Utilisation de la barymétrie pour l’estimation du poids chez le zébu Azawak au Niger

The objective of this study was to establish weight estimation equations from body measurements applicable to the Azawak zebu. The weight and 12 types of measurements were recorded in 343 Azawak zebus at the Sahelian experimental station of Toukounous in Niger. Most of the animals were young: 74% were at most two years old. Out of the 12 types of measurements, three were retained because of their correlation with the body weight (thoracic perimeter, height at the withers and scapulo-ischial length). The weight correlation was higher with the thoracic perimeter (r = 0.97) and the scapulo-ischial length (r = 0.96) than with the height at the withers (r = 0.92). Several types of equations between the weight and two types of measurements (thoracic perimeter and scapulo-ischial length) were compared. The selected equation for all the animals (males and females) was a polynomial regression of the predicted weight (y) over the thoracic perimeter (x) and the scapulo-ischial length (z): y = 0.02697x 2 – 4.25x + 1.535z + 96.145 with a coefficient of determination r 2 = 0.989 and a residual standard deviation (S y ) of 11.23 kg. The error between the observed and predicted weights, expressed as percentages of the observed weight, was lower than 5% in 57.2% of the animals and lower than 10% in 90.1% of them. For the males, an equation also with two variables was selected: y = 0.0260x 2 – 3.856x + 1.211z + 96.114 with r 2 = 0.990 and S y = 10.33 kg. For the females, a regression only using the thoracic perimeter (y = 0.0281x 2 – 3.294x + 125.217) showed great accuracy (r 2 = 0.981 and S y = 15.28 kg). This latter equation was used to establish a conversion table of thoracic perimeters into body weights.