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The main objective was to develop equations to predict body weight (BW) using heart girth (HG) in Pelibuey ewes. A second objective was to evaluate this model for precision using an independent dataset. For model develop a data set composed by 366, 2-3-yr-old, non-pregnant and non-lactating ewes; with a mean BW of 45.7 ± 9.16 kg and HG of 87.55 ± 7.93 cm was used. A linear equation was fitted: BW=-47.97 (±2.01) + 1.07 (±0.02)×HG (r 2 = 0.86, Root mean square error (RMSE)= 3.46, y n= 366). A second data set composed by 67 animals, with similar characteristics (BW of 38.25 ± 8.62 kg and HG of 80.37 ± 7.03 cm) was used to evaluate the developed equations. For the evaluation, the relationship between observed and predicted values of BW by linear regression, the mean squared error of prediction (MSEP) and root MSEP (RMSEP), and concordance correlation coefficient analysis were used. The proposed equation was highly precise (R 2 =0.913) and accurate (Cb=0.996) with a reproducibility index of 0.95. The MEF has indicated a higher efficiency of prediction with higher proportion of the total variance of the observed values been explained by the predicted data (0.91). The partition of the MSEP has indicated a very small mean bias (0.082). The systematic bias has shown that only 1.93 % of the error of prediction was associated with the slope and most of the error was explained by the random component indicating small biases with the predictions. The proposed equation accurately and precisely estimated the BW of non-pregnant and non-lactating Pelibuey ewe using HG and therefore is recommended to be used.

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<p><strong>Background.</strong> In terms of animal management, the measurement of body weight (BW) is important in the design of nutrition and health programs. <strong>Objective.</strong> The objective of the present study was to evaluate the relationship between body volume (BV) and BW in Pelibuey ewe lambs and ewes. <strong>Methodology. </strong>For the model development, the BW and body volume (BV) were recorded in 406 Pelibuey ewe lambs and ewes ranging from two months to one years in age. All animals were clinically healthy, with a BW = 37.62 ± 10.63 kg. The BV was calculated using the heart girt (HG) and the body length (BL). BV was calculated according to the mathematical formulas for calculating the volume of a cylinder, considering biometric measurements in the calculation. The relationship between BV and BW was assessed by linear (Eq. 1), quadratic (Eq. 2) and allometric equation (Eq. 3). The goodness of fit of the regression models was assessed by the Akaike information criterion (AIC), Bayesian information criterion (BIC), coefficient of determination (R²), mean square error (MSE) and root mean square error (RMSE). <strong>Results. </strong>The correlation coefficient (r) between BW and BV was 0.89 (<em>P</em> &lt; 0.001). The quadratic model had the higher value of coefficient of determination (R²= 0.81, and the lower MSE (4.17), RMSE (2.04), AIC (1163.64) and BIC (1175.66) values. The predictive ability of the three live weight prediction models was evaluated using <em>k</em>-folds validation (<em>k</em> = 10). <strong>Implications.</strong> The quadratic model had the higher coefficient of determination and lowest values were found for the mean square error (MSE) and mean absolute error (MAE). This model is practical and predicts with high accuracy the BW of the animals. <strong>Conclusion.</strong> Based on the evaluation approaches used in the present study and the close relationship between BW and BV in Pelibuey ewe lambs and adult ewes, the quadratic model was the mathematical model that had the best performance according to the goodness-of-fit evaluation.</p>

Due to the conditions in which traditional sheep production systems operate, the evaluation of animal growth from live weight (LW) is limited by the high cost of the livestock scale as well as the sophisticated maintenance required. In this scenario, in recent years, biometric measurements have been investigated as an accurate indirect method to predict the LW of farm animals. Therefore, the present study was undertaken to examine different models for predicting the body weight of growing lambs using the body volume (BV) formula. Body volume, heart girth (HG) and body length (BL) data of 290 lambs aged between two and eight months were recorded. Body volume was calculated from HG and BL data using a formula that calculates the volume of a cylinder. The estimation of LW from the BV formula was achieved through regression equations using three mathematical models (linear, quadratic and exponential). The mean values of LW, HG, BL and BV of the lambs were 29.12±12.04kg, 70.00±11.69cm, 38.40±6.43cm and 23.93±9.90dm3, respectively. The correlation coefficient between LW and BV was r = 0.96 (P<0.001). The quadratic model showed the highest coefficient of determination (0.93) and the lowest prediction error (3.29kg). Under the experimental conditions adopted in this study, it is possible to predict the live weight of growing lambs using the body volume formula.

The determination of energy content in the carcass and body of domestic animals by direct method involves very intensive work and it is costly. The aim of this study was to evaluate the relationship between body weight (BW) and body condition score (BCS) with the energy content of muscular and adipose tissues of adult Pelibuey ewes. Twenty two adult non-pregnant, nonlactating ewes of 35.63 ± 5.03 kg BW and 2.47±0.55 BCS were used. The correlation coefficients (r) of BCS between muscle energy (ME), fat energy (FE) and total energy (TE) were all significant (P<0.01) with values of 0.64, 0.66 and 0.69, respectively, while for BW between ME, FE and TE they were all significant (P<0.001) with values of 0.90, 0.76 and 0.89, respectively. The regression equations had high determination coefficients (r 2) ranging from 0.87 to 0.94 when BCS was used as predictor, while using the BW the r 2 ranged from 0.59 to 0.83. The inclusion of both BW and BCS in multiple regressions improved the prediction from 2 to 7%; nonetheless, the inclusion of BCS only was significant in the equation for TE. The use of BCS and BW in Pelibuey ewes provides a good estimate of the ME, TE and FE of the carcass.

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