Rimee Dhakad PhD. Scholar, ICAR-NDRI, Karnal-132001, Haryana

Introduction

Researchers have found that increasing light from less than 12 hours/day to 16-18 hours/day, increases milk production by 7-10%. It is critical for the response that cows have an uninterrupted dark period. Bovine somatotropin(bST) and long-day Lighting increase IGF-I independently so using BST and long-day lighting together will still pay. Photoperiod has also been found to impact dry cows. In the growing heifer, long-day lighting has been found to increase gain, feed efficiency and growth of mammary parenchyma. The experts claim that long-day lighting is very economical and increases income by $0.24 to 0.35/day/cow. Daylight varies with season. In many milk-producing regions of the world, there are a number of months when daylight is less than 12 hours/day. Researchers have shown that controlling and supplementing the amount of light a Cow receives each day can increase milk production.

Long-day lighting (or long-day photoperiod) means that cows have 16 hours of light and 8 hours of darkness each day. Researchers have found that increasing light from less than 12 hours/day to 16-18 hours/day, increases milk production by 7-10%. Milk composition is usually not affected, although some have reported small reductions in milk-fat percentage. Long-day lighting usually increases dry matter intake (up to 6%) to supply the extra nutrients needed for milk production. The initial response takes about 2-4 weeks to be seen.

It is critical for the response that cows have an uninterrupted dark period. Cows under continuous light have production levels similar to cows that don’t have enough light. Dim red bulbs (7.5 watt bulbs at 20-30 foot intervals) can be used during the dark period if cows must be moved or observed during that time.

Hormonal effect of photoperiod on production performance

Melatonin is a hormone produced in the cow’s pineal gland. When light hits a cow’s eye, it signals the cow’s body to produce less melatonin. When it is dark, melatonin is produced. Cows have an internal clock that is set by melatonin production. This internal clock affects the production of other hormones that impact milk production. Long-day lighting increases the production of IGF-I (insulin-like growth factor – I). IGF-I is the same hormone that is increased by bovine somatotropin (BST). More IGF-I production in the cow boosts milk production.

Researchers at the University of Maryland used 40 lactating cows for an 84-day trial. Twenty cows received no supplemental light (

Bovine somatotropin(BST) and long-day lighting increase IGF-I independently so using BST and long-day lighting together will still pay. They have an additive effect. University of Maryland researchers tested the effect of BST and long-day lighting on 40 lactating cows for 140 days. Normal hours of daylight during the study ranged from 9.5 to 14 hours/day. Treating cows with BST alone raised 3.5% fat-corrected milk production (FCM) by 12.54 pounds/day (5.7 kg) from 60.9 to 73.48 pounds/day (27.7 to 33.4 kg). Using long-day lighting increased FCM production by 4.2 pounds/day (1.9 kg), from 60.9 to 65.1 pounds/day (27.7 to 29.6 kg). Using both BST and long-day lighting increased milk production by 16.9 pounds/day (7.7 kg) from 60.9 to 77.88 pounds/day (27.7 to 35.4 kg). The researchers also found that the cows on long-day lighting met their extra nutrient needs by increasing dry matter intake. Cows on BST increased intake more quickly following their initial injection if they were also treated with long-day lighting.

Daily light has also been found to impact dry cows. In one study, cows that received only 8 hours of light per day during the dry period produced 6.8 pounds (3.1 kg) more milk per day during their first 120 DIM than cows that received 16 hours of light per day during the dry period. At freshening, all cows just had ambient lighting (9.5-10.5 hours of light per day). The reason for this response is not fully understood but some have suggested that the short-day lighting during the dry period may make cows more responsive to the positive influence of longer day lighting once they calve. It is also interesting to note that during the dry period, those cows which only had 8 hours of light per day ate 12% more dry matter. The reason for this is unknown but it did result in more energy reserves available for these cows after calving. More research needs to be done on light regulation in dry cows.

In the growing heifer, long-day lighting has been found to increase gain, feed efficiency and growth of mammary parenchyma. One study with long-day lighting (16 hours) increased heifer growth rate by 10%. It is interesting that this extra growth is not just a function of extra dry matter intake. Long-day lighting also results in earlier onset of puberty.

Effect of intensity of light on production performance

The intensity of the light which cows are exposed to is as important as the length of the lighting period. A minimum of 20-30 foot-candles is recommended. Twenty to 30 foot-candles would be enough to read by. Good office lighting is generally about 35-50 foot-candles. Sunny days may be greater than 1000 foot-candles.

A Wisconsin study showed that average light intensity in the feeding area of free stall barns was 14.23 foot-candles and ranged from 2 to 38. In the free stall area, light intensity ranged from 0.1-100 foot-candles and averaged 7.3 foot-candles. Average feeding area lighting in tie-stall barns was 20.35 foot-candles and ranged from 14.7-26. We know from research studies that cows spend about 10-15 hours/day resting and 4-5 hours/day eating. So, for long-day lighting to work, both the resting and eating areas must be provided with adequate light.

Light meters can be purchased from electric supply stores to check to see if your light is right. Remember that dust and age of light bulbs can reduce the actual amount of light received by cows. Check light distribution. Barns with rafters are difficult to light and may need more fixtures to get good light distribution. One recommendation is to have the distance between fixtures at 1.2-1.8 times the mounting height. Use a timer to insure proper timing and save on labor.

Total Lumens Needed

= [Area (sq. ft of barn) x (20 foot candles needed) x Barn Constant* (2 or 3)]

References Rodenburg, J. (2002) Light. Milk Production.com