Friday, September 22, 2017

Anecdotal evidence of the heritability of fertility

All of us are aware of the relentless pace of new technology adapted to dairy management.    Within my lifetime we have seen the development of “OvSynch” hormones for heat synchronization, and then there came the radio pedometer system for natural heat detection.    There are signs that radio pedometers may already make “OvSynch” obsolete as the more effective reproduction management tool (as well as the way to avoid future issues with consumer concerns over synthetic hormones in the food supply)..

One of the farms where I have analyzed for 22 years made the switch from Ov Synch to pedometer heat detection on 400 cows.   Radio pedometers now provide an every-milking milk weight and conductivity (mastitis) score.   Cows in heat are not only identified, but an optimum time of breeding calculated. 

This farm has been selecting service sires on both maternal pedigree longevity and sire DPR rankings for several years, at least three generations for new heifers calving.    The herd manager walking pens would constantly see cows in heat, and found veterinary advice to “just breed on O/S” counterintuitive.  
He had an epiphany:  I have been selecting for fertility but my management system is not testing to see if that selection had any impact.     When their milking equipment dealer presented the radio pedometer option, he was ready to give it a try.

Comparing the up-front costs of radio pedometers and computer links to the ongoing costs of Ov-Synch, the initial calculations showed a four year payback.  ( Dropping once a month DHIA for daily real-time milk weight downloads made it 3.5 years. )   20% savings in semen used per pregnancy made it a 2.5 year payback.      As suspected, genetic selection for fertility had made the Ov-Synch program obsolete. 

More evidence of the heritability of fertility

One of our customers recently proactively assembled their veterinarian, nutritionist, DHIA consultant and major semen supplier for a conference to review the farm’s data and trouble shoot why conception rates are consistently below the goals of the owners (unchanged for several years).    I was invited to sit in as having recently analyzed all the milking herd (after ten years of random mating during expansion).

This farm milks 500 cows, which are housed as six groups in three free stall barns and fed by TMR. 
Production (which was at 90 pounds with 250 cows prior to ten years of expansion) is hovering a bit above 80 pounds, with higher than breed average components, but below the goal of the nutritionists.    Three individuals (two owners plus a key herdsman) do all the AI.    

After a general discussion to familiarize all these advisors with the veterinary, farming, feeding and milking practices, the three who inseminate had some practice with repro tracts and the AI rep made some pointers as to proper site of semen deposition.     (Avoid going too deep into any uterine horn.) 

No one questioned the role of genetics in large herd fertility.    The veterinarian figured they were doing everything “right” as far as vaccinations and herd health protocols.   The nutritionist found the feed quality to be equivalent to other high production herds.    Discussions eventually focused on how long cows stand in the (partially uncovered) holding area for milking, which (especially in summer heat) is a critical factor in retaining early pregnancies (body temps above 105F in sun can cause abortion of early stage pregnancies, undetected because the cow is able to recycle on her normal interval).   Major building modification (and maybe a faster parlor some day?) was the only real solution to this issue.

But if nothing is “wrong” in the daily routine, why do the cows not get bred?    It is exactly at that point that prior genetic choices must be considered.    The DHIA consultant agreed to run a profile on the sire stacks behind these cows, to see if there is a pattern between sire DPR and cow conception.

As of the latest DHIA test day, this farm had 112 cows confirmed as pregnant, whose sires were known.   Of those 112 cows (roughly 25% of the total herd, half of the sire ID herd) the data fell into four groups:

Bottom 25%:    sires’ PTA for DPR (- 1.725 or lower)      cows averaged 157 days open
The next 25%: sires’ PTA for DPR (- 0.35 to – 1.724)      cows averaged 166 days open
The next 25%:  sires’ PTA for DPR (+ 1.04 to – 0.35)      cows averaged 143 days open
The best 25%:  sires’ PTA for DPR (+ 1.05 or higher)      cows averaged 125 days open

Further examination (cows with known sire and grandsire recorded by DHIA) to compare “pedigree index” for DPR vs realized days open had 55 cows confirmed pregnant, as follows:

Bottom 25%: pedigree index DPR –0.865 or lower:         cows averaged 155 days open
Next 25%:     pedigree index DPR –0.35 to –0.864           cows averaged 206 days open
Next 25%:     pedigree index DPR –0.34 to + 0.59           cows averaged 156 days open
Top 25%:      pedigree index DPR + 0.60 or higher          cows averaged 121 days open

The real point of this data (supported by comparison of average DPRs for sires by birth year) is that until 2015 (when a change was made in who purchased semen) no consideration was given to the DPR values of sires purchased.   The breeding selection was random and based on how much PTA milk could be had for a special price.  Until 2015, the average PTA DPR for all sires was negative three years out of four

No comments:

Post a Comment