Here's a Bright Idea

Major changes in how we house dairy cattle and the lighting we provide for them could result from recent University of Maryland research. This dry cow study, and two others like it, cast serious doubt on simply turning on your barn lights to increase milk production.

Over the last 20 years, numerous studies with milking cows have investigated their response to changes in the number of daily hours of light, or daylength as this is called. 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.

The main outcome of these studies has been a general recommendation that cows need 16 hours of day- light 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 Maryland 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 for Maryland -roughly 10 hours of light and 14 hours of darkness. Did longer daylength during the dry period result in a production response? It certainly did, but perhaps not the response expected.

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. Although more research is needed to understand this response, the authors suggest that perhaps the higher yielding cows were reacting to increased daylength rather than to any absolute the light period.

Earlier trials with milking 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.

As with most research, this trial leaves several questions unanswered:

• Were dry cows getting less light stimulated to produce more milk, or did those getting more light produce less than normal? The trial was not designed to address this question. But production in previous and subsequent lactations suggests cows getting less light in the dry period did produce more.

• How dark is dark, or how much light can filter into this area without altering the response? Neither this trial nor any of the others define the amount of light needed to establish a period as light or dark.

• How long a period of short daylength is needed to trigger the response? In this trial cows were kept in the dark for the entire 58 days dry: Perhaps a shorter period would suffice.

This trial's practical implications are quite important. In a barn housing both milking and dry cows, it would appear keeping the lights on for 16 hours and off for eight year- round probably doesn't increase production and likely wastes electricity.

The production increase results from longer daylength. So an effective strategy would house dry cows in a separate area. You would manipulate the lighting in either this area or the milking cow barn or both. Your goal may be to provide a daylength in the milking barn 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.

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. Weekly production of energy-corrected milk in the Maryland trial (see graph) suggests the production difference between the two groups may extend beyond the 120 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 58 cows could invest up to $7,500 per year in additional labour, housing or lighting and break even on manipulating daylength.

Further studies may better define exactly when and how, but the concept of artificially increasing daylength at calving appears to have real potential.

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.

This article appeared in the Ruminations column of the May 2001 Ontario Milk Producer magazine.

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