Monday, December 22, 2014

Net Merit? TPI? Type? Pedigree? How should we pick bulls today ???

The next USDA “base change” is going to occur in 2010.     This means the range of PTA yield values will be slightly reduced.    This change usually subtracts 500 pounds of PTA milk from historical sires, and readjusts downward all current sires according to the relative performance of most recent offspring.

Dairymen today pay less attention to sire evaluation changes than was true ten+ years ago—today it is mostly a concern of purebred breeders trying to compete in the “numbers” game.    But many AI sales people try to inject excitement back into sire selection by making a big deal of base changes—the time when “old” bulls get culled, and “new” bulls show up at the top of indexing lists.

Given we have had +2000m sires for four decades, at the top of AI offerings, and frozen semen to make them more easily available, why is the average base change only +500m per generation?

Is it that we are not able to manage that rate of production gain within basically “fixed” environments, feeding technology our only way to “upgrade” facilities to higher genetic potential?    Or is it, as many commentators always suggest, “we place too much emphasis on ‘secondary’ traits like type”??

Indexing formulas change while no one is looking

In a recent conversation with a fairly aware young Holstein breeder, I was surprised to learn he did not know that, in the current version of “Lifetime Net Merit” (USDAs primary sire ranking index), pounds of Milk carries a zero $ value.        That’s right—times have changed since Clint Meadows taught us all that “PD Milk is the primary selection trait”.     Today, when you analyze milk checks, gross milk yield is equated with the water left after you remove all the Butterfat, Protein and Mineral solids… those milk components that make milk unique and marketable.

Likewise, every couple of years, Holstein’s TPI formula, or Jersey’s JPI formula, will go through some massive recalculation, usually because breeders become dissatisfied with the cumulative impact of the trait preferences of the prior version of the formula.     As casual semen buyers, we see the same term of “TPI” or “JPI” so we assume using it for sire selection keeps us consistent.    In fact, it is pushing your herd from one fad to another, and may not be helping you solve problems unique to your herd a bit.

When you challenge the orthodoxy of “ranking index”, everyone thinks you are crazy—but on any level of biology related to gene pairing, trait heritability, or physical adaptation, the Rel% of an index is zero.   
Indexes were designed to sell semen and embryos—not to guarantee cattle improve from matings.

What kind of cows do you wish to milk??

There is a common sense reason why people today select on more than just PTA Milk.   They wish the increases in milk production to be sustainable, they wish the increases to be cost effective, and they wish to avoid a loss in milk price per cwt as the volume of milk produced increases.

The only way to look at “more genetic milk” is to first determine what changes in milk production will produce the most income gain on your dairy.    For anyone whose SCCs are too high or whose blended bf% and pr% are too low, the more important become pounds and percent butterfat, pounds and percent protein, and lowering the SCC selection level (3.00 is standardized breed average).     Higher bf% and pr% will raise milk price, both on the attained “management” herd average, and the genetic gain if any. 

How important is type?

The less “type” you have, the more important it is.    Why?    Because improving “type” has more impact on reducing the incidence of short herdlife cows, than it really has on gaining cow longevity.  

Weak traits (shallow feet in combination with refined bones, loosely attached udders in combination with weak ligament supports, bad teat placement with strutting teats, shallow and/or narrow chests) can indicate a short herdlife.    When the overall animal just looks “frail” to the classifier, the net result will also be a lower final score.     The highest correlation among bulls with type problems and a negative Productive Life (PTA- PL) is that daughter score averages below 76 indicate “below average” type even if the bull is plus PTA Type (his daughters are bad, but the herdmates were worse= “plus” type).

Type data would correlate higher with PL ratings if the scoring system would (a) quit comparing the new heifers to contemporaries, instead compare them to a minimum standard of functional traits; (b) give the wider bodied heifers more credit for “dairyness” [reduce the weighting of ‘angularity”].

What really drives longevity?

No single trait has more impact on longevity than cow fertility.     Think about your own herd and be honest--   (1)  If an “ugly” heifer breeds back on time, you will keep her; (2)  If a “pretty” heifer does not breed back, you will sell her.      Likewise, no matter how much a heifer milks, if she does not breed on time, and drops below x pounds per day, you will sell her to make room for the next fresh heifer.   Thus all other traits being equal, Fertility determines how long a cow stays in a dairy herd.

Next to “fertility” we also need “health”.    In a broad sense, as an unhealthy cow cannot sustain a level of production profitable to the dairy, only healthy cows are retained for future production.    One of the most important health researches was the Canadian study in which it was found that higher SCC heifers  do not sustain predicted higher levels of production in second or later lactations thus indicates a faster aging, shorter herdlife, and a lower lifetime milk yield.     [The exceptions will be really high bf% and pr% sires—due to inexact methods of SCC testing in use.    “SCC” is not specific to mastitis infection; heel warts and foot rot are more likely to send a cow’s SCC through the roof.]

Foot and Leg problems will cull cows quicker than poor udder traits.    Poor mobility will cause a cow to spend less time at the bunk eating—more time lying in her stall (or in the alley).    Poor udder shapes we put up with as long as lots of milk can be pried from that udder.     Unfortunately, the two most primary type determinants of good mobility—(1) Thurl position, (2) Front leg position—are not measured in any linear type scoring system.     [The “aAa” breeding guide does analyze Thurls and Front Legs.]

Create your own trait selection matrix – then mate cows for physical balance

The lesson in all this is—approach sire selection additively, seeking sires strong in those traits costing you the most in your present herd; approach mating physically, matching sires to cows to produce more structural balance, as well as more uniform expression of growth rates, size and dairy capacity.

Selecting for more PTA Milk than the current frame capacity of your cows (and energy density of your forages) can sustain, is a wasted genetic opportunity.    Mating cows randomly, believing a higher index on paper is going to produce a more lifetime productive cow on the hoof, misunderstands a primary fact of biology: you can only breed a cow to a single bull, not to an “average” of his breed, or the index rank

A sire selection based on longevity of production produces a second income—
                                                                                  From surplus reproduction.

This is part of the message that has always sustained independent AI distribution, and made a good income for its many customers—the understanding that genetic selection can accomplish a multiple of goals simultaneously.

There never was much sense in the “if you want the most milk, you can’t select for type” line—that is a result of obsolete single trait selection concepts.    What has been overlooked is that “index” ranking was really just a continuation of the “single trait” preference of armchair geneticists who could get excited on which bull has the highest (PD Milk) and later the highest (Net Merit).

Single trait selection has been proven to be a failure at sustaining both genetic gains and profitability.    If you wish a sustainable approach to dairy productivity, you need a different, sustainable process for genetic selection, mating and reproductive efficiency.    

No comments:

Post a Comment