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• Selection is the most powerful tool available to the dairy cattle breeder.
• Segregation is one factor responsible for variation in daughter performance.
• Mating services appear successful primarily as a result of improved sire selection.

Recently, a producer asked about the merits of mating strategies. He described his sire selection as choosing AI bulls from the 90 percentile with $550 and above for net merit.

This is an excellent sire selection strategy. Using outstanding sires will lead to an outstanding herd of dairy cattle. Selection is the most powerful tool available to the dairy cattle breeder. Who do you allow to have offspring and how many offspring do you allow? Answers to these questions have the biggest impact on the genetic progress that your herd will make. With my comment about sires, I do not mean to minimize the effect of the dams. Both the sire and the dam are important in determining the quality of the offspring . Segregation, a concept that influences the quality of the offspring, is both good and bad. The good part of the concept is that segregation can be responsible for creating new genetic combinations. These new genetic combinations could be offspring that are better than either parent. Unfortunately, for every offspring that is better than the average of the parents, an offspring is also worse than the average of the parents. Not all new genetic combinations are favorable. Outcome from segregation cannot be predicted or controlled. However, the variations in effects may be slightly less when mating inbred parents. Inbred parents will have slightly more homozygosity than the average individual. More homozygosity reduces the possible outcomes from segregation.

Segregation may require more explanation and the following example is given. If you are not interested in segregation, you may skip to below the tables.

Although segregation applies to most genes in an individual, only four loci (locations of genes) will be considered in this example. Two alleles will be at each locus and each allele will be responsible for a constant (although different) change in performance.

Table 1. Performance of alleles at each of four loci.

This individual will produce gametes with one allele from each of the four loci. An example gamete would be A1, B1, C1, D1 with performance values of +7, +10, +15 and +25 for a total performance value of +57. This gamete would give the best possible performance. The worst possible performance would come from gamete with alleles A2, B2, C2 and D2 with performance values of +5, -12, +3 and -40 for a total performance value of -44. Table 2 contains all of the possible gametes and their values that might be produced from this individual.

Table 2. All possible gametes and performance values.

Returning to sire selection strategies, the producer asked, “Would just using Net Merit give cows that will be around more then just a few lactations, and will they still have sound udders, legs and feet?”

If I just say yes to this question, you will be able to find examples of cows that do not survive. However, Net Merit is the best index to combine several important dairy traits and it does put significant emphasis on type. If you wish to place more emphasis on type, you could alter the index. Unless you are selling a large amount of breeding stock, I doubt if you will increase your return by altering the index.

“Or, would a genetic mating service enhance the breeding of the type traits?”

A genetic mating service may enhance the breeding of type traits by placing more emphasis on type in the selection of sires. Selection not the mating service is what will get the response. A caution regarding mating service is that your herd goals may be altered more than you anticipate. Does the mating service recommend a different set of bulls than what you were using? If yes, then that selection will take you in a different direction. Does the mating service increase the number of bulls that you are using? If yes, the contributions of the outstanding bulls will be diluted in your herd. Testimonials about successes from mating programs should most often be attributed to the improved sire selection that was practiced. I have seen no research studies that found a difference between randomly mating outstanding sires versus using them in a corrective mating program. To restate the bottom line, apparent improvements from mating programs are results of the improved sire selection rather than mating decisions.

”If you were going to use a mating service, do you feel the linear systems that the Bull Distributors use is a good program and would cover all that needs to be addressed or would Triple aAa be a better program to use?”

I think that you know by now that I am not likely to use a mating service. I prefer to bred the herd and see improvements in the herd rather than gamble on finding a great nicking mating. One reason I hesitate to seek a great nicking mating is that I want the genetic benefits to be transmitted to the next generation. A great nicking may be the result of epistatic effects (or particular gene combinations across several loci) that will not be maintained in subsequent generations. Selection for additive effects creates greater chances that the superior genetics will be transmitted to the next generation.

The linear system of bull distributors and Triple aAa are both consistent with finding improvement in additive inheritance. My concern with either system is the impact on changing the number of bulls, and drastically altering the selection goals. I would set selections goals first and then find the bulls to satisfy those goals rather than determining a mating for a particular cow and then later recognizing what that meant for your selection goals. Selection goals are trade-offs.