Any improvements in starch digestion in cattle would undoubtedly be of great benefit to the feedlot industry. There are numerous factors that are likely to vary between animals that may affect both the efficiency and site of starch digestion. The benefits of starch digestion in the small intestine, as opposed to in the rumen, include a higher energetic efficiency, and a reduced risk of acidosis provided that high levels of starch do not reach the hindgut. Recent research has identified genetic differences between similar cattle in their ability to digest starch. The evidence is provided by differences between progeny groups of steers in the level of fermentation occurring in the hindgut. We have also found between-animal differences in total tract starch digestibility that are consistent across diets.

This study describes the impact of Australian Sheep Breeding Values (ASBV) for post-weaning weight (PWWT), C-site fatness (PFAT) and eye muscle depth (PEMD) on lamb carcasses within the Australian Sheep Industry CRC Information Nucleus Flock. These results are taken from the 2007 drop progeny, consisting of ~2000 lambs slaughtered at a target weight of 21.5 kg. These lambs were the progeny of sires selected to ensure genetic diversity across various production traits. As expected, the PWWT ASBV increased weight at slaughter, and hot standard carcass weight. Dressing percentage was markedly improved by increasing PEMD ASBV, thus prime lamb producers will be maintaining an animal of similar weight on farm, but delivering a markedly larger carcass at slaughter. Lean meat yield % (LMY%) was highest in the progeny of sires with low PFAT ASBV, which decreased whole carcass fatness and increased muscularity. PWWT ASBV affected carcass composition but had little impact on LMY%, as the decreased fatness was largely offset by increased bone, with relatively little change in muscle content. Lastly, PEMD ASBV had little impact on whole carcass LMY%, but did appear to cause some level of muscle redistribution to the higher value loin cuts, in turn increasing the value of the carcass lean.

Acidosis is an economically important disease of ruminant livestock, involving both reduced productivity and serious animal welfare implications. Major lactic acid producing bacteria in sheep were identified by Al Jassim and Rowe (1999) and it is likely that the proliferation of these bacteria, under certain feeding regimes, leads to acidosis. Antibiotic feed additives are currently used in management of acidosis but there are serious concerns about this approach and, consequently, vaccination against acidosis-producing bacteria as a means of preventing the condition is under active investigation in our laboratory. The aim of this trial was to measure antibody responses to a range of acidosis-producing bacteria, following administration of experimental vaccines. Forty-nine healthy adult merino wethers were used for this study and run together as a single flock throughout the experiment. Animals were randomly allocated into 7 groups, to be immunized with one of six different bacterial isolates, or non-immunized as controls. Vaccines were prepared from pure bacterial isolates (formalin killed), emulsified in Freund's adjuvant, and administered intramuscularly at weeks 0 and 4. Freund's complete adjuvant was used for the primary immunization, and Freund's incomplete adjuvant was used for the secondary immunization. Samples of venous blood were collected before immunisation and every two weeks for ten week. Concentrations of IgG antibodies in serum were determined by ELISA. Antibody levels produced in response to immunizations with each of the 6 isolates are shown in Table 1. Strong antibody responses were produced by the three streptococcal isolates, with peak antibody concentrations at week 6. There was a 12-fold increase produced by the two 'S. bovis' strains, whereas a 57-fold increase was produced by the 'S. equinus'. Antibody responses were also produced by 'Selenomonas ruminantium', with antibody levels reaching a peak at week 10. There was a relatively weak antibody response to 'Lactobacillus vitulinus'.

