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.

Triticale is a cereal grain that holds great promise as an alternative to wheat and other conventional grains used in poultry diets. Triticale generally has a higher yield than wheat and adapts to more difficult agronomic conditions than wheat (Korver et al., 2004). A crop breeding group at the University of New England (UNE) has developed varieties that are even more high-yielding and more disease-resistant than the current commercial strains. These varieties will need further evaluation to establish their potential for animal, and particularly poultry feeding.

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.

This experiment was done to investigate microbial contamination and in situ disappearance rates of dry matter (DM), N and 15N of fresh labeled ryegrass. Perennial ryegrass (Lolium perenne) were labeled with 15N during growth in a glasshouse, harvested at 4th leaves stage and were incubated up to 34 h in situ in the rumen of 3 individually housed sheep. The animals were fed 800 g/d chopped alfalfa and had free access to drinking water. Six bags were placed in the rumen of ach sheep simultaneously and removed after 0, 3, 7, 12, 21 and 33 h after incubation. The results were fitted to a model describing the degradation of DM and total N with time. It was found that residues from the washed zero time bags had lower e 15N enrichments (7.7% vs. 8.3% enriched) than the original fresh samples. Under-estimation of effective degradability (ED) of protein in fresh forages by about 4% would have potential consequences for predictions of ruminally fermentable and escape protein and thus for dietary protein feeding management. However, because the correction assumes contaminating microbial N is unlabeled, but microbes attached to labeled ryegrass would become labeled to some extent, the true error and effective degradability may still be underestimated. Studies with two markers would help us to better understand the errors associated with the in situ technique.

Current ruminant feeding systems depend on knowledge of the composition of feeds and the rate and extent of degradation of feed organic matter (OM) and crude protein (CP) in the rumen. The effect of storage and preparation of samples on in vitro gas production and fermentation characteristics of two common forage species, namely alfalfa and rye grass were studied. Samples were prepared as fresh (F), frozen-thawed (FT) and FT + starch (FT + S) before in vitro evaluation. The fractional rate of loss of organic matter (OM) and the total N and total VFA production during 12h of incubation were significantly faster for alfalfa than for rye grass. Model parameters describing changes in OM loss and total N appearance differed significantly between F samples and FT and FT + S samples; there was a significant interaction between forage species and preparation method for fractional degradation rate of total N. A significant interaction between forage species and preparation method at 6 h incubation changed the rankings. The propionate:acetate ratios after 12 h incubation were similar for alfalfa and rye grass but were lower for F and FT samples than for FT + S samples. After 12 h of incubation, alfalfa produced more gas, total VFA (mmol/g OM) and microbial crude protein (mg/g OM) than rye grass, whereas F samples produced more fermentation products than FT and FT + S samples. In vitro degradation characteristics of forage samples were influenced by forage species, but also by sample preparation method; therefore, consistent use of one sample preparation method is recommended when comparing degradation characteristics of forage species in vitro.

Supplementing low-quality straw with protein meal, fresh tropical grass or legume forage improves dry matter intake (DMI), digestion and live weight gain in cattle (Doyle et al., 1986). Smallholder cattle farmers in Cambodia mostly use rice ('Oryza sativa') straw as a basal diet, especially during feed shortages. Supplementation of such diets with C4 grasses such as Mulato II hybrid ('Brachiaria' spp.) increases the intake and digestibility of rice straw, but mixed diets of grass and rice straw may still be deficient in rumen degradable N (RDN), especially if the grass is mature when cut. Inclusion of a tropical legume such as Stylo CIAT 184 ('Stylosanthes guianensis') as a source of RDN may further increase microbial activity and DMI. Our objective was to measure the effect of adding Stylo 184 forage to a mixed diet of rice straw and C4 grass fed to cattle in terms of DMI, digestibility, microbial crude protein (MCP) production and live weight gain.

A total of 384 day-old male Ross 308 broiler chicks were allocated to 8 dietary treatments to examine the influence of supplementation with xylanase and phytase, individually or in combination, in diets based on two new cultivars of triticale (Bogong and Canobolas). The inclusion of phytase alone in either Bogong or Canobolas diets increased (P < 0.01) feed intake and body weight; however, the effect of grain was not significant. The ileal digestibility of crude protein, gross energy, starch, calcium, and phosphorus was increased by inclusion of phytase and xylanase (P < 0.05). The interaction between xylanase and phytase positively influenced (P < 0.01) the digestibility of crude protein, gross energy, calcium, and phosphorus. Ileal viscosity was decreased (P < 0.05) by the inclusion of xylanase and phytase individually or in combination. The inclusion of phytase and xylanase increased (P < 0.001) the phytate- P degradation. Birds on Bogong-based diet had a higher (P < 0.05) degradation of phytate than those on the Canobolas-based diet. The weight of various visceral organs on day 7 was not affected by the inclusion of enzymes, nevertheless the weight of proventriculus plus gizzard was higher (P < 0.01) for chickens offered Canobolas-based than chicks on the Bogong-based diets. On day 21, the liver weight was reduced (P < 0.001) by the inclusion of phytase. An interaction (P < 0.01) between grain and phytase inclusion led to an increased weight of proventriculus plus gizzard on the Bogong diets with phytase. The inclusion of xylanase increased (P < 0.01) maltase activity at the jejunum on day 7, while it decreased the pancreatic protein content on day 21. The activity of chymotrypsin amidase was reduced (P < 0.01) by the inclusion of phytase. These results show that supplementation of phytase and xylanase to triticale-based diets can improve broiler performance by increasing the activities of some digestive enzymes and nutrient utilization.

