Use sexed semen and genome testing to get best replacement herd

By Mario Mongeon

When visiting dairy farms, I am often surprised to see the number of heifers. In many cases, pretty much all females born on the farm will be raised and eventually milked. I often ask why such and such animal was raised and the reason is often vague. It usually involves what I call the insurance factor: keeping everything in order to try them out; and making sure that a potentially outstanding milker stays in the herd.

This insurance factor can involve more requirements in terms of labour, barn space, feed and so on. In the long run, the insurance factor becomes costly. What if only the best animals were raised? What if the size of the replacement herd and replacement rate were reduced? The outcome would be substantial financial and labour savings and superior replacement animals.

Selecting and culling is a balancing act that includes economics, milk production, and genetic progress. The selection process can start by ranking animals based on a simple number: their Lifetime Profit Index or LPI. This index is a valuable overall genetic selection tool and considers factors such as production, durability, health, and fertility. LPI aims to identify animals that are expected to transmit superior genetics to their progeny, which makes them more profitable.

For heifers, the LPI value is based on parentage only as no specific data exists for a heifer which has not yet begun milking. There is a new tool that can be used to increase the accuracy of predicting the genetic potential of an animal used to make the selection decision: genomics. Genomic testing looks at specific DNA markers of genes that influence key production traits. These markers are distributed across the chromosomes that compose the genetic makeup of a specific animal. Genomic testing panels come in different sizes based on the number of markers analyzed. Using genomics to select heifers increases the rate of LPI progress made versus traditional selection methods. Genomic testing can be done on dairy calves at an early age, giving valuable information on the genetic value of a potential dairy replacement heifer.

Once the cows and heifers are ranked from highest to poorest LPI value on a piece of paper, the breeder is better equipped to visualize the selection process. Three groups of animals should emerge from this list: the Keepers, the Maybes and the Goners. Other factors might be used to move cows from one group to another such as temperament, or other characteristics not accounted for by the LPI index.

The Keepers are cows and heifers with LPI values above the herd average. Replacement animals should mainly come from these dams. They should be bred with excellent sires in order to optimize genetic gain. Using sexed semen for this group can be beneficial since it can shift the sex ratio of live calves from the standard 50:50 to an average of 90 % females and 10 % males or 90:10 ratio. This can prove invaluable to optimize the number of females born from the best individuals of the herd. Since the fertility of sexed semen may be reduced, it is advisable to privilege its use on heifers.

The Maybes includes animals with average LPI values and may, if needed, give rise to some replacement animals. The number of replacements raised from this group should be kept to a minimum. The Goners are the tail group, LPI wise. Although you will want the milk from these animals, you do not want to keep any heifers as replacements. Since the decision to not keep the calf is already made, breeding should be made accordingly.

Once you know the composition of the Keepers group, it is important to define how many heifer calves will be kept annually for replacement purposes. A good starting point is to have a look at the table below. This table gives the number of replacements to keep annually for a hundred milking cow herd, according to different replacement rates and age at first calving. Find the situation that best describes your farm and look at the number of heifers you should have in your barn at any given time. How does that compare to your actual numbers?

Age at first Replacement rate (%)

Calving (months) 25 % 30 % 35 %

24 26 31 36

26 28 33 39

28 31 36 42

Mario Mongeon is an OMAFRA livestock specialist based in Alfred, Ont.