A 3x2 factorial experiment was designed to examine the effects of dietary fructooligosaccharides (FOS) level, and the presence or absence of an enzyme (inulinase), on aspects of faecal quality and apparent coefficients of nutrient digestibility in doxs. Three extruded dry diets based on wheat, pearl barley and wheat by-products were formulated to contain (dry matter basis) 1.75g/kg (Diet A), 4.7 g/kg (Diet B) and 61.7 g/kg (Diet C) FOS. The FOS content of Diets B and C was achieved by adding 30 and 60 g/kg (DM) Raftilose®P95, a commercial FOS product. The addition of inulinase (500 ml (1.2x10⁶U) per tonne) was examined for each diet to counteract any potentially negative effects of added FOS on faecal quality and digestibility, and was sprayed onto the diet at feeding at a level of 500 ml per tonne of food. The experiment lasted 13 days with faecal collections occurring on the final 5 days. Measurements taken were: faecal score (one indicating hard faeces, five indicating diarrhoea), coefficients of total tract apparent digestibility (CATTD), faecal pH, and volatile fatty acids (VFA) and lactate concentrations. The CATTD for fat and energy decreased with greater levels of dietary FOS. Increased levels of FOS decreased (P<0.05) faecal pH and the content of dry matter (DM) in the faeces and also increased (P<0.05) the faecal score, although this remained in the 'ideal' range of 1.5-2.5. Addition of inulinase increased (P<0.05) the faecal pH. Faecal lactate concentrations increased with greater levels of FOS (P<0.05; 84.9 versus 142.5 versus 288.7 mmol/kg faeces DM for Diets A, B and C, respectively), suggesting that the growth and (or) activity of lactate-producing bacteria in the colon were enhanced. Higher levels of FOS in an extruded dog food caused faeces to become wetter and more acidic, and consequently the number of dogs that had unacceptable faecal scores increased. However, and at the highest dietary FOS level (61.7 g/kg DM), inulinase caused significantly drier faeces and increased the number of dogs within the 'ideal' range of faecal score.

High prices for sheep meat and the need for year-round supply means that grain feeding of sheep will continue as an important component of sheep production. Grain feeding low body weight lambs and cast-for-age (CFA) sheep from pastoral areas of eastern Australia at the end of the growing season can enable critical carcase weight grades to be achieved, sometimes doubling market returns. In parts of Australia sorghum grain is a cheaper alternative to other cereal grains but its use and nutritive value in sheep feeding systems is not well understood. This paper describes results from four experiments conducted by the Sheep CRC to investigate sorghum grain as a major component of diets fed to lambs and CFA ewes and wethers. The experiments involved comparisons of diets based on sorghum with a winter cereal grain and with commercial feed pellets, investigated the effects of various processing methods (whole grain, cracked, steam flaked and expandat®) and the effect of feeding sorghum grain with and without additional true protein and non-protein-nitrogen (NPN) sources. Growth, feed conversion, carcase performance and digestion parameters were measured. There were higher concentrations of starch in the faeces of sheep fed unprocessed sorghum grain (ca. 18 - 31 % of faecal OM) than when steam-processed grain was fed (4 % of faecal OM) to older sheep. Although steam flaking increased the digestibility of sorghum starch by CFA sheep it appears that the benefits of processing do not justify the costs. Substituting true protein sources for NPN did not significantly increase performance of CFA ewes.

The amylolytic enzyme α-amylase is essential for the digestion of starch in the small intestine of the horse. While it had been previously documented that the concentration of this amylolytic enzyme in the equine small intestine is low, the ability of equine α-amylase to degrade cereal grain starch is poorly understood. In an experiment designed to compare the 'in vitro' starch digesting capacity (activity) of equine α-amylase with that of bacterial a-amylase it was observed that the equine α-amylase digested an average of 20% less starch during the 'in vitro' incubations. This result suggests that the apparently limited capacity of equine α-amylase to digest starch along with the low concentrations of α-amylase reported to be present in the equine small intestine may limit pre-caecal starch digestion. A second experiment investigated if the addition of exogenous glycanase enzymes to cereal grain diets fed to horses would improve small intestinal starch digestion. The results showed that the addition of α-amylase and amyloglucosidase (AMG) to a digestible starch source significantly elevated postprandial glycaemic responses suggesting an improvement in precaecal starch digestion . Thus it appears that the concentration and activity of equine α-amylase may be limiting small intestinal starch digestion in the horse.

An important question regarding supplementation of grazing beef cattle is how frequently this should be done. Responses of cattle to supplementation weekly with cereal grains are not as well documented as daily, probably because of the high risk of acidosis in cattle fed rapidly fermentable sources of starch. Successful weekly supplementation of cattle with barley containing virginiamycin to reduce the risk of acidosis has been reported by Zorrilla—Rios et al. (1994). It is possible that feeding whole maize grain to cattle can reduce rate of ingestion, stimulate mastication and saliva secretion compared to ground grain and thereby reduce the risk of acidosis. It is also likely that the amount of forage available (FA) can affect animal response in relation to weekly or daily supplementation.

