Results are reported from four trials in which neonatal calves were given either whole milk or milk substitute containing the lactoperoxidase system.
Trial 1 was a pilot trial conducted in Sweden in which calves given whole milk with the lactoperoxidase system gained significantly more weight than controls (P < 0·05). Trials 2, 3 and 4 were carried out in successive years at the National Institute for Research in Dairying, using large numbers of newborn, female Friesian calves. In trial 2 a significant positive effect of the lactoperoxidase system with whole milk on live-weight gain was established by 3 weeks of age (P < 0·05) and sustained until weaning at 5 weeks. There was no significant effect of the lactoperoxidase system for the milk substitute treatment. In trial 3 the whole milk comparison from trial 2 was repeated. There was a significant positive effect of the lactoperoxidase system on the live-weight change after 2 weeks of age only (P < 0·05). In trial 4 two different methods of activating the lactoperoxidase system were compared for calves given whole milk. There was no effect of either method on the live-weight gain of the calves. However, as the levels of scouring were extremely low for all calves, a comparison of the two methods of activating the lactoperoxidase system was not justified. The combined results from trials 2, 3 and 4 confirmed that the lactoperoxidase system significantly increased the live-weight gain of calves given whole milk, despite the fact that the overall level of mortality and incidence of scouring was low in these trials.