Penney, C. D., B. G. Lowman, N. A. Scott, and P. R. Scott. “Repeated Oestrus Synchrony and Fixed Time AI in Beef Cows at Pasture”. The Bovine Practitioner, vol. 1997, no. 31.2, May 1997, pp. 19-21, doi:10.21423/bovine-vol1997no31.2p19-21.