| Study One - Our objective was to characterize mature range cows based on intake and grazing activity. Starting in the early spring of 2013, 4 experiments were conducted. First, mature range cows ( n = 137) were fitted with radio frequency identification tags (RFID) and placed in a dry-lot pen equipped with GrowSafeRTM technology to monitor DMI of alfalfa hay. These data were then used to assign cows a residual feed intake (RFI) value utilizing the National Research Council (NRC) (1996) model to predict intake of beef cattle. Cattle with negative and positive RFI were characterized as low-intake and high-intake, respectively. In addition, the following data were also recorded: weight (kg), age (mo), days pregnant (d), and body condition score (BCS). Second, 30 mature range cattle were selected from the first trial and fitted with pedometers for 7 d to monitor activity with step counts and estimate distance traveled. Third, mature range cows (n = 25) selected from the first trial were fitted with global position system (GPS) collars, and placed on pinyon-juniper rangeland from 20 June 2014 to 17 September 2014. Forth, mature range cows (n = 28) were fitted with GPS collars, and placed on ponderosa pine rangeland from 17 September 2014 to 15 October 2014. Distance traveled, slope, distance from water, elevation data were collected from both GPS trials. Low-intake and high-intake cows consumed 9.3 and 12.2 kg/d, respectively ( P < 0.0001). Low-intake cattle became pregnant sooner ( P = 0.002) than high-intake cattle (average of 16 d sooner). Cattle age (mo) equaled 90 and 98 for low- and high-intake cows, respectively ( P = 0.04). Weight, predicted DMI, and BCS did not differ between groups (P > 0.06). Step counts for low- and high-intake animals were 5839 and 5383 +/- 2089, respectively (P = 0.61), and estimated distance traveled was 4.31 and 5.35 +/- 1.66 km d-1 for low- and high-intake animals, respectively (P = 0.77). Low-intake cows (6.23 km d-1) traveled farther (P = 0.005) each day than high-intake cows (5.84 km d-1) on pinyon-juniper rangelands, and high-intake cows utilized (P = 0.013) steeper slopes. No differences were detected (P > 0.06) for distance traveled, distance from water, and elevation for cows grazing ponderosa pine rangeland). However, low-intake cattle preferred (P = 0.046) steeper slopes on ponderosa pine rangeland than high-intake cattle. These results indicate that low-intake animals may travel farther on some rangelands and rebreed earlier. Study Two - Commercial grade heifers (n = 173) born and raised on the University of Arizona's V bar V Ranch from 2012 to 2014 were fitted with radio frequency identification tags (RFID) and placed in a drylot equipped with GrowsafeRTM technology (8 bunks) for 60 d in 3 groups based on birth year in order to calculate DMI, residual feed intake (RFI), ADG, G:F, and residual gain (RG). Birth date, birth weight, weaning weight, age at start of trial, initial trial weight, and final trial weights were also recorded. Residual feed intake scores were utilized to place heifers in one of three treatment groups, low-, medium-, and high-intake. Reproductive and calf data were collected on heifers born in 2012. Means for birth date, birth weight, weaning weight, initial weight, final weight, and ADG did not differ among the three treatments. Residual gain for low-, medium-, and high-intake heifers were different (P < 0.05) at 0.07, 0.00, and -0.07 kg d-1, respectively. Low-intake cattle had an improved ( P < 0.05) GF ratio of 0.19 when compared to the medium- and high-intake heifers with ratios of 0.15 and 0.13 (P > 0.05), respectively. Differences (P < 0.05) in DMI were detected with low-, medium, and high-intake heifers consuming 5.2, 6.2, and 7.5 kg d-1 , respectively. No differences were detected for pregnancy rate, calving rate, percent bred artificial insemination (AI), percent bull calves, calf birth weight, and calf birth date among treatments (P > 0.05). (Abstract shortened by ProQuest.). |
