More and more Clostridia in milk


The increasing industrialization of livestock farming has led to a negative trend in one of the most important cheese quality parameters

Version of an article published in the periodical Cheese Time (English translation not revised by the author)

by Michele Corti – lecturer in Livestock and Pastoral Mountain Systems at the University of Milan, Italy

Do increasingly large cattle sheds and massive automation and mechanization of all operations (feeding, milking and cleaning) go hand in hand with milk quality? Yes, according to the “big is clean” agroindustrial ideology, but is it really so? In actual fact, large-scale livestock farming is the cause of a microbiological contamination of milk that seriously affects cheese quality. Some kinds of microbes detrimental to dairy products are “neutralized” by disinfectants and heat treatments, but these methods are ineffective against others (Clostridia). The presence of Clostridia causes late blowing, a cheese defect that leads to the formation of eyes, cracking, flaking, hollows and sometimes a spongy consistency. In addition, the cheese may end up with an unpleasant flavour or odour. This serious problem (against which there are no remedies) occurs after a few weeks/months of ripening and haunts various types of hard and semi-hard cheeses.

The trouble is that the phenomenon is on the rise. In an analysis carried out by the Provincial Association of Breeders of Parma (Italy), the percentage of milk samples that tested positive for Clostridia increased from 9.0% in 1991 to 23.54% in 2001, and exceeded 30% in 2003. The most recent data (2006) for Lombardy indicate a clear and general worsening of the situation.

Clostridia are bacteria that grow under anaerobic conditions (in the absence of air) and form a protective capsule that allows them to survive in the soil for years. They are resistant to high temperatures (and therefore pasteurization) and to common disinfectants.

Feeding cows with silage (fodder stored in the absence of air) is the main cause of the presence of Clostridia in milk. While traditional feed (based on grass or hay) contains less than 200 clostridia spores per litre, feed based on silage can contain more than 2000.

Farmers know this, but since silage cuts the costs of the “ration”, its use continues to increase. However it is not only silage that is to blame. Unifeed is another culprit. The unifeed technique, or “single dish” that provides all the dietary components mixed together in one feed, has been widely adopted to save time in feed distribution. Large highly equipped mixing wagons are used (with a 20 cubic metre capacity!) which “extract” the silage from the silo, “chop” the “long” fodder, and mix it with feed and other raw materials (even liquids) or water. Silage treated this way is consumed without “leftovers”. Furthermore, by serving feed and silage together, the animals can be persuaded to eat greater amounts of feed than they would if the feed was served up alone. Lots of advantages!

Too bad that with this system the dust and soil that contaminate silage end up in the mix, and that the presence of water, sugars and starches favours the growth of Clostridia.

The cows ingest the spores and “return them” in their faeces. When the liquid manure is spread abundantly on the land, the spores return to the soil, the Clostridia proliferate … and the cycle begins again.

What about milk? It is mainly contaminated via faeces and dirty udders.

Modern freestall housing, which does not involve the use of straw, often has very dirty exercise pens, where the cows get smeared with faeces. When the cows are crowded together in milking parlours they get even dirtier.

Undersized sheds and equipment for the ever growing number of cows, shrinking labour forces and the inevitable increase in management problems contribute towards worsening the situation, since the rest pens, equipment in contact with the animals and feeding troughs (full of leftover feed) are not cleaned enough. As for the udders and teats, there is not always time to clean them properly. Industrial use of disinfectants does not solve the problem. If anything it makes it worse because it reduces the “good” microbial flora able to contend with Clostridia. Clostridia, on the other hand, resist.

There are not many remedies in the dairy. Besides using lysozyme (a natural antibacterial agent), remedies consist of eliminating bacterial cells by bactofugation (a process that uses centrifugal force) or ultrafiltration. Natural skimming of the milkfat, frees the milk of many spores, but not all. “Selected” inoculations with lactic acid bacteria able to multiply in the milk and compete with Clostridia can also be used. Lastly, you can count on high temperature curd cooking and on techniques that produce compact, uniformly dehydrated curd able to absorb salt well.

These solutions may only be used in certain dairy techniques and imply thorough milk processing. Since the Clostridia problem is related to increasingly industrialized farming, it is destined to become ever more serious despite these measures.

Michele Corti

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