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.

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.

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.

This communication describes the application of calculations for estimating basal metabolic rate (BMR) and metabolisable energy requirement to sheep exposed to hot climatic conditions. Graham et al. (1974) studied animal factors that affect BMR and found that the BMR of weaned sheep of up to 27 months of age was well described by the following equation. BMR (MJ/d) = 0.257 × FW0.75exp(–0.08A) + 2.8G + 0.046DE where FW is fasted live weight (kg), A is age in years, G is growth rate (kg/d) in the 2–4 weeks before fasting and DE is intake of digestible energy (DE, MJ/d) before fasting.

Active absorption of phosphorus (P) from the alimentary tract is promoted by increased concentrations of active vitamin D [1,25(OH)₂D₃] in blood; however, the production of this active vitamin is determined by plasma concentrations of calcium (Ca) and not P. As a consequence, diets of adequate Ca content, but insufficient P, will not promote active P absorption. Dietary supplements of 25OH-vitamin D (25OHD), the precursor of 1,25(OH)₂D₃, may stimulate P absorption and P retention of ruminants consuming diets marginally deficient in P. To evaluate this hypothesis, steers (n = 18) were fed a pelleted low-quality roughage diet containing an adequate Ca concentration (0.68%). Nine steers received a supplement of 25OHD mixed into their feed, at a rate of 3.25 mg/head.day, before pelleting. The other nine steers were fed the Control diet without supplementation. All steers were individually housed for 10 days before being moved into metabolism crates for a further 3-day period. The steers which received the diet containing 25OHD exhibited increased retention of P and Ca, ~4 and 3 g/day, respectively. Blood samples were taken before the adaptation period and then daily during the period in the metabolism crates. Plasma concentrations of both P and Ca were increased by 25OHD supplementation throughout the collection period. Addition of 25OHD to the diet of grazing animals may reduce the need for P supplementation programs and improve productivity.

Profitable and sustainable agricultural production in resource-limited crop-livestock farming systems is largely dependent on the efficiency with which essential nutrients (N, P, K, Mg and S) are conserved and recycled. Although the economic and environmental importance of N cycling in agriculture is evident, the most feasible, profitable and sustainable practices that resource-limited and financially-challenged farmers can employ to increase N conservation and N cycling efficiency remain scarce. Based on the situation in Cambodia, five studies were designed to identify strategies to improve efficiency of N cycling through livestock in smallholder crop-livestock farming systems.

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.

Anionic salts are widely used to prevent clinical hypocalcemia (milk fever) in dairy cattle (Goff and Horst, 2003) and their effects have often been determined in Holstein cows. At the University of New England, Brangus steers (ca. 25% 'Bos indicus' content) have been selected for use in studies of anionic salts on calcium metabolism. However, the effects of anionic salts may differ between yearling crossbred beef steers and mature Holstein cows. Kurosaki et et al. (2007) showed that Holstein heifers had a much greater ability than Holstein cows to adapt to rapid changes in Ca excretion and Horst et al. (1990) showed that an increase in age is associated with a decrease in the concentration of vitamin D receptors in the intestine and bone.

Urinary Ca excretion in preparturient dairy cows is an indication that plasma ionised Ca is in excess of requirements (Kurosaki et al., 2007). As blood plasma Ca concentration must be maintained within a narrow range, any increase in Ca inflow to the extracellular pool can be expected to increase the outflow of Ca via the kidneys. Ca concentration is under homeostatic control, primarily via parathyroid hormone (PTH) (Horst, 1986).

The studies reported in this thesis were undertaken to investigate the characteristics of the degradation of two species of fresh forages in ruminants, i.e. lucerne (a legume) and ryegrass (a grass). A review of the literature was done to determine current understanding of the degradation of forage protein by plant and microbial processes in the rumen. Knowledge of degradability of fresh forages was found to be limited and so three studies were undertaken using forages labelled with ¹⁵N so that the end-products of forage protein degradation could be identified and their kinetics determined. The ¹⁵N-labelled forage was readily produced by growing the plants in pots watered with a solution of ¹⁵NH₄¹⁵N0₃. Rumen degradability of fresh and frozen-thawed lucerne and ryegrass was evaluated using 'in vitro', 'in situ' and in vivo techniques.