Nutritional characteristics estimated by faecal protein in cattle fed with heterogeneous natural grassland

Abstract

Context Improved knowledge of the quality of the diet ingested by grazing cattle requires measurement of the diets selected, including in native pasture rangeland. Aims The goal of the present study was to develop empirical equations to predict the intake, digestibility and protein concentration of the diet selected from faecal crude protein concentration of cattle grazing heterogeneous native grasslands through seasonal cycles in the Pampa biome of southern South America. Methods In Experiment 1, cattle held in metabolism pens were fed native pasture at 15 and 22.5 g DM/kg bodyweight, or ad libitum. In Experiment 2, cattle also housed in metabolism pens were offered mixtures of the native pasture and Italian ryegrass at a proportion of 0.33 and 0.66 of the mixture, or pure ryegrass. Organic-matter intake (OMI), faecal crude protein excretion (fCP), faecal crude protein concentration (fCPc), OM digestibility (OMD) and diet crude protein concentration (dCPc) were measured in Experiments 1 and 2 and relationships were developed between the diet attributes and faecal crude protein (CP). In the Experiment 3, steers grazed native grasslands (NatG), or native grasslands overseeded with Italian ryegrass (NatG + RyeG). Intake and digestibility equations generated in Experiments 1 and 2 were then evaluated in Experiment 3 to estimate diet attributes from faecal protein measures. Key results Three non-linear models (exponential, hyperbolic and mixed, i.e. exponential + hyperbolic) were examined to evaluate the OMD. The mixed model had the highest R2 value (0.74) and the lowest relative prediction error. OMI and dCPc were both linearly related to fCP. The OMD, OMI and dCPc equations were able to detect differences among diets in Experiment 3. Conclusions It was verified that the faecal CP can be used to estimate key nutritional characteristics in cattle grazing heterogeneous grasslands in the Pampa biome in South America. Implications Relationships between faecal CP and key diet attributes can be used to support further research and models for nutritional assessment of the diet and productivity of grazing cattle in the rangeland system examined.