Assessing the usefulness of faecal NIRS in assisting composite breeds to meet growth targets

Summary

Soil samples across the paddocks were taken at the beginning of the trial. Samples were then taken at about the same time of day every fortnight to determine the feed on offer. In addition, samples were taken of what was thought the cattle was selecting from the pasture. Faeces was sampled every fortnight. At least 20 tagged cattle (including the 10 from which faeces was collected) were weighed and fat scored every four weeks. Weaner steers was selected for the trial so they could be part of the trial for the following 12 months. Cattle were drenched (also for liver fluke) at the start of the trial and then every four months and no growth promotants were used. Cattle were kept in paddocks for at least 4-6 weeks so that reasonable relationships between feed quality, faecal NIRS and animal growth could be made.

To ensure group training, members were instructed and engaged in the processes of feed budgeting, fat scoring, predicting animal growth rates, calculating pasture growth rates and forward planning decisions such as paddock moves or supplementation need, choice and amount. The first objective was to make a preliminary assessment of faecal NIRS to allow better or earlier decisions to be made about matching nutrient supply (either through pasture and/or supplements) to targeted growth rates. Northern calibration equations were used. The results indicate that northern calibration equations do not allow general prediction of growth rate either from estimates of diet quality or from estimates of growth rate.

Cattle performance was better predicted at sites with C4 grasses rather than at sites dominated by sown C3 species. Mean actual growth rate at Mitchell was estimated to within 0.2 kg/day by NIRS predictions on approximately 71 percent of occasions. At this site predicted dietary digestibility also had high utility. The second objective was to ensure composite (or cross bred) cattle met growth targets from weaning to slaughter through the use of feed budgeting (and/or faecal NIRS) and tactical supplementation. Mean start, finish and growth rates at the various sites are detailed in Table 1. Mean growth rates equalled or exceeded 0.6 kg/day at two of the four sites. Given the poor seasonal circumstances, the growth rates at all sites were satisfactory.