Saturday, April 26, 2014

The Genetics of culling rates and cow turnover

Recently published USDA data from 2012 DHIA herd reports indicates that high culling rates continue to plague the dairy farmer’s income and equity statements.     While culling dairy cows when beef price is higher than normal is an aid to cash flow, the cost of raising heifers depends on feed costs (which are high enough to inhibit growth in the beef cow sector).     The simple math is, every time you turn a cow  into a cull and have to replace her, your equity takes a $1000 “hit” (the market difference between culls and replacements today).

Turns out that Holsteins have replaced Guernseys as the breed with the shortest “Productive Life”.   On 2012 data, this is how each major dairy breed “ranks”:

Breed            Cull rate                Breed             Cull rate               Breed              Cull rate                           

Holstein             32.7%                 Brown Swiss       29.8%               3x crossbred        26.9%                                                                                                                Red & White     32.0%                 M Shorthorn        28.6%               2x crossbred        26.1% 
Guernsey           30.8%                 Ayrshire              27.7%                Jersey                  24.9%
Is crossbreeding the answer to improving cow turnover?     The data seems to suggest it, IF you ignore the obvious:    (a)  Jerseys are still better for herdlife than crossbreds;   (b)   crossbreeding beyond three generations is usually accompanied by a loss in milk volume;   (c)   Heterosis response [hybrid vigor] is greatest in the first generation, but declines with each added generation in which the same trait index is used (regardless of breeds added).      Thus crossbreeding alone does not replace gene trait selection IF your goal is to improve herdlife while maintaining or gaining on per-cow production.

Does selection on “health and fitness traits” work?

According to a recent article in Holstein International the low point in Holstein fertility levels was hit in 2005.    Since then, the average DPR (“daughter pregnancy rate”) of AI preferred sires has risen.   But so far, on the 2012 data above, Holstein cows still leave herds 30+% faster than Jerseys.    

How much of the Holstein disadvantage is due to lower fertility rates?

Keep in mind the commercial breed average for crossbreds as well as purebreds in any breed still show the “average” cow and “average” herds only get three lactations per cow.    Dairy profit margin over the cost of replacements would increase by 25% just by getting one more lactation per cow.    Longevity is a heritable characteristic, thus a breeding program seeking longevity will pay dividends in profitability.

The most important trait in selecting for longevity is clearly fertility.    Cows that do not rebreed do not stay in our herds.     Biological research in many different species clearly shows that fertility and a will to live are strongly correlated.    Thus selecting for better fertility will contribute to lower stillbirth rates and is linked to general health qualities in your herd.

How much of the Jersey advantage over all other Breeds is due to inbreeding?

What you really want to know is, “will this computer mating program that adjusts for inbreeding save me from shorter Holstein herdlife?” – and the answer is clearly NO.     In fact, the Jersey breed is the most “pedigree inbred” of all major dairy breeds, yet it remains the longest productive life breed.
Holsteins as a whole are 25% lower in average pedigree inbreeding (ibc%) than purebred Jerseys.  
(continued—how much is due to inbreeding?)

No computer sorting program leading you to the lowest “efi%” matings has ever been proven by any University study to work.    “Avoiding Inbreeding” when all AI sires in every Genomic breed are fast becoming closer related than ever before is a marketing ploy rather than an aid to herd improvement.  

This is why we continue to urge you to give the “aAa” Breeding Guide a try.    The proven solution to avoiding “inbreeding effects” is to recognize that a stronger, well-balanced physique avoids expressing “inbreeding depression”.     Trait selection on health and fertility traits associated with the problems of inbreeding will then synergize with the “aAa” mating to avoid producing “inbred” animals.

How much of Holstein herdlife is due to size?

Not as much as all the dialogue criticizing registered Holsteins would suggest.    Holstein USA studies are showing that the purebred Holstein has been gaining size at the rate of 25 pounds per generation.
If your facilities were built in the 1970s and you have not changed anything, today’s cow is likely 240 pounds bigger than the assumptions of your cow facilities (10 generations x 24 pounds/ generation).   
But if you built fairly recently, your building design would handle the larger cows of modern breeding.

USA type data is hampered in that it only measures “stature”.    Canadian type data measures both size (weight) and stature (height) and their trend lines may reveal the real problem:

1991 to 2001 birth dates:  average stature of first calf cows gained 5 cm (approx 2 inches)        
                                           average weight of first calf cows lost 7 kg (approx 15 pounds)
1996 to 2001 birth dates:  average stature of first calf cows was virtually unchanged; however
                                           average weight of first calf cows lost 21 kg (approx 46 pounds)

Basically, the near-universal preference in classification for a more angular frame (more tall than wide, more lean than fleshy) is producing new cows that are actually lighter in mass, are less sturdy on their front legs, have less muscle control over rear legs, have softer feet, than the sort of physique that gave their maternal ancestors a full productive lifetime.     

Again, the real causative problem is a lack of “balance” in genetic selection.   On the trait selection side, AI studs always preferred milk volume over component density, alongside earlier maturity of the production capability, with the result bigger heifers make the most milk.    Selection sets these trends.
It is disingenuous to blame breed type classifiers for problems that started from index rank selections.
The system they are using (linear trait scoring) was a product of the 1970s University view of “type” based on what sort of first-lactation cow produced the most milk volume.    This was a radical change from the breeder-developed type descriptions that were focused on cow longevity under forage feeding.    

Tell me how to rise from “average” to “exceptional”

If you wish to produce cows that have balance between “tall” enough and “wide” enough, use “aAa”.
If you wish to produce cows that have balance between “strength” and “dairyness”, also use “aAa”.
If you have herd issues with SCCs, fertility or component% levels, the PTA trait data is there to help.
Keep in mind that PTAs for Productive Life contain assumptions that may not fit your environment.
Thus while “PL” may help you avoid short herdlife cows, you need more information to gain herdlife.
Look for evidence of longevity in the maternal lines behind bulls you are considering.

It seems like every “expert” today is picking on the Holstein.

However, it remains true that 88% of the dairy cows in North America are “Holsteins”.
Only 5% are crossbreds, 5% are Jerseys, and 2% represent other traditional breeds.

Thus the productivity and profitability of the Holstein cow remains essential to dairy industry survival.     Holstein breeding must provide the genes to turn around negative trends that have led the Holstein to the shortest average herdlife in breed history.

Inside this newsletter you will find some recent facts and figures that we hope will add to your perspective of your opportunities and exposures in Holstein breeding.    

You might also ponder this idea:  you can create “outcross” hybrid vigor within any breed if in the next generation you pick your sires in a different way.    Different trait patterns require different DNA genotypes—and crossing different genotypes is how we stimulate a “heterosis” response to improve all “vigor” traits.

Mich Livestock Service, Inc  ** For the Best in Bulls ** ph “toll free” 1 (800) 359-1693 

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