Selection to improve natural fertility in your herd

If there is one trait that has more impact than any other on the voluntary culling of dairy cows today, it is failure to breed back.  The trend of lower natural fertility has been a long time coming:   The oldest national AI stud  (at one time they had 1800 inseminators submitting breeding receipts, used to calculate sire conception rates)  reported that in their first 30 years using frozen semen, conception average fell 1% per year  (from 70% non-returns to 40% non-returns).

The AI industry used to explain this away to dairymen as, “well, the heavy milking cows take longer to breed back”.    But looking at genetic trend across those years (prior to Genomics) Holstein cows were only increasing production at a rate of 100 pounds per year (500 pounds per generation “genetic base change”) which is less than 2 pounds of milk per lactation day.   Surely nutritionists could overcome this?

Fertility rates are negatively correlated to increased peak production selection
In the dairy world prior to 1970 the majority of cows were fed forage based rations, which often meant some seasonal pasturage.    Dry hay was the primary forage, supplemented by corn silage at least in the winter (to replace pasture grass).     In those days, higher production cows tended to have “flatter” lactation curves, and cows who milked the most did from lactation persistency.

1970s dairy extension researchers changed the lactation profile of cows by selection, in favor of cows who made more milk from corn and oilseed supplementation.   This has led to dairy forage supplies on expansion dairies being corn silage based, rather than pasture, dry hay, or haylage.   The cows who set the highest “peak” daily production when fresh were the cows who made more milk from corn (and oilseeds) than they did from hay and/or grasses.    So Dairy Extension taught sire analysts and nutritionists to favor cows who set higher peaks, even if it meant they shed most of their body condition to meet the negative energy balance that causes.  

Useful measurements available today
A weakness in linear trait data is that the graphs lead you to believe all traits may have the same heritability.    This in fact has NEVER been true.    Sire conception rates are around 4% heritable; daughter conception rates around 6% heritable;  those levels are not high enough to change the genetics of your slow-breeding cows around to better fertility in your replacements.   IF you use OvSynch (timed breeding) reproduction, the heritability of  Daughter Pregnancy Rate (PTA- DPR) is closer to 15% heritable, but there is no data to suggest this also applies to natural heats.    If you choose to follow “aAa” you will find that aAa 5 Smooth bulls’ daughters have healthier body condition and avoid negative energy states, thus show better natural fertility response.