Near infrared reflectance (NIR) spectroscopy is a rapid and cost-effective method for the measurement of organic constituents of agricultural products. NIR is widely used to measure feed quality around the world and is gaining acceptance in Australia. This study describes the development of an NIR calibration to measure crude protein (CP), predicted in vivo dry matter digestibility (IVDMD) and neutral detergent fibre (NDF) in temperate pasture species grown in south-western Victoria. A subset of 116 samples was selected on the basis of spectral characteristics from 461 pasture samples grown in 1987-89. Several grass and legume species were present in the population. Stepwise multiple linear regression analysis was used on the 116 samples to develop calibration equations with standard errors of 0.8,2.3 and 2.2% for CP, NDF and IVDMD, respectively. When these equations were tested on 2 independent pasture populations, a significant bias existed between NIR and reference values for 2 constituents in each population, indicating that the calibration samples did not adequately represent the new populations for these constituents. The results also showed that the H statistic alone was inadequate as an indicator of equation performance. It was confirmed that it was possible to develop a broad-based calibration to measure accurately the nutritive value of closed populations of temperate pasture species. For the resulting equations to be used for analysis of other populations, however, they must be monitored by comparing reference and NIR analyses on a small number of samples to check for the presence of bias or a significant increase in unexplained error.

Nine groups of four Hereford heifers (mean � s.e. liveweight 223 � 3.1 kg), drank water containing either high (650 ppm) or low (10 ppm) magnesium concentrations combined with varying levels (5000,7000,9000, 11 000 ppm) of total soluble salts (TSS) for 79 days. At each level of TSS, high magnesium treatments were obtained by replacing 2550 pprn sodium chloride with an equal amount of magnesium chloride. A control group drank water containing 10 pprn Mg and 2 10 pprn TSS. All animals werq kept in feedlots and fed on hay ad libitum. Mean daily maximum temperature and mean daily evaporation during the experiment were 23�C and 4.6 mm, respectively. At the various TSS levels, the presence or absence of high levels of magnesium did not significantly affect liveweight gain, feed intake or animal health which suggests that the adverse effects of sodium and magnesium are similar. However, during the first 51 days of the experiment, heifers drinking water containing 11 000 pprn TSS and 650 ppm Mg lost weight and ate less than all other groups. Compared with control animals, those drinking water containing more than 5000 pprn TSS showed reduced liveweight gain (P<0.05) and feed intake during the first 5 1 days of the experiment, but this effect diminished as the experiment progressed. Overall, a TSS level of 5000 ppm caused a large but non-significant reduction in liveweight gain (36.3 v. 25.9 kg) over the 79-day period while a level of 11 000 ppm reduced liveweight by 49% (36.3 v 18.5 kg, P < 0.05)

Near infrared reflectance spectroscopy (NIR) was used to develop calibration equations to measure the magnesium concentration in perennial ryegrass herbage (Lolium perenne). A subset of 72 samples was selected on the basis of spectral variation from 400 samples grown in 1988-1989. Three alternative equations were chosen using stepwise multiple linear regression, with standard errors ranging from 0.4 to 0.3 g/kg DM with corresponding squared multiple correlation coefficients ( R2) of 0.68 to 0.82. The equations had 2, 4 and 4 wavelength terms respectively. When these equations were tested on an independent population of perennial ryegrass samples, a significant bias existed when using the 4 term equations but there was no bias when the 2 term equation was used. We conclude that NIR can be used to screen large numbers of perennial ryegrass plants for magnesium concentration. However, for the calibration equations to be used for the analysis of other populations equation performance must be monitored by comparing reference and NIR analyses on a small number of samples.

The body composition of 23 Hereford steers was related to their liveweight after a 24 h fast (W), total body water (TBW), tritiated water space (T) and age in months (A) by using allometric or linear regression models. Fifteen steers, of similar initial age, were taken at intervals from a grazing experiment having a wide range of stocking rates. These steers were 15-22 months of age and 189-461 kg W at slaughter. Six younger and two older steers were also used to expand the range to 3-33 months and 90-517 kg. The steers were taken from pasture 3 h after sunrise and deprived of feed and water thereafter. After 4 h, tritiated water was given intramuscularly and 20 h later blood was collected and the animals were weighed and slaughtered. Models having the least residual standard deviation (r.s.d.) and the predictors which contributed significantly in the stepwise regression analysis (P i 0.05) are given for each range of W. T greatly improved the estimation of fat and slightly improved the prediction of protein. A only slightly improved the prediction of TBW and fat. Equations applicable to the narrow range of W were: total body water (kg) =

The phenotypic variation of 10 important botanical traits and 2 traits related to herbage quality was measured in tall wheatgrass (Thinopyrum elongatum) cv. Tyrrell. Five certified lines of Tyrrell were compared among themselves and with cvv. Largo and San Jose. Significant differences, both between cultivars and within lines of Tyrrell, were observed for several traits. The phenotypic variability measured confirms that Tyrrell is distinct from its progenitor, Largo, and has sufficient variability to make it suitable for use in a selection program. In a second experiment, from November 1990 to February 1993, the yield and nutritive value of Tyrrell, Largo, and San Jose were compared with perennial ryegrass (Lolium perenne) cv. Ellett and tall fescue (Festuca arundinacea) cv. Demeter. There were no differences (P>0.05) between cultivars for either total dry matter yield or total yield of digestible dry matter. Seasonal differences in growth and nutritive value were observed. Ellett showed superior growth in winter and early spring, while tall wheatgrass and Demeter were more summer-active. In 6 of the 11 harvests measured for nutritive value, there were no differences (P>0.05) between treatments for yield of digestible dry matter; for 2 of the remaining 5 harvests, Tyrrell yielded more digestible dry matter than Ellett. Dry matter digestibility of tall wheatgrass did not fall below 60%. The results suggest that with appropriate management, tall wheatgrass can produce nutritious forage in quantities sufficient for animal production systems, particularly as a special purpose summer pasture.