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Heteropaternal twins refers to twins with different sires. A new study by ICBF reveals how many twin calves have different sires. Twining rates in cattle range from 1% to 5% depending on the breed with dairy breeds typically having the highest rates. Heteropaternal superfecundation (HS) occurs when two or more eggs are fertilised by two or more males during the same reproductive cycle. Typically, HS in cattle is reported when the sire’s breed is phenotypically different such as a Hereford and an Angus sire.

With ICBF recently passing 1 million animals being SNP genotyped and a reported case from a farmer led to the investigation of the ICBF database to identify the rate of bovine HS.

Irish Beef and Dairy farmers allow their cattle to graze for long periods each year if the weather conditions are suitable. AI and stock bulls are often used on Irish Farms with the latter often used a clean- up for any animal that does not become pregnant after AI.

On average, there is approximately 2.14m calves born in Ireland every year and 36,600 sets of twins are born which equates to 1.7% of all calves born. The study was done on 366,000 twin calves recorded on the ICBF database between 2008 and 2017 excluding any embryo transfer calves.  The HS rate was determined using only twin sets for which both calves and the sire were genotyped.


The research established that around 1% of all twins were HS twins with two different sires while the rate of identical twin calves is 5%. Genomics has played a pivotal role to identify HS twins when the sires are of the same breed.

This information is extremely valuable to help clarify why twin dairy and beef animals can have different genomic evaluations.