Productive Life (PL) and Herd Life (HL) are important measures that effect profitability and should be considered as part of an overall selection program
It is not like dairymen have suddenly stopped breeding for high producing cows, but things have definitely changed. Suddenly there is a profound interest around the world in selecting for longevity. Over the years the pendulum has swung back and forth. At times genetic ability of the animal has outpaced management at the farm but more recently the typical dairyman’s management practices may have outpaced genetic capability of the animal. That’s why many farmers maintain that getting milk out of today’s genetics is the easy part. Managing cows to stay in the herd for 4 or 5 lactations – that seems to be a more difficult challenge!
The problem with longevity as a breeding goal is that as a trait it suffers from a very low heritability. That means that making progress genetically for longevity will take much longer than for the relatively highly heritable production traits. The other problem is that most farmers have made extensive use of a bull long before an accurate reading of his longevity has been made. When two-year-old daughters provide their sire with his first genetic evaluation, it is only logical that the rating for Productive Life (PL) or Herd Life (HL) be low on accuracy. After all, the daughters are still milking in their first lactation. How do we know if they will last?
There are type traits in sire proofs that we know influence longevity. Mammary traits in particular combined with sire and maternal grand sire information play a large role in what a sire’s early longevity prediction will be. Then as daughters calve for the second and third time, actual culling begins to offset type proof and pedigree data, so that eventually with many second crop daughters the longevity prediction becomes a true measure of resistance to culling.
Still, to dairymen and to AI organizations trying to make progressive decisions for the future, having traits like PL or HL more heavily weighted within national ranking systems like the TPI & LPI formulas is somewhat problematic. These are traits we know have significant influence on profitability, but their low accuracy levels early in a sire’s career will ultimately lead to significant re-ranking later if those early predictions change dramatically. Although a sire’s fall from grace or rise from obscurity may occur slowly, almost imperceptibly, there are numerous examples of sires that the industry overused and others that were missed. There is no magic formula we can offer so that this doesn’t happen to you, but there are some practical tips that can make minimize exposure and risk:
1. Sons of highly reliable PL and HL specialists will automatically have high PL and HL predictions themselves early into their career. That’s as it should be, but be especially vigilant to changes that occur to the longevity prediction when second lactation daughters provide feed back as the first true longevity test.
2. It’s instructive to recognize that type and longevity are indeed not the same thing. There are high type bulls that do not leave long-lasting daughters and there are also bulls with moderate type numbers at best whose daughters do last. Selecting for extreme type will not guarantee longevity. In fact, it would appear that at times, the way in which we define exceptional type has worked against our longevity objectives (i.e. extreme stature and extreme dairyness).
3. Somatic Cell Score (SCS) proofs on sires show a definite relationship to longevity. When both SCS and longevity measures are highly accurate, it is noticeable that a high percentage of noted longevity specialists also double as low SCS bulls. Perhaps that’s why they are longevity specialists! Check this out – there are plenty of examples in the US and in Canada. Notice also that not all of these bulls sire extraordinary type! Here’s an amazing statistic: when evaluating Canada’s top 30 bulls for HL, every single one of those bulls also sires low Somatic Cell Counts!
Longevity & SCS are Clearly Related (05/02 Data)
|Top PL Bulls (97% Rel)
||Top HL Bulls (no Reliability restriction)
|Schoch Mark Arthur
||Little River Internet
|Valhalla Marked Design
|Paradise-R Sears Saber
The bottomline is that PL and HL are important measures that effect profitability and should be considered as part of an overall selection program. These traits are part of the TPI and LPI formulas and so are taken into consideration in current sire rankings. Still, many dairymen place a much higher emphasis on overall type than on these longevity measures when making semen purchases, often with an independent cutoff eliminating some sires with high longevity predictions