The following article was written by Dr. Mike Wolf for Progressive Dairy.

Utilizing short-day lighting in barns housing dry cows for the entire 60-day dry period may positively impact milk production during the upcoming lactation.

Short-day lighting may be the next low-hanging fruit to address on your dairy. There have been many studies in the last 20-plus years that have found a positive correlation between utilizing a long-day photoperiod in barns housing lactating dairy cattle and increased marginal milk and overall milk production.

Targeted lighting intensity for long-day lighting is 20 foot-candles (220 Lux) for 16-18 hours at a 3-foot plane, where the cow’s eye is located, followed by 6-8 hours of less than 5 foot-candles (55 Lux). This is especially important in feeding and resting areas.

Considerations for a short-day photoperiod (SDPP) during the dry period have also been studied, and we will review some of this research and the measures required to optimize the effects of a SDPP.

What is a short-day photoperiod?

A SDPP, which is the opposite of the long-day lighting specifications listed above, has a lighting intensity of less than 5 foot-candles (55 Lux) for 16-18 hours per day followed by 6-8 hours of 20 foot-candles (220 Lux).

Studies have shown that utilizing short-day lighting for the entire 60-day dry period has a positive effect on milk production in the upcoming lactation when compared to long-day photoperiod experiments. For example, various studies revealed a 6.2-7.7 pounds (2.8-3.5 kilograms) per cow per day advantage in the first 120 days in milk (DIM) for dry cows housed in an environment with short-day lighting versus dry cows housed in an environment with long-day lighting. Although differences in milk production appear to diminish after 120 DIM, it still adds nearly 800 pounds (350 kilograms) to the lactation.

Further studies comparing the effects of short-day lighting during 42-day and 60-day dry periods found similar results. In the 42-day dry period study, the cows consumed the same ration for the duration of the dry period, and the shorter dry period length did not affect post-calving milk production levels in the group housed in the short-day lighting environment. Dry matter intake (DMI), bodyweight and body condition score (BCS) were unaffected between the two groups in this study. We can conclude that a 42-day short dry period gives the same positive results as a 60-day short dry period.

Other studies have shown an increased DMI in the SDPP dry group. However, shortening dry periods to less than 30 days has been found to be detrimental to milk production in subsequent lactations.

Additionally, study results suggest that only implementing short-day lighting during the 21-day close-up transition period does not increase milk production after calving as compared to utilizing short-day lighting for the entire dry period.

What causes the increased milk production?

Short-day lighting during the dry period has a positive effect on the quantity and longevity of milk secretory cells developing, as compared to long-day lighting. Figure 1 illustrates an initial increase in milk yield for those cows who were exposed to a SDPP.

Prolactin, which is one of the hormones positively correlated with milk production, increases significantly after parturition. However, low prolactin levels are required during the dry period to maximize this response. The suppression of prolactin levels caused by the SDPP in dry cows is positively correlated to the development of an increased number of prolactin receptor sites. After parturition, prolactin increased in both short-day and long-day lighting periods, and receptors are enhanced in the short-day lighting group, which drives a larger increase in milk production. In addition to the mammary gland, the increase in prolactin receptors also has positive effects in the liver and immune system.

Implementation of SDPP for dry cows

Since it appears that there is strong evidence for the benefits of developing a short-day lighting environment for your dry cows, the final question is how to implement this on your dairy. Having a separate barn that can be solely dedicated to dry cows would be ideal. As with any dry cow facility, it should meet the needs of this special group of cows. Additionally, the ambient light would need to be controlled by heavy shade cloth, solid or double polycarbonate layers to suppress the intensity of external light and the barn should preferably be positioned in an east-west orientation.

Although dry cows create about 50% of the BTUs per hour of a high-producing cow during lactation, ventilation should also be taken into consideration with the appropriate air changes per hour. It is recommended that air velocity be set at a minimum of 2.25 mph (1 meter per second) at a height less than 6 feet (3 meters) throughout the cow’s occupied zone. Soaker lines may be added as needed.

Dry, comfortable stalls must be sized for the breed and needs of a heavily pregnant cow, and 30 inches of feed lane space per cow during the transition period is recommended.

If a separate facility is unavailable, using the location in the barn furthest from the prevailing midday sun would be preferable, along with sidewall solar blocking. 

When implementing a SDPP in cross-ventilated barns, using pens located away from either sidewall for dry and fresh cows is also an option.

The lighting strategy would be designed the same as for a long-day photoperiod, with the opposite lighting schedule of 6-8 hours of 20 foot-candles (220 Lux) and 16-18 hours of less than 5 foot-candles (55 Lux). Two options that allow working light for employees include using the dimming options available on LED lights or red lighting, which creates lower light levels.

To implement a proper strategy, work with a reputable lighting design firm or expert to assure the short-day lighting pattern within a barn meets SDPP targets for dry cows. This is especially important if milking pens utilizing long-day lighting are within the same facility.