Short day length is associated with reduced milk production in dairy ruminants. Dairy ruminants have been kept in lit sheds during winter to extend the day length and stimulate milk production. However, there studies are few on the effect of an extended photoperiod on the ensuing reproductive performance of dairy goats. The aim of this study was to examine the effect of long day photoperiod (LDPP) and exposure to bucks on milk production and plasma progesterone and prolactin in dairy goats. The study was conducted in 122 non-pregnant lactating dairy goats over 18 weeks from April to August (late autumn and winter in the Southern Hemisphere). The goats were kept in open sided sheds in which the control treatment received ambient lighting while the LDPP treatment received 16 h of light, including artificial lighting. In June, July and August synchronised does were randomly assigned each month to the presence or absence of a buck and ovulatory activity determined from plasma progesterone. Plasma progesterone concentrations were reduced (0.73 vs. 0.46 pmol, p < 0.001) while prolactin concentrations were increased (0.095 vs. 1.33 ng/mL, p < 0.001) in LDPP goats. The former response was most marked in late winter (0.58 vs. 0.004 pmol, p < 0.001) indicating a lack of functional corpora lutea. While there was no overall effect of buck exposure on plasma progesterone concentrations there was a three-way interaction such that plasma progesterone concentrations were increased (p < 0.05) by exposure to bucks in LDPP goats in August (late winter) but not at other times. Milk production was increased in LDPP goats over the latter stages of the study (1. 55 vs. 1.82 L/d, p < 0.05). Also, persistency of lactation was greater in LDPP goats with fewer goats drying off (13 vs. 0%, p < 0.05). These findings suggest that LDPP can increase milk production and persistence while decreasing ovulatory activity in dairy goats.

中文翻译：

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延长的光周期增加奶山羊的产奶量并降低排卵活性

一天的时间短与奶牛反刍动物的产奶量减少有关。冬季，将反刍动物奶牛放在棚屋里，以延长日照时间并刺激产奶量。但是，关于延长光周期对随之而来的奶山羊繁殖性能的影响的研究很少。这项研究的目的是检验全日光周期（LDPP）和暴露于雄鹿对奶山羊产奶量，血浆孕酮和催乳素的影响。该研究在4月至8月（南半球秋季和冬季后期）的18周内在122只未怀孕的哺乳奶山羊中进行。将山羊饲养在敞开的棚屋中，在该棚屋中，对照处理接受环境照明，而LDPP处理接受16小时的光照，包括人工照明。在六月，每月将7月和8月同步做的事情随机分配到是否存在血浆黄体酮降压和排卵活动。血浆孕酮浓度降低（0.73比0.46 pmol，p <0.001），而LDPP山羊的催乳素浓度增加（0.095对1.33 ng / mL，p <0.001）。前者的反应在冬季后期最为明显（0.58比0.004 pmol，p <0.001），表明缺乏功能性黄体。虽然雄鹿暴露对血浆黄体酮浓度没有总体影响，但存在三向相互作用，因此，8月（冬末）LDPK山羊暴露于雄鹿时，血浆孕酮浓度增加（p <0.05），而其他时间则没有。在研究的后期，LDPP山羊的产奶量增加（1.55 vs. 1.82 L / d，p <0.05）。此外，LDPP山羊的泌乳持续性更高，干燥的山羊更少（13％vs. 0％，p＜0.05）。这些发现表明，LDPP可以增加奶产量和持久性，同时降低奶山羊​​的排卵活性。