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

Modelo para estimativa de peso em éguas gestantes mestiças crioulas

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 12^th intercostal space (12^th ICS) and 18^th rib (18^th Rib), to use in a mathematical model to estimate the weight of pregnant mares. Observations were divided into three periods of pregnancy: 5^th to 7 ^h month, 7^th to 9 ^h month, and 9^th to 11^th month. Mares in late pregnancy showed an increase in actual weight and an increase in 12^th ICS and 18^th Rib measurements. Tape weight and body-weight estimation formula underestimated the weight of pregnant mares. However, the regression model using heart-girth circumference, 12^th ICS, and 18^th 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) + (12^th ICS x 1.278) + (18^th Rib x 0.944) can be used to estimate body weight in pregnant mares from the 5^th to 11^th months of pregnancy.

Key words:
pregnant mares; weight tape; body weight estimation