اثر دوره نوری پیش از زایش بر غلظت برخی هورمونها، تولید و ترکیبات شیر میشهای لری بختیاری و افزایش وزن نتاج آنها

Introduction: Milk production in Lori Bakhtiari ewes, especially in the first lambing, is low due to the consumption of energy received for body growth, and the lamb(s), especially if there are twin or multiple, have less growth and will have a lower weaning weight. Long day length during early lactation increase milk production in some livestock as dairy cattle and dairy sheep (Mikolayunas et al., 2008). More recent research in dairy cattle (Velasco et al., 2006) and dairy goats (Bagheri and Karami 2023) suggests that prepartum photoperiod affects mammary development and subsequent milk production, but the positive response is from short day photoperiod. The mechanism of this function is the level and role of circulating prolactin in mammary development. The purpose of this research was to investigate the effects of light length at the end of the pregnancy period on the milk production of Lori Bakhtiari ewes and the growth of their lambs.
Materials and Methods: 40 days before the start of lambing, 40 ewes whose lambing dates were close to each other were selected and randomly allocated in two treatments (n=20 for each treatment). Treatment 1 (control): ewes that were exposed to natural day length during the entire pregnancy period. Treatment 2: Ewes that were exposed to 8 hours of light and 16 hours of darkness during the last 40 days of pregnancy. The ewes of two treatments were reared in two separate places with the same size and environmental and management conditions during the late pregnancy period. The amount of feed and it`s quality was similar for both groups. After parturition, all ewes were exposed to natural day length. Milk production and its compositions, prolactin, melatonin and IGF-1 hormones and growth and weight gain of lambs from birth to weaning were measured. Hand milking was done at one week intervals from one week to one month after parturition. Blood samples were taken from jugular vein at the beginning of the experiment, 20 days before parturition, at the time of parturition, 15 and 30 days after parturition.
Results and discussion: The results showed that the average milk production in the second treatment was 13.6% more than the first treatment (control). According to the results of this research, Mikolayunas et al. (2008) reported that, during the first 8 weeks of lactation, ewes exposed to short day prepartum photoperiod tended to produce more milk than ewes exposed to long day prepartum photoperiod. No significant difference was observed between the treatments in terms of the amount of milk composition. The level of prolactin hormone in treatment 1 was higher than in treatment 2 in 20 days before parturition (P<0.05). Long day exposure increases prolactin in blood as compared to short day. IGF-1 has reverse action as compared to prolactin (Rao et al., 2017). At parturition and fifteen and thirty days after that, the level of prolactin hormone was similar in the two treatments. At twenty days before parturition and parturition, the level of melatonin in ewes of treatment 2 was higher than that in treatment 1 (P<0.01), but at fifteen and thirty days after parturition, the level of melatonin in ewes of both treatments was similar. Secretion of melatonin is stimulated by darkness (Rao et al., 2017). At 20 days before parturition, at parturition, and fifteen days after parturition, the level of IGF-1 hormone in ewes of treatment 2 was lower than that in ewes of treatment 1 (P<0.01). At the age of one, two and three months, the highest weight was related to the lambs of treatment 2 (P<0.01). The lambs of treatment 1 experienced less weight gain than the lambs of treatment 2 from birth to three months of age (P<0.01). The results of this study regarding weight and weight gain of lambs are consistent with the results of the study by Aviles et al., (2019). Kids cared for by mothers who produce more milk grow faster (Garcia Y-Gonzalez et al., 2017).
Conclusion: In general, in Lori Bakhtiari sheep flocks, applying a short lighting period before lambing can increase the amount of milk produced by ewes in subsequent lactation period and the weaning weight of their lambs.
Results and discussion: The results showed that the average milk production in the second treatment was 13.6% more than the first treatment (control). According to the results of this research, Mikolayunas et al. (2008) reported that, during the first 8 weeks of lactation, ewes exposed to short day prepartum photoperiod tended to produce more milk than ewes exposed to long day prepartum photoperiod. No significant difference was observed between the treatments in terms of the amount of milk composition. The level of prolactin hormone in treatment 1 was higher than in treatment 2 in 20 days before parturition (P<0.05). Long day exposure increases prolactin in blood as compared to short day. IGF-1 has reverse action as compared to prolactin (Rao et al., 2017). At parturition and fifteen and thirty days after that, the level of prolactin hormone was similar in the two treatments. At twenty days before parturition and parturition, the level of melatonin in ewes of treatment 2 was higher than that in treatment 1 (P<0.01), but at fifteen and thirty days after parturition, the level of melatonin in ewes of both treatments was similar. Secretion of melatonin is stimulated by darkness (Rao et al., 2017). At 20 days before parturition, at parturition, and fifteen days after parturition, the level of IGF-1 hormone in ewes of treatment 2 was lower than that in ewes of treatment 1 (P<0.01). At the age of one, two and three months, the highest weight was related to the lambs of treatment 2 (P<0.01). The lambs of treatment 1 experienced less weight gain than the lambs of treatment 2 from birth to three months of age (P<0.01). The results of this study regarding weight and weight gain of lambs are consistent with the results of the study by Aviles et al., (2019). Kids cared for by mothers who produce more milk grow faster (Garcia Y-Gonzalez et al., 2017).
Conclusion: In general, the results of the present study showed that applying a short light period before lambing in Lori Bakhtiari sheep increased the amount of milk produced by ewes and the weaning weight of their lambs.