Ultrasonic assessment of body condition changes of the dairy cow during lactation

A method for measurement of subdermal fat thickness in dairy cows by digiti zing cross-sections of ultrasonic scans was investigated. A commercial ultr asonic system was modified for acquiring and presenting A-mode and B-mode u ltrasonic images. Two sires were selected for a series of successive measur ements: one was on the flat area of the rear of the rump between the pin bo ne and the tail head; the other was between 12th and 13th ribs, below the b ack rump. Several points were measured in each site. Two probe holders were fabricated to fit each site and to ensure successive measurements at exact ly the same points. A 7.5-MHz probe was used. Both A and B scans were condu cted and recorded on videotape. A computer program was written to acquire a nd digitize data from A-mode scans to a depth of 30 mm. An algorithm locate d signal peaks to distinguish among skin, subdermal fat and muscle, and the n calculated thickness of layers at each point. A trial was conducted to ev aluate 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 scared weekly for body condition and weighed daily. It was concluded that successful ultrasonic measurements for body condition assessment, to d etect energy balance changes, depend on accurate and reliable standardizati on of measurements, at a responsive site. The between-ribs site was more re sponsive, and a single point (usually just below the spine) provided suffic ient data for the required purpose. Given the conditions described, the sys tem can measure quantitatively changes of subdermal fat thickness in lactat ing dairy cows.