Formulation of teat sanitiser

A wide range of teat sanitiser formulations is available commercially. In general, teat sanitisers contain a germicidal compound, a skin-conditioning agent and a diluent, usually water. The germicidal compounds destroy bacteria by chemical or biological action. They include iodophors, chlorhexidines, linear dodecyl benzene sulphonic acid, sodium hypochlorite, sodium chlorite, lactic or mandelic acid, hypochlorous acid, quaternary ammonium, or antimicrobial proteins and fatty acids (NICKERSON 1998).

Few countries require that these products be tested for efficacy in preventing mastitis. In the US, the National Mastitis Council (NMC) has collated recommended experimental protocols, with standardised procedures, by which efficacy of teat sanitisers can be tested (HOGAN et al. 1990). NMC standards for the ideal teat sanitiser include proven antimicrobial activity on teat skin, reduction of the incidence of new IMI, insusceptibility towards organic matter, inoffensiveness to teat skin, good healing properties of lesions and no risk of leaving residues in milk or tissue (BODDIE et al. 1997). Few products can meet all of these standards.

The six most commonly used teat germicides are described here and efficacy data, where available, are summarised in the Appendix.

In most countries, iodophors are the most popular teat sanitisers (PANKEY et al.

1984). These products contain iodine and a complexing agent or carrier, such as poloxamers or quarternary ammonium compounds, because iodine itself is poorly soluble in water. The carrier molecules associate closely with the iodine molecules (I2) and ions (I). A proportion of the I2 molecules are free in the solution and in equilibrium with the complex. These free molecules are the active germicidal form.

When I2 is used, additional iodine is released from the complex. Complexed and free iodine is termed the ‘available’ iodine.

Iodine destroys microorganisms by a chemical action, through a rapid oxidation-reduction mechanism, and has a wide spectrum of antimicrobial activity, being active against bacteria, fungi, viruses and even bacterial spores. Iodophors are considered relatively non-toxic, but alcoholic solutions are irritating to the skin. The products are coloured which is mostly regarded as an advantage on the farm. However, the germicidal activity can be reduced or inactivated by contamination with organic material (PANKEY et al. 1984).

Quaternary ammonium teat dips are composed of the germicidal quaternary ammonium compound, emollients, wetting agents, colour agents, pH buffers, thickening agents and water. The emollients, lanolin and glycerine, are most commonly used and colours are included to allow the user to see which teats have been dipped. Quaternary ammonium products denature cells or inhibit enzymes and therefore kill the cells, but they are limited in use because of their weaknesses in killing Pseudomonas spp. (BUSHNELL et al. 1978). They are considered as safe, non-toxic and promote healing.

Chlorhexidine is a colourless, odourless base and moderately or freely soluble in water.

Emollients and dyes are usually added. Chlorhexidine is adsorbed onto the surface of cells where it causes a coagulation of the cytoplasm and therefore kills most bacteria. Products are relatively non-irritating and the oral toxicity is low. The reduction in activity by organic matter is less significant than for most other germicides.

Sodium hypochlorite solutions usually contain no emollients, because formulation problems occur. It acts as a strong oxidising agent and is highly active with proteins.

In teat dips of high concentrations, skin irritations have been observed. Products are usually low cost and efficient, but they are of strong odour and bleach when in contact with fabrics (PANKEY et al. 1984).

Dodecyl benzene sulfonic acid (DDBSA) dips typically consist of an acid-anionic surfactant as the active ingredient and emollients. It functions via general denaturation of protein, inactivation of enzymes or disruption of cell membranes, but the exact mechanism is not fully understood. Toxicity is low, products are non-staining and teat skin is not irritated. Organic materials inhibit DDBSA only to minimal extent and its residual activity after dipping is extended. Efficacy is limited against Gram-negative bacteria, if pH increases above 3.5 or 4. Spores are relatively resistant against DDBSA dips, but yeasts and most bacteria are inactivated (PANKEY et al. 1984).

Barrier teat dips have recently emerged on the market. Early barrier products contained acrylic latex to protect the teat during the inter-milking period against contamination with environmental bacteria. Some products contain germicides others do not. Studies have shown that some of the available barrier teat dips are either ineffective in reducing new IMI, or even increase the development of new IMI (NICKERSON and BODDIE 1995).

Due to the high or low pH of a formulation, germicides can damage the skin.

Therefore, skin-conditioning agents are added and most of these are emollients or humectants (NICKERSON 1998).

In the human cosmetic and medical fields, glycerine, sorbitol, urea, alpha-hydroxy acids and sugars are considered as humectants because they attract water when applied to the skin, and increase pliability. This water is derived mainly from TEWL, as atmospheric water is rarely absorbed by skin below a relative humidity of 80 per cent (WEHR and KROCHMAL 1987). Emollient systems that contain mineral oil, fatty acids, squalene, cholesterol, lanolin or lanolin alcohols are thought to smooth the rough skin surface by filling spaces between the dry skin flakes with oil droplets (WEHR and KROCHMAL 1987).

Glycerine is regarded as the most effective humectant for controlling teat chapping and is effective at levels as low as five per cent (SOMERVILLE and ROSE 1978). It is hygroscopic, water-soluble and draws water into bovine skin from the air. Lanolin and other water-insoluble emollients form an occlusive layer on skin that prevents moisture loss into the atmosphere (SOMERVILLE and ROSE 1978).