HOW DO WE MEASURE “FEED EFFICIENCY” GENETICALLY?

From the September 2013 Dairy Route letter

In the beginning, we sorted breeds into “dairy” breeds and “beef” breeds, based on whether they turned feed into milk or weight gain.     Then evolved defining the “dairy” cow as milking a 305d lactation, and the “beef” cow as drying up after weaning a calf (calving every year, in either case, with the new grass).

We measure average cow size.    The bigger cow is “less” efficient, the smaller cow is “more” efficient.   (This is the New Zealand BW model.)     In other cases we do not even bother to measure size, we just will impute it from stature.   The tall cow is assumed bigger thus less efficient, therefore the shorter cow is more efficient.    (This is the USA Net Merit model.)

In the abstract, these approximations seem more true than false.    They are also virtually meaningless, as no feed has been put in front of any of these cows yet, to see what they do with it.

It depends.

The NorthCoast Group [Jersey breeders in Ohio] sets their genetic model for optimal production as:

“15 times body weight annually of milk volume testing 5%bf and 4%pr calving annually over a 14 year lifetime “ (12 calvings, 12 lactations).    The feed efficiency is thus predicated on “milk x body weight”.      An 800 pound cow needs to produce at least 12,000 pounds, a 1000 pound cow at least 15,000 pounds, a 1200 pound cow at least 18000 pounds… (testing like a real Jersey).    The record holding Jersey cows have produced over 30x body weight (in individual record lactations).     More realistic, the lifetime record Jersey cows have produced 20x body weight over all their lactations.  

Many feed nutritionists compare cows on an “Energy Corrected Milk” basis.     Roughly, a Jersey cow milking 50 pounds daily with 5%bf and 3.7%pr equals the caloric value of a Holstein cow milking 80 pounds daily testing 3.5%bf and 3.1%pr.       Thus, any “efficiency” measuring must reflect the value of the milk, not just the gross volume of fluid produced, against the cost of the feeds consumed.

This is the next step in genomics?

Most population geneticists remain excited by Genomics because they wish to figure out the “genetics” of feed efficiency.     They want to locate the “f/e” genes, so they can feed it into their index models and tell us who is the “perfect” bull to sire “it”.

So far, this has not happened.    Our DHI testing systems collect data for herd averages and bull proofs, but they really do not measure every trait needed for describing phenotypes on relative efficiency.

Meanwhile, the latest generation of animals most favored by Genomic ranking are being criticized in some circles for actually lacking competitive growth rates, which most of us would see as a starting point for assuming “feed efficiency” genes are present and acting.

How much “milk” do we produce per acre?

The most basic ration assumption is --- one pound of dry matter intake produces one pound of milk.   The more feed the cow eats, consistently, day after day after day, the more likely she will milk.    

Our summer newsletter showed various grass forage varieties that produce from 3.5 to 6 tons D/M per acre (7000 to 12000 pounds of milk per acre, IF totally digestible forage energy).      

How many acres does it take to feed a cow?

On the above basis, you might assume you need two acres per cow, IF she would eat the volume of forages implied:    (14000 pounds = 45.9 pounds DM/day; 21000 pounds = 68.85 pounds DM/day)

Interestingly, a typical 1000 pound Jersey will make 14000 pounds, and a typical 1500 pound Holstein will make 21000 pounds, because they would eat 45 or 68 pounds of feed daily if offered.     50% more size = 50% more milk volume.     Thus size and average milk yield have near linear relationships.

To push production beyond the physical limitations of cow appetite and functional body capacity, we have one genetic option (faster metabolism) and one feed preparation option (more energy density).   It is in the development of “Total Mixed Rations” that first, we figured out how to get cows to eat stuffs she would not eat by itself, and then, how to process supplements into more energy-dense particle sizes.

This is the real reason why the conventional (TMR) industry argues their approach is more efficient—it is a “production per cow” capability that cannot be matched in a rotational grazing system.   However, the grazing community can argue that they may harvest more pounds of milk per acre than is possible under higher cost mechanized harvesting.     Neither has answered the question of “feed efficiency” but I would argue it is more important to answer the question of farm profitability first, of which gene choices is just part of the total management puzzle we must assemble.

Impact of assumptions over time    

    

Does it imply some eventual stupidity if we continue to expect new heifers to milk more than their dams but we follow genetic models that make the heifers smaller than the dams?    Perhaps.     It is more true that in the AI era, we have made small breeds taller, big breeds leaner, by skewing type selection toward models of faster maturing individuals found by production breeders and their AI sire partners.   We also tended to favor milk volume over component % density (creating the illusion of more feed efficiency) as well as extended lactation over reproductive regularity (delaying added energy demand for rebreeding)-- until the milk market reality penalized that stupidity with the multiple component pricing program, and later cow markets penalized low reproductive rates with higher replacement cow prices.

In any biological system, each choice creates a multiple of possible outcomes

 

What we must conclude is this – the feed efficient cow is not the tallest, or shortest – is not the biggest or smallest – is not the highest producing or high milk price generating –

                 IT IS THE COW WHO SUCCEEDS IN ALL REQUIRED ENERGY DRIVEN FUNCTIONS.

As a calf, she must live.     As a baby, she must thrive.    As a weaned adolescent, she must grow on the available forages and reach puberty on time to stay in her group.     As a yearling she must conceive as a result of visible cycling and receptive breeding.     She must calve unassisted or risk severe setbacks in first lactation that could end her life prematurely.    She must nurture her calf to life.    She must eat and come into competitive production while also succeeding at postpartum recovery.      Next she must be returning to cycling so as to conceive again as required under the management design.   She must stay healthy given the impact of systemic health on milk quality measures.    She must finish growing into the mature physique dictated by her genotype.    If successful on all these energy driven functions, she will attain longevity as a productive herd member and produce genetically superior replacements.    In this appraisal, I continue to believe that feed efficiency is implied genetically in proven longevity.

Is “feed efficiency” more important than “longevity” ??

We are very aware of the next focus of Genomics—it is going to be “feed efficiency” because of the industry’s ongoing concerns over feed cost vs milk price ratios.

I would be the first to agree that feed costs must be under control (it remains a major reason why we converted our dairy to rotation grazing a dozen years ago).    I have become a bit slower to assume that population genetics will give us the right answers.

The dairy cow, unlike any other farm animal measured, produces a multiple of energy driven products and required functions.    To measure the genes of each of these on an individual basis will be successful.    To prioritize them in selection, when all will be needed in any functioning animal, will be more difficult.

We may already have the gene selection and mating selection processes that will lead us to profitability over current feed costs—we just have to step back and see the big picture of what has to fit together, and what the real limitations of land acreage base and forage production of NDFd from that base mean for our production targets.