Friday, September 24, 2010

Supplemental data

In addition to meeting performance standards for growth, parasite resistance, and parasite resilience, the bucks chosen for the sale must meet minimum standards for reproductive soundness and structural correctness.  On September 9, the goats were evaluated for these criteria.

Scrotal circumference and scrotal splits were measured by Shannon Uzelac. Among the 67 bucks, scrotal circumference (SC) ranged from 11 to 26 centimeters.  Scrotal size varies mostly by the age and size of the buck, though there are also significant differences within a weight group. Scrotal size is also affected by feeding level.  Overfeeding can have detrimental consequences on reproduction in the male.

Unlike other livestock species, minimum standards have not been established for the different breeds of goats.  Consequently, the scrotal circumference data is presented for informational purposes only.  However, it is known that testicle weight is related to sperm production.  In other species, scrotal size is also linked to ovulation rate in the female progeny. Scrotal size is a highly heritable trait at 50 percent.

There is disagreement in the goat industry as to whether scrotal splits over 5 centimeters (2 inches) are problematic.  Fourteen bucks had measurable scrotal splits, but none were over 5 cm.  Some central performance tests eliminate bucks with splits over 5 cm, despite the lack of scientific proof.

5 cm (2 in) scrotal split

Shannon counted teats and characterized the teat structure of each buck.  Only four of the 67 bucks in the test have more than two teats.  While there is some disagreement in the meat goat industry, two teats (one on each side) is the preferred teat structure in goats.  Only one buck showed a teat defect (fish teat).  In goats, teat placement is a moderately heritable trait at 30 percent.

Shannon assigned each buck a "hoof" score.  The hoof score (1-5) is indicative of hoof growth and the need for hoof trimming.  As hoof trimming is one of the "worst" jobs on a goat farm, I doubt any goat producer would not favor a goat that has less hoof growth.  Last year, we had to disqualify one of the best performing goats in the test as he had extremely "abnormal" hoof (heel) growth.

Susan Schoenian evaluated the bite of each buck.  A few bucks had "slight" underbites, but none of the bucks had serious jaw defects.  Bucks with serious jaw defects should be culled as this is a heritable trait that would be passed onto many of the buck's offspring.  Goats with severe jaw defects could have difficulty foraging.  Slight deviations in the bite are not a problem.

Jim Pritchard from West Virginia University scanned the goats to determine back fat (BF) thickness and rib eya area (REA). The scans were sent to Iowa State University for processing. As with scrotal circumference, rib eye area varies mostly with the weight of the goat, though there are also significant differences within a weight group.

Rib eye area ranged from 0.5 to 1.3 square inches and averaged 0.91 square inches. In the carcass study, we take actual measurements of the rib eye muscle.  The heritability of rib eye area is 40 to 45 percent.

The goats have so little external fat that the back fat measurements are largely meaningless. In the carcass study, body wall thickness is measured as opposed to 12th rib back fat thickness.  Unlike most other meat animals, goats deposit fat internally around their organs. In the carcass study, we weigh the kidney and heart (KH) fat.

Ultrasound carcass measurements are provided for informational purposes only.  Because it is not yet known how accurate ultrasound scanning is in goats, minimum standards cannot be established.  Nor is it known if rib eye area is the best indicator of carcass muscling (or lean meat yield) in a meat goat.

After the aforementioned measurements were taken, the bucks were carried to a pen to observe their structure and movement.  David Gordon evaluated the bucks for structural correctness.  None of the bucks were deemed to have functional structure problems. 

It is the opinion of this writer that goats should not be expected to have the same structure as other meat animals, as they are far more agile and "athletic."  Only functional structure problems should be considered an issue in commercial meat goat production.

Download supplemental report