The effects of increasing levels of soluble non-starch polysaccharides (NSP) in extruded dog diets were studied in a 3×2 factorial arrangement of treatments using six dogs per diet. The factors examined were diets of different composition giving varying levels of dietary soluble NSP (11, 16 and 20 g/kg), and the presence or absence of an enzyme containing xylanase, β-glucanase and amylase. The diets varying in soluble NSP content were assigned diets A, B and C, respectively, with enzyme or water being added at feeding to each to comprise the six diets used in the experiment. The feed enzyme mixture was sprayed onto the diet at the time of feeding, at a level of 400 ml/tonne of diet. The trial lasted 13 days with faecal collections occurring on the final 5 days. Measurements taken were; faecal score (1 indicating hard faeces, 5 indicating diarrhoea), coefficient of total tract apparent digestibilities (CTTAD), faecal pH, volatile fatty acids (VFA) and lactate. Significant interactions (P<0.05) were present for dietary soluble NSP content and enzyme for CTTAD of starch, fat, dry matter and gross energy. Diets containing 16 g soluble NSP/kg (diet B) and 20 g soluble NSP/kg (diet C) soluble NSP caused decreases in CTTAD (P<0.05), but presence of the enzyme reversed these effects (P<0.05) such that results were equivalent to those in diet A. The CTTAD of protein was decreased (P<0.001) with increased soluble NSP level but increased (P<0.01) with addition of the enzyme. Increased soluble NSP levels caused faecal deterioration (2.2 versus 2.5 versus 3.0 for diets A, B and C, respectively), however the enzyme decreased faecal score (2.7 versus 2.5, P<0.05). Increased dietary levels of soluble NSP decreased faecal pH (P<0.001) and caused the faecal lactate and VFA concentrations to increase and decrease, respectively (P<0.05), indicating that fermentation in the large intestine was increased. Increasing levels of soluble NSP in dog diets caused some anti-nutritive effects and deteriorated faecal quality, however the addition of the enzyme alleviated some of these effects to the extent that a moderate increase in dietary soluble NSP levels could be tolerated in dog diets based on wheat, barley and mill mix without major detrimental effects on digestion and faecal quality.

The replacement value of sorghum and maize for rice in extruded dog foods was studied. The diets contained 552 g sorghum/kg diet, 535 g maize/kg diet and 521 g rice/kg diet. The addition of a feed enzyme product containing a cocktail of carbohydrates to the sorghum- and maize-based diets was also tested, with the enzyme being sprayed on to the dry diets at feeding at a level of 1000 ml/t. The experiment lasted 13 days with faecal collections occurring on the final 5 days. Measurements taken were: faecal score (1 indicating hard faeces, 5 indicating diarrhoea), macronutrient digestibilities, faecal pH and volatile fatty acid (VFA) and lactate concentrations. The coefficient of total tract apparent digestibility (CTTAD) for starch was complete in all diets. The CTTAD of fat, protein and energy in the sorghum- and maize-based diets was lower (P<0.05) compared to the rice based diet, and were not increased (P>0.05) by enzyme addition. Consequently, the digestible energy (DE) content of the rice-based diet was 0.3-0.8 MJ DE/kg DM higher (P<0.001). The faecal score of dogs fed rice was higher (P<0.05) than their counterparts fed sorghum and maize, with the enzyme increasing faecal score (P<0.05) and making it equivalent to that of dogs fed the rice-based diet (P>0.05). The faeces of dogs fed rice had a higher pH (P<0.05) compared to dogs fed the sorghum- and maize-based diets. The improved quality of faeces seen in dogs fed sorghum and maize, balanced by only minor decreases in digestibility and DE content, suggests that maize and sorghum are suitable alternatives to rice as the primary cereal in extruded dog foods.

Grinding cereal grains for cattle feeding is generally considered to be important for efficient digestion and to minimize waste. Maize could be an exception as whole maize (WM) is commonly used in lot—fed cattle when the diet contains less than 20% roughage (NRC 1996) and can be used to supplement grazing animals (Beretta et al. 2001). Mastication of grain during eating will probably play a major role in reducing particle size, given the bigger size of maize with respect to other grains. However, grinding maize can modify the site of starch digestion increasing rumen degradability without necessarily increasing the grain whole tract apparent digestibility.