Between different breeds of boars, we also observed
differences in sperm output, with some interesting age
interactions. Boars first entered the stud at 7–9 months
of age. These young boars often had ejaculates
discarded for low volume or low concentration. Soon
after their initial collection, terminal line boars
(crossbred and purebred) will usually have passing or
processable ejaculates. These ejaculates are usually low
in sperm output, commonly producing between 8 and 15
doses (2.5 109 viable sperm per dose), but they meet
the minimum passing criteria for concentration and
volume. The maternal boar lines seem to lag behind by
approximately 2–8 weeks, before they consistently
meet the minimum passing criteria for concentration
and volume. Once they begin to consistently produce
acceptable ejaculates, they produced in the lower sperm
output range (8–15 doses per weekly ejaculate).
The terminal boar lines continued to improve in sperm
output as they grew older. Between the two crossbred
terminal lines and the purebred Duroc, they continued to
have similar sperm output as they got older. Looking at
general production reports, however, it appeared that the
crossbred terminal lines had more sperm output on
average than the purebred Duroc, due to slightly lower
trash rates. The crossbred boars were also noticeably
more physically durable, and had less health and
structural issues as they become the older boars within
the stud. Therefore, if boar culling within a stud is based
partially on natural attrition, the crossbred terminal lines
will have a higher percentage of older boars with greater
semen output potential. This can skew the production
data, and make it appear that the crossbred terminal boar
has a much greater sperm output than the purebred Duroc,
but in reality it is an age difference. If the boar stud has
culling practices that are more based on production, and
genetic indexes, and the supply of new boars is
consistent, then this stud will likely view the semen
output of the purebred Duroc as equal to that of the
terminal crossbreds. Then, the only major difference
observed with the purebred Duroc will be the slightly
higher trash rate and sensitivity to seasonal infertility.
Also, as boars matured, the maternal boars’ average
ejaculate volume increased and eventually surpassed the
average volume of all the terminal boar lines. This
improvement in volume that eventually eclipses the
terminal lines was mainly in seminal plasma and the nonsperm
fraction. The average sperm output of thematernal
boars continued to be less than the terminal lines, but the
volume was higher.
We also observed a noticeable difference between
breeds in their libido and the age at which they reach
puberty. Maternal lines appeared to be approximately 2
months behind the terminal lines. Nearly all terminal
line boars reached puberty and were receptive to
training at the boar stud between 6 and 7 months of age.
This value appeared to be 8–9 months of age for the
maternal-line boars, and there also appeared to be a size
component as well. The maternal boar that was 8–9