What Is Long-Day Lighting For Dairy Farms?

Long-Day Lighting (LDL) is an established strategy in the dairy farming industry, but not universally implemented. LDL uses lighting to boost both productivity and animal welfare. This lighting strategy seeks to create the optimal light-dark cycle for heifers’ health and productivity. LDL as a lighting strategy seeks to elongate the day using artificial lighting.

LDL is now a widely-followed practice that provides heifers with 16 to 18 hours of light, followed by 6 to 8 hours of darkness. LDL theory says heifers have physiological responses to light that impact hormonal balances, growth, and milk production patterns. The guildelines for LDL in heifers are similar to those for lactating cows. The primary characteristic is the uniform and constant light for 16 to 18 hours followed by uninterupted darkness for 6 to 8 hours. The light period has a target of 15-20 foot-candles (160-215 lux), while the darkness period has a goal of 1-4 foot-candles (10-40 lux). It is also critical in LDL that there be high uniformity of light distribution across the heifer’s resting area.

The original research on photoperiod manipulation was directed at LDL for lactating cows and short-day lighting for dry cows. It should be noted that few recommendations exist regarding LDL for heifers. Two pioneering and important studies for the field are from University of Minnesota (2008) and Michigan State University (2022). They both provide comprehensive summaries of the ongoing research into growth and development in heifers and calves living with LDL.

The research shows benefits of LDL on calf and heifer development, but little evidence for lactating cows and dry cows. There is also a gap in research around the return on investment (ROI) for LDL. There similarly is a lack of extensive case studies, which is challenging for producers.

Multiple studies suggest that LDL for heifers and calves can result in accelerated puberty in dairy heifers by up to a month, higher milk production at their first lactation, and an increase in average daily gain (ADG). There is some disagreement among researchers, however. Some studies have not detected a significant effect on feed consumption and growth when LDL is applied. The majority of researchers agree on LDL enhancement in growth and performance by using LDL on heifers.

LDL has been show to elevate a hormone known as insulin-like growth factor 1 (IGF-1), that acelerates growth. Several studies have measured higher IGF-1 levels in LDL heifers.

Research has shown the health of an entire herd can be improved with LDL, including better reproductive efficiency. LDL aligns the estrus cycles and enhances visibility for better detection of health issues. Utilizing LED lighting can counteract the longer lighting run times prescribed by LDL, in terms of energy use. Timers and automated controls can deliver consistent cycles. Despite a 40 year history of research in the field, academic research continues into LDL, striving to optimize the health and productivity benefits for both the animals and producers alike.

Visit these resources for more insight: Deciphering Beef-on-Dairy Mating: The Significance of Mean Breed Performance and Understanding Seasonality in the Dairy Production System.



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David Shiller
David Shiller is the Publisher of LightNOW, and President of Lighting Solution Development, a North American consulting firm providing business development services to advanced lighting manufacturers. The ALA awarded David the Pillar of the Industry Award. David has co-chaired ALA’s Engineering Committee since 2010. David established MaxLite’s OEM component sales into a multi-million dollar division. He invented GU24 lamps while leading ENERGY STAR lighting programs for the US EPA. David has been published in leading lighting publications, including LD+A, enLIGHTenment Magazine, LEDs Magazine, and more.


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