You're Kidding! 

Basics of Small Ruminant Reproduction

Part One

 By Beth A. Pelletier, DVM

 

It's that time of year again!  No, I'm not talking about Valentine's Day.  I'm talking about kidding and lambing season!  Goats and sheep are short day breeders, which means they conceive mostly during the autumn.  Their gestation length is 5 months, resulting in most kids and lambs being born between January and April.  With these happy little bundles of joy come many questions and potential problems, especially if you are new to the small ruminant scene.  If you are an old pro, you may still find some helpful tidbits, so read on.

Female goats and sheep (does and ewes, respectively) reach sexual maturity between 6-9 months of age, or at 60-65% of their adult weight.  Please note: does can have their first estrus as early as 3 months of age, so keep them separate from bucks!  If ewes and does get bred at too low a body weight, their growth may be stunted, resulting in increased risk of dystocia (difficulty giving birth).  As I mentioned above, small ruminants undergo estrus only during the shortest days of the year (August-March).  Throughout the breeding season, the females continue to cycle through heats unless bred.  Behavioral estrus is when the female is receptive to the male and allows herself to be mounted.  This stage lasts 12-36 hours.  Diestrus is the stage when the uterus prepares for pregnancy.  This lasts 14-20 days.  If the females are not pregnant, the cycle starts over again with behavioral estrus.  If they are pregnant, the female is no longer receptive to the male and you can expect delivery of a kid or lamb 145-150 days from the breeding.  During the longest days of the year, most females stop ovulating altogether and this is referred to as anestrus.            

Male kids and lambs should have testicles in the scrotum at birth.  If one or both testicles are undescended, the male is referred to as a cryptorchid.  This usually means that the undescended testicle is within the abdomen and nonfunctional.  In breeding males, this is a concern since it reduces their breeding potential, both because they have a lower sperm count and because they may pass on this undesirable trait if they do successfully breed.  Therefore, breeding them is not recommended.  In males not intended for breeding it is a concern because the undescended testicle may cause undesirable male traits, unless it is surgically removed from the abdomen.  Puberty occurs in the ram between 6-10 months but they are not considered mature and effective until 18-20 months.  Bucks may show sexual behaviors as early as 1 month and produce mature sperm at 3-4 months.  However, they are generally considered fertile at 5 1/2 months.  When choosing a male for breeding purposes, studies have shown that males with larger testicles (scrotums) produce daughters that reach maturity at an earlier age.  This is important in production situations where breeding new females as early as possible is beneficial.  Also helpful to production farmers is a practice called "flushing".  This involves increasing the breeding females' plane of nutrition just prior to the start of mating in an attempt to increase their ovulation rate (and hopefully acquire twins or triplets!).  

A note about bucks during breeding season: it is normal for males to urinate on their own heads to scent themselves.  If you wash them off, they will do it again!   

During pregnancy, 85% of fetal growth occurs during the last trimester, so female nutrition does not need to be increased until days 100-150.  In fact, overweight does and ewes are prone to pregnancy toxemia, a metabolic disorder that occurs during the last few weeks of pregnancy as the energy demands of the kids or lambs increase and the mother starts metabolizing fat.  Keeping your pregnant ewes and does in a fit body condition and increasing nutrient consumption only during the last trimester should prevent pregnancy toxemia.  Signs of this disease include lethargy, inappetance, weakness and poor muscle control/balance.  Unfortunately, treatment of pregnancy toxemia is usually unsuccessful, so prevention is the key.  Exercise is encouraged during pregnancy because it not only helps maintain a good body condition but it reduces the risk of dystocia.   

Pregnancy is identified by either failure of the doe or ewe to return to behavioral estrus, hormonal blood tests, or ultrasound.  Pregnancy can be detected by abdominal ultrasound at 35 days post breeding.  At 45-75 days, the number of fetuses can be determined. 

As parturition (birthing) approaches, it is helpful to move the doe or ewe to a clean, dry place where she can be monitored.  It is also recommended that ewes and does be vaccinated against clostridium perfringens type C & D and clostridium tetani (CDT vaccine) late in pregnancy so that antibodies for these diseases will be passed onto the kids and lambs via the milk after they are born. 

Next month, check in again for part two of "Basics of Small Ruminant Reproduction" where I will cover parturition (including dystocia), colostrum and processing of young lambs and kids!           

Glossary:

Ruminant - one of the order of animals, including cattle, sheep, goats, deer, and antelopes, which have a stomach with four complete cavities (rumen, reticulum, omasum, abomasum), through which the food passes in digestion.

Small ruminant includes sheep and goats

Goat terms

            Doe - adult female

            Buck - adult male

            Wether - castrated male

            Kid - young goat

            Kidding - birthing

Sheep terms

            Ewe - adult female

            Ram - adult male

            Wether - castrated male

            Lamb - young sheep

            Lambing - birthing

Parturition - birthing process

Dystocia - difficult or abnormal birth

Estrus - the state of sexual excitability when the female of most mammals is receptive to the male and capable of conceiving, aka "heat"

Diestrus - a period of sexual quiescence that intervenes between two periods of estrus

Anestrus - An interval of sexual inactivity between two periods of estrus in female mammals that breed cyclically