Ultrasonic Assessment of Body Condition Changes of the Dairy Cow During Lactation

A method for measurement of subdermal fat thickness in dairy cows by digitizing cross-sections of ultrasonicscans was investigated. A commercial ultrasonic system was modified for acquiring and presenting A-mode and B-modeultrasonic images. Two sites were selected for a series of successive measurements: one was on the flat area of the rear ofthe rump between the pin bone and the tail head; the other was between 12th and 13th ribs, below the back rump. Severalpoints were measured in each site. Two probe holders were fabricated to fit each site and to ensure successivemeasurements at exactly the same points. A 7.5-MHz probe was used. Both A and B scans were conducted and recordedon videotape. A computer program was written to acquire and digitize data from A-mode scans to a depth of 30 mm. Analgorithm located signal peaks to distinguish among skin, subdermal fat and muscle, and then calculated thickness oflayers at each point. A trial was conducted to evaluate the use of this system to detect body condition changes of the dairycow during lactation. Six cows were monitored and measured from calving to late lactation: subdermal fat wasultrasonically measured weekly, and cows were scored weekly for body condition and weighed daily. It was concludedthat successful ultrasonic measurements for body condition assessment, to detect energy balance changes, depend onaccurate 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 conditionsdescribed, the system can measure quantitatively changes of subdermal fat thickness in lactating dairy cows.