Linear type trait genetic trends in Irish Holstein-Friesian dairy animals

The objective of the present study was to investigate the genetic trends of 18 subjectively scored linear type traits describing animal morphology, as well as udder, teat, feet and leg conformation. The analysis was undertaken using 2,932,700 Holstein-Friesian females born in the Republic of Ireland between the years 2000 and 2020, inclusive. The results indicate that Holstein-Friesian females have progressively become shorter in stature as well as shallower (i.e. body depth) and less angular. The reduction in genetic merit for stature score since the year 2004 was, however, only observed in non-herdbook-registered heifers. Furthermore, the reducing score in body depth (i.e. narrower) and angularity (i.e. less angular) was approximately twice as fast in non-herdbook-registered heifers as it was in herdbook-registered heifers. Differences in the genetic merit of the body-related traits for calves born versus those that became cows only existed prior to 2010 with little biological differences thereafter; this observation was common across most of the linear type traits. Genetic merit for locomotion in non-herdbook-registered animals has deteriorated over the 20-yr period, while the foot angle over that period is becoming lower; no such trends were observed for the herdbook-registered animals. Large differences not only in the trends themselves, but also in the mean genetic merit for udder traits existed when comparing herdbook-registered calves versus non-registered calves. In conclusion, genetic merit for many of the traits evaluated has trended relatively consistent in a given direction, albeit the cumulative change in genetic s.d. units per traits over the 20-yr period was very small.