Effects of abomasal infusion of long-chain fatty acids on intake, feeding behavior and milk production in dairy cows

Fat is often fed to dairy cows to increase the energy concentration of thei r diet; however, feeding fat often reduces dry matter intake (DMI), which l imits its impact on metabolizable energy (ME) intake. To investigate the ef fects of postruminal fat infusion on intake, feeding behavior, and milk pro duction of dairy cows at two stages of lactation (55 and 111 d postpartum), six Holstein x British Friesian cows were infused into the abomasum, with a mixture of rapeseed and sunflower oils supplying predominantly unsaturate d long-chain fatty acids (LCFA). Dry matter intake was significantly depres sed by oil infusion, but estimated ME intake was unchanged, and thus there was no effect of oil infusion on milk yield. There was no effect of stage o f lactation on the DM or ME intake response to oil infusion. Milk fat conce ntration was increased by oil infusion in midlactation but not in early lac tation, suggesting that the infused LCFA were utilized differently in early compared with midlactation. Cows spent an average of 654 min idling, 462 m in ruminating, and 248 min eating during the last 22.8 h of each infusion. There were no significant effects of oil infusion or stage of lactation on the total time spent engaged in these activities. An assessment of the circ adian pattern of feeding behavior suggested that the depression in DMI in r esponse to oil infusion occurred after the 1630 and 2230 h feeding times. T his may reflect differences in mechanisms regulating feed intake behavior a nd appetite during the day. Comparison of the results of the present study with the results of other trials involving postruminal fat infusion suggest s that poly-unsaturated nonesterified fatty acids have the most potent effe ct on DMI intake.