Nematodes

Physical examination of milk for its general appearance, odor, color, and consistency

General rules

• First step – Accurate Sampling for proper examination of milk
• Careless preparation of samples will lead to incorrect results. 
• The whole body of milk from which a sample is to be drawn should be uniform in its composition
• Sample of milk drawn out of it for analysis must be a true the representative of the whole body of milk.
• The factors disturbing the uniformity of the composition of milk are mainly the separation and partial churning of fat.
• Thorough mixing of milk must be ensured either by stirring with a long-handled dipper if the container is big or by pouring from one vessel to another or by shaking gentle
• If the sample bottle has been standing for some time resulting in the separation of fat in the cream layer or lumps of fat appear, the bottle may be heated in a water bath up to 38°C (100.4°F) to melt the fat before mixing.
• Under no circumstances should milk be shaken very violently since viscosity does not allow air bubbles to rise easily.
• Moreover, agitation of milk tends to churn with the result that even distribution of fat becomes difficult
• When milk from an individual animal is to be sampled, the whole amount of milk is taken and a sample was drawn from the middle of the vessel containing it
• For the usual analysis of milk, collect 250 to 500 ml of the sample in a wide-mouthed bottle.
• When the sample is only to be collected for carrying out the fat test, 50 to 60 ml would suffice.
• Fresh samples of milk should be examined, since important changes in its physical condition, chemical composition & bacterial content may take place even within a short time.
• When samples are to be sent some distance to a laboratory for examination, they should be first preserved by the addition of certain preservatives.
• Twenty drops of formalin to a liter of milk or half a gram of potassium dichromate to a liter of milk is enough for the purpose.
• The milk should better be sent in a previously sterilized bottle closed by a sterilized stopper.
• For bacteriological examination, antiseptics, and preservatives should not be added. 
• For a preliminary examination general appearance, odor, color, consistency, and taste of milk should be observed.
• Milk, when freshly obtained, is a white, opaque fluid when seen in bulk.
• It has a characteristic faintly sweetish taste and peculiar odour.1Sweetness is due to its lactose (milk sugar) content.
• The so-called cowey odor is due to manure gaining access into milk and due to the absorption of the characteristic odor from the atmosphere of dairy sheds.
• The white color of the milk is due to the calcium-caseinate content and the opacity is due to the same substance and fat.
• Sometimes a more or less yellowish tinge is noticeable, which is due to a pigment (lactochrome) associated with the fat.
• It is yellowish in cow’s milk.
• During the colostral period and near the end of the period of lactation, milk may acquire a saltish or bitter taste.
• The development of bitter taste in milk in late lactation is due to the activity of lipase enzyme which hydrolyses milk-fat.
• Abnormal odors can be due to diseased udder or the growth of bacteria in milk.
• Further, certain aromatic feeds also impart a characteristic odor & taste to milk such as rape, cabbage, beets, turnips, carrots, etc.
• Among the wild plants the garlic have such strong oniony flavor.
• Take immediate steps to eradicate all such plants from the feed of milch animals.
• A blue tinge in milk may indicate a low percentage of fat due to either skimming or watering.
• The amount of dirt in milk can be a carrier of bacteria. Moreover, visible dirt is an indication of the care exercised in milk production.

For descriptive purposes the following schedule will be useful: 

1. General appearance: Note whether clear or any visible dirt or foreign matter is present. If so describe its nature.
2. Odor: Record odor as normal, none, very mild, or strong (cowey, manure like fishy, turnippy, oniony, etc.). Heat the samples of milk to 60°C (140°F) and note the odor by smelling. Heat accentuates any undesirable odors present.
3. Colour: Note the color and record it as milk-white, light yellow, reddish, bluish, etc. Describe any abnormal color (what it may be due to).
4. Consistency: Record consistency as normal, watery, thick, slimy, shredded, etc.