Ruminal disappearance of phosphorus and starch, reticuloruminal pH and total tract nutrient digestibility in dairy cows fed diets differing in grain processing

Ruminal disappearance kinetics of nutrients such as phosphorus (P), starch and protein in cereal grains is determinant of their nutritional and health value in ruminants. The objective of the present in vivo and in situ trials was to evaluate whether feeding barley grain processed with lactic acid (LA), with or without thermal treatment, affects in situ degradation kinetics of nutrients, reticuloruminal pH dynamics, and apparent total tract digestibility (ATTD) in dairy cows. The experiment involved 6 rumen-fistulated Holstein cows in a double 3×3 Latin square design fed a diet based on differently processed barley grain: untreated grain as control (CON), or grain treated with 1% LA alone (LA diet), or 1% LA plus oven-heating (LAH diet) prior to feeding. Each experimental period lasted 21 d, with the first 11 d used for adaptation to the diets. The in situ trial consisted in the incubation of the differently treated barley grains (i.e., CON, LA, LAH) up to 48h in the rumen of cows fed diets containing the respective barleys. The reticuloruminal pH and temperature were continuously measured throughout the experiment via wireless indwelling sensors. In situ data demonstrated increased (P<0.001) disappearance of barley P, being on average more than twice as high during the first 24h of incubation with LA and LAH compared to CON barley. In contrast, the degradation of starch decreased (P<0.05) after 2h and 4h of the ruminal incubation, but not thereafter. Feed intake remained unchanged among treatment groups, whereas ATTD of dry matter was slightly greater (P=0.05) in cows fed the LA-treated barley. There was no effect of diet on reticuloruminal pH and temperature dynamics either. In conclusion, the present study indicates that treatment of barley grain with LA and LAH lowers rumen degradability of starch early after incubation, without affecting reticuloruminal pH and the ATTD of most nutrients. The improved ruminal disappearance of barley P suggests an improved solubility and faster ruminal availability of organic P of the treated grain, and warrants further investigations to tap its potential with regards to improved P nutrition and minimization of P excretion in dairy cows.