Inclusion of nitrate (NO₃⁻) in ruminant diets is a means of increasing non-protein nitrogen intake while at the same time reducing emissions of enteric methane (CH₄) and, in Australia, gaining carbon credits. Rumen microorganisms contain intracellular enzymes that use hydrogen (H₂) released during fermentation to reduce NO₃⁻ to nitrite (NO₂⁻), and then reduce the resulting NO₂⁻ to ammonia or gaseous intermediates such as nitrous oxide (N₂O) and nitric oxide (NO). This diversion of H2 reduces CH₄ formation in the rumen. If NO₂⁻ accumulates in the rumen, it may inhibit growth of methanogens and other microorganisms and this may further reduce CH4 production, but also lower feed digestibility. If NO₂⁻ is absorbed and enters red blood cells, methaemoglobin is formed and this lowers the oxygen-carrying capacity of the blood. Nitric oxide produced from absorbed NO₂⁻ reduces blood pressure, which, together with the effects of methaemoglobin, can, at times, lead to extreme hypoxia and death. Nitric oxide, which can be formed in the gut as well as in tissues, has a variety of physiological effects, e.g. it reduces primary rumen contractions and slows passage of digesta, potentially limiting feed intake. It is important to find management strategies that minimise the accumulation of NO₂⁻; these include slowing the rate of presentation of NO₃⁻ to rumen microbes or increasing the rate of removal of NO₂⁻, or both. The rate of reduction of NO₃⁻ to NO₂⁻ depends on the level of NO₃⁻ in feed and its ingestion rate, which is related to the animal's feeding behaviour. After NO₃⁻ is ingested, its peak concentration in the rumen depends on its rate of solubilisation. Once in solution, NO₃⁻ is imported by bacteria and protozoa and quickly reduced to NO₂⁻. One management option is to encapsulate the NO₃⁻ supplement to lower its solubility. Acclimating animals to NO₃⁻ is an established management strategy that appears to limit NO₂⁻ accumulation in the rumen by increasing microbial nitrite reductase activity more than nitrate reductase activity; however, it does not guarantee complete protection from NO₂⁻ poisoning. Adding concentrates into nitrate-containing diets also helps reduce the risk of poisoning and inclusion of microbial cultures with enhanced NO₂⁻ - reducing properties is another potential management option. A further possibility is to inhibit NO₂⁻ absorption. Animals differ in their tolerance to NO₃⁻ supplementation, so there may be opportunities for breeding animals more tolerant of dietary NO₃⁻. Our review aims to integrate current knowledge of microbial processes responsible for accumulation of NO₂⁻ in rumen fluid and to identify management options that could minimise the risks of NO₂⁻ poisoning while reducing methane emissions and maintaining or enhancing livestock production.

In the Australian sheep industry, Estimated Breeding Values (EBVs) are being increasingly used to select Merino sheep for excellence in traits such as high clean fleece weight (CFW), low fibre diameter (FD) and high yearling live weight (YLW). It has been proposed that genetic differences in CFW may be related to skin protein metabolism and that it is sensitive to the level of nutrition (Williams and Morley 1994; Liu et al. 1998). The underlying physiological responses to EBV and plane of nutrition are not well understood.

Nitrate (NO₃¯) is an effective non‐protein nitrogen source for gut microbes and reduces enteric methane (CH₄) production in ruminants. Nitrate is reduced to ammonia by rumen bacteria with nitrite (NO₂¯) produced as an intermediate. The absorption of NO₂¯ can cause methaemoglobinaemia in ruminants. Metabolism of NO₃¯ and NO₂¯ in blood and animal tissues forms nitric oxide (NO) which has profound physiological effects in ruminants and has been shown to increase glucose uptake and insulin secretion in rodents and humans. We hypothesized that absorption of small quantities of NO₂¯ resulting from a low‐risk dose of dietary NO₃¯ will increase insulin sensitivity (SI) and glucose uptake in sheep. We evaluated the effect of feeding sheep with a diet supplemented with 18 g NO₃¯/kg DM or urea (Ur) isonitrogenously to NO₃¯, on insulin and glucose dynamics. A glucose tolerance test using an intravenous bolus of 1 ml/kg LW of 24% (w/v) glucose was conducted in twenty sheep, with 10 sheep receiving 1.8% supplementary NO₃¯ and 10 receiving supplementary urea isonitrogenously to NO₃¯. The MINMOD model used plasma glucose and insulin concentrations to estimate basal plasma insulin (Ib) and basal glucose concentration (Gb), insulin sensitivity (SI), glucose effectiveness (SG), acute insulin response (AIRg) and disposition index (DI). Nitrate supplementation had no effect on Ib (p > .05). The decrease in blood glucose occurred at the same rate in both dietary treatments (SG; p = .60), and there was no effect of NO³¯ on either Gb, SI, AIRg or DI. This experiment found that the insulin dynamics assessed using the MINMOD model were not affected by NO₃¯ administered to fasted sheep at a low dose of 1.8% NO₃¯ in the diet.

