Evaluation of perennial ryegrass (Lolium perenne L.) for digestibility using thermogravimetry

Studies have shown that thermogravimetric (TG) analysis can highlight differences in the combustion patterns of high, medium and poorly digestible ryegrass samples as measured by pepsin cellulase assay. The samples used in our study were obtained from experiments completed in England and Wales during 1980-1988. The objectives were to develop regression models based on the thermal characteristics of ryegrass and validate the models using 20 samples from two experiments completed in Northern Ireland for in vivo organic matter (OMD) and dry matter digestibility (DMD). Differences in combustion patterns of the samples from 30 to 600 °C were compared and four segments of the thermal data were regressed against OMD and DMD by employing the partial least squares regression method in which a number of equations were developed. The best TG models were generated using the 300-1450 (i.e., 133-516.3 °C) segment (OMD, R2 = 0.76, standard error of cross validation [SECV] = 28.9 g/kg DM; DMD, R2 = 0.84, SECV = 35.5 g/kg DM) and R2 values for validation of the best models were 0.74 (standard error of prediction [SEP] = 28.6 g/kg DM) and 0.72 (SEP = 28.8 g/kg DM) for OMD and DMD respectively using 20 samples of herbage and grass silage from two animal feeding experiments. Thermogravimetry can be used as a rapid quality assessment tool to monitor changes in composition of stem, sheath, young and mature leaves of F2 and F3 progeny with minimal labour cost. The technique has the potential to enhance understanding of ruminant digestion of plant cell wall fractions.