To estimate seasonal variation in herbage quality from a Friesian bull beef production system, 50 hand-plucked herbage samples were taken approximately every 2 weeks from paddocks about to be grazed at the Tuapaka bull beef unit, Massey University, between December 1998 and February 2002. The pastures were perennial ryegrass and white clover. Herbage mass (kg DM ha -1 ) was estimated using a calibrated rising plate meter. Herbage samples were assessed for crude protein (protein), lipid, ash, acid detergent fibre (ADF), neutral detergent fibre (NDF), non-structural carbohydrates (NSC), organic matter digestibility (OMD) and metabolisable energy content (ME) by near infra-red spectroscopy. A correlation analysis between variables was performed and an analysis of variance was carried out by month and season using year as a block. Additionally, a Bayesian smoothing analysis was applied to the complete data set of ME and protein. Fibre variables (NDF and ADF) had the strongest relationship between themselves and with other variables, and were negatively related to NSC, ME, and protein.The content of non-structural carbohydrates was positively associated with herbage ME and protein.
A04009; Online publication date 30 May 2005 Received 26 January 2004; accepted 17 December 2004Values of herbage quality were high throughout the measurement period (80.6% OMD, 11.3 MJ ME kg -1 and 25.8% protein). Protein levels for autumn, winter, spring, and summer were 26.4, 26.7, 26.9, and 23.3%, and ME levels were 10.9, 11.6, 11.8, and 10.9 MJ ME kg -1 , respectively. Non-structural carbohydrates had the highest variability (31% coefficient of variation), followed by the fibre variables (15 and 16% for ADF and NDF respectively). In the smoothing analysis, both ME and protein showed a seasonal behaviour with a tendency for herbage protein to peak before ME in spring. Seasonal variation of specific nutrients and implications for animal performance are discussed, with particular reference to the influence of high herbage protein levels on protein and energy utilisation.
