Predicting 305-Day Yields from Short-Time Records
C.Y. Cannon, J. B. Frye, John Albert Sims · Journal of Dairy Science · 1942
One of the great difficulties confronting dairymen when purchasing cows is the lack of information about their producing ability.Without production records dependence is placed only on the visible characters of the animals.The relationship of these characters to production and the ability of men to estimate production from type have been examined (2).The discrepancies between the actual yields of milk and fat and the estimates • generally have been large.Since only a small percentage of the cows offered for sale have known records, a quick, easy and accurate method of estimating the producing ability would be useful.It is sometimes possible to get a one-day test from which an estimate could be made if the cow's month to month decline in yield (lactation curve) was known.Lactation curves, although not all alike because they are affected by certain environmental and inherent factors have so much in common that an average curve can be used to obtain a prediction of yield accurate enough to be useful in supplementing the judgment made from examination of the cow's physical characters.Such information has been used (3, 5) to convert incomplete or partial lactations to 10-month and yearly records.Our investigation was initiated to obtain factors by which predictions of the 10-months lactation can be made from the yield of any one month or day in the lactation. EXPERIi~ENTALThe data were derived from two sources: The dairy herd maintained by Iowa State College, and the Iowa Dairy Herd Improvement Associations.College dairy herd material.The first ten months of all normal lactations made in the College Dairy Herd during the period 1908-1938 were used.Every record beginning with an abnormal calving or influenced by serious sickness was discarded.Prediction factors for production were determined by using only 400 records, all made by Holstein-Friesian cows.Daily milk weights were used in determining monthly milk yields.Dur-