Wednesday, July 4, 2012

Dairy Cow Culling Decisions

The goal of a production medicine veterinarian is to help clients maximize profitability per slot, which is equivalent to one freestall or defined bed-pack space.  Maximizing profit per slot means that first, the slots must be full, and second, they must be filled with the most profitable animals.  Maximizing profitability per slot encompasses both replacement and cow management including making intelligent and timely culling decisions. 

Culling Introduction...

A dairy has an optimal stocking density.  Within the defined space, economic decisions must be made to fill each slot with the most profitable cows.  Those economic culling decisions are very farm and cow specific.  Most dairies are missing an opportunity to make more intelligent culling decisions. 

The goal of dairy management should be to avoid damaging cows which lowers cow value and increases culling risk.  Factors affecting cow value are milk production level, fertility status, age, health status, and stage of lactation.  A cow’s income is derived from milk volume, milk composition (components and quality), calves/embryos, and carcus value.  Disease decreases cow value through drug and veterinary costs and death.  More importantly, disease reduces production efficiency, reproductive performance, milk quality, and life expectancy which increase culling risk.

Culling Rate Defined... 

A herd analysis of culling should begin with cull rate.  So, what is your herd’s culling risk or rate?  How do you define your Cull Rate?  Unfortunately, the experts disagree on the true definition of cull rate.  To clear the muddle, Fetrow et al 2006 recommended changing the term cull rate to “Herd Turnover Rate.”  So now we need to ask, “What’s your herd turnover rate?” 

Herd Turnover Rate is defined as [the number culled over a specified time (Year)] / [ mean cow inventory for the same time period].  Using this definition, you should be able to gain an appreciation for your herd turnover rate. 

Defining the optimal herd turnover rate is dependent upon the current dairy herd dynamics.  As stated earlier, economic culling decisions are very farm specific with dependency on the business need to push return on assets.  The herd needs to find the balance between the need to maintain optimal stocking density, preferably grow considering the Internal Herd Growth Model, while maximizing profit per freestall.  The Internal Herd Growth Model is dependent on Replacement management, reproductive management and herd turnover rate.  Herds with excellent heifer management (low mortality and morbidity rates and age at first calving ~23 months) and reproductive management (21-24% preg rates) can withstand a high cull rate and maintain herd size. 

Let’s consider this scenario. The national cull rate is ~40%.  Depending on heifer completion rate and calving interval, an average herd would achieve a 34-36% lactating herd entrance rate for first calf heifers.  Therefore, a herd with a 40% herd turnover rate with a reasonable 34-36% entrance rate would have a need to purchase lactating cows simply to maintain herd size (to keep the slots full).  Considering the average heifer entrance rate, a 34-36% herd turnover rate would seem reasonable if you want to maintain herd size.  However, agriculture economists prefer to see lower target levels between 23-28%.  Why?  Cows are considered capital, a depreciable asset.  The longer the asset remains in the herd, replacement costs are spread over more years which frees up more capital to invest in other areas of the business.  At current milk and feed prices, a cow takes almost 2 lactations to cover her rearing or replacement cost. 

But keep this in mind.  Herd turnover rates are poor monitors of the quality of culling decisions.  You could have an incredibly low turnover rate with excellent internal herd growth.  However, you could be holding on to more unprofitable cows – two-quartered cows with average milk production comes to mind.  You must continually strive for greater returns on your assets by replacing current genetics with better genetics. 

Herd Turnover Rate Cohorts or Subgroups

Herds should have an understanding of several herd subsets that may point to specific problem areas.  The most important cohorts to analyze are Cull Rate Less Than 60 DIM and Cull Rate Less Than 30 DIM, measurements providing an assessment of transition cow management.  To accurately calculate Transitional Cull Rates divide the number culled (30 or 60 DIM) by the number fresh during a defined period (Year, past 6 months, etc).  Benchmark cull rates should be less than 6% and 4% respectively.  Also, analyze and compare the early culling rates for each lactation group in order to pinpoint problem areas with particular focus on first calf heifers and mature cows. 

