EFFECT OF EXTREME WALKING CONDITIONS FOR DAIRY-COWS ON MILK-YIELD, CHEMICAL-COMPOSITION, AND SOMATIC-CELL COUNT

Thirty-two cows (16 Montbeliardes and 16 Tarentaises) in midlactation were used in an experiment utilizing a 2 x 2 factorial arrangement of treatments. Throughout the trial, cows received first-cutting cocksfoo t hay for ad libitum intake supplemented with a fixed amount of concen trate that was individually adapted to the milk yield of each cow. Dur ing a 23-d experimental period, one group of cows walked 9.6 km/d; the other group of cows remained in the barn. Cows that walked daily ate less hay (-1.3 and -2.1 kg/d of dry matter for Tarentaise and Montbeli arde cows, respectively) and yielded less milk (-1.7 and -2.5 kg/d for Tarentaise and Montbeliarde cows, respectively) than did cows that di d not walk daily. A residual effect of walking on milk yield was obser ved during the 10 d following the experimental period. For both breeds , fat content and, to a lesser extent, protein content were higher (+6 .4 and +1.0 g/kg, respectively) for cows that walked. Somatic cell cou nt was also higher for cows that walked (+115,000 cells/ml). This diff erence was more marked in cows that were initially infected by a minor or major pathogen (+185,000 cells/ml) than in uninfected cows (+47,00 0 cells/ml) and on the 1st d of walking when walking was linked to inc reases in pH, bovine serum albumin, and immunoglobulin G(1) contents o f milk (+0.08 unit, +0.16 g/L, and +0.19 g/L, respectively). Throughou t the experimental period, walking induced a rise in body temperature (+1 degrees C) and in plasma nonesterified fatty acids (+0.63 mM/L). O n the 1st d of walking, plasma glucose, lactic acid, and cortisol cont ents were significantly higher for cows that walked (+0.25 g/L, +0.64 g/L, and +28.8 ng/ml, respectively).