A comparison of various parameters for estimating the extent of the microbial deterioration of hay was made, these parameters being viable microbial counting by dilution plate and air sampling techniques, viable and non-viable microbial material estimates by chitin and diaminopimelic acid level determinations and finally temperature measurements. The inhomogenous nature of hay created considerable sampling errors and it was therefore concluded that heat production, expressed as degree days, was probably the most convenient measure of microbial activity. A microbial succession was found to occur in deteriorating hay which frequently caused two separate heating phases, and it was concluded that in the first phase readily available nutrients were utilised and the second phase was due to microbial metabolism of nutrients produced by extra cellular enzymes especially cellulases. Several chemicals and chemical mixtures were assessed as hay preservatives by three methods. Firstly, using chemically defined agar media buffered at p.H values of 5, 6, 7 and 8. Secondly, by their application to re-wetted hay stored in dewar flasks and thirdly by their application to hay at baling. It was found that higher levels of these chemicals were needed on hay, than in agar media, to inhibit microbial growth and certain compounds, e.g. formaldehyde, were inactivated on hay. Also the minimum effective levels of preservative were found to increase with an increase in the moisture content of the hay and it was concluded that propionic acid was the most practical preservative, the addition of sorbic acid possibly being of some benefit. There appeared to be three problems concerned with the chemical preservation of hay. Firstly, poor preservative distribution, secondly preservative loss by evaporation and microbial degradation and thirdly a lack of information relating the minimum effective levels of preservative with nutrient and water content or, probably more important, the water activity of hay. Possible means of overcoming these problems are discussed.
|Date of Award||1976|