Polycultural aquaculture typically utilises a mix of low trophic level species to increase yield above that which can be obtained from a single species. Low trophic level species are not widely accepted for consumption within Australia, so this study focussed on two species that have market acceptance, the yabby (Cherax destructor) and the silver perch (Bidyanus bidyanus). Laboratory scale trials examined the effect of each species on the growth and survival of the other species as well as the role of shelter for crayfish in this system over a 13.5 week period. Neither species negatively impacted the growth of the other, however, survival was negatively impacted. Shelter enhanced crayfish survival, although fish survival was impacted in those treatments. A higher total biomass was harvested from polyculture treatments than monoculture treatments. The positive results warrant further investigation at the scale of mesocosm, prior to large-scale pond trials.

Effective university level education in animal nutrition requires both research-led teaching and motivated students (Brew, 1999). With the aim of providing both of these requirements, we established the "State of Origin Chicken Challenge" competition. This annual event capitalises on Australian students' love of sporting competition (albeit linked to sport in name only) and incorporates this into the teaching of animal nutrition. Practical activities involving diet formulation and the effects of different diets on chicken growth have been part of the traditional animal nutrition curriculum at most universities. The basis of the current competition was that students at the University of New England, Armidale (UNE) and The University of Queensland, Gatton (UQ) would formulate diets and subsequently feed these diets to chickens at both campuses. The competition winner is the university that grows the greatest weight of chicken per dollar of feedstuff.

One of the major effects of climate change is disruption in normal weather patterns, especially an increase in long-term annual temperature, and more frequent and intense droughts and floods. These changes have impact on the natural resource base that includes plants, animals and biodiversity. Consequently, this diminishes feed and water resources which livestock depend on to survive and therefore impacting negatively on food security and household incomes of smallholder livestock producers and pastoralists, the majority of whom are found in the tropics. Efficient utilization of available feed resource by ruminants, most of it being high in fibre and low in protein content is often constrained by low digestibility and inefficient metabolism of absorbed nutrients at the tissue metabolic level. The low digestibility of high fibre forage in ruminants is mainly attributed to a high level of lignification and a deficiency of essential nutrients, especially nitrogen (N) and sulphur (S) that are required by rumen microbes for optimal growth. Furthermore, the absorbed nutrients also tend to be imbalanced in the ratio of protein to energy and/or acetogenic to glucogenic substrates. As a result the intake of high fibre forages in ruminants is often associated with a significant loss of feed energy as heat increment and methane (CH4) gas production, with the later also contributing significantly to global warming through greenhouse gas emissions. This review gives an overview of the various strategies in the form of treatment and supplementation that have been shown to improve digestion and intake of high fibre forages in ruminants, and also reducing CH4 gas production. The role of rumen degradable nutrients as well as by-pass nutrients in enhancing digestion and absorption of nutrients that are balanced in protein: energy ratio and/or acetogenic: glucogenic substrates is also reviewed and suggested as one way of increasing metabolic efficiency of absorbed nutrients at the tissue level to reduce heat increment. The role of glucogenic substrates such as propionate and protein/amino acids in ensuring an adequate supply of reducing equivalents in the form of reduced nicotinamide adenine dinucleotide phosphate (NADPH) that is required for the conservation of excess acetate as fat in the adipose tissue and also for regeneration of oxaloacetate for efficient VFA energy metabolism in the body tissues is also reviewed. It is concluded that a multipronged approach combining treatment with supplementation with cheap and locally available rumen degradable nutrients (e.g. molasses-urea liquid mixture and the urea-molasses-mineral based multi-nutrient block) and bypass nutrients that are compatible with low input ruminant production systems holds the key to increasing efficiency in the utilization of high fibre-low protein forage in ruminants. This can play a major role in increasing the capacity of smallholder livestock producers and pastoralists in most parts of the tropics to adapt and therefore mitigate the adverse effects of climate change.

