Pelvic Structure & Capacity
Maxine Kinne

The  rump is much more than a handy place for the tail - it is integral to standing, walking, breeding and kidding. Simple everyday functions require good pelvic conformation. Reproduction also depends on the pelvis - breeding, carrying the pregnancy, delivery and feeding kids. Good pelvic structure helps the goat toward a comfortable, productive life, and selecting for it is a high priority.

Small or poorly shaped pelves often result in arthritic wear on the thurl joints and repetitive strain to the rear legs and feet. The thurls (hips) are ball-and-socket joints joining the hind legs to the pelvis. The shape and slope of the pelvis determine hing leg angulation and the width between the rear legs. Pelvic abnormalities create rear leg abnormalities, such as one or both stifles deviated outward, straighter angulation of the hind legs when viewed from the side (post-leggedness), rump steepness from hips to tail, and levelness from side-to-side. Too short a pelvis very seriously handicaps the ability to give birth normally.

While a doe has a limited number of offspring in her lifetime, a buck can sire all your kids every year and have great impact on the conformation and durability of his offspring. His breeding ability depends on the strength and correctness of his rear legs and pelvis. The heritability of pelvic traits is fairly high (Table 1). 

Breeding ease in the doe is associated with structural correctness in the rump and hind legs. A steep rump has a similarly steeply angled vaginal vault, and a buck may have a difficult time finding that angle with his penis. Stability of the doe's rear legs during mating is seriously compromised when she has poorly rear quarters. Kidding ease is the most critical pelvic function. Pelvic structure is a large component of the breeding ease and kidding ability of your bucks, your does, and their sons and daughters. This structural element affects your herd and impacts other herds who own your stock.

 

Table 1
 Average Heritability of Traits Related to the Pelvis *
 

Heritability Rate ** 

Trait 

Relationship to Pelvis 

21%

Rear Legs Attach to pelvis at the thurls

32%

Rump Angle Steep: thurls set too high
Level: thurls set too low

27%

Rump Width Narrow: thurls and hind legs close together.

25%

Fore Udder Attachment Steep rump shortens extension of fore udder

25%

Rear Udder Height Steep rump lowers rear udder and tilts teats forward
Level rump forces udder back and teats less accessible

33%

Medial Suspensory Ligament Steep rump shortens medial ligament
  * From 1997 USDA heritability estimates of 13 dairy goat type traits, nearly half of which are related to pelvic structure soundness.
** The average percentage of improvement that can be made in one generation.

 

(Figure 1 - Click here to see pelvic bone structure.)
 

Correct structure is species specific. Whether they are goats, cows, sheep or Loch Ness Monsters, evolution selected for function. When humans interfere with the selection process, they often face unintended consequences. On the farm, we breed for the type we think we like or that the judges want to see in the show ring. Nature isn't nearly as picky: if a trait doesn't work well in nature, the trait disappears immediately.

Meat and dairy traits (carcass evaluation and milk production) are based on statistically proven performance criteria. These industries have raised selective breeding to an art form, as their animals are expected to produce well over a long period of time. Structural and production traits are, indeed, their meat and milk. Pygmy goats need the same structural qualities to remain viable. Pygmy goats in the United States are bred toward meat type with a bone thrown to dairy. They are strongly judged on breed type, but their style has changed over the years. (See Old vs New: A Comparison of Styles.) Judging the U.S. Pygmy goat is highly subjective, as that has been our only way to establish "quality". Kids are their most valuable asset, so the ability to reproduce easily is very important.

 

Pelvic Dimensions

Length and width are the dimensions we see when we look at the rump or feel it through the hair coat. There is length from hips (hooks) to pins, width from hip to hip (thurl to thurl), and width between the pin bones (on either side of the vulva in does and similar location in bucks and wethers). Levelness of the rump is also taken into account, meaning a flatter rump from side to side. This does not mean horizontal to the ground - it means that the rump is more flat. Each part of the rump is important unto itself and as it correlates with the whole. Length and width should be more nearly level, not flat or rounded or steep in slope. If you are confused about levelness, look at dairy goats or dairy cows - they carry less flesh and it is easier to see the underlying structure.

 

 Figure 2
Slope of the Rump
 
 
 

Abundant hair makes it is impossible to see the slope of the rump on most  buck goats. Their structure must be felt with the hand.

Correctly sloped rump.
This trait correlates with more
correctly angulated rear legs.

Her loin rises from the chine to yield a steep rump, a  trait which usually causes post-leggedness.

 

The most desirable slope to the rump in dairy goat linear appraisal is a 25o angle from hips to pins. Pygmies should maintain that standard for functionality. A dairy cow body type evaluation study based only on rump angle showed that a medium rump angle resulted in the lowest culling rates (highest productivity). Cows with flat or steep rump angles were far more likely to be culled for poor productivity. (Productivity includes the ability to deliver young with the fewest problems.)

A good combination of pelvic length and the levelness from hip-to-hip correlate positively with kidding ease. Widely spaced thurls result in widely spaced rear legs. This width gives stability to the rear legs and width to the pelvic inlet (birth canal) on the inside. Thurls should be high enough to impart levelness of the rump from side-to-side. Increasing rump steepness from spine to thurl compresses pelvic width and interferes with kidding ease by compressing birth canal width. Total length of the pelvis should be medium long, a measurement which is proportionate to the goat's size. Pelvic length equates with kidding ease better than pelvic width, although both dimensions are important to have together. Pelvic length is well demonstrated in the side-by-side comparison of a longer pelvis and a shorter one in Figure 3. (Also see Fig. 5, the pelvic bones of two 10-month-old kids and a 2 1/2-year-old wether. These show incomplete fusing of some pelvic bones due to young age and to castration.) 

