Proc. Aust. Soc. Anim. Prod. 2014 Vol. 30
171
Effects of Pasture Topography on Physical Activity and Meat Colour of Suckling Beef Calves
I.D.M. GangnatA, M. KreuzerA, P.-A. DufeyB, F. LeiberA,C, J. BerardA
A ETH Zurich, Institute of Agricultural Sciences, Zurich, Switzerland, Universitaestrasse 2, CH-8092
B Agroscope Institute for Animal Science Posieux, Posieux, Switzerland, Route de la Tioleyre 4, CH-1725
C Research Institute of Organic Agriculture (FiBL), Frick, Switzerland, P.O. box 219, CH-5070
Physical activity was suggested to be responsible for the darker colour of beef from grazing cattle compared with grain-fed cattle (Dunne et al 2011). However, in most experiments physical activity is confounded with diet type. In the present experiment, alpine pastures differing in topography but similar regarding forage quality were used to vary physical activity of suckling beef calves at unchanged diet type. Hypotheses tested were that the higher physical activity load on inclined pastures compared with flat pastures leads to (i) lower growth performance, (ii) higher heart weights and haemoglobin levels and (iii) darker meat due to the higher oxidative muscle metabolism although different muscles might be differently affected.
Two groups of 12 Angus-sired suckling calves (initial liveweight 185±22 kg) were kept with their dams on pasture at 2000 m a.s.l. either on a flat pasture with 0% slope (FL) or on an inclined pasture with an average of 35% slope (IN). Proximal analysis of the grass showed no difference between FL- and IN-pastures for grass nitrogen (21.7 vs. 19.4 g/kg DM; P=0.13), acid detergent fibre (287 vs. 295 g/kg DM; P = 0.41) and organic matter (929 vs. 927 g/kg DM; P = 0.66) contents, only levels of neutral detergent fibre (541 vs. 487 g/kg DM; P
= 0.04) and lignin (45.7 vs. 55.8 g/kg DM; P < 0.01) moderately differed. In addition, suckling calves were chosen for this experiment in order to dilute the effect of grass proximate content differences with the dams milk, assumed to have an identical composition in both groups. The calves were equipped with pedometers (IceTag, IceRobotics Ltd, Edinburgh, UK) in order to record their activity. After 11 weeks, the calves were slaughtered, blood was taken at exsanguination to assess haemoglobin levels, and hearts were weighed. Meat ultimate pH (24 h post mortem) and colour (L*a*b values 21 days post mortem; Chroma Meter 300-CR, Minolta, Dietikon, Switzerland) were assessed on the longissimus thoracis (LT) and the biceps femoris (BF) muscles. Data were subjected to ANOVA using a mixed model (SAS version 9.3, Carry NC, USA) testing for the effect of pasture inclination.
IN-calves spent more time lying (44.4 vs. 43.5%; P < 0.05) and walked more (251 vs. 238 steps/h; P=0.01) than FL-calves. Furthermore, IN-calves walked on sloped areas whereas FL-calves walked on a flat terrain, which likely emphasized the physical activity differences between groups. Despite weight gain differences between IN- and FL-calves (1.21 vs. 1.35 kg/day, respectively; P < 0.01), the duration of the experiment and the amplitude of the difference between groups was not sufficient to observe significant differences in liveweight at slaughter (277±24 kg; P > 0.2). Hearts were lighter (1195 vs. 1333 g; P < 0.01) and haemoglobin levels tended to be lower (138 vs. 146 g/L; P = 0.09) for IN-calves compared with FL-calves. Although the opposite results were expected based on the hypothesis that IN-calves had a higher physical activity load than FL-calves, heart weights and blood haemoglobin differences still confirm an effect of physical activity. Regarding meat quality analyses, ultimate pH did not differ between groups (5.8±1.1) and the LT muscle tended to be brighter (P = 0.08) and more yellow (P = 0.07) for IN-calves compared with FL-calves, whereas colour of the BF muscle was similar for both groups. Similar trends towards a brighter meat on steep pastures were observed by Willems et al (2013) in lambs although pasture quality was then confounded with physical activity. Previous findings suggest that the darker meat colour of FL-calves might indicate a higher aerobic metabolism compared with IN-calves (Vestergaard et al 2000). IN-calves would have rather developed resistance to intensive short term exercise (anaerobic metabolism) and FL-calves would have rather developed resistance to moderate long term exercise (aerobic metabolism). Since only the LT muscle was affected by the colour change, this type of exercise in the slope probably involved more the LT than the BF muscle.
Tendentially different haemoglobin levels and significantly different heart weights confirmed a different physical activity load for the calves depending on pasture inclination. However, the effect on meat colour showed only a trend and was muscle-specific. Further analysis of the muscle metabolism, namely fibre typing, will allow a better understanding of the effect of physical activity.
Dunne P.G., Monahan F.J. and Moloney A.P. (2011). Livestock Science142, 1.
Vestergaard M., Oksbjerg N. and Henckel P. (2000) Meat Science54, 177.
Willems H., Kreuzer M. and Leiber F. (2013). Livestock Science151, 80.
Email: isabelle.gangnat@usys.ethz.ch
PU- 214054
