DUODENAL RAPESEED OIL INFUSION IN EARLY AND MIDLACTATION COWS .2. VOLUNTARY INTAKE, MILK-PRODUCTION, AND COMPOSITION

Rapeseed oil was infused continuously (1.0 to 1.1 kg/d) into the proximal duodenum of rumen- and duodenum-fistulated Holstein Friesian multiparous cows from 17 d before to 21 d after calving (6 oil-infused cows vs. 6 controls) (early lactation trial) or after 100 d of lactation (mid-lactation trial, 9 cows in a crossover design). Oil-free DM intake was lower in oil-infused than in control cows in early (wk 3) and midlactation trials. In early lactation, milk production tended to be lower in oil-infused cows but milk composition was unchanged. In the midlactation trial, milk yield and lactose content were unaffected, milk fat content was slightly increased, and protein content sharply decreased in oil-infused cows. Rapeseed oil infusion had a positive effect on the total metabolizable energy absorbed during the wk 1 and 2 of lactation but not in the wk 3 or in the midlactation trial. Calculated energy balance was higher in oil-infused cows in both trials. In early lactation, oil infusion did not reduce losses in empty BW, condition score, subcutaneous adipose cell diameter, and estimated body lipids. In midlactation, empty BW and body condition score were decreased by oil infusion. Results suggested that energy control mechanisms limited DM intake in oil-infused cows, possibly limiting milk yield increase and the availability of precursors for milk protein synthesis. Body reserve mobilization was not reduced but could even have been increased by oil infusion.