Repellent effects of Melaleuca alternifolia (tea tree) oil against cattle tick larvae (Rhipicephalus australis) when formulated as emulsions and in β-cyclodextrin inclusion complexes

Rhipicephalus australis (formerly Boophilus microplus) is a one host tick responsible for major economic loss in tropical and subtropical cattle production enterprises. Control is largely dependent on the application of acaricides but resistance has developed to most currently registered chemical groups. Repellent compounds that prevent initial attachment of tick larvae offer a potential alternative to control with chemical toxicants. The repellent effects of Melaleuca alternifolia oil (TTO) emulsions and two β-cyclodextrin complex formulations, a slow release form (SR) and a modified faster release form (FR), were examined in a series of laboratory studies. Emulsions containing 4% and 5% TTO applied to cattle hair in laboratory studies completely repelled ascending tick larvae for 24 h whereas 2% and 3% formulations provided 80% protection. At 48 h, 5% TTO provided 78% repellency but lower concentrations repelled less than 60% of larvae. In a study conducted over 15 days, 3% TTO emulsion applied to cattle hair provided close to 100% repellency for 2 days, but then protection fell to 23% by day 15. The FR formulation gave significantly greater repellency than the emulsion and the SR formulation from day 3 until the end of the study (P < 0.05), providing almost complete repellency at day 3 (99.5%), then decreasing over the period of the study to 49% repellency at day 15. Proof of concept is established for the use of appropriately designed controlled-release formulations to extend the period of repellency provided by TTO against R. australis larvae.

Inclusion of cottonseed meal into loose mineral mix supplements increases the voluntary intake of the supplement by grazing heifers

Loose mineral mix (LMM) supplements based on ingredients such as salt, urea and minerals offered ad libitum are widely used to provide additional nutrients to grazing cattle, but it is often difficult to achieve target intakes. An experiment with heifers grazing mature tropical pasture examined the effects of substituting 80, 160 or 320 g/kg of the salt in a LMM supplement with cottonseed meal on the voluntary intake of the LMM supplements by paddock groups of heifers over 10 weeks. Average voluntary intake of a LMM containing (g/kg) 640 salt, 300 urea and 60 ammonium sulfate (40.2 g DM and 6.14 g total nitrogen/day) was increased linearly (P < 0.001) to 50.8 g DM and 8.88 g total nitrogen/day when up to 320 g/kg cottonseed meal was substituted for salt in the LMM. This increase in intake of nitrogen in LMM was due to the increase in voluntary intake of the supplement rather than the increased nitrogen concentration of supplement. The distribution of daily intake of supplement within paddock groups of heifers was estimated during Weeks 5 and 10 using supplements labelled with lithium sulfate. Neither the coefficient of variation within paddock groups of heifers in supplement intake (mean 96%), nor the proportion of non-consumers of supplement (mean 17%), was changed (P > 0.05) by substitution of salt with cottonseed meal. In conclusion, the inclusion of a palatable protein meal into LMM increased the voluntary intake of this type of supplement.