Artificial long-day photoperiod in the subtropics increases body weight in goat kids born in the autumn

Abstract

To determine whether exposure to artificial long days increases the body weight of subtropical goat kids born in autumn, sixty-four goat kids were distributed in a completely randomized design with a factorial arrangement. Experimental groups consisted of two photoperiod treatments (natural or artificial photoperiod, 16 h light: 8 h darkness), and two suckling types (natural or artificial). The mean body weight, recorded at day 27 of age, was higher in goat kids subjected to artificial long days (7.7 ± 0.2 kg) than in those maintained under a natural photoperiod (7.0 ± 0.2 kg; P < 0.05). The mean daily gain was higher in light-treated kids (163 g/d) than in those maintained on a natural photoperiod (141 g/d; P < 0.001). Likewise, the mean blood glucose concentration was higher in goat kids submitted to artificial long days (102.0 ± 1.3 mg/dL) than in those kids maintained on the natural photoperiod (92.5 ± 1.3 mg/dL; P < 0.001). The suckling type had an effect on the plasma insulin-like growth factor-1 concentrations (IGF-1) of the kids (P < 0.01), and this effect was more pronounced in goat kids under artificial long days (P < 0.05). The results of the present study show that in subtropical goat kids born during the autumn, exposure to an artificial long-day photoperiod promotes a high body weight during the early phase of growth, independent of whether they are reared or not by their dams. In addition, these results also showed that, depending on suckling type, exposure to artificial long days increase the concentrations of IGF-1 in goat kids.