Two feeding trials were carried out with Israeli Friesian male calves, commencing at an average age of 7 to 10 days, and covering a suckling period of 30 days followed by a further 90 days. A conventional starter, or one that contained cotton hulls, was used. In each experiment one group of 10 animals served as a control and a similar group was monensin-supplemented. No coccidia were found in the animals. In experiments 1 and 2 monensin supplementation was associated with increased daily gains of 10% and 47% during the suckling period and of 6% and 17% during the next 90 days, but only the differences obtained in experiment 2 were significant. In both experiments, dry-matter intake relative to body weight was higher with monensin supplementation in period 1, but reduced in period 2. The effect of monensin on molar proportions of acetic and propionic acids was smaller than that reported by previous authors for older cattle.

A separate digestibility trial showed that monensin administered to suckling calves, either with milk replacer or directly into the rumen, improved dry-matter digestibility, increased the excretion of amylase, and tended to reduce that of trypsin and chymotrypsin.