Influence of liquid supplement delivery method on forage and supplement intake by grazing beef cows1

In Experiment 1, 28 heifers were individually fed on low quality hay ad libitum along with one of seven levels of liquid supplement (0, 0.23, 0.45, 0.68, 0.90, 1.13, and 1.36 kg/day) during a 24-day trial to evaluate the use of YbCl3 and Cr2O3 as external markers to estimate forage and supplement intake. A linear relationship was found between supplement DM intake predicted by the dual marker technique and actual supplement DM fed (p < 0.001; r2 = 0.92). In Experiment 2, 60 crossbred 2- and 3-year-old pregnant cows were assigned to one of the three native range pastures to evaluate forage and supplement intake, and supplement feeding behavior as affected by cow age (2 versus 3 years) and liquid supplement delivery method. Treatments were: (1) no supplement (control); (2) ad libitum access to a liquid supplement feeder (ADLIB); and (3) ad libitum access to Regulate® liquid feed delivery system (REGULATE; Agri-Beef, Boise, Idaho, USA). The REGULATE feeder was computer controlled to dispense 18 kg/day liquid supplement. Liquid supplement (28.5% CP as-fed) used in both feeders contained ytterbium chloride. Chromic oxide boluses were used to estimate fecal output (FO). Forage intake was estimated from FO, and 48 h DM indigestibility of extrusa samples collected using ruminally cannulated cows, and incubated in situ. Forage 48 h DM and NDF digestibility values were greater (p < 0.01) for ADLIB and REGULATE than for Control (average 67.1 versus 49.4% for DM; average 63.7 versus 42.7% for NDF). Three-year-old cows consumed 11% more (p < 0.05) forage DM than 2-year-old cows (15.3 versus 13.8 kg/day), but no differences (p > 0.10) were significant when expressed on a g/kg body weight basis. Cows receiving REGULATE and ADLIB consumed 49% more (p < 0.01) forage DM than control cows (average 16.3 versus 11.0 kg/day). Individual supplement DM consumption ranged from 0.002 to 2.54 kg/day. A cow age by treatment interaction was detected for supplement consumption. Two- and 3-year-old cows on REGULATE and 2-year-old cows on ADLIB consumed less (p < 0.01) supplement DM than 3-year-old cows on ADLIB. Liquid supplement increased forage intake and digestibility by cows grazing fall native range. A computer controlled liquid supplement feeder equalized supplement intake by 2- and 3-year-old cows.