A normal llama and alpaca pregnancy lasts for an average of 11 and 11.5 months, respectively. Pregnancy is not visually obvious until late pregnancy (if at all) in either species of camelid. The traditional alpaca “spit off” method, where the female treats the male with hostility, actually only confirms ovulation – not a successful pregnancy. It would have to be repeated multiple times several weeks after the last mating to confirm that the female is not pregnant, and even this is not fool-proof, with less experienced female alpacas known to accept the male even when pregnant. It also, of course, cannot tell us anything about the viability (health) of the pregnancy.
Ultrasound is therefore a very important tool in confirming pregnancy in alpacas and avoiding many months of false hope.
When to scan
Pregnancy can be reliably confirmed before 30 days’ gestation by a veterinarian using transrectal ultrasound, but such call-outs are expensive, and not every vet has equipment suitable for use on llamas and alpacas.
Pregnancy can be confirmed transabdominally using a convex probe, ideally at a frequency no higher than 3.5MHz. The earliest you can hope to confirm pregnancy abdominally is at 45 days, but if you are performing a scan for someone else, it is better to wait for 60 days or even 90, unless you are very experienced. If the owner is willing to wait for 90 days, this is an ideal time point, because the probability of a 3 month pregnancy going to full term is high. Before this time, resorption is very common and not easily noticed, so unless the owner brings you back for a rescan later in the pregnancy, they may think they are caring for a pregnant animal when, in fact, she has resorbed.
Other benefits of ultrasound
The precise gestational age in pregnant alpacas and llamas is difficult to estimate because neither come into season. Instead, their ovaries contain follicles at a range of different stages of development (Gazitúa et al., 2001), with ovulatation induced by mating. If a follicle is not quite ready at this time, ovulation may often be delayed, or may not happen at all. Of course, it is possible to estimate gestational age using your ultrasound machine, but the calculation has to be performed manually as alpaca and llama gestational age calculations are not built into veterinary ultrasound machines as standard.
After obtaining a biparietal diameter (BPD), you can calculate gestional age using the following formulas prepared by Gazitúa et al. (2001) from a study of 126 animals:
Alpaca gestational age (in days) = (biparietal diameter in cm – 0.11376) x 47.23287
Llama gestational age (in days) = (biparietal diameter in cm – 0.002399) x 43.02293
For example, if the BPD of a llama foetus measured 3cm, you would do 3 – 0.002399, and multiply this by 43.02293. This would indicate that the cria was at 129 days.
The best method for performing a BPD measurement are the same on alpacas and llamas as on dogs and cats. If you are a member of the Animal Ultrasound Association, you can access a tutorial video on this method here.
Preparation is the key to success!
Imaging on llamas and alpacas can be challenging, so it is best to skew the odds in your favour as much as possible. This can be done by good preparation.
– Clean the skin on the animal’s flank, under one of the back legs (in the ‘armpit’ of the back leg). You can remove grease (which forms a natural barrier to your ultrasound gel) with alcohol, but be sure to wipe the area with water before applying gel, to prevent the alcohol from damaging the membrane of your transducer.
– Scan under shelter. Light is your enemy, so the darker, the better! Particularly on machines like the Scan Pad which have large, smooth and reflective screens, it is imperative that you warn the owner that you will need to scan in the shade. In bright sunlight, you will not be able to see anything. This is also a problem when scanning goats and sheep.
– Make sure you are scanning at an appropriate frequency and depth. Ideally, use a large convex probe; if you only have a microconvex, then make sure it’s at its lowest frequency setting (usually 3.5MHz, or “HPen” on machines like the Scan Pad). Increase your depth when performing your first sweep. You can always reduce depth and try increasing frequency once you locate the cria.
Remember, it is important to locate movement – ideally a heartbeat – to confirm viability of the pregnancy. Be sure to capture a cine loop of this to demonstrate that you have achieved this. If anything happens later in the pregnancy you will always have evidence that, at time of scanning, the foetus was viable.
Gazitúa, F., Corradini, P., Ferrando, G. et al. (2001). Prediction of gestational age by ultrasonic fetometryin llamas (Lama glama) and alpacas (Lama pacos). Animal Reproduction Science 66 (2001) 81–92