Birthing Season, Part 2
Last week we compared some unique aspects of the equine and bovine reproductive physiology, focusing on birth. This week, let’s take a look at small ruminants such as goats and sheep, and the camelid species, llamas and alpacas.
1. Small ruminants
Both sheep and goats have gestations of five months. Seasonally polyestrus, sheep and goats are commonly called “short day breeders,” meaning they are the most fertile in the autumn and winter, so that five months later, they are delivering young in the warmer spring months.
Interestingly, some breeds of sheep are more “seasonal” than others. Sheep breeds with black-faces (commonly referred to as black-faced breeds), such as Suffolks and Hampshires, can be extremely seasonal breeders, meaning it’s difficult to get them to breed at any other time of the year. Conversely, white-faced sheep breeds, such as Dorsets, aren’t quite as strict in their estrus cycling and are easier to breed in the spring and summer months.
Sheep and goats quite commonly give birth to sets of twins, triplets, and even quadruplets without any problems. The placentas of small ruminants are also independent enough from a blood supply point of view, unlike cattle, that male and female lambs or kids can develop normally in the same womb.
Certain breeds of sheep and goats are known for being more prolific than others. The Finnsheep and the Romanov breed of sheep are well known for being highly prolific, topping the charts, although rarely, at seven or eight lambs! However, this extreme is not preferred, since lambs at these numbers tend to be very small and weak.
Reproductive seasonality is also observed in male sheep and goats. During the breeding season throughout autumn and winter, bucks and rams go into what is called “rut.” This is when the males are at the peak of their reproductive hormones and become primarily focused on breeding. This focus is so intense that rams and bucks actually eat less and lose weight as they constantly court females.
Bucks in rut are particularly noticeable, as they produce a very distinctive and very stinky pheromone from scent glands on their body. Take my word for it — once you’ve smelled a buck in rut, you’ll never forget it!
The gestation period for llamas and alpacas is eleven months, like horses, although this period is notoriously variable and I’ve known alpacas go for twelve months before giving birth.
Many aspects about the physiology of camelids is still unknown due to their relative recent emergence within the U.S. (the last thirty years for llamas and twenty years for alpacas), and this includes many mysteries of reproduction. In other species, if a female is carrying a fetus over-term, the birth would likely be induced by administering exogenous hormones. However, anecdotally, camelid experts strongly recommend not inducing birth in alpacas or llamas. Cases of mine that have gone overdue have not had any after-effects.
emale alpacas and llamas are different than other farm species in that they are induced ovulators. Instead of releasing ova independently, camelids are stimulated to ovulate by the act of mating (this is also the case in cats).
Baby camelids are called cria. Twins are rare in both alpacas and llamas, and, like horses, are unfavorable because twins are often born very small and very weak. Carrying twins is a common cause of abortion in camelids.
One unique aspect of camelids is their preferred time to give birth. Most prey species prefer to give birth in the quiet of night. This is certainly true of horses, where a vast majority of equine births are at night (much to the chagrin of the veterinarian on call!). However, camelids more commonly give birth during the day (much to the happiness of the veterinarian on call!).
Birthing is also a very social event among a group of camelids — often the other mothers will gather around as soon as a cria is born and sometimes form a sort of circle, almost as if to form a welcoming party. It’s a very special thing to watch.
Dr. Anna O’Brien