Abstract
Growing concerns have been expressed regarding cardiovascular performance in modern farm pigs, which has been proposed as a critical factor contributing to the reduced adaptability of modern pigs to stress. Here we tested the hypothesis that cardiac dimensions and pump function in modern heavy farm pigs are disproportionally low for their body weight, and investigated potential underlying mechanisms. The results from the present study indeed demonstrate disproportionally low values for stroke volume and cardiac output in pigs with bodyweights over 150 kg. Importantly, these low values were not the result of impaired left ventricular (LV) systolic contractile function, but were due to a disproportionally small LV end-diastolic volume. The latter was associated with changes in determinants of LV passive stiffness, including (i) an increase in LV myocardial collagen, (ii) a shift from the compliant N2BA titin isoform towards the stiff N2B, and (iii) a marked elevation of aortic blood pressure. Taken together, these results demonstrate reduced pumping capacity of the hearts of heavy modern pigs, due to structural abnormalities in the LV myocardium.
Highlights
We tested the scaling hypothesis for CO and SV in modern growing pigs and in adult sows at the end of their gestation, and found that, while CO and SV of pigs up to 75 kg scaled proportionally with BW11, adult sows demonstrated a disproportionally low CO and SV12
The present study was performed in modern farm pigs, covering a wide range of BWs, to test the hypothesis that cardiac weights, dimensions and function obey quarter power scaling laws
The main findings were that: (i) HW and left ventricular weight (LVW) increase commensurately with BW according to the quarter power scaling laws; (ii) CO and SV failed to increase proportionally to BW, which (iii) was not due to impaired left ventricular (LV) systolic function, but rather (iv) appeared due to a similar lack of proportional increase in LV dimensions, as measured with echocardiography and conductance catheter; (v) haemodynamic analysis revealed marked increases in arterial blood pressure, while analysis of myocardial tissue revealed increases in interstitial collagen content and in the stiff N2B titin isoform of the myocytes in animals with the highest BW
Summary
We tested the scaling hypothesis for CO and SV in modern growing pigs and in adult sows at the end of their gestation, and found that, while CO and SV of pigs up to 75 kg scaled proportionally with BW11, adult sows demonstrated a disproportionally low CO and SV12. We included two sets of pigs that had different genetic backgrounds, underwent different anesthesia regimens and were studied in different laboratory settings. In our previous study we did not further investigate the mechanisms underlying the disproportionally low levels of SV in adult pigs. In the present study we investigated the proportionality of the cardiovascular system over a wide range of BW (22–216 kg) in pigs of a single (female) sex, with a similar genetic background, undergoing invasive haemodynamic studies in a single laboratory using a uniform anesthesia regimen. In the present study we explored the mechanisms underlying the disproportionally low SV by assessing left ventricular dimensions as well as LV systolic and diastolic function, and by performing myocardial tissue analysis
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