Measurement of energy expenditure in the grazing ruminant

Genetic variation in residual feed intake is associated with body composition, behavior, rumen, heat production, hematology, and immune competence traits in Angus cattle1

This experiment was to evaluate a suite of biological traits likely to be associated with genetic variation in residual feed intake (RFI) in Angus cattle. Twenty nine steers and 30 heifers bred to be divergent in postweaning RFI (RFIp) and that differed in midparent RFIp-EBV (RFIp-EBVmp) by more than 2 kg DMI/d were used in this study. A 1-unit (1 kg DM/d) decrease in RFIp-EBVmp was accompanied by a 0.08 kg (SE = 0.03; P < 0.05) increase in ADG, a 0.58 kg/d (0.17; P < 0.01) decrease in DMI, a 0.89 kg/kg (0.22; P < 0.001) decrease in FCR, and a 0.62 kg/d (0.12; P < 0.001) decrease in feedlot RFI (RFIf). Ultrasonically scanned depths of subcutaneous fat at the rib and rump sites, measured at the start and end of the RFI test, all had strong positive correlations with RFIp-EBVmp, DMI, and RFIf (all r values ≥0.5 and P < 0.001). Variation in RFIp-EBVmp was significantly correlated (P < 0.05) with flight speed (r = -0.32), number of visits to feed bins (r = 0.45), and visits to exhaled-emission monitors (r = -0.27), as well as the concentrations of propionate (r = -0.32) and valerate (r = -0.31) in rumen fluid, white blood cell (r = -0.51), lymphocyte (r = -0.43), and neutrophil (r = -0.31) counts in blood. RFIp-EBVmp was also correlated with the cellular immune response to vaccination (r = 0.25; P < 0.1) and heat production in fasted cattle (r = -0.46; P < 0.001). Traits that explained significant variation (P < 0.05) in DMI over the RFI test were midtest metabolic-BW (44.7%), rib fat depth at the end of test (an additional 18%), number of feeder visits (additional 5.7%), apparent digestibility of the ration by animals (additional 2.4%) and white blood-cell count (2.1%), and the cellular immune response to vaccine injection (additional 1.1%; P < 0.1), leaving ~23% of the variation in DMI unexplained. The same traits (BW excluded) explained 33%, 12%, 3.6%, 3.7%, and 3.1%, and together explained 57% of the variation in RFIf. This experiment showed that genetic variation in RFI was accompanied by variation in estimated body composition, behavior, rumen, fasted heat production, hematology, and immune competence traits, and that variation in feedlot DMI and RFIf was due to differences in BW, scanned fatness, and many other factors in these cattle fed ad libitum and able to display any innate differences in appetite, temperament, feeding behavior, and activity.

Energy expenditure of cattle grazing on pastures of low and high availability

The energy expenditure of freely grazing cattle was investigated in the National Institute of Agricultural Technology and Agricultural Science College of Balcarce, Argentina (37° 45'S, 58° 18'W), by the CO2 entry rate technique. Two experiments were carried out in the autumn in March 1994 (experiment 1) and in April 1995 (experiment 2) with animals prepared with catheters in the parotid gland (collection of saliva) and into the peritonea for infusion of a solution of 14C. Six Angus steers (259 (s.e. 11) kg) were used in experiment 1 and seven (298 (s.e. 36) kg) in experiment 2. In experiment 1 animals grazed ryegrass pastures for 5·5 h in two periods of 1·5 h in the morning and of 4 h in the afternoon and in experiment 2 animals grazed oat pasture in one period of 1 h in the morning. Twenty hours before and during the experiments a solution ofNaH14CO3 was infused at a rate of 9·4 (experiment 1) and 8·1 (experiment 2) μiCi/h for 48 h with portable peristaltic pumps carried by each animal. Saliva samples were collected at least after the first 20 h of infusion. The first sample was collected in the corral just before grazing and two samples were collected in each grazing period. Also, in experiment 1 three samples were taken during resting (noon, 1 h after grazing and the next morning). In addition, bite frequency, pasture availability, plant height, in vitro digestibility and crude protein were measured. Carbon dioxide production was calculated as the ratio between the rate of infusion of 14C (μCi/h) and the specific activity of CO2 (μCi/l CO2) in saliva samples. Bite frequency was 59 and 28 bites per min on the respective pasture of ryegrass (148 g dry matter (DM) per m2 and 10·5 cm height) and oat (228 g DM per m2 and 27 cm height). Energy expenditure (EE, kJ/h per kg M0·75) in corrals was 14·9 (experiment 1) and 14·3 (experiment 2), increasing to 22·6 (proportionately 0·52) when grazing at 59 bites per min and to 16·6 (0·16) when grazing was at 28 bites per min. One hour after grazing at 59 bites per min (experiment 1) the EE was as high as during grazing, and in the next morning (after 5·5 h) of grazing remained at 19·7 kJ/h per kg M0·75 (0·32). No differences in energy expenditure were found between periods of grazing in experiment 1. It was concluded that the increase in energy expenditure of cattle due to the activity of grazing depends on the rate of biting. Grazing for 10 h at a moderate rate may boost EE proportionately by only 0·06, however grazing at the highest rates could easily add proportionately 0·20.

Energy expenditure due to forage intake and walking of grazing cattle

The relative increment in daily maintenance requirement by physical activity was estimated in free-grazing cattle. The effects of forage harvesting and walking were measured and expressed as an index in relation to the value of energy expenditure of animals in corrals. All indices were obtained from experiments conducted in Balcarce (Argentina) from 1993 to 1995. Energy expenditure of Aberdeen Angus steers was estimated by the 14C-entry rate technique, on animals standing still in a corral, grazing at two different biting rates or walking at four different speeds. Information on time spent on grazing and distance traveled was obtained from the literature. These estimations indicate that the maintenance cost of cattle in corrals could be increased on pastures by a factor of 1.08 to 1.30, depending upon the grazing conditions. It was observed that grazing at high biting rate was the variable of highest effect on maintenance energy cost, and that walking or grazing at moderate biting rate was of lower incidence.

The energy costs of walking on the level and on negative and positive slopes in the Granadina goat (Capra hircus)

The energy expenditure of six goats averaging 35 (SE 0.3) kg was measured when the animals were standing or walking on a treadmill enclosed in a confinement-type respiration chamber at different speeds (0.167, 0.333 and 0.500 m/s) and slopes (-10, -5, 0, +5 and +10%). The energy costs of locomotion, estimated from the coefficients of linear regressions of heat production (HP) per kg body weight v. distance travelled were 1.91, 2.33, 3.35, 4.68 and 6.44 J/kg BW per m for -10, -5, 0, +5 and +10% inclines respectively, indicating that the energy expenditure of walking over standing changes with slope according to a slightly curvilinear relationship. The energy cost of raising 1 kg body weight one vertical metre was found to be 31.7 J, giving an average efficiency for upslope locomotion of 30.9%. The energy recovered on vertical descent was estimated as 13.2 J/kg per m, indicating an efficiency of the energy recovered above the theoretical maximum.