ANSC20003 Chap.3 Bacterial Disease in the Egg and Dairy Industries
Bacterial Disease in the Egg and Dairy Industries
What the resident population is worth
This lecture takes the organisms of the previous one and asks what they are worth in a production system. A balanced microbial population supports immune function and resistance to pathogens. Rumen bacteria synthesise B vitamins including B12 and vitamin K, and break down cellulose and hemicellulose into simpler sugars, which is the basis of grazing as a production system.
They ferment carbohydrates into volatile fatty acids and support their absorption, and they convert non-protein nitrogen into microbial protein, supplying amino acids from material the animal could not otherwise use.
Probiotics as that logic in a bag
Poultry probiotics are drawn from a short list of genera and are sold to achieve crowding pathogens out, holding the resident gut population in good order, cutting Salmonella carriage and producing antimicrobial peptides.
The claimed effects split into improved production, meaning feed conversion and egg quality and quantity, and improved food safety, meaning cleaner eggs. Keeping those two groups apart matters, because they are argued for to different audiences.
Five places a bacterial disease costs money
Animal health and welfare, through debilitating disease and culling.
Production costs, through medication, vaccines, labour, biosecurity spend, worse feed efficiency and a larger environmental footprint. Consumer prices, since protein becomes less affordable. Production quantity and quality. And antibiotic use, with the resistance that follows it and moves between animals, people and the environment through food, waste, water and crops.
Trade disruption is the cost that arrives without a sick animal, through restrictions on exports and imports.
Mastitis, and who acts on it
Mastitis is bacterial inflammation of the udder.
Clinical cases announce themselves through yield, milk quality, temperature and intake, while subclinical cases change yield and quality without changing the animal's demeanour, which is why the industry monitors somatic cell counts against published thresholds.
Pathogens divide into contagious organisms spreading cow to cow and environmental organisms coming from where the cow lives, and that division decides the intervention. Control runs across milk testing centres, veterinarians, scientists, industry bodies and government.
What this chapter covers
- 01
The four jobs a resident bacterial population does in a production animal
- 02
Probiotics in the egg industry, and the two groups of claims made for them
- 03
Five headings under which a bacterial disease imposes cost
- 04
Antimicrobial resistance moving between livestock, food, people and the environment
- 05
Clinical against subclinical mastitis, and why a number is monitored instead of cows
- 06
Somatic cell count thresholds and what each one triggers
- 07
Contagious against environmental pathogens, and the different control each needs
Turning a rising bulk tank count into an intervention
- 1Place the count against the published thresholds.
- 1Explain why no clinical cases is consistent with the finding.
- 1Name two requests and say what each one settles.
Key terms
- Subclinical mastitis
- Mammary inflammation that lowers yield and milk quality without producing visible signs in the animal.
- Somatic cell count
- The concentration of immune and epithelial cells in milk, used as an indicator of infection before clinical signs appear.
- Contagious pathogen
- A mastitis organism that spreads from cow to cow, typically at milking, rather than from the animal's surroundings.
- Environmental pathogen
- A mastitis organism acquired from bedding, yards or other features of where the cow lives.
- Competitive exclusion
- The suppression of a pathogen by an established resident population occupying the same site and consuming the same resources.
Bacterial Disease in the Egg and Dairy Industries FAQ
Why is a bacterial disease described as costing more than the affected animals?
Because four of the five published cost headings fall outside the sick animals themselves: production costs including biosecurity and feed efficiency, consumer prices, lost production quantity and quality, and antibiotic use with the resistance that follows. Trade restrictions add a further cost that is felt by producers whose own animals are healthy.
What does a somatic cell count of 250,000 cells per millilitre indicate?
It sits above the published level of 200,000 associated with potential subclinical mastitis and below the 300,000 associated with likely infection by a significant pathogen. It is a signal to investigate at individual cow level rather than a diagnosis in itself.
How does knowing the pathogen group change what a farm does?
A contagious organism spreads between cows at milking, so the levers are milking order, teat disinfection, hygiene and machine function. An environmental organism comes from where the cow lives, so the levers are bedding, yard drainage and teat condition between milkings. Listing organisms without sorting them into those groups leaves the control decision unmade.
What are probiotics actually sold to do in poultry?
Crowding pathogens out, holding the resident gut population in order, cutting Salmonella carriage and producing antimicrobial peptides. The downstream claims split into production effects, such as feed conversion and egg quality, and food safety effects, such as cleaner eggs.
Exam move
Learn the somatic cell count thresholds exactly, since they are among the few hard numbers in the bacteriology block and they appear in both the practicals and the assignment. Practise sorting a list of organisms into contagious and environmental groups and stating the control that follows, because that pairing is what a question about a herd is really asking for.
For the cost material, memorise the five headings rather than the examples, and be ready to supply an example for each from a different industry than the one in the question.
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