Due to their high energy requirements, high-yielding dairy cows receive high-grain diets. This commonly jeopardises their gastrointestinal health by causing subacute ruminal acidosis (SARA) and hindgut acidosis. These disorders can disrupt nutrient utilisations, impair the functionalities of gastrointestinal microbiota, and reduce the absorptive and barrier capacities of gastrointestinal epithelia. They can also trigger inflammatory responses. The symptoms of SARA are not only due to a depressed rumen pH. Hence, the diagnosis of this disorder based solely on reticulo-rumen pH values is inaccurate. An accurate diagnosis requires a combination of clinical examinations of cows, including blood, milk, urine and faeces parameters, as well as analyses of herd management and feed quality, including the dietary contents of NDF, starch and physical effective NDF. Grain-induced SARA increases acidity and shifts availabilities of substrates for microorganisms in the reticulo-rumen and hindgut and can result in a dysbiotic microbiota that are characterised by low richness, diversity and functionality. Also, amylolytic microorganisms become more dominant at the expense of proteolytic and fibrolytic ones. Opportunistic microorganisms can take advantage of newly available niches, which, combined with reduced functionalities of epithelia, can contribute to an overall reduction in nutrient utilisation and increasing endotoxins and pathogens in digesta and faeces. The reduced barrier function of epithelia increases translocation of these endotoxins and other immunogenic compounds out of the digestive tract, which may be the cause of inflammations. This needs to be confirmed by determining the toxicity of these compounds. Cows differ in their susceptibility to poor gastrointestinal health, due to variations in genetics, feeding history, diet adaptation, gastrointestinal microbiota, metabolic adaptation, stress and infections. These differences may also offer opportunities for the management of gastrointestinal health. Strategies to prevent SARA include balancing the diet for physical effective fibre, non-fibre carbohydrates and starch, managing the different fractions of non-fibre carbohydrates, and consideration of the type and processing of grain and forage digestibility. Gastrointestinal health disorders due to high grain feeding may be attenuated by a variety of feed supplements and additives, including buffers, antibiotics, probiotics/direct fed microbials and yeast products. However, the efficacy of strategies to prevent these disorders must be improved. This requires a better understanding of the mechanisms through which these strategies affect the functionality of gastrointestinal microbiota and epithelia, and the immunity, inflammation and ‘gastrointestinal-health robustness’ of cows. More representative models to induce SARA are also needed.

1. The aim of this experiment was to study the interactive effect of rearing temperature and dietary supplementation of arginine (Arg) or guanidinoacetic acid (GAA) on performance, gut morphology and ascites indices in broiler chickens raised under the same condition in the first 2 weeks and then reared under normal (23–26°C) or subnormal (17°C) ambient temperatures for the next 3 weeks. 2. This experiment was conducted as a split plot with 900 Ross 308 male broiler chicks that were allocated to two houses (as main plots); each consisted of 5 treatments (as sub-plots) with 6 replicates of 15 birds. The 5 diets were (1) control, (2) control + 0.60 g/kg GAA, (3) control + 1.20 g/kg GAA, (4) control + 0.86 g/kg Arg and (5) control + 1.72 g/kg Arg. 3. Feed intake (0–35 d) of birds fed on a diet containing 1.2 g GAA/kg and reared under normal temperature was reduced compared to control fed birds. Birds fed on a diet containing 1.72 g/kg Arg and reared under subnormal temperature had higher weight gain compared to those fed on control or GAA-added diets in overall study period. 4. Supplementation of diets with Arg alleviated the adverse effect of cold stress as reflected by reduction in blood haematocrit (41% vs. 37%), and right ventricle to total ventricle ratio (0.28 vs. 0.25) at 35 d of age. Addition of Arg to the diet of birds reared under cold stress resulted in a higher jejunal villus surface area compared to those fed on control or GAA-added diets. 5. Findings of this study revealed that Arg or GAA supplementation of diets did not affect performance of birds under normal temperatures, but Arg supplementation of the diet significantly alleviated the adverse effect of cold stress on performance, gut development and ascites syndrome. In addition, GAA supplementation at 1.2 g/kg improved jejunal villus surface area in birds raised under subnormal temperature.

The disappearance of dry matter (DM), crude protein (CP), and amino acids (AA) in steers after rumen incubation and intestinal passage of alfalfa hay, barley hay, corn silage, barley grain, corn grain, wheat bran, meat meal, fish meal, cottonseed meal, and soybean meal were measured in 3 steers using a mobile nylon bag technique. Ruminal degradation of individual AA differed between feedstuffs. For barley hay and corn silage, the ruminal disappearance of total AA was higher and lower than the other feedstuffs, respectively. The intestinal digestibility of total AA in alfalfa hay was lower than the digestion of CP. The intestinal digestibility of Arg and His was higher than that of total AA in alfalfa hay, meat meal, cottonseed meal, soybean meal, barley hay, and wheat bran. In addition, the intestinal digestibility of Lys was higher than that of total AA in alfalfa hay, meat meal, cottonseed meal, soybean meal, barley hay, corn silage, and wheat bran. The intestinal disappearance of CP in most cases was higher than that of DM. The results indicated that feedstuffs with lower ruminal disappearance of DM, CP, total AA, essential AA, and nonessential AA generally had a higher intestinal disappearance, resulting in a relatively constant total tract disappearance. These results could be used to improve the current system of diet formulation in ruminants.