| Abstract |
In view of the remarkable decrease of
the relative heart weight (HW) and the relative blood
volume in growing pigs, we investigated whether HW,
cardiac output (CO), and stroke volume (SV) of modern
growing pigs are proportional to BW, as predicted by
allometric scaling laws: HW (or CO or SV) = a∙BWb, in
which a and b are constants, and constant b is a multiple
of 0.25 (quarter-power scaling law). Specifically,
we tested the hypothesis that both HW and CO scale
with BW to the power of 0.75 (HW or CO = a∙BW0.75)
and SV scales with BW to the power of 1.00 (SV =
a∙BW1.0). For this purpose, 2 groups of pigs (group 1,
consisting of 157 pigs of 50 ± 1 kg; group 2, consisting
of 45 pigs of 268 ± 18 kg) were surgically instrumented
with a flow probe or a thermodilution dilution catheter,
under open-chest anesthetized conditions to measure CO and SV, after which HW was determined. The 95%
confidence intervals of power-coefficient b for HW were
0.74 to 0.80, encompassing the predicted value of 0.75,
suggesting that HW increased proportionally with BW,
as predicted by the allometric scaling laws. In contrast,
the 95% confidence intervals of power-coefficient b for
CO and SV as measured with flow probes were 0.40 to
0.56 and 0.39 to 0.61, respectively, and values obtained
with the thermodilution technique were 0.34 to 0.53
and 0.40 to 0.62, respectively. Thus, the 95% confidence
limits failed to encompass the predicted values of b for
CO and SV of 0.75 and 1.0, respectively. In conclusion,
although adult breeding sows display normal heart
growth, cardiac performance appears to be disproportionately
low for BW. This raises concern regarding the
health status of adult breeding sows. |