Dairy Cattle Genetics: Traits to Cultivate

After graduating from university, I spent a short time managing the family farm. One of the more memorable additions I made to the dairy herd was a heifer named Miranda. She brought with her a special talent-an aversion to being milked. What's more she could hit! She was big, strong and accurate. She was the Mark McGwire of the cow world. And, unlike the famed home run hitter, she didn't need performance-enhancing drugs.

Miranda's first swing usually took care of the milker unit and the next, a part of the anatomy of the poor unfortunate trying to place the machine on her udder, pick up the pieces or otherwise deal with this deadly force of the animal. Occasionally, she would do a "change-up": clobber the person good and hard first and then polish off the milker unit. Unfortunately for my father and my brother-in-law, who subsequently took over the farm, Miranda was a well above average milk cow. So she stayed around and even blessed the farm with two female offspring. Both turned out to be big, black, strong cows like their mother... and carried on the family tradition.

Temperament is important, especially when you are on the receiving end of a rather large cow's vindictiveness, fear or whatever compels her to be difficult.

Calving ease and milking speed are rather important to many dairy farmers as well. Calving ease is especially important when you make decisions about breeding heifers. The incidence of dystocia or difficult calving with first-lactation heifers is double that of later lactation cows. Milking speed is important to someone milking cows in a double-fourteen parlour when there seems to be just the right number of slow milking cows to have one in each string entering the parlour.

These characteristics are usually called auxiliary traits. That's truly a misnomer for a rather diverse group of traits for which we collect information, evaluate dairy cattle and publish genetic evaluations so we can improve them. If we have to group these traits by name, let's get rid of the term auxiliary. Maybe we should call them workability or functionality traits because they are a measure of how functional cows are in a dairy setting.

If we want evaluations of these traits to be useful, the industry needs to do a better job of recording the related data. That means the owner or operator needs to write down notes on animals at the right times.

Calving ease

To record calving ease, choose the category that best fits the relative difficulty of the calving (see Table 1) and write it on the DHI event calendar when you record the calving event of each cow.

Difficult calving incidence with first lactation heifers is about 8.7 per cent-about double that of later lactation cows.

Calving ease is really two traits: direct, or how easily or difficultly the calf is born, and maternal, whether the mother is prone to more or fewer difficult calvings.

Research at the University of Guelph by Dr. Paul Boettcher and co- workers found that heritability is low to moderate for direct calving ease at about 0.20. The heritability for maternal calving ease is about half that.

Direct calving ease and maternal calving ease have a small positive genetic relationship. Contrary to popular belief, a calf that was calved easily will tend to calve easily herself as a cow. The Guelph study also found that calving ease has a negative genetic relationship to sire ETAs (estimated transmitting abilities) for frame and capacity.

These results indicate daughters of bulls that transmit large body size are not only born with more difficulty but they may also have more difficulty when giving birth themselves.

Recent research at Iowa State University also linked difficult calving and sire proofs for traits related to size, with a positive correlation of about 0.35.

Bulls that transmit more size will also transmit more calving difficulty, possibly related to calf size. Both studies indicate that as we select for larger size in dairy cattle, we might increase calving difficulties.

When using this information for sire selection, most breeders use calving ease proofs to avoid using difficult calving sires on virgin heifers.

Milking speed

Milking speed is measured in first lactation only. Slow Milker ranks ninth in the list of disposal reasons in Ontario DHI herds, followed by Bad Temperament in 10th place. In Quebec, PATLQ data ranks these in reverse order at 12th and 13th. These reasons aren't the highest on either list by any means, but are significant factors in why cows are culled.

Temperament

Temperament is the newest auxiliary trait. There aren't too many explanations of how it's measured or reported.

Temperament is only measured in the first lactation. It's best to measure temperament during the second test day, or the second month in the lactation. This gives the heifer some time to become accustomed to the milking routine before you evaluate her.

Milking behaviour has a heritability of about 0.16 and it's positively related to ease of handling, as well as milking speed. There seems to be no relation with another aspect of cow behaviour: aggressiveness at feeding. Even though a cow may be rated calm or very calm for milking temperament, the scoring should bear no relation as to how she fends for herself at the feed bunk.

Table 1: Recording Auxiliary (Functionality) Traits

Trait	Measured on:	Categories:
Calving Ease	All Cows	Unassisted Easy Pull Hard Pull Surgery
Milking Speed	First Lactation	Very Fast Fast Average Slow Very Slow
Temperament	First Lactation	Very Nervous Nervous Average Calm Very Calm

Reading Sire Proofs

The heritability of these functionality traits is low to medium, in the 0.10 to 0.20 range for all three traits. Genetically, this means there's little variation due to additive genes being passed on. However, they are worth selecting for-some progress can be made.

Observations are best made within the herd and are most accurate when made by the owner or operator. A reasonably accurate bull proof requires records from 75 to 100 daughters, so it is important that information is obtained from every daughter possible and that it's recorded accurately (see Table 2). The information is best used to avoid the extremes rather Than make measurable differences in genetic gain, such as we would for milk production.

Table 2: Reading Sire Proofs

Trait	Reported As:	Average Sire Proof	Normal Range
Calving Ease	% Easy and Unassisted	85 %	75 % to 90 %
Milking Speed	% Fast and Average	69 %	55 % to 80 %
Temperament	% Average to Very Calm	90.2 %	70% to 97 %

Table 3: Heritability of Traits

Heritability
Calving Ease	0.20
Maternal Calving Ease	0.08
Milking Speed	0.20
Milking Temperament	0.16

Dairy producers do take proofs for auxiliary traits into consideration decisions but they also have some criticisms of the information.

"Most are average anyway." This is a common complaint about the observations and the ratings. This is as it should be - most will be average. It's truly the extremes that we want to identify.

We want to avoid breeding to sires that produce a high percentage of difficult calvings, extremely slow milkers, cows with poor temperament and so on.

"The evaluations are not very accurate." The accuracy of the numbers really depends on the dairy producers who provide the information. You can help improve this by writing down calving ease when the calving is entered on the DHI event calendar. Write the milking speed rating on the event calendar before the DHI tester arrives for the first test after calving, and write down the temperament for first-lactation heifers before the second test in the lactation.

Avoid being put on the spot when it comes time to enter information on six or more cows and finding you have no written records.

In situations like that, lots of cows become "average" that might not have been otherwise, and useful information is lost. In some past situations, operators have recorded only 30 per cent of possible information. The old saying still holds: garbage in equals garbage out.

There's a renewed emphasis by DHI staff on collecting accurate auxiliary trait information. The genetic evaluation organizations commit a lot of money towards collection of these data and calculation of accurate breeding values. Something as simple as consistently marking events on the calendar when they happen will give us accurate and meaningful information to help avoid calving ease problems, slow milking and poor temperament.

Points to Remember:

     * Auxiliary traits should be considered to be workability or functionality traits.
     * The usual goal is to avoid the problems: very slow milkers, difficult calvings or extremely nervous temperament at milking.
     * Heritability of these traits is medium to low, but we can still select to eliminate problems.
      * The information is best recorded by the owner or operator.
     * We need to do a better job of recording milking speed, calving ease and temperament if the evaluations are going to be of any use.
     * Record events on the DHI calendar (available to all milk producers) in a timely fashion.

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Dairy Cattle Genetics: Traits to Cultivate

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