Jeff Held
Extension Sheep Specialist
Department of Animal and Range Sciences

 INTRODUCTION

The Dakota Ram Testing program was established primarily to identify differences in wool traits for rams managed under the same environmental conditions and plane of nutrition and, secondly, to measure postweaning growth rate as indicated by weight gain. An added feature is evaluation of animal carcass merit using real-time ultrasound technology.

Fleece weight and staple length were calculated on a 365-day basis. Side and britch wool samples were sent to the Yocum-McColl Testing Laboratory to determine fiber diameter and variability, and clean wool yield. Average daily gain was calculated based on the total weight gain (including fleece) during a period of 140 days.

Fiber Diameter: Determined for each sample using laserscan technology method. The diameter is estimated by measuring four hundred clean fibers to determine an average (mean). In addition, the variation within a sample is determined. The standard deviation (std. dev.) and coefficient of variation (C.V.) are given to provide numerical indications of the variation. A fleece sample with a small C.V. should be considered more uniform than one with a large C.V. (C.V.= std. dev./mean fiber dia.).

Staple Length: Determined by measuring with a ruler at the shoulder, side, and britch. Values were adjusted (less 1/8") for the stubble remaining after the initial shearing and an average calculated from these three sites. 

Clean Wool: Determined from the laboratory scoured clean yield estimates on side samples. Analytical procedures meet ASTM standards.

Face Cover and Body Skin Fold Scores: Determined by averaging subjective scores from a three person committee selected by the ram test committee. Scores were assigned from 1 to 4 for each trait. The lower the value the more open faced or freedom from skin folds.

Average Daily Gain: Calculated by dividing the total gain by the number of days in the test period (140 days).

Index: Utilized the following formula established by the Texas and Wyoming Ram tests and the approved index for the American Rambouillet Sheep Association's register of merit program (ROM) [Revised July 8, 1993].

3 (22 - actual microns) = + points up to 9
3 (actual microns - 22) = - points up to -6

Variability-Britch compared to side

2.5 deduction for each micron the britch is coarser than the side. No points given if britch is finer than side.

Index Ratios: To compare one ram with another an index ratio was calculated by the following formula. The average index ratio for all rams is 100; an individual with an index ratio of 130 would be 30% higher than the average and so on.

Certified Ram Classification: The top 30% of the registered Rambouillet rams as indicated by index are eligible for the Certified Ram Classification. In addition to the above requirement, a ram must meet acceptable standards from the standpoint of body type, amount of body skin folds, freedom from anatomical weaknesses and wool defects, including extremely hairy britch or excessive amount of belly type wool. All certified rams must have a minimum of 4.0 inches staple length, 9 lb clean wool, a wool grade of 60's or finer on the side and 56's or finer on the britch, a maximum of 2.7 face cover score, and must have gained at least .55 lb per day on test.

Carcass Merit: At the beginning and end of the test, fat cover and rib eye area were measured at the 12-13^th rib by real-time ultrasound. This information is not included in the index. However, these measures may help producers identify rams with superior carcass merit. Rib eye area is a good indicator of overall muscling, rams with larger rib eyes would be expected to be more muscular compared to those with smaller rib eyes. More muscular individuals would be expected to exhibit high growth rated relative to those with less muscularity. Fat cover is an indicator of maturity pattern, i.e., frame-size. Those rams carrying less fat (finish) would likely be later maturing, or perhaps younger, than those with greater amounts of fat cover. For fat cover, the only valid comparison for this set of rams is the final measurement (Tables 1 and 6).

Discussion

The index system used to rank the rams within a breed takes into account growth rate, wool, and anatomical traits. In most cases the higher indexing rams are those which produced the most pounds of clean wool (CFW). The data would indicate that the pounds of clean wool was a function of grease fleece weight, yield, and staple length. Growth rate and anatomical measures have less impact on the index value in most instances since there was less variation between rams for these parameters. The index system fits the objectives of our testing program quite well since it ranks rams on the most economically important traits (Tables 2 and 7). Rams were also sorted by clean fleece weight (Tables 3 and 8) and average daily gain (Tables 4 and 9).

The ram testing committee would like to thank the following sponsors for their contributions to the program:

NDSU-Hettinger Extension and Research Center
Tim Faller, Superintendent
Dave Pearson-Ram Test Manager