Or in other words, what are we trying to breed?
Holstein, Friesian (yes, they are now recognised in New Zealand as two separate breeds), Jersey, Ayrshire or a cross of two or more of them for some hybrid vigour?
Big and tall or smaller? Do we need better feet or are we more interested in a nice udder?
Or how about a cow that doesn’t kick the cups off at every milking, and gets in calf every year, and has low somatic cells and – well, it’s a bit of a list isn’t it?
To make it easy for NZ farmers we have the New Zealand Animal Evaluation (NZAEL) breeding worth known to everyone as BWs.
As we are continually breeding better animals, obviously the young ones are going to be better than their dads, uncles and definitely better than their great, great grandads so genomic bulls to be used for breeding tend to have the highest BWs.
BWs incorporate eight traits that are identified at the moment as having a measurable economic value to NZ famers – it ranks cows and bulls on their ability to breed profitable and efficient replacement dairy heifers.
The eight traits are milk fat and protein produced, milk volume, liveweight, fertility, somatic cell count, residual survival and body condition score.
Obviously, some of these traits are plus and others are negative – the more potential for milk fat and protein production the higher the BW score but high milk volume, high liveweight and high somatic cell counts lower it.
Each trait is financial, ranked on the influence of it on the economic value of the cow and these amounts change as the influence of them on farmers change.
The big one in the past few years is the increase in the weighting of milk fat.
So if your perfect cow is all about production and economics (smaller cows eat less) then you don’t need to look any further than BW.
However, there are also TOPs. Pronounced T – O – P, it stands for traits other than production and it is these you will see listed among bull lists on web pages and in those nice glossy catalogues.
TOPs include farmer-scored management traits (adaptability to milking, temperament, milking speed and overall opinion) and inspector-scored conformation traits (stature, rump angle, rump width, udder support, teat placement and a whole heap more.)
While much of the BW information comes from herd testing, TOPs comes from people who look at individual cows.
TOP inspectors evaluate daughters from sire proving schemes when they start lactating and this information, along with that from the farmers milking them, is fed into NZAEL for the bulls’ rankings.
Some of the TOPs might sound strange but they all have a purpose.
For example, rump angle is the angle from the middle of the hip to the top of the pin bone. A flat to slightly sloping angle (low pins) is what is desirable because cows with it calve easier.
The rump width is the distance between the posterior point of the pin bones in relation to the size of the cow and is a good indicator of the width of a cow throughout her body.
And the wider the cow, the more space she has to stick that 18kg drymatter (DM) of grass she should be eating each day.
Some bulls, though, are selected on the genes and are known as “genomic or “InSires” instead of “daughter-proven” bulls.
The bulls, as calves, have had their DNA profile examined to come up with their genomic BW (gBW).
As we are continually breeding better animals, obviously the young ones are going to be better than their dads, uncles and definitely better than their great, great grandads so genomic bulls to be used for breeding tend to have the highest BWs.
So it all sounds too easy doesn’t it? I’m not too happy with the teat placement of this cow so I’ll mate it with semen from a bull with really good figures for that trait.
Or I’m going to target fertility because I’m having problems getting my cows in calf.
Well, sorry, this is where nature gets involved. Just because you have brown hair, and your partner has brown hair, that doesn’t mean all of you kids will have brown hair.
It’s called phenotype variation. So, although your cow may have some really good genes for milk production, she will also have some not so good ones. She may pass on the good ones to her offspring or she may pass on the dud ones.
And then there’s this thing called heritability. Heritability tells us how much of the difference is due to genetics, as opposed to management or the environment.
The heritability of protein production is 31%, and in the thirties are milk fat, milk volume and liveweight.
That means about a third of a cow’s production is because of its genetics and two thirds because of how well she is fed and cared for. Somatic cell counts is down at 15% and fertility is a very low 9%.
In fact, coat colour (an extremely important trait for the economic NZ dairy cow) has the highest heritability.
There is a nice mathematical equation that explains it all: genetic gain in a herd is the result of selection intensity multiplied by heritability multiplied by phenotype variation multiplied by accuracy of selection. And all of that is divided by the generation interval.
In other words, the quickest way to increase your BW, or a trait that you want, is too use the sires with the highest proven genetics that you are wanting, identify the cows in your herd that have the desired traits and only keep calves from them and have excellent records so that you know that you are only keeping those calves.
Mating your heifers with the semen from your chosen bulls will tighten up the generation interval.
But, and it’s a big but, don’t go chasing fertility or rump angles to the detriment of milk production.
Milk production, the main thing that puts money into your bank account, should always come first – a bull should sire high-producing cows which also, fantastically, have great feet to make sure she can walk to the dairy every day.
Also check that those bulls are proven, either by genomics or by daughters milking.
And that is thousands of daughters milking in NZ – don’t pick some gorgeous looking bull with only five daughters which all live in a barn on one farm in Wisconsin.
The more data coming in from lots of cows milking across a multitude of farm systems and environments about a sire then the better the reliability. Don’t ever forget that.
