Intensive animal industries create large volumes of nutrient rich effluent which, if untreated, has the potential for substantial environmental degradation and to recover valuable nutrients that would otherwise be lost. Members of the family 'Lemnaceae' are widely used in lagoon systems, to achieve inexpensive and efficient remediation of effluent. Only limited research has been conducted into their growth in highly eutrophic media and there has been little done to systematically distinguish between different types of media. This study examined the growth characteristics of duckweed in abattoir effluent and explored possible ways of ameliorating the inhibitory factors to growth on this medium. A series of pot trials was conducted to test the tolerance of duckweed to abattoir effluent partially remediated by a sojourn in anaerobic fermentation ponds, both in its unmodified form and after the addition of acid to manipulate pH, and the addition of bentonite . Unmodified abattoir effluent was highly toxic to duckweed, even at dilutions of 3: 1. Duckweed remained viable and grew sub-optimally in simplified media with total ammonia nitrogen (TAN) concentrations of up to 100 mg/L. Duckweed grew vigorously in effluent diluted 1:4 v/v, containing 56 mg TAN /L when modified by addition of acid (to decrease pH to 7) and bentonite at 0.5%. The results of this study suggest that bentonite plays an important role in modifying the toxicity of abattoir effluent to duckweed.

A 70-day residual feed intake (RFI) test on a barley-based feedlot ration was conducted, over which daily feed intake (FI) and weekly liveweight of 91 Angus steers were recorded. Rate of enteric methane production (MPR) was measured in a series of 5×2-day consecutive measurement periods using a marker-based method with the marker gas (SF₆) released from an intraruminal permeation device. Data for 76 steers with 3 or more valid 2-day methane collections were analysed. The 43 low. RFI (high efficiency) line steers (progeny of 9 sires) and the 24 high-RFI (low efficiency) line steers (5 sires) represented approximately 2.4 generations of divergent selection for postweaning RFI. An additional nine intermediate unselected line steers were included. MPR (g/day) was highly, significantly related to daily FI (kg/day) over the 10-day gas-collection period: MPR=13.0±3.0 (se) × FI+34.9, although FI (P<0.0001) explained only 20% of the variance in MPR. From this relationship MPR over the 10-week RFI test was predicted. MPR predicted for the low-RFI line steers was not significantly lower than for the high-RFI line steers (187±4 v 199±4 g/day; P>0.05). Regression analyses showed MPR to be significantly related to genetic variation in RFI (P<0.05), such that a 1 kg/day reduction in estimated breeding value for RFI would be accompanied by a 13.0±5.1 g/day, or 7%, reduction in methane production. This result supports predictions that reduction in methane emissions should accompany the reduction in FI following from selection for lower RFI.

Sulphur hexafluoride (SF₆) released from permeation tubes is used as a tracer gas for the estimation of ruminal methane emissions and (e.g . Ulyatt et al. 2002) there is usually a wait of seven days or longer after tube insertion to allow intra-rumina] SF₆ to plateau prior to sampling. Our theoretical calculations, however. suggested that intra-rumina] SF₆ would plateau within 2-3 h of permeation tube placement. Because permeation tubes being developed (Hegarty and Woodgate 2003) have release rates ~ I00 times higher than those used in previous studies they run for shorter periods, and the time available for calibration and achieving plateau is critical. Permeation tubes releasing an average of 170 mg SF₆/d (Hegarty and Woodgate 2003) were placed via rumen cannulae into two cows . Rumen gas was regularly sampled (900 ml) through the rumen cannulae over a 5 d period, collected in Tedlar gas sampling bags and immediately analysed for CH₄ and SF₆ concentrations.

The daily methane output of sheep is strongly affected by the quantity and digestibility of feed consumed. There are few widely applicable technologies that reduce the methane output of grazing ruminants without limiting feed intake per head or animal numbers. In contrast, there are many opportunities to increase the amount of animal product generated per unit of feed eaten. These include improving growth and reproductive rates of livestock and will reduce methane emission per unit of product (called emissions intensity) for individual animals. Producer responses to such improvements through changes to stocking rate and total area grazed will have a major effect on the total emission and profitability of the enterprise. First mating of ewes as lambs (~7 months of age) rather than as hoggets (~19 months of age) reduces the emissions intensity of self-replacing flocks but not that of flocks for which replacement ewes are purchased. Selection of sheep for improved residual feed intake reduces emissions intensity at the individual animal level as well as at the enterprise level. At present, emissions policies that motivate farm managers to consider generating fewer emissions rather than more profit or product are lacking.

