How many cows do you need to breed to dairy AI?
The genetic potential of an animal initially comes from the average of both sire and dam figures; therefore mating your best females to dairy AI is as important as selecting the correct bull team, James Dunne, Teagasc Dairy Specialist, explains more.
As always there should be particular focus placed on breeding the maiden heifers to dairy AI, as these should be your highest genetic merit animals. Thereafter the question is how many cows do you need to breed to dairy AI to ensure adequate numbers of replacement heifer calves? This number will depend on the number of heifer replacements required and also whether the semen being used is conventional, sexed or a combination of both. Reducing the number of cows that need to be bred to dairy AI will increase the genetic merit of your replacement heifers, reduce the number of dairy male calves bred on farm, while increasing the number of cows bred to high Dairy Beef Index (DBI) AI bulls - thus increasing the beef merit of your calves.
Worked examples
See worked examples below where a 100-cow herd requires 22 replacements heifers. In these examples, we examine how many cows need to be bred to dairy AI depending on the breeding plan for the maiden heifers and the type of semen being used. The remainder of the cows are available to be bred to high DBI beef AI. In each of these examples, the conception rates used are guide and somewhat conservative to ensure enough replacement heifer calves are born. There shall be herds that will achieve higher results. Trial work would show, on average, a 10% lower conception rate when using sexed semen over conventional semen, although the number of animals that need to bred to dairy AI reduces. These examples assume a 100% submission rate with the maiden heifers and 90% with the milking herd in the first three weeks of breeding. It also assumes that all dairy AI is used in the first three weeks. The probability of getting a heifer calf using conventional semen is 50%, while it stands at 90% if using sexed semen.
Example 1
Example 1: Conventional dairy AI on both the maiden heifers and the cows
| Straws | Conception (%) | Number of heifer calves | |
|---|---|---|---|
| Maiden heifers sexed straws | 0 | 55% | 0 |
| Maiden heifers conventional straws | 22 | 65% | 7.2 |
| Total | 22 | 7.2 | |
| Straws | Conception (%) | Number of heifer calves | |
| Cows sexed straws | 0 | 45% | 0 |
| Cows conventional straws | 55 | 55% | 15.1 |
| Total | 55 | 15.1 |
| Total heifer calves from cows and heifers | 22.3 |
|---|---|
| Total sexed straws | 0 |
| Total conventional straws | 77 |
| Total dairy straws | 77 |
In example 1, using all conventional dairy AI will mean that seven heifer calves are produced from the replacement heifers when a 65% conception rate is assumed. Assuming a slightly lower 55% conception rate, 55 cows must be bred to conventional dairy AI to produce the further 15 heifer calves required. Therefore, 22 dairy-bred males shall also be born on farm during the same period. There shall be 35 cows bred to high DBI beef AI in the first three weeks when a 90% submission rate is assumed.
Example 2
Example 2: Sexed dairy AI used on the maiden heifers with conventional dairy AI used on the cows
| Straws | Conception (%) | Number of heifer calves | |
|---|---|---|---|
| Maiden heifers sexed straws | 22 | 55% | 10.9 |
| Maiden heifers conventional straws | 0 | 65% | 0 |
| Total | 22 | 10.9 | |
| Straws | Conception (%) | Number of heifer calves | |
| Cows sexed straws | 0 | 45% | 0 |
| Cows conventional straws | 40 | 55% | 11.2 |
| Total | 40 | 11.2 |
| Total heifer calves from cows and heifers | 22.1 |
|---|---|
| Total sexed straws | 22 |
| Total conventional straws | 40 |
| Total dairy straws | 62 |
In example 2, using dairy sexed AI on the maiden heifers will mean that 11 heifer calves are produced from the replacement heifers, assuming a 55% conception rate. Assuming the same 55% conception rate, 40 cows must be bred to conventional dairy AI to produce the further 11 heifer calves required. Therefore, the number of dairy-bred males born on farm during the same period has reduced to 12. The number of cows bred to high DBI beef AI in the first three weeks increases to 50.
Example 3
Example 3: Sexed dairy AI used on the maiden heifers and cows
| Straws | Conception (%) | Number of heifer calves | |
|---|---|---|---|
| Maiden heifers sexed straws | 22 | 55% | 10.9 |
| Maiden heifers conventional straws | 0 | 65% | 0 |
| Total | 22 | 10.9 | |
| Straws | Conception (%) | Number of heifer calves | |
| Cows sexed straws | 28 | 45% | 11.3 |
| Cows conventional straws | 0 | 55% | 0 |
| Total | 28 | 11.3 |
| Total heifer calves from cows and heifers | 22.1 |
|---|---|
| Total sexed straws | 50 |
| Total conventional straws | 0 |
| Total dairy straws | 50 |
In example 3, using dairy sexed AI as seen above will mean that 11 heifer calves are produced. Assuming a conservative 45% conception rate, 28 cows must be bred to sexed dairy AI to produce the further 11 heifer calves required. The number of dairy-bred males born on farm reduces to three due to 90% female probability of sexed semen. The number of cows bred to high DBI beef AI in the first three weeks increases in this example increases to 62.
Summary
In summary, it’s important to work out how many cows you need to breed to dairy AI for your own farm. The best predictor of future performance is past performance, so look back at previous breeding seasons and make an informed decision. The use of sexed semen will ensure you breed your replacement females from your best cows, reduce the number of dairy-bred male calves born on farm, while increasing the beef merit of your calf crop. The obvious concern when using sexed semen is reduced conception rates. Therefore consideration must be given when selecting the animals for sexed dairy AI, the timing of AI and the handling of the straws. The reduction in conception rate is somewhat offset by the fact that its only being used on a percentage of the herd and allows for a larger proportion of the herd to be bred to conventional high DBI beef AI at normal conception rates. Each individual herd should consider how much of their dairy AI should be sexed based on the previous year’s breeding performance.
More information
In the video below, Dr. Stephen Butler, Teagasc Moorepark, gives an overview of how to maximise the success of using sexed semen during the breeding season.
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