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.

In Cambodia, seasonal flooding of land each year by the Mekong river limits the availability of feed for cattle. To alleviate this feed shortage, the concept of forage banks was developed by CIAT (2003-05) and feed banks are being exploited in our current ACIAR project (AH/2003/008). 'Brachiaria' mulato II hybrid (CIAT 36087) is a promising grass for these fodder banks but its nutritive value for cattle when used as a supplement with rice straw has not been widely investigated. The aim of this study was to provide basic information on the in situ rumen digestibility of mulato II hybrid relative to rice straw and to determine the effect of the animal's diet on rumen degradability estimated by the in situ method. In situ evaluations of dried samples of rice straw and sun-dried, first-cut mulato were made using 3 fistulated steers (c. 2.5 years, 248 ± 38kg). In Expt 1, bags were placed in steers ingesting 30% fresh-cut mulato II and 70% rice straw and, in Expt 2, the steers ingested only freshly cut mulato ad libitum. In Expt 1, feed bins were emptied each morning and then filled with rice straw followed by half of the daily ration of fresh mulato; the second half was given in the evening. Both feeds were cut to 2 mm, placed in nylon bags (pore size 40 μm) and incubated (in triplicate) for 3, 12, 24, 36, 48, 72 and 96 h in all three steers. All bags were removed together and washed with 9 additional bags, similarly prepared but never placed in the rumen (to give washing loss). Results for loss of OM (Y) during the incubation period (t) were fitted to a curve, Y=A+B(1-e⁻ct) where A, B, c and lag time are as described by Dhanoa et al. (1996). Rumen NH₃ was also determined (Beecher and Whitten 1970). Effective degradability of both feeds was higher (P<0.05) when steers were ingesting 100% mulato, and lag time (the period before there was net loss of OM) was shorter by 3-4 h (P<0.05), indicating that rumen digestion was markedly inferior when the diet was 70% rice straw and only 30 % mulato (Table 1). Effective degradability of OM, washing loss and rate of degradation of B were higher (P<0.05) and lag time was shorter (P<0.05) for mulato than for rice straw. The degradable OM percentage, excluding washing loss (WL) was similar for mulato and rice straw but with WL included, total potential degradability was higher (P<0.05) for mulato. Thus, the main reason that mulato hybrid exhibited a higher nutritive value than rice straw was its higher washing loss (higher level of soluble components) and its apparently more rapid colonisation by rumen microorganisms.

Nitrate supplementation has been shown to be effective in reducing enteric methane emission from ruminants, but there have been few large-scale studies assessing the effects of level of nitrate supplementation on feed intake, animal growth, or carcass and meat quality attributes of beef cattle. A feedlot study was conducted to assess the effects of supplementing 0.25 or 0.45% NPN in dietary DM as either urea (Ur) or calcium nitrate (CaN) on DMI, ADG, G:F, and carcass attributes of feedlot steers (n = 383). The levels of NPN inclusion were selected as those at which nitrate has previously achieved measurable mitigation of enteric methane. The higher level of NPN inclusion reduced ADG as did replacement of Ur with CaN (P < 0.01). A combined analysis of DMI for 139 steers with individual animal intake data and pen-average intakes for 244 bunk-fed steers showed a significant interaction between NPN source and level (P = 0.02) with steers on the high-CaN diet eating less than those on the other 3 diets (P < 0.001). Neither level nor NPN source significantly affected cattle G:F. There was a tendency (P = 0.05) for nitrate-supplemented cattle to have a slower rate of eating (g DMI/min) than Ur-supplemented cattle. When adjusted for BW, neither NPN source nor inclusion level affected cross-sectional area of the LM or fatness measured on the live animal. Similarly, there were no significant main effects of treatments on dressing percentage or fat depth or muscling attributes of the carcass after adjustment for HCW (P > 0.05). Analysis of composited meat samples showed no detectable nitrates or nitrosamines in raw or cooked meat, and the level of nitrate detected in meat from nitrate-supplemented cattle was no higher than for Ur-fed cattle (P > 0.05). We conclude that increasing NPN inclusion from 0.25 to 0.45% NPN in dietary DM and replacing Ur with CaN decreased ADG in feedlot cattle without improving G:F.