Angus calves born and raised at high altitude adapt to hypobaric hypoxia by increasing alveolar ventilation rate but not hematocrit1

Abstract

The objective of this study was to evaluate the effect of altitude on arterial blood-gases and hematocrit in Angus-based calves. It was hypothesized that alveolar ventilation rate, as indicated by arterial pCO, would increase with altitude but hematocrit would not. Five Angus-based herds ( = 30 to 80 per cohort) located at 105 m, 1,470 m, 2,010 m, 2,170 m, and 2,730 m above sea level were enrolled in this prospective cohort study. A portable analyzer measured blood-gas tensions in coccygeal arterial blood. Calves at 1,470 m, 2,170 m, and 2,730 m were sampled twice, at approximately 4 mo and 7 mo of age. Calves at 105 m and 2,010 m were sampled once, at 7 or 4 mo of age, respectively. Linear regression analyses were used to determine the fixed effect of herd (a proxy for altitude) on the 4 outcome variables pCO, pO, pH, and hematocrit, while controlling for age and sex. As hypothesized, alveolar ventilation rate increased with altitude ( < 0.001). Hematocrit, however, did not show a clear association with altitude except for an increase from 105 m to ≥ 1,470 m ( < 0.001). Arterial pO decreased significantly with increasing altitude in calves at 4 mo and 7 mo of age ( < 0.001). The adjusted mean values of the 4 variables studied were similar at 4 and 7 mo of age for all of the herds studied. This indicates that suckling calves show minimal respiratory or erythrocytic adaptation to hypoxemia and hypocapnia with increasing age, regardless of altitude. We propose that the lack of an erythrocytic response in hypoxemic calves born and raised at high altitude prevents a deleterious increase in viscous resistance and, consequently, pulmonary arterial pressure. This physiological response, or lack thereof, may be a survival adaptation in a species predisposed to hypoxia-induced pulmonary hypertension.

Hematological and vasodilator characteristics for high altitude acclimatization in Holstein heifers ascended to high altitude

“…In most mammals alveolar ventilation improves during hypoxemia to help them maintaining a normal blood oxygen content and arterial oxygen tension [29]. Increased alveolar ventilation, as indicated by decreased arterial PaCO 2 , by increasing altitude was previously reported in Angus cattle [2]. In the present study, the lower PaCO 2 in AH and CB than in the other cattle breeds suggest that both AH and CB improved their alveolar ventilation rate.…”

“…The mPAP in CB, AH and LH did not reach statistical significance (P > 0.05). The low barometric pressure at high altitude causes pulmonary hypoxia, which result of high prevelance of HAPH in Holstein and Angus [2,3,16]. However, Tibetan cattle (Bos taurus) is an native breeds inhibitng at elevations lower than 4,000 m it adapting at high altitude [7].…”

“…High altitude hypoxic environment presents extreme challenges for cows because they have a small lung volume relative to oxygen consumption [1,2]. Holstein and Angus cattle at high altitude were found to have high prevalence of brisket disease (BD) [3,4] that imposes huge financial losses to farmers.…”

Hypoxia induces an increase in intestinal permeability and pulmonary arterial pressures in neonatal Holstein calves despite feeding the flavonoid rutin

“…Unlike rodents and other mammals, cattle are reported to be particularly susceptible to hypoxemia due to their small lung volume relative to body mass (Jensen et al, 1976;Veit and Farrell, 1978;Kainer and Will, 1981). Immature lung function (Lekeux et al, 1984;Neary et al, 2014), respiratory compromise, and hypobaric hypoxia (Gulick et al, 2016) could all feasibly contribute toward a hypoxia-induced increase in intestinal permeability with deleterious consequences on animal health. Hypobaric hypoxia, even at the modest altitude of 975 m, appears to have predisposed the normoxic control calves in our study to pulmonary vascular remodeling, as no difference occurred in the proportion of calves with at least mild arterial lesions between those housed under hypoxic conditions versus normoxic controls.…”

N-carbamylglutamate restores nitric oxide synthesis and attenuates high altitude-induced pulmonary hypertension in Holstein heifers ascended to high altitude

“…Acute altitude exposure results in marked reduction of arterial oxygen saturation and oxygen supply to the cardiovascular system [5], whereas it increases mPAP in unadapted individuals. This disease commonly occurs in beef and dairy cattle grown at high altitudes, and there is currently no effective therapy [6–8]. …”