Seventy-six Angus steers chosen from breeding lines divergently selected for residual feed intake (RFI) were studied to quantify the relationship between RFI and the daily rate of methane production (MPR). A 70-d feeding test using a barley-based ration was conducted in which the voluntary DMI, feeding characteristics, and BW of steers were monitored. The estimated breeding value (EBV) for RFI (RFI'EBV') for each steer had been calculated from 70-d RFI tests conducted on its parents. Methane production rate ('g'/ d) was measured on each steer using SF⁶ as a tracer gas in a series of 10-d measurement periods. Daily DMI of steers was lower during the methane measurement period than when methane was not being measured (11.18 vs. 11.88 kg; P = 0.001).Asignificant relationship existed between MPR and RFI when RFI (RFI₁₅'d') was estimated over the 15 d when steers were harnessed for methane collection (MPR = 13.3 × RFI₁₅'d' + 179; r² = 0.12; P = 0.01). Animals expressing lower RFI had lower daily MPR. The relationship established between MPR and RFI₁₅'d' was used to calculate a reduction in daily methane emission of 13.38 g accompanied a 1 kg/d reduction in RFI'EBV' in cattle consuming ad libitum a diet of 12.1 MJ of ME/kg. The magnitude of this emission reduction was between that predicted on the basis of intake reduction alone (18 g.d⁻¹kg of DMI⁻¹) and that predicted by a model incorporating steer midtest BW and level of intake relative to maintenance (5 g.d⁻¹.kg of DMI⁻¹). Comparison of data from steers exhibiting the greatest (n = 10) and lowest (n = 10) RFI₁₅'d' showed the low RFI₁₅'d' group to not only have lower MPR (P = 0.017) but also reduced methane cost of growth (by 41.2g of CH₄/kg of ADG; P = 0.09). Although the opportunity to abate livestock MPR by selection against RFI seems great, RFI explained only a small proportion of the observed variation in MPR. A genotype × nutrition interaction can be anticipated, and the MPR:RFI'EBV' relationship will need to be defined over a range of diet types to account for this.

Daily methane production (DMP) and 1-hour methane production (1-h MP) were measured twice, 4 weeks apart, on Merino wethers fed 'ad libitum'. This study aimed to determine the 4-week repeatability of DMP and 1-h MP as well as determine how well 1-h MP predicts DMP. After a 4-week interval, the repeatability of DMP was 0.49, while the repeatability of 1-h MP was 0.24. The correlation between DMP and 1-h MP was 0.56 for the first measurement and 0.66 for the second. It was estimated that the mean of 3 independent 1-hour measurements would be at least as repeatable as the DMP measurement. A 1-h MP measurement is a moderate predictor of DMP when sheep are fed 'ad libitum', which may occur during generous grazing conditions, and thus using 1-h MP as tool to select animals for low methane production may be feasible.

Rumen acidosis, acute and sub-acute, is an ongoing bane of the dairy and feed-lot sectors, resulting in animal deaths, morbidity and diminished productivity (Owens et al., 1998). Major impediments to improving understanding of these conditions include the large range of animal responses observed under identical conditions (Schwartzkopf-Genswein et al., 2003) and the difficulty encountered in measuring rumen pH itself, which has historically required either rumen cannulation or oesophageal intubation, both of which are likely to affect animal behaviour.

Steers (12) previously screened using the SF₆ measurement technique and found to have either high or low methane yield (MY: gCH₄/MJ DEI) were re-tested on the same diet. Several steers changed their MY, but the group characteristic of High (1.3 g/MJ) or Low (0.8 g/MJ) MY persisted between the measurement periods as did differences in propionate concentration and protozoal density. This suggests that one or more innate animal attributes must affect MY. The need to consider intake variation of cattle in extrapolating short term measures of methane measurements to annual emission estimates was also highlighted.

Rumen cannulated sheep (n = 12) were tested at each of three feeding levels: 0.8, 1.24 and 1.6 times maintenance. The ration (lucerne chaff) was provided in eight equal portions to emulate morning and afternoon grazing. After at least 10 days adaptation to each feeding level, methane production was measured in an open circuit calorimeter for 22 h using the same feeding regime. During measurement, 10 rumen samples were taken for volatile fatty acid (VFA) analysis by an indwelling rumen probe with a sampling tube that passed outside the calorimeter. Feed intake was strongly correlated with daily methane production (DMP, r = 0.87). Both methane production and VFA concentrations showed bimodal patterns related to the feeding cycle, but feed intake had a much smaller effect on VFA concentrations than on methane production rate. Average VFA concentration was a poor predictor of DMP. The best predictor, propionate concentration, explained 26% of the variance in DMP. The weakness of the association between VFA concentrations and methane production could be a consequence of differences in rumen volume and differences in VFA absorption associated with feeding level, although the possibility of accumulation of alternate fermentation end products or re-fermentation of VFA cannot be excluded. It is concluded that none of the suite of VFA parameters assessed offers a useful tool to predict daily methane production in grazing sheep.

The family of lemnacae colloquially known as duckweed contains the world's smallest species of flowering plants (macrophytes). Aquatic and free-floating, their most striking qualities are a capacity for explosive reproduction and an almost complete lack of fibrous material. They are widely used for reducing chemical loading in facultative sewage lagoons, but their greatest potential lies in their ability to produce large quantities of protein rich biomass, suitable for feeding to a wide range of animals, including fish, poultry and cattle. Despite these qualities there are numerous impediments to these plants being incorporated into western farming systems. Large genetically determined variations in growth in response to nutrients and climate, apparent anti-nutritional factors, concerns about sequestration of heavy metals and possible transference of pathogens raise questions about the safety and usefulness of these plants. A clear understanding of how to address and overcome these impediments needs to be developed before duckweed is widely accepted for nutrient reclamation and as a source of animal feed.