Introduction: Lactic acidosis is due to the over production of lactic acid in the rumen by the bacteria, 'S. bovis' or a combination of 'S. bovis' and 'Lactobacillus' when sheep and cattle consume large amounts of grain. It was hypothesised that the risk of lactic acidosis could be reduced by immunisation against the lactic acid producing bacteria. The present studies were conducted to test this hypothesis and investigate several key factors for developing an immunisation strategy against lactic acidosis. ... General discussion: Results from the studies in sheep and cattle support the hypothesis that the risk of lactic acidosis can be reduced by immunisation against 'S. bovis' or 'S. bovis' and 'Lactobacillus'. Live vaccine (using DEAE-dextran combined with mineral oil as an adjuvant) may provide a suitable protection using one booster following a primary immunization administered intramuscularly. This novel approach to reducing the risk of lactic acidosis associated with grain feeding offers a promising alternative to current practices of using feed additives, such as antibiotics active against the lactic acid-producing bacteria.

Sixty mature crossbred ewes were grouped into four different feeding treatments on day 110 of pregnancy until lambing to evaluated the effect of prepartum protein intake on mammary development and subsequent productive performance. Treatments were similar for the amount of crude protein (60 g/h/d) and differed in the quality of protein content. Following parturition, all ewes were fed the same feed. Ewes did not differ in initial body weight and body condition score. Ewes fed the protein diets exhibited greater liveweight gain during gestation and then increased weight loss after lambing. Mean liveweight for the protein fed ewes at parturition was greater than the controls. Change in body condition score was greater for the high UDP group than for the low UDP group at lambing, but riot in early lactation. Lamb birth weight and growth rate did not differ significantly between treatments. Prepartum diets influenced mammary development and subsequent milk production. Ewes given lupin supplement produced more milk (P<0.05) with highest milk protein (P<0.05) production. Milk and milk fat production were influenced by prepartum undegradable protein. Supplemental protein prepartum may improve postpartum performance by minimising mobilisation of maternal labile protein pools to meet foetal and maternal growth requirements in late gestation and subsequently improve lactation performance.

The continuing decline in the terms of trade of the Australian rural industries is maintaining pressure on agricultural industry to assess and modify the manner in which resources are applied to the production of food and fibre. Management practices in industries based on ruminant livestock are changing, particularly with an increase in the economic importance of grain based feedlots and the use of nutritional supplements for livestock on pasture in the meat, wool and dairy industries. These changes result from a need to use particular feed supplements as a means of manipulating and optimising production systems with respect to some limiting resource or factor. Such factors include periodic reductions in pasture quality or a window of opportunity for feeding to meet the production requirements of a particular market. There is also greater acceptance by the livestock industries of the use of novel feed materials, generally the byproducts of the cropping and horticultural industries, as nutritional supplements for cattle and sheep on pasture. Modification of a novel feed material to change its physical and/or nutritional form is often required before it can be optimally incorporated into a livestock production system. Processing increases the cost of the material. There are therefore financial benefits to the livestock producer in using feed supplements that require little processing. Cottonseed is a significant feed resource for ruminant livestock production in eastern Australia. The irrigation districts of Queensland and New South Wales, currently growing all of Australia's cotton crop, produce on average of 583 kT of cottonseeds each year (1990 to 1996) as a byproduct of cotton lint production (ABARE 1996).

A series of experiments was undertaken to explored the general hypothesisin that the rate of production and accumulation of lactic acid is more important than the buffering capacity within the gut in the development of fermentative acidosis. A comparative study of the absorption of lactic acid, volatile fatty acids (VFAs), glucose and ammonia from caecal and rumen pouches was undertaken in anaesthetised sheep. Test solutions varying in pH, osmolarity, lactic acid concentration, and with fixed concentrations of VFAs, ammonia and glucose (100 mmol/L, 7 mmol/L and 4 mmol/L, respectively) were introduced into clean, surgically sealed pouches. Studies were undertaken in nine sheep, each with two pouches in the caecum and one in the rumen. Samples were taken at 10-minute intervals for 50 minutes to determine rates of absorption. On the other hand, the buffering capacities of caecal and rumen digesta of sheep fed oaten chaff and pasture and fasted were determined by titration with lactic, acetic and hydrochloric acids. On the basis of integrating the experimental data in this study and incorporating this with information already available in the literature, a computer modelling approach was developed using the program STELLA II to study acid production and absorption, and to predict pH during fermentation. ... The results are very useful for investigating effective methods and their mechanisms for the prevention and treatment of lactic acidosis. It appears that the rate of fermentation and the amount of substrate are important factors in terms of the development of fermentative acidosis.

The Australian feedlot industry has sufficient capacity to feed approximately 870 000 head (ALFA Lotfeeding 1997) and contributes approximately 25% of total beef production in Australia. The industry is composed of feedlots incorporated into vertically integrated companies, custom feedlots, pastoral operations and opportunity feedlots. Custom feedlots feed and market cattle for other owners, the pastoral operations value add and retain control over breeding programmes and opportunity feedlots feed cattle on a opportunistic basis when market conditions, eg. feed costs, cattle costs and selling price, are economically beneficial.