Improvements in the Productive Life Scale

Since 1994, longevity of animals has been genetically evaluated in the US. However, for at least the first 3-4 years that Productive Life was being evaluated, it was generally only used as a gauge to figure out which type traits were highly correlated with longevity. Few producers put large amounts of selection pressure on this trait, as most still believed that selection for type traits was an easier way to make progress and you could actually “see” the results in the resulting offspring. Times have certainly changed, as more and more producers heavily weight longevity in their selection practices. To accommodate this change, the definition of Productive Life has also changed slightly.

Productive Life still measures the longevity of animals, relative to the average of the breed, and for all practical purposes, Productive Life is still explained the same way. However for evaluation purposes, the definition will change to give animals more credit for longer lactations. Previously, a cow was only given “credit” for the first 305 days (10 months) of her lactation, and each month was considered equal. Now the definition will include “credit” for longer lactations, thereby giving credit to those animals that continue to be profitable even though they are past 305 days in lactation. With more herds moving their voluntary waiting period back to 70 days and having shorter dry periods, few cows are dried up prior to their 305 days in milk, and therefore this change will properly count those extra months in milk.

Including those later months, does however become somewhat tricky since cows past 305 days in milk are generally not making as much money for their owners, as cows at the peak of their production, so the new evaluation also accounts for this. Instead of a cow getting the same “credit” for going from 90 DIM to 120 DIM as she did for going from 285 DIM to 305 DIM, now the “credit” will be based on a similar curve as that of the cow’s lactation curve, thereby giving the most credit for another month of productivity during the peak production months, and less credit for a month of production at the tail end of her lactation. Additionally, more credit is given for a month in later lactations than the first lactation, again signifying that a month of production in later lactations is worth more economically than a month in 1st lactation.

Simply put, the definition of Productive Life needed to be changed slightly to accommodate the fact that most cows milk longer than 305 days and to give credit to those cows. The old system actually undercounted the productive days that a cow had in the herd and this gave an inaccurate evaluation of how long a cow was productive and in turn, being profitable for the producer.

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Posted Oct 2nd

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