It was hypothesised that the inclusion of nitrate (NO₃^–) or cysteamine hydrochloride (CSH) in a protein deficient diet (4.8% crude protein; CP) would improve the productivity of sheep while reducing enteric methane (CH₄) emissions. A complete randomised designed experiment was conducted with yearling Merino sheep (n = 24) consuming a protein deficient wheaten chaff control diet (CON) alone or supplemented with 1.8% nitrate (NO₃^–; DM basis), 0.098% urea (Ur, DM basis) or 80 mg cysteamine hydrochloride/kg liveweight (CSH). Feed intake, CH₄ emissions, volatile fatty acids (VFA), digesta kinetics and NO₃^–, nitrite (NO₂^–) and urea concentrations in plasma, saliva and urine samples were measured. There was no dietary effect on animal performance or digesta kinetics (P > 0.05), but adding NO₃^– to the CON diet reduced methane yield (MY) by 26% (P = 0.01). Nitrate supplementation increased blood MetHb, plasma NO₃ ^– and NO₂^– concentrations (P < 0.05), but there was no indication of NO₂^– toxicity. Overall, salivary NO₃^– concentration was greater than plasma NO₃^– (P < 0.05), indicating that NO₃^– was concentrated into saliva. Our results confirm the role of NO₃^– as an effective additive to reduce CH₄ emissions, even in a highly protein-deficient diet and as a source of additional nitrogen (N) for microbial protein synthesis via N-recycling into saliva and the gut. The role of CSH as an additive in low quality diets for improving animal performance and reducing CH₄ emissions is still unclear.

About 4 treatments (control, fresh barley sprouts, freeze-dried barley sprouts and barley grain supplementation) were used in a latin square design. Oaten chaff basal diet was used in testing the assertion that hydroponic barley sprouts gave better animal performance than the grain supplement. Results showed increase in DM intake on supplementation, there were differences (p<0.001) among treatments in DM intake. The increased intake due to sprouts supplementation however, did not translate to better digestibility, microbial outflow and nitrogen retention. Total ammonia concentration was higher (p<0.001) for the fresh barley sprouts supplements than for the barley grain and control suggesting that poor quality roughage yields more rumen ammonia when supplemented with fresh hydroponic barley sprouts. The total ammonia concentration did not however, differ (p>0.05) between the fresh or freeze-dried hydroponic barley sprouts. The total VFA concentrations were higher for the freeze-dried and fresh hydroponic barley sprouts than the control but not different (p>0.05) from the barley grain supplementation in the current study. This suggests that sprouting did not give rise to a higher VFA concentration when poor quality roughage was supplemented. It was concluded from this study that supplementing poor quality roughage (oaten hay) with hydroponic barley sprouts increased DMI and total rumen ammonia concentration. However, there was no confirmation of the presence of a grass juice factor purported to be present in sprouts which gives increased performance.

Australian sheep are transported to the Middle East where excessive temperatures (>45°C) can cause heat stress and inappetence, compromising the welfare of animals in the post-discharge phase of an industry worth $1.8 billion annually (Hassall and Associates 2006). There is little published research on the importance of drinking water temperature in managing heat stress in sheep. There are also no recommendations. Recommended water temperatures for cattle in hot climates are 16 to 18°C (EA Systems 2004). This study found that as drinking water was increased from 20°C to 40°C water intake increased and that sheep prefer to drink water of 30°C rather than 20°C in hot climates. These are new findings with important implications for the industry.

In the Australian sheep industry, Estimated Breeding Values (EBVs ) are being increasingly used to select Merino sheep for excellence in traits such as high clean fleece weight (CFW), low fibre diameter (FD) and high yearling live weight (YLW). It has been proposed that genetic differences in CFW may be related to skin protein metabolism and that it is sensitive to the level of nutrition (Williams and Morley 1994; Liu et al. 1998). The underlying physiological responses to EBV and plane of nutrition are not well understood. We selected 20 wethers from a commercial flock (18 month-old weighing about 33.3 kg) with similar EBV for FD and YLW, but 10 wethers had high EBV for CFW (F+), and 10 had low EBV for CFW (F-). We used a 2 x 2 experiment (F+ and F- wethers at two levels of intake, i.e. 0.8 and 1.8 x maintenance of commercial pellets) and determined CFW and protein synthesis rates (FSR) in their skin and muscle pools using the flooding dose technique (Rocha et al. 1993, i.e. i/v injection of deuterium-labelled [L-ring-D⁵] phenylalanine). The commercial pellets contained 13.3% crude protein, 20% crude fibre, 9.5 MJ/kg ME.