B ody condition (BC) score is recognized in the dairy industry as a necessary tool for managing energy reserves of the dairy cow for optimal and efficient production through various stages of lactation (Edmondson et al., 1989; Ferguson and Otto, 1989; Chilliard et al., 1991). The BC score is based on subdermal fat thickness at key body locations, and is determined by visual scoring on a 1.0 to 5.0 scale with 0.25-unit steps (Edmondson et al., 1989). Lower BC scores usually represent thin cows and higher scores represent those with more subdermal fat. Fat thickness at any of the key sites is correlated with that at other key sites (Edmondson et al., 1989). However, BC scores represent a subjective, indirect classification and visual evaluation of the subdermal fat content. Standardized BC scoring can be incorporated into a management expert system, together with other animal-status monitoring indicators, such as body weight (BW), milk yield, etc. (Maltz et al., 1992; Grinspan et al., 1994). These indicators have become practical tools for optimizing lactation performance (Spahr et al., 1993). Ultrasound pulse-echo measurements of livestock physical composition have been used since the late 1950s. Some early basic work in this area has been described by Johnson et al. (1964); it concerns measurement of fat depth in cattle and other animals. Sensors normally used to measure fat thickness and muscle area are available off- the-shelf. Non-destructive evaluation through ultrasonic excitation is widely applied in medicine and in the metal industry. Adaptation of this technology to other areas requires thorough investigation, since special measurement techniques, sensors, modes, standardization and data processing have to be developed. This has been discussed in relation to quality evaluation of food (Mizrach et al., 1989, 1991, 1996a) and meat (McLaren et al., 1991; Park and Whittaker, 1991). The B-mode technique was used in a program for improving meat animals; it was discussed by Thane et al. (1989), McLaren et al. (1991), and Park and Whittaker (1991). There is worldwide interest in the use of ultrasound for measurement of body composition in live meat animals (Robinson et al., 1992). Recent publications have discussed the beef and pork industries’ interest in the use of ultrasonic technology for improving meat quality (Brethour, 1992; Gresham et al., 1992; Cross and Whittaker, 1992), and principles and potential application of the technology to BC scoring (Whittaker et al., 1992). Park and Whittaker (1991) determined optimum parameter values for design of a prototype ultrasonic probe for predicting intramuscular fat on beef carcasses. In beef finishing programs, ultrasound, at times, has been used successfully ULTRASONIC ASSESSMENT OF BODY CONDITION CHANGES OF THE DAIRY COW DURING LACTATION A. Mizrach, U. Flitsanov, E. Maltz, S. L. Spahr, J. E. Novakofski, M. R. Murphy ABSTRACT . A method for measurement of subdermal fat thickness in dairy cows by digitizing cross-sections of ultrasonic scans was investigated. A commercial ultrasonic system was modified for acquiring and presenting A-mode and B-mode ultrasonic images. Two sites were selected for a series of successive measurements:one was on the flat area of the rear of the rump between the pin bone and the tail head; the other was between 12th and 13th ribs, below the back rump. Several points were measured in each site. Two probe holders were fabricated to fit each site and to ensure successive measurements at exactly the same points. A 7.5-MHz probe was used. Both A and B scans were conducted and recorded on videotape. A computer program was written to acquire and digitize data from A-mode scans to a depth of 30 mm. An algorithm located signal peaks to distinguish among skin, subdermal fat and muscle, and then calculated thickness of layers at each point. A trial was conducted to evaluate the use of this system to detect body condition changes of the dairy cow during lactation. Six cows were monitored and measured from calving to late lactation: subdermal fat was ultrasonically measured weekly, and cows were scored weekly for body condition and weighed daily. It was concluded that successful ultrasonic measurements for body condition assessment, to detect energy balance changes, depend on accurate and reliable standardization of measurements, at a responsive site. The between-ribs site was more responsive, and a single point (usually just below the spine) provided sufficient data for the required purpose. Given the conditions described, the system can measure quantitatively changes of subdermal fat thickness in lactating dairy cows. Keywords. Ultrasound, Cow, Dairy, Body-condition-scores, Subdermal fat. Article has been reviewed and approved for publication by the Information & Electrical Technologies Division of ASAE. Presented as ASAE Paper No. 96-3016. This research was supported in part by Grant No. IS-2181-92R from BARD, the United States-Israel Binational Agricultural Research and Development Fund. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 1931-E, 1996 series. The authors are Amos Mizrach, ASAE Member, Ephraim Maltz, Senior Scientists, and Uri Flitsanov, Scientist, Institute of Agricultural Engineering, A.R.O., the Volcani Center, Bet Dagan, Israel; and Sidney L. Spahr (deceased), Jan E. Novakofski, and Michael R. Murphy, Professors, Department of Animal Sciences, University of Illinois, Urbana, Ill. Corresponding author: Dr. Amos Mizrach, Institute of Agricultural Engineering, The Volcani Center, A.R.O., PO Box 6, Bet Dagan 50-250, Israel; voice: 972-3-9683451; fax: 972-3-9604704; e-mail: amos@ agri.gov.il. Transactions of the ASAE © 1999 American Society of Agricultural Engineers 0001-2351 / 99 / 4203-805 805 VOL. 42(3): 805-812