I am not a veterinarian and I am not giving veterinary advice in this post. I am providing opinions and breeder to breeder advice based on my experience and my discussions with other breeders.

Many alpaca breeders rely on progesterone tests to assess pregnancy in alpacas.

The veterinary literature on camelids states that a progesterone level of 2.00 or greater indicates pregnancy. Many breeders and veterinarians – and remember that very few large animal veterinarians in this country have much experience with camelids – immediately jump to the conclusion that if a progesterone level over 2.00 indicates pregnancy, a progesterone level of less than 2.00 indicates a lack of pregnancy.

Except, it doesn’t quite work that way.

A level above 2.00 is a very strong indicator of pregnancy. If a test comes back above 2.00, you can be pretty darn sure you have a pregnant alpaca.

Depending on how low it is, a progesterone level below 2.00 doesn’t necessarily indicate a lack of pregnancy. A better interpretation – at least in my opinion – is lack of confidence in the diagnosis of pregnancy – and the lower the progesterone level, the lower the confidence! 2.00 is what the literature says and therefore it’s what the test manufacturer says – and I’m assuming the test manufacturer sticks to the literature for reasons of liability risk. According to our vet and to many experienced breeders we have spoken with, a progesterone level over 1.00 is probably an indication of pregnancy while a level below 0.20 is a safe indicator of no pregnancy. Between 0.30 and 1.00, there is a broad gray area where interpreting the test is difficult. A veterinarian with limited camelid experience is not necessarily going to be aware of this information and they’re going to go with what the literature says and what the test manufacturer says.

To oversimplify the biology, the function of progesterone in a female alpaca is to tell her body, “Hey, I’m pregnant.” and therefore maintain the pregnancy. Progesterone in the bloodstream carries this signal and it must remain about some threshhold level to maintain the pregnancy. This threshold probably varies from alpaca to alpaca and may vary with conditions in the same alpaca.

A few years back, I dealt via e-mail with a distraught breeder who’s precious newly purchased female came back not pregnant because the progesterone level was only 1.97 and it needed to be 2.00 for the animal to be pregnant. I don’t know what the margin of error is in a progesterone test, but I have done enough other chemical tests that I wouldn’t be surprised if 1.97 is within error of being 2.00. I have seen progesterone levels of 0.07 indicating not pregnant when there should be no progesterone in the body. Whether these levels are due to a trace of progesterone actually being produced or whether they are indicators of the error in the test, I don’t know. (Yes, the alpaca with the 1.97 level turned out to be pregnant.)

Let’s think about the test a moment. Did the vet put the blood sample on ice in the truck and go right back to the office, or did that sample sit in a hot truck for eight hours while the vet did his rounds? Once back at the office, was it refrigerated and sent promptly to the lab, or did it sit out for a couple days before being sent off? Take two samples from the same alpaca and treat them differently and you’re going to get different results. How different? I don’t know.

Next, let’s talk about the testing lab. How good is the lab your vet uses? Do they control their reagents carefully and calibrate their equipment regularly? I don’t know about veterinary labs, but I’m familiar with dramatic differences in other types of chemical testing labs. I have no reason to believe veterinary labs are any different.

Finally, lets talk about differences in individual alpacas. Some individuals will require a lot more progesterone to maintain pregnancy than others. I don’t know how big the difference is, but I guarantee a difference. I suspect the same individual will require different amounts of progesterone under different conditions. I can’t tell you what the conditions are or what the variation in the require progesterone level is, but I can almost guarantee variation within an animal according to conditions.

All in all, the progesterone test is a good guide to pregnancy and 2.00 is a very good indication of pregnancy, but the whole test needs to be taken in context. My preference is to use behavior testing as a primary testing means of determining pregnancy. Progesterone testing becomes useful when behavior testing is inconclusive and as an aid in learning a particular alpaca’s behavior.