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AIMS: To investigate the effect of parenteral vitamin B12 supplementation on the growth rate of dairy heifer calves over the summer and autumn on seven farms from the Central Plateau of New Zealand, an area historically associated with low cobalt levels in grazing pasture. METHODS: This was a controlled clinical trial conducted on a convenience sample of seven farms with young female calves randomly assigned to three vitamin B12 treatment groups and followed through a grazing season. Two treatment groups received either monthly SC injections of a short-acting (SA) B12 formulation or 3-monthly injections of a long-acting (LA) B12 formulation and the third group received no treatment (NT). No additional parenteral vitamin B12 was given; however, all calves received additional cobalt (0.04-0.4 mg Co/kg liveweight) in the mineralised anthelmintic drenches given orally every month. Liveweight was recorded in December/January and at the end of the trial in May/June/July depending on farm. Pasture cobalt concentrations (mg/kg DM) were measured every month using 500-g herbage samples from 100-m transects in the area about to be grazed by the trial groups. RESULTS: There was evidence for a difference in growth rate between groups with mean final weight of 228 (95% CI = 212-243) kg for the LA groups, 224 (95% CI = 209-239) kg for the SA groups and 226 (95% CI = 211-241) kg for the NT groups respectively, (global p-value = 0.014). Calves given SA vitamin B12 were 3.77 (95% CI = 0.71-6.82) kg lighter than calves given LA vitamin B12 (p = 0.011). There was no evidence for a change in pasture cobalt concentrations (p = 0.32). CONCLUSIONS AND CLINICAL RELEVANCE: The results of this trial raise the question as to whether the routine use of vitamin B12 supplementation in young cattle from areas traditionally thought to be cobalt deficient is necessary, and further raise the possibility that vitamin B12 supplementation by repeated injection of SA products may negatively impact growth rates.

Hyperaccumulation of heavy metals was studied with the intention of elucidating the mechanisms of tolerance of hyperaccumulator plant species. Two main areas are covered; cobalt and copper accumulation by plants from Shaba Province, Zaïre, and nickel accumulation by species of the genus Alyssum. In surveys of vegetation of metalliferous soils of Shaba, nine or ten new hyperaccumulators of cobalt were discovered along with eight or nine very strong accumulators. For copper, seven hyperaccumulators and five or six very strong accumulators were discovered. Some families contained a higher frequency of hyperaccumulators than others. There is also a difference in superorder classification of cobalt and copper hyperaccumulators on one hand and nickel hyperaccumulators on the other. Surveys of the genera Aeolanthus, Ipomoea and Pandiaka were made but only one new copper hyperaccumulator was found: no new cobalt hyperaccumulators were found. Several species had their abilities to accumulate confirmed. Pot trials on three hyperaccumulators Aeolanthus biformifolius, Haumaniastrum katangense and H. robertii, showed accumulation of cobalt but not the expected accumulation of copper. The uptake curve was of the exclusion-breakdown form. The limit of breakdown, for each metal, was similar from species to species. Cobalt was less readily excluded than copper. The tolerance tests showed that some species have individuals with greatly enhanced abilities to survive higher metal concentrationsthan is normal for that species, while other species have more uniform tolerances. There appears to be no requirement for large metal concentrations at germination and seeds germinate more readily in the absence rather than the presence of the metals. The distribution of cobalt and copper within leaf tissues, of five species, appears to be parallel within each species. For each metal, the distribution is parallel between different species with the exception of Buchnera metallorum. More detailed studies on cobalt in H. robertii showed the distribution to be even over the leaf area but with small anomalous regions of high concentration. The possibility that some of the cobalt was precipitated as oxalate crystals is considered. The water-soluble cobalt fraction ligand could not be identified but was not proteinaceous. It has a mass of 5,200 g per mole of cobalt. A survey of the genus Alyssum revealed thirty-four taxa as hyperaccumulators to add to the fourteen previously known. All the taxa are from section Odontarrhena. The geographical distribution of the hyperaccumulators is discussed as is the possible evolution of hyperaccumulators in subsections Compressa and Samarifera from non-accumulators within them. Studies of nickel accumulation by eleven Alyssum species and the closely related Bornmuellera tymphaea showed similar characteristics for all hyperaccumulators but two non-accumulators differed. A rise-to-saturation uptake form was noted. In the absence of nickel, cobalt could be accumulated with a similar uptake form. Cobalt accumulation in the presence of nickel is unknown. The rate of uptake is relatively rapid. The tolerance of hyperaccumulators to high nickel concentrations was confirmed in two types of tolerance tests; a substrate medium test and a solution test. The results from the two tests are compared. The distribution of nickel between the plant organs is discussed. The analysis of mineral elements in leaf material showed interesting differences between hyperaccumulators and non-accumulators for calcium, magnesium and manganese content but these could not be related to differing nickel concentrations. A similar find was made for glucosinolates. An organic acid survey was restricted by the non-identification of many acids. Separation of the nickel complexes was made. Identification of ligands involved in nickel complexatian was attempted but few positive results were found. Two ligands were common in significant quantities for all species studied. The results of these experiments were used to discuss possible evolution of hyperaccumulator species both in terms of their superorder distribution and their method of metal ion uptake. An equilibrium mechanism of uptake is proposed which involves a multiplicity of complexes for the ion absorbed. The mechanism differs from that which is commonly proposed for micronutrient elemental uptake.

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