Effect of draught work on performance and metabolism of crossbred cows. 2. Effect of work on roughage intake, digestion, digesta kinetics and plasma metabolites

Forty F1 crossbred dairy cows (20 Friesian X Boran and 20 Simmental X Boran) in a 2x2 factorial arrangement (not working-not supplemented, NWNS, not working-supplemented, NWS, working-not supplemented, WNS and working-supplemented, WS) were used to study the effect of work and diet supplementation on roughage intake, apparent digestibility of nutrients, digesta kinetics and plasma metabolites. Dry matter (DM) and organic matter (OM) intakes were greater for working than for non-working cows. Work and supplementation increased DM and OM in vivo apparent digestibility. This effect was particularly significant when comparing working cows at rest and at work. Passage rate and rumen mean retention of Cr-mordanted hay were similar for working and for non-working cows. Liquid turn-over rate of Co-ethylene diamine tetra acetic acid (EDTA) was lower and rumen mean retention time of Co-EDTA was greater in working than in non-working cows whether supplemented or not. Working cows had lower plasma glucose during and immediately after working than non-working cows. Plasma non-esterified fatty acid (NEFA) was higher in working cows at the end of the working period and after rest between working hours. This effect was greater in non-supplemented than in supplemented cows. In working cows, B-hydroxybutyrate was lower at the end of working hours than in non-working cows. Lactate was greater in working than in non-working cows after the 3rd and 4th hours of work. Digesta kinetics could explain only partially the possible mechanisms responsible for greater roughage intake and apparent digestibility in working cows. The decrease of plasma glucose and the increase in NEFA during work indicates an increasing utilization of NEFA by muscle during consecutive working hours