By W.L. Flowers, North Carolina State University Department of Animal Science
The majority of artificial insemination boars in the United States currently are housed in crates. Given the current movement to gestate sows in pens, boar housing may become a production issue that requires additional attention in the future.
As a result, we recently completed a study examining the effect of housing on spermatogenesis, libido and other behaviors in a cross-over design (Tosky et al., 2013). Boars were acclimated to either pens (6.5 x 8 feet) or crates (3 x 7 feet) for five weeks and then their behavior and performance were monitored over a 12-week period.
After this, boars housed in crates were moved to pens and vice versa and the study was essentially repeated — there was a five-week acclimation period and then 12 weeks of data collection. The five-week acclimation period is critically important for sperm production variables since spermatogenesis takes about 35 days in boars. What this means is that only ejaculates after Week 6 would contain mostly sperm that began and completed spermatogenesis under the new housing environments.
Behavioral responses were obtained by videotaping boars for six hours daily for five of seven days each week. Relative fertility was evaluated by mixing semen from a boar housed in crates with one of its counterparts housed in pens and then determining which individual sired each of the piglets in the resulting litters via DNA fingerprinting techniques. A summary of selected data from the study is shown in Table 1.
In general, housing type had minimal effects of sperm production and libido and did not influence estimates of boar behaviors or fertility. Boars in pens tended to make contact with the collection dummy sooner; stay on the collection dummy longer; and have higher ejaculate volumes compared with their counterparts housed in crates. Sperm concentration was not different (data not shown) so the advantage observed in total sperm per ejaculate was due to the increased volumes of the boars housed in pens.
There were no differences in the frequency of several types of behaviors often used to estimate frustration in boars between those housed in crates versus pens, at least during the recording period.
It is important to remember that in a cross-over design each boar at some point during the study was housed in both treatments — pen versus crate. The only difference was that some boars began in pens and were switched to crates while others were housed in crates first and then moved to pens. What is very interesting was that there were some boars (n=3) whose total number of sperm per ejaculate actually increased when they were moved from pens to crates as well as some whose sperm production decreased when they were switched from crates to pens (n=2).
While the overall trend was for boars housed in pens to have increased sperm production about 25% (five of 24) of those studied performed better during the period of the study in which they were kept in crates. Consequently, it is reasonable to speculate that there may be individual characteristics that vary among boars which allow them to perform better in one type of housing environment than another.