EXPOSURE MALE GOAT KIDS FROM SUBTROPICAL REGIONS TO ARTIFICIAL LONG DAYS, STIMULATE A HIGHER GROWTH RATE, BETTER BODY DEVELOPMENT AND INCREASED GLYCEMIA

Abstract

Background. Small ruminants from subtropical regions are sensitive to respond physiologically to natural photoperiodic changes. In some subtropical goat production systems as located in semi-arid areas of México, the main objective is to obtain in the shortest possible time, males with a suitable weight and body development for sale. Objective. The present study determines if the exposure to artificial long day photoperiod could promote a growth rate, body development and an increased glycemia in male goat kids compared with those under natural short days. Methodology. Starting on late September, 21 creole male goat kids (13 ± 0.1 week aged; mean ± SEM) were assigned to one of the two experimental groups. In the natural short days group, males remain under natural short days from autumn-winter (GDC, n = 10). In the artificial long days group, males were exposed to artificial photoperiod consisting in 16 h light and 8 h darkness (GDL, n = 11). The study lasted until the animals had 35 weeks of age. All animals were fed according their nutritional requirements. Results. During the study, the body weight of the GDL animals was higher than that of the GDCN males (P < 0.05). Due to this, the daily weight gain (GDP) obtained at 23 weeks of age was higher in the GDL males (165 g/day) than that registered in the GDC males (143 g/day; P <0.05). In some periods, the males of the GDL had higher body mass index (IMC) than the males of the GDC (P < 0.05). Thoracic perimeter at week 32 was greater in the GDL males than in the GDC males (P <0.05). The height at the withers did not reach significant differences in the comparisons between groups in the different weeks measured (P > 0.05). However, the total height at the withers gained during the study was significantly higher in the GDL males than in the GDC males (P < 0.01). Under fasting conditions, GDL males had higher levels (P < 0.05) of blood glucose in some periods than GDC males. Implications. The present study demonstrate that artificial long days stimulates growth in goats as occurs in other ruminants. Conclusion. Exposure of the male goat kids from subtropical regions to artificial long days, promotes a higher growth rate, better body development and increased glycemia compared to kids maintained under natural short-day photoperiods.