Objective measurement in beef cattle showring judging

Introduction

Many show societies now either provide beef cattle judges with EBVs and/or objective measurements, or run separate performance classes.

If kept in perspective, raw objective measurements can be useful in assisting visual appraisal. The measurements have limitations, however, when comparing animals where the background management and environment are largely unknown. BREEDPLAN EBVs (estimated breeding values) offer a considerable improvement to judging. These EBVs compare only like-treated animals, are adjusted for age, and allow comparison across herds.

Raw measurements

The raw measurements most often available are:

• actual weight
• weight per day of age
• ultrasound subcutaneous fat depth at P8 rump site and the 12th/13th rib
• eye muscle area
• intramuscular fat
• frame score
• scrotal circumference of bulls

Weight

Actual weight is a measurement of limited usefulness. It is influenced by the age of the beast as compared with the class age range, and the amount and duration of feeding and preparation used. However, it does give some indication of the overall development of the beast when it is being judged.

Weight is most useful if fat measurements are also provided. Judges can then adjust the weight for fatness.

Another refinement is to calculate the weight per day of age , by dividing the beast’s actual weight by its age (in days). This does remove the variability of age, but you must remember that the gain per day of age slows down as a beast gets closer to maturity. Therefore, do not compare animals with an age difference greater than 3 months.

If you assume that all the animals in the class have had optimum growing conditions, then large differences in weight per day of age will be significant and more likely to reflect genetic differences between individuals.

Ultrasound fat and eye muscle scans

Subcutaneous fat depth is measured in millimetres using ultrasonic scanning devices. This is very accurate when taken by accredited technicians. Fat scans are taken at the 12th/13th rib and P8 rump sites. In abattoirs, fat depth is measured at these sites. Scan measurement at both sites helps to better describe liveweight measurements and allows you to assess whether the difference in weight is due to muscle or fat.

A fat scan also indicates the rate of maturity of the beast, but only when other factors are fairly constant. For example, a bull carrying more fat than his classmates of similar age and weight would be considered to be earlier maturing. Conversely, a lean bull of similar age and weight would be considered later maturing.

Eye muscle area (EMA) can also be measured by ultrasound although not as accurately as subcutaneous fat, hence measurements on individuals need to be interpreted with caution if being used by judges. The EMA scan should be related to the fat-corrected liveweight.

Percentage of intramuscular fat (IMF%) is another carcase measurement now possible by ultrasound on live cattle. Results should be interpreted with caution, given the different backgrounds of show cattle.

Frame score

‘Frame score’ is the height-to-age relationship of a beast. It categorises cattle according to their growth and maturity patterns. ‘Maturity pattern’ or ‘maturity type’ refers to the age and size at which an animal tends to ‘finish’, that is, to lay down subcutaneous fat to the level desired by a particular market.

Frame scores are made on a ‘1 through to 7+’ basis, from the smallest to the largest (or from the earliest maturing to the latest maturing) types of cattle.

Scrotal circumference

Scrotal circumference is measured in centimetres around the widest part of the scrotum when both testicles are firmly forced down. This measurement is valuable because of its proven relationship to fertility:

• It has been well documented that scrotal circumference is highly related to both the quantity and the quality of semen produced by the bull.
• Bulls with a scrotal circumference less than 30 cm at 18 months of age are usually subfertile.
• Scrotal circumference is known to be highly heritable and also related to the puberty and later fertility of female relatives.

The following scrotal circumferences are considered acceptable minimums in Bos taurus bulls :

Well-grown bulls should have scrotal circumferences 3–4 cm greater than these. However, subjective assessment of firmness, by palpitation, is as important as the measurement of circumference when assessing fertility. Scrotal size, like most raw measurements, is also influenced by nutrition and age.

The place of raw objective measurements

The objective measurements, if used as described above, can be a useful aid in the showring. They should complement, not replace, visual judging. There are many important traits that cannot be measured objectively, such as structural soundness, conformation, breed type, degree of muscling and market acceptability. Experience is needed to evaluate these traits, but if objective measurements are used in conjunction with visual assessment, more accurate and confident decisions will be made.

Objective measurements can also assist the judge and provide the exhibitor with valuable information . For example, an exhibitor might learn that they are overfeeding their cattle, or that their cattle are maturing too early.

Prospective buyers can have a much better ‘look’ at animals in the ring when they are paraded together. However, they should keep in mind the following points:

• Do not compare individuals with an age range greater than 3 months.
• Do not pay too much attention to the one point (either a measurement or a visual assessment) as this can cause other equally important, if not more important, points to be overlooked.
• Recognise the influence that differences in feeding and management can make, and do not worry about small differences in measurements between individuals of different backgrounds.

EBVs in the showring

Some show societies now provide BREEDPLAN EBVs for cattle judges. This can range from just giving the judge access to the EBVs, to sophisticated performance classes with methods of weighting the EBVs according to market class. In the latter case, points are allocated, say 50% on visual assessment and 50% on EBVs — these must be from GROUP BREEDPLAN (the system which compares across herds within a breed).

BREEDPLAN performance classes

Organisers must carefully specify market end point and define the management situation, for example:

• Bull to breed supermarket cattle (200–260 kg with 6–12 mm P8 fat).
• Self-replacing herd.
• Calving ease is important.
• Yearlings will be finished on improved pasture at high stocking rates.

Example of a performance judging system

The following performance judging system was used by the Angus Society at the 1998 Sydney and Wodonga Shows. The EBVs of the entries and the score sheet are shown in Table 1. Performance points in Table 1 were allocated mainly on the position of a bull’s EBV for each trait on the breed’s percentile table (e.g. from Table 2 the maximum points are allocated for weight if 600 day EBV is in the top 5% of breed).

Some points were also given on the BreedObject $INDEX. This index is derived by a computer program (BreedObject) which allocates weightings to each EBV according to their economic impact on herd profitability. These are now available on most breed society websites.

Some other performance classes use BreedObject more strongly. In the following example it contributes only 10 points, but it also helped the Society decide on point allocation to the individual traits. The BreedObject $INDEX was also included here for educational purposes (see also Table 3).

Note: BREEDPLAN Breednotes describing the BREEDPLAN system and BreedObject are located on the BREEDPLAN home page, which is part of the Agricultural Business Research Institute website.

An example judging sheet is shown below in Table 1:

1998 Royal Easter Show — Angus Performance Class 18

For led bulls suitable for use over moderate-sized Angus cows in a self-replacing herd targeting the production of feeder steers for the high quality Japanese market, 380–420 kg carcase weight, AusMeat marble score 3 or higher. Animals will be judged on their Angus GROUP BREEDPLAN EBVs and visual assessment of structural soundness and market suitability.

Entries:

* The BreedObject $INDEX is calculated by an economic weighting of the EBVs according to their importance in commercial beef production. (See also Table 3.) Points for Entry No. 1 have been completed. See Table 2 to check the EBV points for yourself.
^† Refer to Table 4.

Performance class points are allocated according to the following:

BreedObject $INDEX is calculated with the following emphasis: