Artificial long-day photoperiod enhances growth performance and metabolic indicators in young male goats

This study aimed to evaluate whether exposure to artificial long-day photoperiods stimulates growth performance in young male goats, either intact or castrated. Forty young male goats (13 wk old), either intact (I) or castrated (C), were assigned to one of two photoperiod treatments: artificial photoperiod (AP; 16h light:8h dark) or natural photoperiod (NP; 12h light:12 dark). Animals were housed individually, and four experimental groups were established: NP-I (n = 10), AP-I (n = 11), NP-C (n = 10), and AP-C (n = 9). Males were weighed weekly; glucose, testosterone, and insulin-like growth factor 1 (IGF-1) concentrations were monitored biweekly; and feed intake was measured every 3 wk from September to February. At 38 wk of age, males were slaughtered to assess carcass yield. Each animal was considered an experimental unit, and the data were analyzed using mixed models and repeated measures of SAS. Goats exposed to AP gained more weight and had greater final body weights than those under NP conditions (P < 0.001). Intact males also gained more weight than castrated males (P < 0.001). Feed intake was greater in AP-treated animals (P < 0.001). Carcass yield was greater in both AP- and I-males compared to NP- and C-males, respectively (P < 0.001). IGF-1 concentration increased in AP- and I-males than in NP- or C-males (P < 0.001), and glucose concentration increased in AP-treated animals compared to those exposed to NP (P < 0.001). Testosterone concentration increased in AP males than in NP males in weeks 15 and 17 (P < 0.01), but not at the other time points (P > 0.05). These findings suggest that exposure to artificial long-day photoperiods increases daily weight gain, feed intake, final body weight, and carcass yield in young male goats, regardless of their reproductive status. These improvements were associated with increased IGF-1 and glucose concentrations, while testosterone concentration remained unaffected.