IMPROVEMENT OF SHEEP THROUGH THE SELECTION OF PERFORMANCE-TESTED AND PROGENY-TESTED BREEDING ANIMALS1996-1997 Central Ram Performance Test ResultsThe 1996-97 Ram Performance Test was completed with a final weigh day on February 12, final shearing on Feb. 14 and a Field Day on March 13. A total of 172 rams from 23 flocks completed the test.
The rams were delivered to the test station in mid-September and after a two week warm-up period were shorn on September 23 and weighed on September 25. Side and britch fiber diameter measurements were obtained from samples collected on January 9. Staple length was measured on February 10.
The average daily gain was calculated and reported for the 140-day test period. The fleece growth period was 144 days. The fleece weights and staple length measurements were converted to a 365-day basis. In order to account for shearing stubble, 1/8 inch was subtracted from the staple length measurements. Fleece yields, and thus clean fleece weights, were determined from 32 core samples removed from the entire fleece after shearing.
The rams were scored for face covering, belly wool and skin folds by a committee of 3 people. The lower values are more desirable. The range in scores is theoretically 1 to 4. However, in the case of face cover some values of less than 1 were assigned. Also, a skin fold score as high as 4 is now very unusual since it signifies animals possessing very heavy folds, some of which were present at the time this testing program was started in the 1950’s.
The scrotal circumference measurements reported in centimeters were determined by measuring the circumference of the scrotum at the widest point. Fat thickness measurements (inches) and ribeye area measurements (square inches) were taken by ultrasound between the 12th and 13th ribs on February 14. The ultrasound measurements are indicators of these traits. Research work is being conducted to get a better estimate of the accuracy of the ultrasound measurements.
A table with average performance values for many of the measurements of the Fall and Spring test groups is included in this report. Along with the averages are the minimums and maximums of each trait. The column marked ‘STD’ is the standard deviation calculated from all animals.
The ROM (Registry of Merit) Index was calculated as follows:
I = 60 x [average daily body weight gain in pounds]
+ 4 x [365-day staple length in inches with no credit above 5.5 inches]
+ 4 x [365-day clean fleece weight]
with � fiber diameter and variability points according to the following schedule:
Fiber diameter on side:
-3 x (fiber diameter in microns ( m) – 22.9)
Therefore, a ram that measured 22.9 received 0 fiber diameter points;
a ram that measured 23.9 received -3 fiber diameter points;
a ram that measured 22.8 received +3 fiber diameter points ;
No further credit was given for rams finer than 19.9 (+9 points)
No further points were subtracted for rams coarser than 24.9 (-6 points)
Variability (Britch diameter as compared to side):
5 – (2.5 x the number of microns the britch was coarser than the side)
with no advantage if the britch was finer than the side, and no further penalty if the britch was more than 4 microns coarser than the side. Therefore, a ram that had no difference between the side and britch fiber samples received +5 variability points, a ram that had a 4 micron difference received -5 variability points, and rams that were between these values received a proportional amount of points.
The method of calculating the ROM index has changed over the years. In order to make comparisons across years, a value known as index ratio was calculated as follows:
Index ratio = Actual index value divided by Average index value (within age group) X 100.
An index ratio permits ranking of animals around a mean with above-average animals having values greater than 100 and vice versa.
As an example, the index for test number 149 was 114.40 and was calculated as follows:
|60||x||.73321||=||43.99||ADG (body) in pounds,|
|4||x||5.0622||=||+20.25||365- day Staple Length in inches,|
|4||x||10.94||=||+43.76||365- day Clean fleece weight,|
|-3||x||[-.92]||=||+2.76||Fiber Diameter on side,|
|5 -(2.5||x||.55)||=||+3.62||Fiber Diameter variability,|
Registered rams that are in the top 30% on Index are eligible for the Certified Ram Classification. The top 30% was calculated independently for the fall and spring groups with January 1 being the dividing date.
In addition to the above requirements, a Certified ram must have:
gained at least 0.55 pounds per day on test,
produced a minimum of 9.00 pounds of clean wool (365-day basis),
produced a minimum of 4.0 inches staple length (365-day basis),
wool not coarser than 60s (24.94 microns) on the side or 56s (27.84 microns) on the britch,
a face covering score less than 2.7,
weighed at least 100 lbs at the start of the test (Spring lambs),
weighted at least 135 lbs at the start of the test (Fall lambs),
weighed more than 200 pounds at the end of the test,
passed inspection by a sifting committee before and after shearing.
Animals considered unsound from the standpoint of breed type, amount of skin folds, or from anatomical weakness and wool defects, were sifted from the Certified and Sale lists.
All animals completing the performance test tested negative for Brucella ovis at the beginning of the test.
The following ration was formulated by a nutritionist and fed free-choice in 1/4″ pellets. This ration was the same as fed in the previous 4 tests.
Ration ingredients by Percent (as fed)
|Alfalfa, dehy., 17%||28.24|
|Soybean meal, 44%||7.30|
|Trace mineral salt||0.97|
The trace mineral salt mixture was formulated for use in complete feeds for sheep. It added a minimum of 20 ppm of both manganese and zinc but contained no copper. The Vitamin A premix provided a minimum of 1,000 IU of Vitamin A per pound of feed.