Two experiments were conducted to determine whether exposure to a photoperiod of artificial long days in autumn increased milk yield in subtropical goats milked once (Exp. I) or twice daily (Exp. II). In Exp. I, starting at d 10 of lactation, 1 group of does was kept under naturally decreasing photoperiod (DD1X; n = 8), whereas the other group was submitted to an artificial photoperiod of long days (LD1X; n = 8; 16 h light:8 h darkness). The kids were weaned 28 d after parturition, and dams were manually milked once daily. Milk yield and milk components (fat, protein, and lactose) were assessed up to 140 d of lactation. From d 0 to 28 of lactation (suckling phase), mean daily milk yield did not differ between DD1X and LD1X goats (2.3 ± 0.2 kg vs. 2.4 ± 0.2 kg; P = 0.717). However, between d 29 and 84 (early milking phase), mean daily milk yield was greater in LD1X does than in DD1X does (2.6 ± 0.1 kg vs. 2.1 ± 0.1 kg; P = 0.001). Finally, between d 85 and 140 (late milking phase), mean daily milk yield was greater in LD1X goats than in DD1X goats (P ≤ 0.05) only during the first 2 wk. In Exp. II, one group of goats was exposed to a photoperiod of naturally decreasing days (DD2X; n = 8) and another group was submitted to an artificial photoperiod of long days (LD2X; n = 7). In both groups, kids were weaned on d 28 of lactation and the dams were manually milked twice daily. During the nursing phase, mean daily milk yield did not differ between the DD2X and LD2X groups (2.5 ± 0.3 kg vs. 2.6 ± 0.2 kg; P = 0.767). In the early milking phase, mean daily milk yield was greater in LD2X than in DD2X goats (3.3 ± 0.2 kg vs. 2.8 ± 0.2 kg; P = 0.022), whereas during the late milking phase, milk yield did not differ between the 2 groups (P = 0.946). In both experiments, milk composition was not significantly influenced by exposure to long-day photoperiod. We conclude that, in subtropical female goats that start lactation in late autumn, exposure to an artificial long-day photoperiod stimulates milk yield, even if goats are milked once daily. In addition, combining exposure to long days with twice-daily milking will increase further milk yield in such goats without affecting milk components.

In experimental murine infections with

This study was designed to determine whether any relationship exists between exposure to artificial long days, milk yield, maternal plasma insulin-like growth factor 1 (IGF-1) levels, and kid growth rate in goats. One group of lactating goats was maintained under naturally decreasing day length (control group; n = 19), while in another one, they were kept under artificial long days (LD group; n = 19). Milk yield was higher in goats from the LD group than that in the control group (P < 0.05). Maternal IGF-1 levels at day 57 of lactation were higher (P < 0.05) in goats from the LD group than the levels in the control group and were positively correlated with the total milk yields per goat at days 43 and 57 of lactation (r = 0.77 and r = 0.84, respectively; P < 0.01). Daily weight gain at week 4 was higher (P < 0.01) in kids from the LD group than that in kids from the control group and was correlated with total and average IGF-1 maternal levels (r = 0.60 and r = 0.60, P < 0.05). It was concluded that submitting lactating goats to artificial long days increases milk yield, plasma IGF-1 maternal levels and the growth rate of the kids.

Introducción: la carnitina es clave en el adecuado metabolismo de los lípidos por lo que su deficiencia puede desencadenar problemas metabólicos y productivos durante el periparto, por esto, el objetivo de este estudio es evaluar la aplicación parenteral de diversas dosis de L-carnitina a vacas durante el periparto.Metodología: cada tratamiento estuvo conformado por seis vacas entre el segundo y sexto parto en vacas Holstein de alta producción, fueron alimentadas con pasto kikuyo (Cenchrus clandestinus [Hochst. ex Chiov.] Morrone) y un suplemento alimenticio. Se aplicaron vía intramuscular 0, 5, 10 y 15 gramos de L-carnitina en solución cada 5 días desde el día 20 preparto hasta el día 15 posparto sobre el consumo de materia seca (CMS), balance de energía (BE), producción (PL) y contenido de en grasa (GrL) y proteína (PrtL) en la leche. Usando la técnica de indicadores se estimó el CMS, los días 5, 10, 15 y 20 de lactancia se midieron PL, GrL y PrtL., al día 270 de gestación, a los días 10 y 20 posparto se calculó el BE de cada vaca.Resultados: los resultados de estas mediciones se analizaron en un diseño de parcelas divididas en el tiempo.Conclusiones: los tratamientos no afectaron CMS, PL, PrtL, GrL y el BE (p>0.05); bajo las condiciones experimentales descritas en este trabajo, la L-carnitina parenteral no tiene efecto sobre la producción, composición de la leche y el BE.

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