Effects of the infusion of non-selective β-, and selective β1- or β2-adrenergic agonists, on body fat mobilisation in underfed or overfed non-pregnant heifers

The aim of this study was to analyse the effects of the intravenous infusion of a non-selective beta-agonist (beta-A) (isoproterenol, ISO), and selective beta 1-A (dobutamine, D) or beta 2-A (terbutaline, T) on body fat mobilisation in non-pregnant heifers, in a 2 x 2 crossover design with two treatments (underfeeding or overfeeding) and two periods. The effect of the duration of submission to each energy level on basal and ISO-induced fat mobilisation was also studied. ISO had a high and significant lipolytic effect whatever the energy level. Nevertheless, the response area of non-esterified fatty acids (NEFA) to ISO in underfed cows was 1.7 times greater than that in overfed cows. T had a slight but significant lipolytic effect on NEFA plasma response in the underfed group. D had no lipolytic effect. Basal and ISO-stimulated plasma NEFA levels were similar after 1 or 4 weeks of underfeeding. (C) Inra/Elsevier, Paris.