Ultrasonographic measurements of kidney fat thickness and Longissimus muscle area in predicting body composition of pregnant goats

Non-invasive methods for estimating body composition to monitor nutritional status in goats have been less studied. Therefore, this study estimated the body composition and fat depots of pregnant goats by using indirect measurements, such as bodyweight (BW) and ultrasound measurements of the Longissimus muscle area (LMA) and kidney fat thickness (KFT). Forty-three pregnant goats were slaughtered at 50, 80, 110 and 140 days of gestation to determine the gross energy and fat content in the body, as well as to obtain the mass of renal fat, omental fat and non-carcass fat. After the slaughter, the mass of fat depots was recorded and the whole body of the each animal was ground to take samples for determining gross energy (using a bomb calorimeter) and fat (Soxhlet extraction with ether). Animals were weighed, and ultrasonographic measurements were taken at the time of slaughter. The LMA and KFT measurements were taken between the 12th and 13th rib and after the 13th rib space, respectively, and these measurements were used to estimate total gross energy, body fat content and the renal fat, omental fat and non-carcass fat mass. Multiple regressions were performed using Proc mixed of SAS. No significant correlation was observed between gross energy and body fat composition, the number of fetuses or the days of gestation. LMA and BW were positively related to body fat and gross energy contents. KFT and BW showed a positive correlation with renal fat depots, omental fat content and non-carcass fat mass. The estimated models revealed that the total body fat increased from 15.6% to 20.8% of bodyweight from 50 to 140 days of gestation. This report is the first study using kidney fat thickness as a tool to predict fat depots in goats. LMA, BW and KFT measurements will enable the development of models to aid in the monitoring of the nutritional status of goats during pregnancy.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP