Development and validation of an objective method for the assessment of body condition scores and selection of beef cows for timed artificial insemination

The objectives of this study were to: 1) evaluate the relationship of the angle formed between the left and right sides of the rump with body condition score (BCS) in cattle; and 2) develop an objective tool to select cows for timed artificial insemination (TAI) based on their BCS. In Experiment 1, 801 lactating Nelore cows, 3-12 years old and weighing 400-625 kg were enrolled. All females were evaluated according to BCS (scale 1-5). In addition, the angle formed between both sides of the rump was measured in all cows with a goniometer. The relationship between BCS and the rump angle was analyzed by linear regression. There was a positive relationship between BCS and rump angle (P<0.0001). The linear regression equation was angle =77.76+9.94 x BCS; R2=0.67. The aim of Experiment 2 was to evaluate BCS in a simple, direct and objective way using rump angle and related BCS to TAI performance. A device was developed called Vetscore® to determine BCS according to rump angle. Using the Vetscore, cows were classified into three different categories of BCS using a color-based method: red, BCS<2.75; green, BCS between 2.75 and 4.5; and yellow, BCS>4.5. A total of 429 Nelore suckling cows, 4-8 years old, were subjected to a TAI protocol based on estradiol benzoate, exogenous progesterone, prostaglandin F2α, equine chorionic gonadotropin and estradiol cypionate. At Day 0, all cows were evaluated with the Vetscore® and classified according to the device's BCS color scale. Pregnancy diagnosis was performed by ultrasonography 30 d after TAI. Pregnancy per AI (P/AI) was analyzed using the chi-square test. A good level of agreement was observed between Vetscore's scale and visual BCS (82.9%). Cows classified as “green” had higher P/AI than cows classified as “red” and “yellow“ (60.4%, 168 of 278; 42.4%, 61 of 144; and 28.6%, 2 of 7; respectively; P<0.001). These results demonstrate that Vetscore® is an efficient and low-cost methodology for the assessment of BCS and, indirectly, nutritional status of beef cows. Finally, cows classified as adequate according to Vetscore® color scale had higher P/AI at 30 d compared with those considered inadequate.