Funding for this research was provided by:
Biotechnology and Biological Sciences Research Council (BB/K006096/1, BB/K0070921/1)
Received: 20 January 2020
Accepted: 6 July 2020
First Online: 27 July 2020
Ethics approval and consent to participate
: The experiments were carried out at Roslin under the Animals (Scientific Procedures) Act 1986, project license 70/7909 and individual experiments were approved by the institute Animal Welfare & Ethical Review Body at the Roslin Institute. For comparison of the top and tail of the distribution no work involved experimentation on living animals. Material was collected at the end of the breeding cycle after euthanasia using an overdose of barbiturates.
: No applicable.
: The authors declare that they have no competing interests with the exception of WI, DC who are, respectively, employees of Lohmann Tierzucht and H&N.