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In reply to the discussion we had at Wellingtons about whether red stags can achieve puberty in their first autumn, here is the gospel according the Geoff Asher:

Stag puberty normally occurs between 12-15 months of age, during which time spermatogenesis is initiated. While absolute timing is influenced by growth and body mass, by in large it is constrained by photoperiod. Generally, even very well grown stags are still constrained from entering puberty until the end of their second summer/start of their second autumn, because they are not sufficiently photoperiodically responsive in their first summer/first autumn.

However, there have been reported incidences of precocious puberty in R1 stags (termed ‘bolters’) over the years. In these cases the stags go through their first antler cycle during their first year, casting the antler during spring and initiating the next antler cycle. These individuals are invariably extremely well grown stags leading up to the completion of their first antler cycle, although often go into a severe growth slump after casting their first antler (probably related to entering a precocious rut cycle) to the point that any growth advantage they have over herd-mates is lost as they become an R2.

It became apparent to me some years back when I was focussed on earlier calving in red deer at Ruakura (mainly through use of exogenous melatonin) that these ‘bolters’ were invariably born earlier than their herd-mates, and that their size advantage was largely through being born earlier (in some cases as early as mid-September). Animals of near equal body mass born during the normal calving season did not enter precocious puberty. I therefore hypothesised that ‘bolters’ represented individuals that had, by virtue of their early birth date, acquired sufficient photoperiod responsiveness by their first autumn to undergo the transition into puberty as R1s. I also saw this phenomenon in fallow deer, in which females ovulated and got pregnant in their first year (which proved disasterous as the does underwent severe birthing difficulties). I did not observe precocious puberty in any female red deer.

With the selection of rapid R1 growth traits in red deer (i.e. the strong focus on W12 in DEERSelect) we are now producing stags that way surpass the growth rates that I was getting on Ruakura but I have not observed or had reported any significant increase in the incidence of ‘bolters’. However, as DEERSelect also focusses on early calving traits (CDATE), I do foresee a time when ‘bolters’ may become a significant issue. Already we have herds that are consistently calving in mid-late October.