Development of a weight-estimation model to use in pregnant criollo-type mares

ABSTRACT: The aims of this study were: 1) to compare the tape weight and associated weight-estimation formula to evaluate weight gain in pregnant mares, and 2) to develop a mathematical model to estimate the weight of pregnant mares using body measurements. Thirty-four criollo-type mares were evaluated every two weeks during the middle and late pregnancy. The mares were weighed on a livestock scale, and we estimated body weight using tape weights and an associated body-weight estimation formula. Also, heart-girth circumference (heartgirth) and abdominal circumference were measured; the latter at the 12th intercostal space (12th ICS) and 18th rib (18th Rib), to use in a mathematical model to estimate the weight of pregnant mares. Observations were divided into three periods of pregnancy: 5th to 7 h month, 7th to 9 h month, and 9th to 11th month. Mares in late pregnancy showed an increase in actual weight and an increase in 12th ICS and 18th Rib measurements. Tape weight and body-weight estimation formula underestimated the weight of pregnant mares. However, the regression model using heart-girth circumference, 12th ICS, and 18th Rib measurements showed high correlation (r2 = 0.87, P<0.001) with actual weight. Finally, the alternative methods usually used in horses are not accurate to estimate body weight in pregnant mares. In conclusion, the regression model Y=-540.143 + (heartgirth x 3.068) + (12th ICS x 1.278) + (18th Rib x 0.944) can be used to estimate body weight in pregnant mares from the 5th to 11th months of pregnancy.摘要：本研究旨在达成两大目标：其一，对比带尺估重法及其配套体重估算公式，用于评估妊娠母马的体重增长情况；其二，构建基于体尺测量数据的数学模型，以估算妊娠母马的体重。本研究于妊娠中晚期阶段，每两周对34匹克里奥尔型（criollo-type）母马开展一次观测。研究人员使用牲畜秤称量母马实际体重，同时通过带尺估重法及配套体重估算公式计算其预估体重。此外，测量了胸围（heart-girth circumference）以及腹围，其中腹围分别于第12肋间（12th intercostal space，12th ICS）和第18肋（18th Rib）处进行测量，上述体尺数据将用于构建妊娠母马体重估算的数学模型。本研究按妊娠阶段将观测数据划分为三个时期：妊娠5至7月龄、7至9月龄及9至11月龄。结果显示，妊娠晚期母马的实际体重、第12肋间及18肋处的腹围测量值均有所升高。带尺估重法及配套估算公式均低估了妊娠母马的实际体重。然而，以胸围、第12肋间腹围及第18肋腹围为自变量构建的回归模型，与实际体重呈现极高相关性（决定系数r²=0.87，P<0.001）。最终证实，常规应用于非妊娠马匹的体重估算方法并不适用于妊娠母马。综上，本研究构建的回归模型Y=-540.143 + (胸围 × 3.068) + (第12肋间 × 1.278) + (第18肋 × 0.944)，可用于估算妊娠5至11月龄母马的体重。