EFFECT OF ISOCALORIC INFUSION OF GLUCOSE IN THE RUMEN OR PROPIONATE IN THE DUODENUM

This study was undertaken to understand better the mechanisms causing increased milk protein. Cows fed steam-flaked sorghum have increased m ilk protein compared with that of cows fed dry-rolled sorghum because of a large shift of starch digestion from the intestine to the rumen. Five cannulated lactating cows were infused with glucose in the rumen or with propionate in the duodenum in two trials. The experimental des ign was a 2 x 2 Latin square with 7 d of adjustment and 7 d of infusio n. During the experiment, cows received a TMR containing 19.3% CP and 1.56 Mcal/kg of NE(L) (on a DM basis); alfalfa hay and dry-rolled sorg hum grain were the principal ingredients. Similar concentrations in fe ces of cows among propionate treatments suggested complete absorption of infused propionate. Milk yield did not differ, but protein percenta ge of milk was higher (2.88 versus 2.72%) for cows infused ruminally w ith glucose than for those infused in the duodenum with propionate. Fo r the respective treatments, duodenal flows were 2.11 and 1.76 kg/d fo r microbial protein and 3.44 and 2.73 kg/d for total CP (or 85 and 74% of CP intake). These data demonstrate that increased propionate avail ability for gluconeogenesis and a possible sparing of essential AA did not result in increased milk protein content, but ruminal infusion of glucose, which tended to increase microbial protein synthesis, did in crease the protein percentage of milk.