Effects of exposure to artificial long days on milk yield, maternal insulin‐like growth factor 1 levels and kid growth rate in subtropical goats

Abstract

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.

Subtropical goats ovulate in response to the male effect after a prolonged treatment of artificial long days to stimulate their milk yield

“…In the present study, the continuous exposure to an artificial longday photoperiod of 14 hr of light per day increased milk production during the first 100 days of lactation in goats that had given birth during late autumn. The findings of the current study agree with those described by Garcia-Hernandez et al (2007) and Flores et al (2011Flores et al ( , 2015 and Hernández et al (2016). Indeed, goats exposed to 20 or 16 hr of light per day showed an increase in milk production level compared with control animals.…”

“…(, ) and Hernández et al. (). Indeed, goats exposed to 20 or 16 hr of light per day showed an increase in milk production level compared with control animals.…”

“…This F I G U R E 2 Mean (± SEM) content of fat (upper), protein (middle) and lactose (bottom) in milk from subtropical goats kidding during late autumn and maintained under natural short-day photoperiod (n = 17; control, ▪ ) or submitted to an artificial long-day photoperiod consisting in 14 hr of light per day (n = 22; treated, □). For the three components, ANOVA only revealed an effect of time of lactation (p = .0001), but neither treatment effect nor time × treatment interaction was significant (p ≤ .94 and p ≤ .99, respectively) effect was observed regardless if animals were milked once or twice per day (Flores et al, 2011;Hernández et al, 2016) or if they were under extensive grazing conditions with a food supplement . The results of the current study clearly show that the administration of 14 hr of light per day in goats starting their lactation during late autumn is a skeleton photocycle that results in a strong galactopoietic effect.…”

“…In fact, in subtropical goats, it is well documented that exposure to artificial long days consisting in 20 (Garcia‐Hernandez et al., ) or 16 hr of light/day during natural decreasing photoperiod increased milk yield level. This effect was observed regardless if animals were milked once or twice per day (Flores et al., ; Hernández et al., ) or if they were under extensive grazing conditions with a food supplement (Flores et al., ). The results of the current study clearly show that the administration of 14 hr of light per day in goats starting their lactation during late autumn is a skeleton photocycle that results in a strong galactopoietic effect.…”

“…In goats, Garcia‐Hernandez, Newton, Horner, and Nuti () reported that exposure to a photoperiod consisting in 20 hr light and 4 hr of darkness was effective to increase the milk yield. In subtropical goats that gave birth during autumn, several studies demonstrated that exposition to artificial long days consisting of 16 hr light and 8 hr darkness increased by 21% the milk yield compared with animals under natural decreasing days (Flores et al., , , ; Hernández et al., ). However, in these animals, it remains unknown if reducing the exposure from 16 to 14 hr of light/day can be effective to stimulate milk production, like reported previously that this light regime inhibits ovulation (Duarte et al., ).…”