Calculate the number of females that you need to breed to Dairy AI

As always when breeding your replacement heifer calves there should be particular focus placed on breeding the maiden heifers to dairy AI as these should be your highest genetic merit animals. James Dunne tells us more.

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 but also reduce the number of dairy male calves bred on farm while increasing the number of cows bred to high Dairy Beef Index AI bulls thus increasing the beef merit of your calves.

See worked example for a 100 cow where there is a requirement for 25 replacements heifers. In this example all dairy straws used are female sexed semen and are all used in the first 3 weeks of breeding. The conception rates used are guide and should be adjusted to reflect past herd performance. This example assumes a 100% submission rate with the maiden heifers and 90% with the milking herd in the first 3 weeks of breeding.

As seen below 13 heifer calves are produced from the maiden heifers. Assuming a 60% conception rate to dairy sexed semen on the cows a total of 27 cows must be bred to dairy sexed semen to produce the further 12 heifer calves required. The number of dairy bred males born on farm reduces to 3 due to 90% female probability of sexed semen. The number of cows bred to high DBI beef AI in the first 3 weeks in this example is 63 therefore increasing both the beef merit and also the total sale value of the overall calf crop.

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. The example in question is for a herd achieving high levels of fertility performance, each individual farmer in consultation with their advisor should develop a plan that aligns with the herd’s fertility targets.