Infection of the udder

The first successful active immunization is ascribed to Edward Jenner, an English country physician who in the I790 s tested a belief common among local dairymaids—that prior exposure to a mild cowpox infection of the udder on a cow provided immunization against smallpox. Beginning in 1796, Jenner carried out tests in which he intentionally infected people by applying cowpox lymph obtained from a lesion to small slits cut in the arms of volunteers. During a subsequent epidemic, none of the inoculated individuals developed smallpox. Jenner called the practice vaccination, from vacca, Latin for cow. 

Increased milk production. Much controversy exists over providing cows with supplemental bovine somatotropin (BST), also called growth hormone, a hormone that increases metabolism and milk production in dairy cows. Tbe controversy centers on human consumption of the hormone. However, BST is a peptide hormone, so it is hydrolyzed in the digestive tract and is not absorbed directly into the human bloodstream (Section 24.2). Furthermore, aU milk must contain some of this hormone, because the cow cannot produce milk without it. A more soundly based concern about BST supplementation in dairy cows is that the cows given extra BST often develop mastitis, an inflammation of the udder caused by bacterial infection. Mastitis is frequently treated with high doses of antibiotics, and some of these antibiotics could end up in tbe mUk, causing problems for people with certain food sensitivity. 

There are a few examples where bacteriocins and bacteriocin-producing bacteria are presently in use. Mastitis is a bacterial infection of the mammary gland and udder tissue of dairy cattle and is usually treated with antibiotics. For years nisin A has been used in prophylactic treatment of and protection against mastitis. SevCTal commercial nisin-based products are presently on the market and these include products under the labels MastPro , Mast Out , Wipe Out , Consept , Nisin Z SUver-Elephant , and othCTS. 

The infection process and disease development process can be related to a range of factors that affect various udder tissues (localisations). There are also a range of interactions between the udder tissues and mastitis pathogens. These were recently reviewed by Hamann 2001 (see also Table 11.1). 

The objective of antibiotic treatments is to reduce the density of microbial pathogen in infected udder tissues and thereby improve the capacity of the animal s immune system to deal with the infection. The effect of a successful antibiotic treatment is therefore self-cure of mastitis (Hamann and Kromker, 1999). However, some antibiotics (e.g. tetracycline and gentamycine) may also have negative side effects on the animal s immune response to udder infection, as they have been shown to inhibit/reduce phagocytosis of the animal s own defence cells (Nickerson et al 1986). 

Signs and Symptoms Initial symptoms include fever, watery eyes, increased nasal secretions, drooling (ptyalism), diarrhea, loss of appetite, reduced milk production, depression, and reluctance to move. This is followed by the eruption of various sized skin nodules that may cover the whole body. They can be found on any part of the body but are most numerous on the head and neck, perineum, genitalia and udder, and the limbs. The nodules are painful and involve all layers of the skin. Skin lesions may show scab formation. Regional lymph nodes are enlarged and full of fluid. Secondary bacterial infection can complicate healing and recovery. Final resolution of lesions may take 2-6 months, and nodules can remain visible 1-2 years. 

Specific conductivity continues to attract interest as a convenient, objective means of detecting mastitis at the subclinical level. Although somatic cell counts do correlate with specific conductivity, the cell counts appear to be more sensitive for mastitis detection (Kozanecki et al. 1982). Fernando et al. (1982) found that the ratio of specific conductivities of fore-and postmilking strippings was an effective index of mastitis due to the sharp rise in the conductivity of the postmilk from infected quarters. Introduction of a foreign body, sterile polyethylene, into the udder caused changes in somatic cell counts and conductivity similar to those of mastitis (Jaster et al. 1982). 

The normal levels of the major mineral constituents of cow s milk are listed in Table 5-1. These are average values there is a considerable natural variation in the levels of these constituents. A number of factors influence the variations in salt composition, such as feed, season, breed and individuality of the cow, stage of lactation, and udder infections. In all but the last case, the variations in individual mineral constituents do not affect the milk s osmotic pressure. The ash content of milk is relatively constant at about 0.7 percent. An important difference between milk and blood plasma is the rela-... 

Since antibiotics are prohibited, the attention to a clean and dry environment for the animal is critical. The key is the ounce of prevention. If a cow lies in a wet, manure-laden stall every day, the chance of bacterial introduction to the udder increases 10-fold. However this is easily changed in most cases, and becomes the strongest asset to a clean herd. If a cow becomes infected with mastitis, there is a choice of many isolated natural whey antibodies, which when injected boost her immune system to fight the infection. Vitamin C is also widely used on animals suffering from infection. Antibiotics are used in extreme cases, and the animal cannot return to the organic production line, although her life is spared. In many cases the producers sell the animal to a neighbour or to a local stockyard. 

