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 400–625kg 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.