Impact of a 1;29 Robertsonian translocation on a herd of purebred beef cattle

This paper examines the spread and influence of a 1;29 Robertsonian translocation in a purebred beef herd. An entire herd of 94 Charolais cattle has been karyotyped since discovery of a 1;29 Robertsonian translocation in two yearling bulls entered in the Saskatoon R.O.P. bull test station in 1987. The translocation was inherited through their maternal grandfather. Approximately 46% (43) of the 94 cattle karyotyped possessed this translocation, including one cow which had two copies (58, XX, tt). The test herd consisted of 59 cows, 4 bulls, and 31 calves with 27, 2, and 14 animals affected respectively. In addition one cow with an additional X chromosome was detected (61, XXX). The overall fertility of this herd had been low but alterations in management practices lessened the negative impact. Prolonged bull exposure, first exposure of females at 2 y of age, and continued surveillance of cows returning to heat followed by rebreeding ensured that most cows did produce calves in most years. However, although such practices reduced the culling rate, they maintained the translocation carrier cows in the herd. Key words: Beef cattle, translocation, embryonic loss, subfertility