazing system, retention of at least reasonable groundcover is important for rainfall capture, protection of soil from erosion, as well as for productivity. Also research has shown that for some species, like lucerne and phalaris, a degree of rotational grazing is important for persistence.

The authors point out that many factors are important for livestock profitability and having more paddocks was commonly beneficial such as to reduce the distance that cattle walk and achieve more even grazing. Also, while the results were clear in this situation, rotational grazing can be beneficial in managing some other pasture species especially if they become unpalatable when they grow tall. Tim Schatz said rotational grazing of Gamba grass produced much better results than continuous grazing at Douglas Daly Research Farm.

For more details contact Tim Schatz: tim.schatz@nt.gov.au

Next week: Research progresses towards better crown rot resistance.