The dairy cow does not attain her maximum producing ability during her first lactation period. This is appreciated in practical work and is taken into consideration in formulating the production requirements for entrance into the Advanced Registers, Registers of Merit and other official lists of producing cows maintained by the various dairy cattle breed organizations. In spite of this, the exact relationship between age and producing ability, if such exists, has never been definitely determined.
Additional importance is given to a study of the influence of the age of the cow on production by the fact that large numbers of cows, still in their prime, are annually disposed of by dairymen. The fact that these cows are capable of further profitable production should be recognized.
McCandlish, A. C.
"Influence of age at the time of freshening on production of dairy cows,"
Research Bulletin (Iowa Agriculture and Home Economics Experiment Station): Vol. 5
, Article 1.
Available at: https://lib.dr.iastate.edu/researchbulletin/vol5/iss73/1