Effects of rare earth elements (REE) supplementation to diets on the health and performance of male and female pre-ruminant calves and growing female calves
Two feeding trials with pre-ruminant and growing Holstein calves were carried out in order to investigate the effect of rare earth elements (REE) on feed intake and performance parameter. In the first experiment, applying a complete two by two factorial design, 87 calves (45 female and 42 male) with a mean age of 9.6 ± 1.8 days were randomly assigned to one of two treatments (Con or REE). The animals received milk replacer either with or without 200 mg/kg REE-citrate containing mainly cerium (57.9 %), lanthanum (34.0 %) and praseodymium (6.5 %) as well as concentrate and grass hay over a period of 44 days. The feed intake and performance parameter were not significantly and interactively affected by sex and REE supplementation. However, the supplemented animals consumed numerically less concentrate (13.5 %) and grass hay (26.3 %) compared to control animals which led to a slightly reduced live weight gain (496 g/day in REE group vs 525 g/day in control group). In the second experiment, a total of 47 growing female calves (average initial live weight of 108 ± 9 kg) were divided into four treatment groups (n = 11 or 12 per group): one control group and three REE-treated groups fed a supplement of 100, 200 and 300 mg REE-citrate per kg dry matter (DM). The calves were offered grass silage, grass hay and concentrate. The experiment was terminated when the calves reached a live weight of approximately 182 kg. The feed intake, live weight gain, feed-to-gain ratio and ME-to-gain ratio were not significantly influenced by increasing REE-citrate supplementation. Also, a numerically tendency towards reduced feed intake and live weight gain could be observed for the group fed with the highest amounts of REE. Thus, it can be concluded that REE-citrate are not suited to improve the performance of calves.