Photoperiod manipulation offers dairy producers a management tool that increases efficiency of the lactating cow. The technique is cost-effective, simple, and does not involve extra labor or cow handling. It's as simple as leaving on the lights. Use of photoperiod to stimulate milk production in dairy cattle should be considered in all dairy housing.
In general, milk yield increases 8 - 10% on long days, and cows eventually increase intake to support the greater milk yield. Photoperiod does not affect protein or solids content of milk, but can cause slight decreases in fat content. The increase in milk yield more than compensates for the effects on fat and feed intake.
A diagram and table summarize the results of several studies and confirm the stimulatory effect of long days on milk production in cattle in North America and Europe.
Light hitting the eye initiates a cascade of hormonal events beginning with a signal to suppress the release of the hormone melatonin. As darkness falls, the inhibitory impact of light is removed, and melatonin secretion increases. Consequently, long photoperiodic days are associated with a shorter duration of high concentrations of melatonin. Animals use the daily pattern of melatonin to set their internal clock which influences the secretion of a number of hormones (e.g., insulin-like growth factor-1 (IGF-1) and Prolactin). Recent evidence indicates long days increase IGF-1 circulation, and, increases in IGF-1 are generally believed to mediate the effect of Bovine Somatotropin (bST) in cattle (although long day induced increases in IGF-1 are independent of changes in circulating somatotropin). In a recent University of Maryland experiment in which cows were treated with bST, long days, or combination of the two effects, the greatest milk yield response was observed in the long day plus bST treated cows. These results support the notion that bST and photoperiod have an additive effect on milk yield.
Maintenance of 6 - 8 hours of uninterrupted darkness each day is required. In some cases, especially with 3X milking situations, the need for 6 hours of uninterrupted darkness may require multiple lighting schedules within separate barns. Continuous, 24 hour lighting is NOT recommended as it provides no additional milk productivity. Dim red bulbs (approximately 7.5 Watts) may be used to facilitate cow movement and observation during darkness. The low intensity red light has no effect on the cows perception of darkness, and thus, melatonin secretion. Installation of timers to control the lights is recommended, as timers eliminate human error and maintain consistency of the lighting schedule. Timers can also be set to turn lights off once full daylight intensities are attained, thereby reducing electrical costs.
Lag time in response to photoperiod is usually between 2 - 4 weeks. The response of milk yield to photoperiod is gradual and may not stand out from normal daily variation. However, the response is consistent and repeatable. Thus, patience is necessary to use photoperiod
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