Abstract
Simple SummaryShort day length is associated with reduced milk yield in dairy ruminants possibly as animals prepare for the subsequent reproductive cycle. This study was conducted to determine the effect of an artificially increased daylength on milk production and ovulation in lactating goats. Increased daylength increased milk yield although the responses were only apparent during late lactation. Increased daylength reduced ovulation rate as lactation advanced although this reduction could be partially mitigated by exposing the lactating females to entire males. These findings suggest that artificially extending daylength can increase milk production and persistence while decreasing ovulatory activity in dairy goats.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.
Highlights
The seasonal reproductive activity of temperate and subtropical goats is largely influenced by photoperiod [1,2]
Milk yield declined between weeks 12 and 18 of treatment as lactation advanced, in the goats that were not exposed to the long day photoperiod (LDPP)
The proportion of goats that dried off during this period was lower in goats that had been exposed to a LDPP (13 vs. 0%, p < 0.01)
Summary
The seasonal reproductive activity of temperate and subtropical goats is largely influenced by photoperiod [1,2]. As the days begin to shorten in Autumn, a regular oestrous cycle is initiated and when days are lengthening in Spring, anoestrus occurs. These responses to changing photoperiod have been utilised commercially by exposing goats to 16 h of light during winter through the provision of supplemental lighting. The goats are returned to ambient shorter day lengths, which results in mating activity in spring. In this production system, the goats are six months out of phase with when they would naturally cycle, enabling year-round milk production if implemented across some of the herd. There is little scientific literature to support this practice of delaying ovulation
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