The essentiality of trace minerals has been known since the 1930s (Suttle 2010). Deficiencies in trace minerals can cause severe abnormalities and in some cases death. Conversely, high concentrations of trace minerals can cause acute or chronic toxicity, also leading to death in some cases. Due to the serious consequences of deficiency and toxicity, these areas have been the focus of most trace mineral training and research. However in recent times a new concept has developed which considers the use of injectable trace minerals at critical time points in the production cycle when trace mineral demand is greatly increased. This includes before parturition, before joining, at dry off (dairy cattle) and during high stress times such as marking, weaning and following transport.
-It is well known that trace mineral demands are not constant throughout the production cycle. For example, trace minerals can influence embryonic and foetal survival (Hidiroglou and Knipfel 1981), and during late pregnancy the foetus accumulates trace minerals in the liver, thereby increasing the trace mineral requirements of the dam (Hostetler et al 2003). At calving, lactation and increased stress on the immune and reproductive systems leads to increased demand on trace mineral requirements. Trace minerals are essential components of the immune and reproductive systems, mostly due to their roles as metalloenzymes such as manganese superoxide dismutase (MnSOD), copper zinc superoxide dismutase (CuZnSOD) and selenoproteins such as glutathione peroxidase (Suttle 2010).
This review will attempt to summarise some of the research on fertility and health benefits of administering injectable trace minerals at critical times in the production cycle, in both beef and dairy cattle. Increasing trace mineral supply via injection rather than oral supplementation was used for a number of reasons. Absorption of trace minerals through the rumen is quite poor- manganese ~1%, copper ~5%, zinc ~15% and selenium ~30% (NRC 2001). High levels of other minerals in the feed or water such as iron, calcium, molybdenum and sulphur can also cause antagonism in the rumen, binding to the trace minerals and preventing absorption or utilisation (NRC 2001). Injecting trace minerals avoids antagonism and absorption issues and allows the trace minerals to be immediately absorbed into the blood stream.
The trace mineral injection used in the studies discussed in this review, Multimin®, contains disodium zinc EDTA, disodium manganese EDTA, disodium copper EDTA and sodium selenite in an aqueous formulation. Unless otherwise indicated, in all of these studies the cattle were also supplemented with free choice oral minerals and controls were treated with physiological saline only.
Injectable trace minerals (ITM) have been shown to increase conception in cattle. In crossbred beef heifers with given either ITM or nil treatment at the beginning of a fixed time embryo transfer synchronisation protocol, 17 days before embryo transfer (Sales et al 2011), 23 and 48 day conception rates (embryo survival) improved by 12% and 13%, respectively, with injectable trace mineral treatment. There was no effect on number of synchronised heifers.
In another beef cattle study, mature beef cows were treated with ITM 105 days prepartum and 30 days before fixed time AI (Mundell et al 2011). Calves were given the same treatment as their dams at birth and at 71 days of age. All cows were exposed to fertile bulls 10 days after AI for 50 days. Cows given ITM had a greater increase in BCS between calving and AI. Conception to AI was greater in cows that received the trace mineral injection (51.2% vs 60.2%), although final pregnancy rate did not differ. While the number of cows pregnant at the end of joining did not differ, there was a difference in the calving distribution between groups. A greater proportion of cows treated with ITM calved in the first 20 days of the calving season (65% vs 77.5%). The importance of early calving cows was demonstrated by Funston et al (2012), who found that the proportion of heifers cycling at the start of the breeding season decreased as calving interval increased. Consequently, 45 day pregnancy rates were lowest for heifers born later in the calving period compared with heifers born earlier (78% vs 90%). In steers, as calving period increased the marbling grade decreased and total carcass value declined.
Injectable trace minerals have also been demonstrated to reduce negative impacts of transport. Genther and Hansen (2012) investigated the effect of injectable trace minerals in transport stressed cattle, backgrounded with a diet that was either sufficient or deficient in trace minerals. For 88 days steers were fed either a diet supplemented with NRC (2001) recommended levels of copper (Cu), manganese (Mn), selenium (Se) and zinc (Zn) or were fed a diet without supplemental Cu, Mn, Se or Zn that was also supplemented with iron and molybdenum as dietary trace mineral antagonists to induce mild deficiencies. On d 88 steers were trucked for 20 hours to induce transport stress and two days later injected with either saline or ITM. This resulted in four treatment groups- supplemented diet + saline, supplemented diet + ITM, deficient diet + saline and deficient diet + ITM. All steers were then fed a diet supplemented with trace minerals for 90 days then slaughtered. It was found that steers fed a diet deficient in trace minerals before transport tended to lose more weight during transport than supplemented steers and had lower dry matter intake after transport. The authors commented that this suggests trace mineral status is important in the stress response. Steers that were fed the deficient diet and received ITM after stress had greater average daily gain than steers on the deficient diet + saline and had similar ADG to both groups that received the supplemented diet. This demonstrated that providing injectable trace minerals after transport stress to steers previously fed a deficient diet enabled those steers to perform as well as steers that had been fed a well supplemented diet before stress. This could have important implications for feedlot operations buying cattle from known trace mineral deficient areas. As well, regardless of the trace mineral status of the diet fed before transport stress, steers that received the injectable trace minerals had larger rib eye area (77.7cm2 vs 80.43cm2) and greater marbling scores at slaughter (533 vs 569), adding significant value to the carcass.
An improvement in health and production following transport of cattle to feedlots has also been demonstrated with the use of ITM (Richeson et al 2011). At induction heifers were treated with one of two injectable trace mineral formulations or were given no treatment. Average daily gain, dry matter intake and gain:feed were greater for heifers that received ITM. Heifers that received injectable trace minerals also had reduced bovine respiratory disease morbidity rates and less antibiotic treatment costs.
In dairy cattle injectable trace minerals were shown to reduce the incidence of infection, improve conception and decrease days open. In a study by Machado et al. (2012), treatment of dairy cattle with ITM at dry off, 30 days prepartum and 35 days postpartum reduced somatic cell count and decreased the incidence of subclinical and clinical mastitis in multiparous cows. Injecatble trace mineral treatment also decreased the odds of cows having endometritis and stillbirth calvings (Machado et al 2012). The trace minerals treatments did not have an effect on milk production, survivability or reproduction in this trial. However in another study that treated dairy cattle with ITM 30 days prepartum and 30 days before planned start of mating, fertility of dairy cattle was improved (Hawkins 2007). In this study ITM increased pregnancy rate by 3.3% and decreased median days open by 4 days. Injectable trace mineral treatment had no effect on health parameters in this study. The difference in the fertility and health results of these two studies is most likely related to the health and reproduction status of the herds used.
In summary, recent research has investigated the potential of trace minerals injected at critical times in the production cycle to improve fertility and immune function in cattle. These studies have shown improvement in conception rate and embryo survival, increased proportion of cows conceiving on first oestrus, reduced incidence of infection and disease and improvement in production of transport stressed cattle. Research is currently being conducted which will elucidate further the mechanisms behind these improvements in health, fertility and production.