Pick of the Crop: Developing Your Selection Strategy
When visiting dairy farms, I am often surprised to see the number of heifers raised. 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. Examples of insurance factors have included: keeping everything in order to try them out; and, making sure that this potentially outstanding milker stays in the herd. Selecting based on actual results, not prediction is appealing to many. This can become very expensive. 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 quite costly. What if only the best animals would be raised? What if the size of the replacement herd was reduced? What if the replacement rate was reduced? These three objectives could potentially be met if a plan was put in place and a selection strategy was implemented. The outcome would be substantial financial and labour savings and superior replacement animals.
Selection and culling is a balancing act between economics, milk production, and genetic progress. In order to implement the best strategy, one needs to identify goals. Genetic progress goals will determine selection intensity and vice-versa. In order to achieve a fast genetic gain, the selection needs to be more intense. As the selection intensity increases, only the best cows and superior heifers will be selected to give rise to replacement animals and only the best bulls will be used as sires for replacement heifers. Calves from the remaining animals in the herd will not be kept for replacement purposes.
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 Maybe's 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 group consists of 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 might be reduced, it is advisable to privilege its use on heifers.
The Maybe's group 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 group is 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 Table 1. 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?
Table 1. Number of replacement animals kept annually for a hundred cow herd*
|Age at first calving
|Replacement rate (%)|
* Mortality rate from weaning to calving:2%
- Limit the number of heifers raised on your farm
- Raise only the best ones, it makes economic sense
- Define your objectives and develop a selection strategy
- Use new tools such as sexed semen and genomics wisely to improve your strategy
- Pay attention to calving dates in order to distribute replacements over the whole year
- Stick to your plan
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|Author:||Mario Mongeon - Livestock Specialist/OMAFRA|
|Creation Date:||October 2014|
|Last Reviewed:||November 21 2014|