Mastitis may be observed at any stage of lactation and has also been seen in non-lactating, nul-liparous mares and in fillies. Mastitis occurs most commonly in the summer months and is often associated with Strep, equi subsp. zooepidemicus infection. The treatment of mastitis usually includes the parenteral administration of appropriate antimicrobial agents (see Ch. 2). The udder may also be treated using frequent milking, hydrotherapy and infusion of commercially available intramammary preparations for cattle. A NSAID may be administered to treat both the fever and the discomfort associated with mastitis. 

But this was not the first description of the possible association since an experienced inoculator by the name of Dr. Fewster had sent a report to the Medical Society of London in 1765 entitled Cowpox and its ability to prevent smallpox. It is also alleged that a Dorestshire farmer, Benjamin Jesty, inoculated his wife and two sons using cowpox virus taken from an infected udder. Jenner s own experimental contribution was much more scientific, if wholly unethical by today s standards. In a letter of July 1796 sent to his friend, the wine merchant Edward Gardner, he described his first experiments carried out in May 1796 ... 

Viral Vaccines. The first human vaccine against a viral disease was created in the l790 s through a serendipitous discovery by British physician Edward Jenner. He observed that people previously infected with material from lesions on the udders of cattle (cowpox) became immune to smallpox. Although Jenner was unaware of why cowpox provided immunity to smallpox, scientists later determined that the cowpox virus contains proteins that cross-react with those of smallpox and produce immunity in those exposed to it. The process of immunization became known as vaccination, derived from the Latin word vacca, which means cow. 

Milk may be a carrier of diseases from animals or from other sources to humans. To avoid contamination before pasteurization, healthy animals should be separated from sick animals or those with infected udders. The animals should be clean, kept in clean housing with clean air, and handled by workers and equipment under strictly sanitary conditions. Post-pasteurization contamination can occur as a result of improper handling, due to exposure to contaminated air, improperly sanitized equipment, or an infected worker. 

Both clinical and sub-clinical mastitis are usually accompanied by an increase in the somatic cell count (SCC a measure of white blood cells (95%) such as macrophages, segmented neutrophil granulocytes or lymphocytes) in milk. SCCs above a certain level are an indication of immune-system activation and are used as an indicator of sub-clinical , latent or chronic udder infections/mastitis (Concha, 1986 Ostensson et al., 1988), which were shown to affect milk quality, composition and shelf life. Dairy companies therefore impose SCC thresholds or reduce payments to farmers if certain thresholds are exceeded (Hamann, 2001 Urech et al., 1999). 

The objective of mastitis treatments is to cure the infected udders from the infection, but cure is defined in very different ways. For example, in economic terms, the farmer needs to achieve a level of udder health that allows expected milk yields and quality parameters specified by processors/ national regulations to be achieved. On the other hand, cure with respect to antibiotic treatments, is often defined in terms of absence of bacterial pathogens in milk (bacterial cure), with the proportion of cows without detectable pathogen presence following treatment being defined as the bacterial cure rate (BCR). The main problem with using BCR as the main indicator of cure is that it was frequently shown to include a proportion of cows with drastically elevated SCC values (indicative of sub-clinical mastitis) after treatment, but without clinical (sensory) symptoms. 

There is an additional protection against residues, because antibiotics in meat tend to be destroyed by cooking.. For example, Broquist and Kohler found that chicken breast muscle containing 12 parts per million of chlortetracycline had 0.14 parts per million after roasting at 230 C for 15 minutes and no detectable amounts after half an hour. The original level of 12 ppm was about 60 times as high as would be produced by 400 ppm in the animal feed, without a withdrawal period W. The UK Swann Committee reported that the only possible effect of residues on consumers arose from penicillin in milk from cows treated for udder infections in which the withdrawal time for the antibiotic had not been observed. Cases of skin rashes were reported from the consumption of such milk by sensitive patients. The Committee commented that "there are no known instances in which harmful effects in human beings have resulted from antibiotic residues in food other than milk" ( ) ... 

The means to achieve this apparently unattainable goal had their origins in the centuries-old observation that those who were actively involved with dairy cows rarely contracted smallpox. Jenner s seminal contribution was to establish that this was linked to their contraction of cowpox, a relatively minor variola-induced disease that caused cows to become moderately unwell and produced eruptions on their udders. Milkmaids and others who milked infected cows usually became unwell with a slight fever and (in Jenner s own words) ... 

Precautions A possible allergen. Overuse of antibiotics can lead to the development of resistant strains of antibiotics. Some antibiotics enter humans via the food chain. Antibiotics from cattle that have been treated with antibiotic medication and slaughtered too early can reach the consumer. The same can happen with milk cows that have had udder infections. 

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