Cohorts based on calving date also present fresh insight into the herd’s culling pattern.  Seasonal differences are typically observed.  Particularly focusing on summer calving cohorts, the seasonal differences will show the value of heat abatement strategies for both fresh cows and dry cows.     

Develop a consistent system for recording the culling reason for every cow or heifer sold or died.  Record accuracy and consistency is very important in order to avoid confusion and to make analysis easier.  Fifty reasons for culling create confusion.  Initially, categorize culls based on destination:  dairy sales, slaughter, death.  Use simple and broader categories, like Digestive, Lame/Injured, Reproductive, etc.  Herds with high cull rates and/or mortality rates must use the data, the accurate and easily interpreted reason, to identify and correct management problems. 

Heifer Culling Strategies

High heifer raising costs mean that culling decisions should be made <12-13 months of age.  Again, we are trying to fill the barn with the most profitable cows and heifers.  Therefore, we should raise our most valuable replacements with the greatest potential for future profit.  Greater heifer culling options and flexibility are achieved with low heifer mortality rates, high heifer completion rates at an age of first calving between 22-24 months, low cow cull rates, high pregnancy rates, and use of gender select semen.  With greater culling flexibility several culling strategies can be utilized.  New developing genomic testing will continue to improve and provide a tool for improving your herd.  Heifers experiencing pneumonia and coccidiosis have been shown to produce less than their herdmates and should be considered for culling.  Heifers from the lower 25% of your herd and from Johnes positive cows would fit into a herd culling strategy as well.


Cow Culling Strategies

A cow culling strategy, with greater emphasis on economic culling (replacing a cow with a more profitable individual) is useless if biological or forced culling threatens the viability of your herd.  How many times have we heard, “I can’t sell that chronic mastitis cow because too many cows are leaving on the trailer.”  Therefore, the first step to developing an intelligent culling strategy is to initially address and reduce biological or forced culling by working with your herd management team. 

We are striving to define what is breaking or damaging cows.  Significant opportunities exist in many herds to quickly address forced culling by correcting cow comfort problems which create higher levels of lameness and injuries.  Exceeding a facilities optimal stocking density will impact culling.  Transition cow management, reproductive management, and milk quality are noteworthy segments that significantly impact forced culling.

Use herd testing programs to identify potential biological cull cows.  Infectious disease herd testing programs can be utilized to identify carriers of  Johnes, BVDV, etc.  Utilize DHIA records, mastitis treatment records, and milk culturing programs to identify chronic mastitis cows and individuals infected with contagious mastitis pathogens.   

Work with your veterinarian to devise and use treatment decision trees to help determine whether there is economic justification to either treat or cull the cow.  The fifth lactation cow with a high SCC and LDA may be a better candidate for culling rather than a surgery.  Use pharmaceutical treatment strategies, particularly for groups at greater risk to be culled, that provide greater culling flexibility by using drugs with low and clearly defined withhold periods.

The financial penalty for forced culling is huge.  First, you are selling a cow prematurely before a replacement is available to take her place.  Second, you are selling a broken cow at a loss compared to selling the average valued cow for dairy purposes.  Third, you lose the entire value of a dead cow, and unfortunately compost will not breakeven with her value. 

After making corrections in the management areas of cow comfort, transition, forage quality and feeding management, replacements, milk quality, and reproduction, the herd begins to grow because conception rates improve, heifers flood the herd, and forced culling declines.  As a result, the dairy can begin to focus more on herd goals and economic culling.  Can a cow be replaced by a more profitable animal?  Options are now available to sell heifers and cows for dairy purposes.  DHIA production records can be analyzed after 60 DIM to closely compare a cow’s average production to a first-calf heifer.  As long as data inputs are accurate, DC305 COWVAL and PREGVAL provide reasonable culling decision tools.  Genomic testing is another potential tool that can be used for economic culling decisions.

Culling Conclusion

A dairy has an optimal stocking density.  Within the defined space, economic decisions must be made to fill each slot with the most profitable cows and heifers.  Most dairies are missing an opportunity to make more intelligent culling decisions.  By focusing the dairy management team on opportunities to decrease forced culling, dairies can increase economic culling strategies. 

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