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Yields Of Milk And Eggs: Able risk of diminished vigour and inherited defects. Crossbreeding to overcome this is a regular commercial practice, particularly with sheep and beef cattle, where the hardy hill breed is mated to a less hardy but quicker-growing breed.
Improvement of performance within breeds has come to depend increasingly on detailed records: yields of milk and eggs, and speed of growth and feed economy in meat animals. This entails elaborate testing procedures and statistical analysis of records.
The Ayrshire from Scotland and the Jersey from the Channel Islands; the latter is the smallest of all widespread modern breeds, giving milk containing one and a half times the average content of butterfat.
Much of the world's meat and milk supply comes from cattle that can be regarded as dual purpose. Of these the most numerous are the black and white Friesian or Holstein cattle, that originated in The Netherlands but which now show local variations of type. The Friesian is a large animal that produces heavy yields of milk whose composition has been greatly improved since the advent of artificial insemination. It has displaced the once dominant Shorthorn.
An index for the increase in the dairy herd is the output of milk—1.7 million gallons in 1946 and 2.5 million gallons in 1963-1967. Annual milk yields per cow increased in the same period from about 550 gallons to 803 gallons. Simultaneously the output of beef and veal rose from 537,000 tons to 919,000 tons. |
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