Beef Cattle Ultrasound Measurements
3.7 Ultrasound measurements
3.7.1 Introduction
Real time ultrasound imaging equipment to record carcass characteristics in live animals for livestock improvement programs has been in use for more than two decades. Its usefulness in beef cattle has been well demonstrated e.g. Brethour (1994), Wilson et al. (1998).
Ultrasound scanning has been used since the late 1980’s in many beef cattle breeding programs to overcome the inherent difficulty of recording carcass data from progeny tests under extensive production systems and in performance test situations where access to carcass information is not possible. A number of genetic evaluation programs have now included scan data in their routine analysis.
3.7.2 Practical Application of ultrasound imaging
The application of ultrasound is highly technical and requires:
a. The use of sophisticated equipment. b. Strict adherence to proper equipment calibration. c. Proper animal preparation. d. Adherence to a standard scanning protocol. e. Adherence to a standard image interpretation protocol. f. Suitable animal handling facilities. 3.7.3 Animals to be scanned 3.7.3.1 Scanning for genetic evaluation It is important for genetic evaluation that animals are allowed to express their inherent genetic potential. As fat measurements are directly related to the nutritional state of the animals it is essential to record only groups of animals which are on a reasonable level of nutrition. Otherwise too many animals will be recorded with minimum fat levels and no intramuscular fat thus generating information of little value since the true genetic potential will not have been expressed. Such data is useless for genetic evaluation where the intention is to identify genetic differences. As ultrasound measurements are used to provide an insight into a number of carcass characteristics and to a limited extent into meat quality, the most valuable records will come from young animals undergoing selection for breeding and on which no direct carcass information can be collected. Yearling bulls and yearling heifers are the most obvious animals to scan. In many commercial production systems a progeny test through steers or bulls is also possible. In summary scanning can provide useful information for the estimation of carcass EBVs or EPDs using records from a. Yearling bulls. b. Yearling heifers. c. Groups of progeny fed for slaughter. The most common age window for young breeding stock is between 320 to 500 days. It may vary depending on production system. The development of body composition EBVs or EPDs requires that scanned animals be associated with a well-defined contemporary group. For animals scanned on the farm of birth a contemporary group is comprised of all animals of the same sex that are reared and managed together. A 60 days birth window is recommended. Where herd sizes are small and calving season extended the contemporary group may cover a longer birth season window. A typical contemporary group definition would include herd code, birth season, weaning group (date, location, and management), operator (if scanned by more than one operator) and scanning group (date, location, and management). For animals scanned at a central station test, the contemporary group should include animals from the same sex born within 60-90 days age window and the same test end. The herd of origin and other birth and weaning group information may also be included. The practise of harvesting/slaughtering animals from groups when they reach market target weights reduces the management group size as records from animals slaughtered on different days and in particular in different abattoirs should not be directly compared. Scanning for carcass traits of all animals prior to the first selection of any animals to be slaughtered will provide a basis for direct comparison of all animals in the group. 3.7.3.2 Scanning of slaughter animals Real time ultrasound scanning for subcutaneous fat can also be used to determine market suitability of commercial slaughter animals. However, scanning of animals that have reached target market specifications should not be compared with the use of the same technology for performance recording purposes. Special care must be taken to avoid any bias in the mean of the observations. Such a bias could have severe financial implication if animals are slaughtered and found to be outside market specifications. For the purpose of genetic evaluation a consistent bias will be part of the management group effect and will not affect the accuracy of genetic evaluation. 3.7.4 Technical requirements 3.7.4.1 Recording device A number of real time ultrasound recording devices are on the market. Most of them have been developed for human health or veterinary purposes (e.g. pregnancy testing). The small transducer used for medical purpose is of limited use for scanning of carcass characteristics and so special transducers are required when scanning for carcass traits. For a list of scanning devices used in animal recording see Appendix 1 following. Ultrasound equipment is undergoing continuous improvement resulting in smaller and more sophisticated models being developed and marketed on an ongoing basis. 3.7.4.2 Facilities Efficient ultrasound scanning of large groups of animals requires well designed yards, races and chutes to hold the animals in a stress free and secure manner and release them as soon as all necessary information has been recorded. The operator should insure that the cattle handling facilities for scanning are adequate in respect of health and safety considerations before he commences scanning. A squeeze chute with fold-down side panels is best for scanning beef cattle. A shaded area is required to allow the operator a good view of the monitor, as direct sunlight will make it difficult to see the images on the screen. Therefore, the chute should be located under a roof that can block direct sunlight and provide protection from rain or other inclement weather conditions. A clean and grounded power signal is required at the chute-side. It is best if the electrical circuit is a dedicated line to the chute, free from the interference of other electrical equipment such as motors etc. Most ultrasound equipment does not operate efficiently and accurately when the ambient air temperature falls below 8 degrees Celsius or 45 degrees Fahrenheit. The breeder should make provisions to keep the facility heated in these situations. The operator should provide some portable supplemental heating systems to keep the ultrasound equipment warm if required. 3.7.4.3 Preparation of the animal Animals should be cleaned and clipped particularly in winter or early spring when their hair is too long to get quality images. The requirement for clipping is even higher if scanning is used to determine intramuscular fat % (IMF%) as the lack of complete contact between the ultrasound transducer and the animal’s skin can have a direct effect on the predicted IMF%. In general the length of hair coat should be no more than 1,5 cm or 1/2 inches. Prior to scanning a liquid, commonly vegetable oil, should to be applied to the scan site to provide maximum contact between transducer and skin. The temperature of the oil applied to the skin should be above 20 degrees Celsius or 68 degrees Fahrenheit for best results. This might require a warm water bath for the bottle containing the oil during times of lower temperatures. Wet animals can be scanned successfully as the water can easily be removed from the scan area. For the scanning of eye muscle area a curved guide or offset made from super-flap will help and will allow a curved image to be recorded without the need to apply excessive pressure to maintain good contact as this would result in distortions of the muscle or fat measurements resulting. 3.7.4.4 Recorded Traits Real Time ultrasound imaging has so far been used for the measurement of subcutaneous fat cover as well as for Eye Muscle Area and Muscle Depth and the Intramuscular Fat Percent in the longissimus dorsi. The appropriate areas of interest are shown in Figure 3.3.
