Monday, March 7, 2022

Breeding selection for a more fertile herd of cows


Over the last two decades, the calculation of milk checks has clearly gone in favor of component volumes over fluid milk pounds.    This has been difficult for AI studs who had focused on fluid milk volume (PTA Milk) with so few bulls initially offering truly good components.  Their advice to dairymen was to keep selecting “pounds” (PTA Fat and PTA Protein) when for breeding, the genetic response was twice as strong when you select “percents” (PTA Fat % and PTA Protein %).     Number of Jersey and Crossbred cows increased, but Holstein cow numbers remained static.
In that time period blended milk market butterfat in FMO 40 climbed from 3.50% to 3.75%.     Protein in comparison changed very little.

Genetic selection  and feeding  helped butterfat increase, but still holds back protein

Protein % is one of the most heritable of linear trait measurements.   Why do we not gain more protein yields?    This is important again after a generation of focusing on butterfat %.    This has been related to the continuing insistence on “higher PTA Milk” in sire selection, still followed by the larger AI systems.   They sell what they have, because they breed future bulls from the past success;  but this is done in a vacuum of understanding the limitations on performance that the prior selection emphasis has placed on the current breeding population.

One of the major limiters of higher protein yields is selecting for high angularity physiques.   The AI industry has ignored “Body Condition” as a genetically selectable trait.    Linear type has favored the high angularity type cow since 1970, and it has taken a toll on herd fertility.  

“First service conception” has fallen 1% per year in the first 30 years of “linear”

This data came from a conversation at an NAAB technical conference held around 2000.   (The reports from staff inseminators in the largest AI system at that time were this data’s source. )
It is noted that type scoring in all dairy breeds switched over from descriptive to linear methods from 1968 to 1972 – a highly suggestive coincidence.      What else could contribute to this?   The first Net Merit composite index (created by Dr Cint Meadows at MSU) shifted sire ranking from pounds of butterfat to pounds of milk, and the linear preference for “angularity” defining “dairy quality” came from corn feeding trials at MSU and other colleges following USDA’s lead in crop subsidies for corn and soybeans, rather than forage crops used for ruminant animals.

In other words, to make milk from corn instead of hay, we have to change the cow’s type.

Why such a trend in fertility?     First and most importantly, early indexes ignored fertility.   If a cow set a higher peak, she might extend her lactation.    Selection for bulls began to favor cows with the highest and most extended “peak” production.    Geneticists in that era truly ignored or had no understanding of how the genotype “rations” nutrient energy between four uses:

(One)      Finish growing  (first lactation cows were only 2/3 grown at that time)
(Two)      Make a lot of milk volume  (encouraged by new milk order fluid premiums)
(Three)   Put some useful nutrient solids in the milk  (butterfat, protein, lactose)
(Four)     Breed back as required to optimize productive life  (recover rearing cost)

What did selection favor?     Geneticists assumed all lactation “curves” were identical, and that culling the lower PD Milk yield bulls would also cull the cows that did not milk for 305 days.    As we now know, the cows with the longest productive life and the most regular calving tend to be the more persistent, “flat” lactation curve cows.     “Flat”, persistent lactation curves allow for a great many benefits:   Lower ration costs…   Lower reproduction costs…   Less metabolic disease and fewer veterinary costs…   less fluctuation in Body Condition score.     Taking a lesson from the Beef breeding industry and Grass dairymen, biologists observe that body condition score is highly correlated with optimal reproduction rates.

Cows in a “negative energy” state produce less protein and are slower to breed back.

Until a cow is on a positive energy plane, protein produced in the rumen will be converted into energy in the abomasum and absorbed to help the body keep up with its total energy demands.   Thus less protein shows up in the milk… and repro is slower.    Cows with lower Body Condition scores (condition lost from setting aggressively high peaks early in lactation) usually require Ov Synch intervention to get back with calf.    

Sires with “plus” PTA Protein % values are thus more likely to sire cows with optimal fertility.     

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