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We have studied the pulmonary circulation of three closely related animals, the llama, alpaca, and guanaco. The mean pulmonary arterial pressure of 12 llamas and one alpaca indigenous to high altitude in the Andes was found to be slightly but significantly higher than that of three llamas and three guanacos born and bred at low altitude in England. On the other hand, the medial thickness of the muscular pulmonary arteries and the relative weights of the two ventricles were the same in three llamas and one alpaca at high altitude as they were in one llama and two guanacos at low altitude. It is concluded that the pulmonary vasoconstrictive response to hypoxia, while present, is greatly reduced in this species and it is suggested that this may have taken place by evolutionary adaptation.

Factors which allow the adaptation of adult llamas to oxygen limitation include principally: low P50, small elliptical red cells with high hemoglobin concentration, high muscle myoglobin concentration, high capillary density and a more efficient O2 extraction at tissue levels. The fetal llama is known to have blood with a low P50 but it is not known whether it has further cardiorespiratory adaptations which could allow it to cope with a low oxygen milieu. To investigate this, we have measured fetal blood flow and blood oxygen content in 8 fetal llamas and compared the findings to similar measurements in 10 low altitude bred fetal sheep, during the last third of gestation. The llamas were born and raised at 4500 m. They were brought to Santiago (586 m) and were studied one week later. The results show that there was higher hemoglobin concentration and higher oxygen capacity in blood from the fetal llama compared to the fetal sheep. Fetal llama combined ventricular output and umbilical blood flow were less than one fourth of those found in fetal sheep. Regional blood flows and oxygen delivery to fetal tissues were in most cases less than half those found in the fetal sheep. Calculated vascular resistances in the fetal llama in almost all vascular beds are higher than those in fetal sheep. These studies suggest that basal fetal llama oxygen uptake is maintained due to an increased oxygen extraction by fetal llama tissues. This increased oxygen extraction may be the result of a high capillary density.(ABSTRACT TRUNCATED AT 250 WORDS)

For each of 3 separate evaluations, 6 fasted llamas (Lama glama) were sedated with xylazine (1.1 mg/kg of body weight, IV) and then 15 minutes later were given normal saline solution (5.0 ml, IV; control values), doxapram (2.2 mg/kg, IV), or 4-amino-pyridine (0.3 mg/kg, IV) and yohimbine (0.125 mg/kg, IV). After administration of 4-aminopyridine and yohimbine, the llamas stood in a mean of 11 minutes and resumed eating in a mean of 34 minutes; both means were significantly less (P less than 0.05) than control values (46 minutes and 67 minutes, respectively). Doxapram induced muscle fasciculations, and (compared with control values) did not significantly decrease the time to standing (41 minutes) or the time until the animals resumed eating (68 minutes). Yohimbine and 4-aminopyridine in combination rapidly antagonized xylazine-induced sedation in llamas, whereas doxapram was ineffective as an antagonist of xylazine-induced sedation.

The cycle of the seminiferous epithelium of the llama was divided into eight stages, using as criteria the shape and distribution of the germ cell nuclei, the location of the spermatids, the presence of meiotic figures and the release of spermatozoa from the tubular wall. Cell populations making up each stage are described. The relative frequencies of stages 1 through 8 were: 9.86, 12.46, 17.65, 14.12, 5.81, 8.09, 13.04 and 18.89%, respectively. In the seminiferous epithelium, spermatogonia of the A and B type are present and twelve spermiogenic steps can be recognized. Interstitial (Leydig) cells are packaged together forming large masses and elongated cords and share the intertubular space with one or two central great lymphatic vessels and few capillaries. Season male Leydig cells contain lipid droplets in their cytoplasm and show a marked immunoreactive testosterone reaction.

Llamas are anesthetized conveniently with guaifenesin thiamylal mixes, or, for short periods of time, with xylazine/ketamine. Small individuals must be accurately weighed. Estimating weight without experience is dangerous in this species. The greatest levels of safety and control, especially for critical patients, is afforded by inhalation anesthesia techniques using small animal equipment. All neonates and juveniles can be masked readily but in adults intravenous induction is most satisfactory. Intubation is aided by a long blade laryngoscope. Blood pressure monitoring is best accomplished with an arterial line in the ear artery. However, doppler equipment on the tail or distal leg usually works well.

Like many mammalian species, man responds to exposure to high altitude with an increasing hemoglobin concentration and a decreasing blood O2-affinity. The Lama vicugna of the Andes does not show this kind of adaptation to altitude. Even at high altitude its hematocrit is unusually low and its O2-affinity is the highest known among mammals. Additionally, it is characterized by a high capillary density of the muscles and a large relative heart weight. The consequences of these different strategies of altitude adaptation of the oxygen supply system and the capability for physical performance are discussed.

Five male alpacas native to high altitude, of approximately 40 kg, were studied first at 3,300 m and again after a 3-month sojourn at sea level. Measurements were made with the animals standing, unsedated and breathing air. Cardiac output was measured by the dye dilution technique. Blood gas tensions and contents were measured in arterial and mixed venous blood. Blood samples were also equilibrated with different oxygen tensions to construct O2-Hb dissociation curves. The P50 was 17.8 and 19.7 torr at 3,300 m and at sea level, respectively. The higher P50 values at sea level were associated with higher values of base excess. PaO2 was lower at 3,300 m but SaO2 was always above 90%. No significant changes in [Hb], Hct, Q, CaO2 and CvO2 with changes in elevation were observed. PaCO2 tended to be lower at altitude indicating a mild hyperventilation. The values of PvO2 were lower than those reported for other mammals but similar to those of the llama. A higher PvO2 was measured in the alpacas at sea level. The alpaca under conditions of chronic hypoxia presents only minor cardiorespiratory adjustments suggesting the possibility of tissue characteristics well suited for life at high altitude.

The NWC are capable of assimilating a much lower plane of nutrition than we are accustomed to offer conventional domestic herbivores. Their unique gastric anatomy and physiology no doubt contribute to this apparent superiority, which is most evident when compared with sheep under lesser planes of nutrition. Llamas tend to be "cafeteria style" eaters, with some preference being given to taller, coarser forages. Absolute maintenance requirements for caloric, protein, fiber, and mineral content of NWC rations are yet to be finalized using North American feedstuffs, but some guidelines are offered. Proper assessment of body condition, acknowledgment of any nutritional problems, ration analysis, and assessment of management procedures likely will keep NWC nutrition on an even plane here in their new-found environment.

Anesthesia for llamas is similar to other domestic species, although adjustments in technique are required to allow for species variations. Xylazine (0.4-0.6 mg/kg) is well tolerated for sedation. The thiobarbiturates (8-10 mg/kg), ketamine (2.5-5.0 mg/kg), or combinations of guaifenesin and thiobarbiturates or guaifenesin and ketamine (to effect) can be used for induction of anesthesia. In juvenile or debilitated animals, anesthesia can be induced with halothane or isoflurane administered by mask. After tracheal intubation, anesthesia can be maintained with the inhalation agents, usually halothane or isoflurane. Supportive therapy and many anesthetic monitoring techniques used in domestic animals can be used in llamas. While under marginal planes of anesthesia, llamas can have more active physiologic responses to pain, including bradycardia and vasoconstriction, than domestic animals. Llamas are more prone to airway obstruction after tracheal extubation than domestic ruminants but otherwise recover as well from general anesthesia as domestic ruminants.