The pelvis grows gradually until maturity. There are no magic pelvic length or width measurements for optimum reproductive success. Measuring the rump does not indicate the capacity of the birth canal, but measuring is a tool for improving reproduction in Pygmy goats. Radiographs are more reliable, but they are expensive and may not give you good enough information. (Delivering a large single buckling is harder than delivering small triplet doelings.) If you have to ask, "Could this doe big enough to deliver vaginally if I breed her," you might as well not. Goats with questionable pelvic structure should not be used for breeding. If she cannot deliver or be manually delivered vaginally the first time she gives birth, don't breed her again, and castrate her buck kids. Making pelvic capacity an important criteria in your selection program is the most important decision you can make with regard to the future productivity of your herd.

The American Dairy Goat Association's Linear Appraisal program measures the width between the pin bones as an indicator of kidding ease. I kept those measurements, in addition to pelvic length and width, until it became apparent that pin bone measurements had nothing to do with easy delivery in Pygmy goats.

By using the pelvic measurements of your own animals, you can determine individual growth rates to decide at what age and size the does are good candidates for breeding and which ones need improvement in pelvic structure.

Below is a sample chart for tracking pelvic measurements0. I measured with a 9-inch slide caliper with a broken dial indicator (that's why it was a cast-off by my husband's business). Before that, I used a 12" ruler. It helps to record all measurements for the same goat on its own form.

After you have taken some mature adult measurements, rank them from longest to shortest pelvic length (hip to pin). You may find that does with longer pelves have easier births and fewer complications during birth. Within-herd comparisons may reveal that a certain sire produces easy kidding daughters. This is what we should all strive for as replacement breeding animals.

When you see older does at the top of the rump length list who have kidded multiple times, and with relative ease, you will have identified your most valuable productives does.

 

Table 2
Pelvic Measurement Chart
 

Name Age (yr - mo) Hip to Pin Hip to Hip Sire Name Dam Name
  -        
  -        

 

Short and Deformed Pelvic Bones

I will never forget a 2-year-old buck I saw at a show a few years ago. He shuffled along on his rear legs but was made champion because he had a beautiful head and neck. I asked the owner if I could feel his structure. His neck and shoulders were impressive. His loin was narrower than average width, and his pelvis was narrower than the loin and very short. His shuffling gait was due to a very small pelvis. His debility had also crippled his sire by the time he was 3 or 4. His owners were ecstatic that he'd won the show because all of their does were currently bred to him.

Short-bodied animals have a distortion which can be felt on top of the rump as an unusual bump on the top of the spine. This deformation is thought by some experts to be the body's vain attempt to create some kind of pelvic capacity to allow kidding. I believe it is a deformation in which Mother Nature decrees, "Thou shalt not reproduce without much pain and grief and with, yea verily!, much enrichment to thy veterinarian's wallet." A short pelvis is often more steep from side-to-side than it should be.

While shorter-bodied goats don't have a corner on the market on a steeper rump from hips to pins, this type of structure is quite common in them. A steeper rump angle straightens the angulation of the stifles and hocks to result in post-legged condition which is hard on all the joints from the hips to the toes, and it shifts additional weight to the front end.

As the pelvis shortens, it can slightly twist. A goat who always stands with one stifle cocked out at an angle, while the other hind leg is correctly aligned may have a twisted pelvis. I have seen this physical abnormality run in herds and bloodlines, and it is accompanied by poor kidding due to less width in the birth canal. There are a number of other causes of incorrect hind leg alignment or attachment, but many are due to pelvic structure.

Deviations from normal in the rump generate abnormalities in one or both hind legs, both in angulation viewed from the side and straightness viewed from the front or back. There is more wear and tear on the hip joint (acetabulum) with over- or under-angulated hind legs. In the side view, Pygmy goats are far more often under-angulated (post-legged) than over-angulated (sickle hocked). When the goat's rear end is set up in a show class, ideally, a straight line from the pinbone should pass the back edge of the hock and cannon. Spreading the hind legs further apart than the normal stance will drop the rump and turn the hocks inward. In the rear view, ruminants are normally "cow hocked," with the rear legs pointing more toward the center line rather than forming a straight line. We have unnaturally selected for straight alignment of the rear legs. Go to the zoo or watch wild animal programs on the television and pay attention to their rear legs. Yes, they're always hocked in. Mother Nature isn't stupid.


Fat and Pelvic Capacity

Overweight does have fat deposits in the pelvic cavity that reduce the space available for kids to come through. Besides physical obstruction, excess fat hinders kidding because it interferes with the action of hormones to initiate labor and help with uterine contractions. Hormones work very inefficiently through fat tissue. That is main reason why fat does have sluggish, prolonged labor. Take a doe with so-so pelvic capacity, add excess fat, and you have the recipe for kidding disaster.

Older first-kidding does often have hormonal and physical problems due to age and body condition. The hormones estrogen and relaxin act on the pubic symphysis and other cartilaginous joints and ligaments to relax the pelvis for delivery. By the time a nulliparous (never kidded) doe is fully mature, the pubic symphysis is ossified (rigid) and her pelvis inflexible. (In the photos of my younger animals' pelves, notice that the pubic symphysis cartilage dissolved during preparation, and the halves are wired together. This joint is permanent in adult does and bucks, but it may never completely ossify in wethers.) It is far better to get the Pygmy doe kidding before absolute physical maturity and breed her every year than it is to wait too long and end up with a rusty hormone system, an inflexible pelvis and an excess of body fat. To me, this means first breeding by 2 years old, and certainly before 3. Every 4-year-old first-kidding Pygmy doe I know of has had serious problems.

 
  

Related Reading

Relationship between Linear and Fertility Traits in Goats (rump angle is emphasized)

U.S. Animal Improvement Programs Laboratory

 



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