Alpaca Temperatures and Fertility: We Checked Some Numbers
December 2016. Those of you who are familiar with our alpaca breeding effort know that we are quantitatively oriented and research-focused. We also like to share what we learn as broadly as possible. Some of our research results – especially those from projects led by the human embryologist and fellow alpaca breeder Dr. Kim Gleason, of Dancing Horse Farm – find their way to formal publication. Sometimes, though, there is incremental yield from our research and data collection that we can distribute more informally, and that is what we will be using this blog for going forward.
It was because of one of the preliminary results from participation in one of Kim’s long-term studies (in this case, on the effect of various husbandry choices on the sex ratios of crias produced,) that we began to collect temperatures on all of our sires and dams at the time we used them for breeding. Previously, we had seen a close association between high ambient (i.e., environmental) temperatures and the production of a disproportionately large number of male crias relative to females. We also understood that it was not the ambient temperature per se that was affecting the sex ratio, but rather the tendency of the animals’ temperatures to vary as a function of it. In addition, we knew that looking at ambient temperature alone overlooked many important contributors to the animals’ response to heat and cold. Accordingly, we begin to collect breeding-time animal temperatures in the summer of 2016. In a year or so, we will be able to discover how those internal temperatures at the time of breeding correlate with the sex ratio of offspring produced by our animals.
In the meantime, however, the analysis of animal temperatures and breeding outcomes has begun to produce other useful feedback. For instance, we were able to look at this year’s breeding data to see if the fertility of our animals declined when they were hot, as has been documented in other livestock species. We found that it did. In particular, our data suggests that the likelihood that a breeding produces a pregnancy is lower when the females, but not necessarily the males, are very hot. More surprisingly, we also find some evidence that even females with internal temperatures in the warmer part of the so-called “normal temperature range” (usually described as between 99.0 and 102.0 Fahrenheit) show a reduced likelihood to produce a successful breeding outcome compared to those with temperatures under 100.0 degrees. It does make you wonder where that referenced “normal range” came from. In any case, the results are pretty dramatic, and, in combination with the tendency of heat-stressed animals to produce male offspring, are causing us to rethink our breeding calendar.
In Exhibit 1 below, we show both the breeding success rate and average temperature of our dams and sires during August through October 2016. Although we breed animals year round, this represents our busiest season, and overall, we did 100 breedings of our farm’s females during that time. As Exhibit 1 reveals, we had a horrible time getting our animals pregnant in August, when they were hot, with only about one out of every three breedings leading to a confirmed pregnancy. By contrast, in October, when the average animal’s temperature was about two degrees lower than in August, roughly two out of every three breedings produced a confirmed pregnancy (please note that we have removed from this analysis all breedings we conducted with either an unproven sire or dam, as their fertility status is unknown.)
Exhibit 1: Breeding Success Rates By Month
|Month||Total Breedings||Total BreedingsConfirmed||BreedingSuccess Percentage|
Of course, other things besides temperature change with the seasons. For instance, the amount of daylight varies, as may the amount of fresh forage versus hay, along with other factors that could conceivably affect fertility. So we looked at the relationship between animal body temperature and breeding success to see if the apparent relationship between the two persisted regardless of the month of the year. As Exhibit 2 shows, it did. But the difference between the results for dams and sires begs the question of whether one gender is more important than the other with regard to our fertility results.
Exhibit 2: Breeding Success Rates By Temperature of Sire and Dam
Of course, overall temperatures of both sires and dams are positively correlated. A hot day here heats everyone up. But for various reasons — including but possibly not limited to differences in phenotype, age, condition, and housing — our males’ and females’ temperatures are not perfectly correlated. Sometimes we do a breeding where the female’s temperature is relatively high and the sire’s is not, or vice versa. Looking at this particular subset of “mismatched” temperatures shown in Exhibit 3 gives us further insight – though we must be careful not to draw too strong a conclusion at this point because the amount of data we have for this way of looking at things is particularly limited.
Exhibit 3: Breeding Results When Dam and Sire Temps Vary
|Dam Temp||Sire Temp||SuccessfulBreedings||FailedBreedings||Percentage|
It is notable in these limited results that breedings of males with temperatures above 102 degrees to females with temperatures within the normal range (even though many of them were on the higher side of normal) resulted in pregnancies 56% of the time. By contrast, females with elevated temperatures bred to males with normal-range temperatures conceived only 36% of the time. Again, caution is warranted because the total number of observations is very small. But together they do suggest that it is not so much that our males’ fertility is impaired when they are hot, but that our females have trouble either conceiving or holding the pregnancy until it can be confirmed, or both. Similarly, a cool female (temperature under 100 degrees) conceived 65% of the time when bred to a high or high-normal temperature male (temperature above 100,) while the reverse situation, a cool sire with a warmer dam, resulted in a much lower pregnancy rate.
Can we ultimately infer more about whether heat interferes with conception, or whether early pregnancy failure is higher when it is hot in weeks after conception (and even before we can confirm pregnancy), or both? The answer is yes, possibly: By introducing temperature data (in this case, historical ambient temperatures as we do not routinely take our animals temperatures) for the time between breeding and confirmation, we can examine the relationship between those conditions, the animals’ temperatures at breeding, and the ultimate confirmation rate. We have noted in years past that we tend to have a higher slippage of confirmed pregnancies when the weather is hot. Presumably this is also true in the weeks between conception and confirmation of pregnancy. It will take us a while to discern this in our data, though, even if it is there, because there is a close correlation between the ambient temperatures at breeding and in the early stages of any animal’s pregnancy that will make it more challenging to separate out these two potential effects. But we are working on it.