Source: Ontario Ministry of Agriculture, Food and Rural Affairs
Research at the University of Maryland sheds a different light on the photoperiod research previously conducted with milking cows. This article provides a summary of the study and explores practical ways the results can be implemented.
Numerous studies with milking cows have investigated their response to changes in the number of daily hours of light, or daylength. These studies have consistently shown increased daily milk yields of two to three kilograms per cow when supplementary light extends winter daylength to 16 hours.
Study Results
The main outcome of these studies has been a general recommendation that cows need 16 hours of daylight and eight hours of darkness each day to produce a maximum amount of milk. On the basis of this advice, many dairy producers have added timers to barn lights to provide this regimen 365 days a year.
In the study, cows in the university herd were dried off in the fall and winter 60 days before expected calving date. Researchers paired them off by dry-off dates and randomly assigned them to one of two daylength treatments during the entire dry period. One of each pair was housed in a barn in which natural daylight was supplemented with fluorescent lighting. This provided a daylength of 16 hours followed by eight hours of darkness. The other group was housed in an identical barn, but windows were covered and lights were shut off in mid-afternoon. These cows were exposed to eight hours of light and 16 hours of darkness. Both groups were fed identical rations during the dry period and after calving.
After calving, all cows were housed and milked in the same group in a barn receiving natural winter daylight – roughly 10 hours of light and 14 hours of darkness.
Milk production was monitored for the first 120 days of lactation. Cows given 16-hour days and eight-hour nights during the dry period produced an average 34.9 kilograms of milk per day. This was 3.2 kilograms less than the average 38.1 kilograms produced by cows kept in the dark for 16 hours per day during the dry period. The authors suggest that the higher yielding cows were reacting to increased daylength rather than to any absolute light period.
Earlier trials with milking cows always involved extending daylength of the treatment during fall and winter when daylength was getting shorter. The positive milk production happened regardless of stage of lactation. Those trials increased daylength by adding supplementary light for milking cows. The Maryland trial increased daylength during the milking period at calving. But, in this case, researchers did it by restricting light during the dry period.
The production increase results from longer daylength. An effective strategy would be to house dry cows in a separate area from milking cows. The lighting in either this area or the milking cow barn or both could be manipulated. Your goal may be to provide a daylength in the milking barn that is always significantly longer than in the dry cow area. Either darkening the dry cow barn or using lights to lengthen the day in the milking barn may be equally effective.
How Dark is Dark?
Cows can find their way around in the dark. However, some light may be necessary for management purposes. Dim red lights do not appear to affect the cow’s perception of darkness. Low intensity red lighting (7.5W bulbs) mounted 20-30 ft. apart and 10 ft. above the floor provide adequate lighting for observing cows without upsetting the photoperiod response
How long do cows have to be housed in shorter daylength?
The research does not offer a clear answer, but studies on the rate of response suggest cows react to lengthened days quite quickly after the change occurs. Assuming this implies only a short period is needed, it may be acceptable to house only the close up dry cows in the darkened area for the last 2 to 3 weeks before calving.
However, you need to consider the economics of changing housing and management. While darkening the dry cow area might cost less than supplementary lighting for milking cows, eliminating light from a modern naturally ventilated barn by 4 p.m. in July could be difficult. On many farms, finding separate housing for the dry cows without creating new bottlenecks in feeding, manure handling and so forth would pose another challenge.
Nevertheless, we can make some calculations. The graph of weekly production of energy corrected milk in this trial, (black squares plot the short daylength group and white squares the long) suggests that the production difference may extend beyond the 100 days. At 3.2 Kg per day extra milk in the first 120 days, a conservative estimate of the difference over a complete lactation might be 650 Kg per cow.
If net returns on extra milk-after deducting feed, quota and other variable expenses-are roughly 20 cents per kg, the benefit is $130 per cow. On this basis the average Ontario dairy herd of 78 cows could invest up to $10,000 per year in additional labour, housing or lighting and break even on manipulating daylength.
The research was by A.RE. Miller, RA. Erdman, L. W: Douglass, and G.E. Dahl at the University of Maryland, reported in the Journal of Dairy Science, volume 83, number 5.
