16 Hours photoperiod in holstein heifers in the subtropics: Effects in development and age to first estrus

espanolEn vaquillas el fotoperiodo largo estimula el crecimiento y la produccion lactea, pero esto no se ha probado en areas subtropicales. Para evaluar el efecto de 16 h luz (L16) durante la lactancia (PW) y/o la etapa prepuberal (PP) en un area subtropical, 325 becerras (36 ± 0.4 kg) fueron distribuidas a: L16 o fotoperiodo natural (LNAT). A los siete meses de edad, 198 de esas becerras (195 ± 2 kg) se asignaron aleatoriamente a L16 y LNAT. Al inicio y final de PW y PP se determino: peso (PC, kg), altura (AC, cm), grosor de grasa dorsal (GG, cm) y del musculo Longissimus dorsi (LD, cm); area pelvica (AP, cm²), condicion corporal (CC), edad al primer estro, profundidad (PGM, cm) y anchura (AGM, cm) de la glandula mamaria. El analisis estadistico fue por ANDEVA para arreglos factoriales 2X2. Al final de PW, GG fue menor y LD fue mayor en L16. Al nal de PP, las vaquillas L16 tuvieron mas PC (260 ± 3 vs 250 ± 3), AP (166 ± 1.2 vs 153 ± 1.2), LD (3.18 ± 0.04 vs 2.90 ± 0.04) y AGM (2.41 ± 0.02 vs 2.21 ± 0.02), pero menos GG (0.114 ± 0.003 vs 0.139 ± 0.003) que las de LNAT. Mas vaquillas L16 (67 %) presentaron estro que LNAT (38 %) y la edad al primer estro fue menor en L16 (278 ± 2 vs 288 ± 2 d). Consecuentemente, la exposicion a L16 durante PW promueve crecimiento magro y durante PP induce crecimiento magro, mayor pelvis y glandula mamaria. Se concluye que vaquillas PP expuestas a L16 tienen mayor potencial productivo y menor riesgo de distocia que las LNAT. EnglishBoth growth and milk production in heifer calves are stimulated by a long photoperiod, though this has not been proven yet in subtropical areas. To evaluate the effect of 16 hr of light (L16) on calves suckling (LAC) and/or pre-pubertal stages (PP) in a subtropical area, 325 calves (36 ± 0.4 kg) were randomized into two groups: L16 or natural photoperiod (LNAT). At seven months of age, 198 of these calves (195 ± 2 kg) were randomly assigned to L16 or LNAT. The following were determined at the beginning and end of LAC and PP stages: Weight (PC, kg), height (AC, cm), thickness of back-fat (GG, cm) and of Longissimus dorsi (LD, cm); pelvic area (AP, cm²), body condition (CC), age at first estrus, mammary gland depth (PGM, cm) and width (AGM, cm). The statistical analysis was made using ANOVA for a 2 X 2 factorial arrangement. At the end of LAC, GG was lower and LD greater in L16 animals, while, at the end of PP, L16 heifer calves had a greater PC (260 ± 3 vs 250 ± 3), AP (166 ± 1.2 vs 153 ± 1.2), LD (3.18 ± 0.04 vs 2.90 ± 0.04), and AGM (2.41 ± 0.02 vs 2.21 ± 0.02), but a lower GG (0.114 ± 0.003 vs 0.139 ± 0.003) as compared to LNAT heifer calves. More L16 animals (67 %) presented estrus versus LNAT (38 %) and the age of the rst estrus was lower in L1 (278 ± 2 vs 288 ± 2 d). Consequently, exposure to L16 during LAC promotes lean growth while lean growth and a bigger pelvis and mammary gland are prompted during PP. Hence, it may be concluded that PP heifer calves exposed to L16 have a higher production potential and lower risk of dystocia than LNAT animals.