Photobiology in the dairy barn.

In the dairy business we have assumed for some time that today's cows are no longer seasonal breeders, not in the way sheep and goats are. Given this premise, we have also assumed that shorter days would not affect them one way or another. This is simply not the case.

Poultry farmers learned years ago that chickens lay more eggs when given supplementary light exposure. This discovery led to the understanding that light, more specifically than length of days, is a daily requirement of laying hens, just as much as feed or water is. The supply of light is converted by the chickens into hormones, which turn on or off the reproductive organs that produce eggs.

Not surprisingly, what works in chickens can also be applied to sheep, goats, deer, and plants; that is, the amount of light, measured in hours, and its intensity, influence reproductive performance.

Now some really exciting research results come out of work at the National Agricultural Experiment Station at Beltsville, MD. Amounts of light have been studied as to their effects on forcing plant seeds to germinate and plants to grow leaves, flowers or set seeds.

The new idea was not just to expose plants to rays from light bulbs of different intensities, but to grow plants on plastic sheets of different colors that, in turn, would reflect light onto the plants in various ways. Growing tomatos over red plastic mulch increased fruit harvest by 10 to 15 percent over the traditional black plastic mulch. Blue or white plastic mulch increased potato harvest by as much as 15 percent. Infra-red light was effective in making plants grow stemmy and tall, while red caused shorter stems and bigger roots. Blue mulch on turnips accumulated more compounds responsible for their strong flavor and taste. Mulch color also affected the number of insects and nematodes found on cotton and other plants.

Thus a new science was born: photobiology, the study of how we can change normal biology of plants and animals by manipulating light, both in quantity and quality, and by the color of the light.

So, what does this have to do with dairy cows? Maybe, more than we know. Some years ago, a well-known dairy herd in New Jersey was stabled in a barn that was painted bright blue for the expressed purpose of affecting fly pests and their numbers. This novel idea did not catch on, but as far as I know, neither has it received research attention.

However, work at Michigan and at British and Canadian research stations has established that we were wrong in assuming that only chickens, poinsettias, soybeans, tomatos, turnips, goats, sheep and deer respond to photobiological light manipulation. We now know that light manipulation induces growth of Holstein heifers via their gonads. We also know now that eight hours of light per day causes heifers to get fat, while 15 hours makes them grow taller, more muscular and leaner by a significant difference of 28 percent. This seems to explain why pork producers of 50 years ago preferred to feed their pigs in dark barns. I well remember this practice from where I grew up. Today's consumer wants lean meat instead, which calls for keeping the lights on in the pig barn.

In terms of milk production, Holstein heifers develop much better mammary growth and udders when exposed to 16 hours of light, regardless of their genetics or feed supply! Most importantly, light-supplemented cows produced 10 to 17 percent more milk over control cows in Michigan, Oregon, Bulgaria, England and Denmark research for most of entire lactations, starting with the second month.

Was there a difference in color? Apparently no one has studied this intriguing question, but we do know that the intensity of white light has to be at least 40 foot-candles (lux), and that an average of 100 lux for 16 hours will stimulate body growth and milk production in dairy cattle. All this without injections or other supplementation!

Will it pay? At current prices of $11.60 per 100 pounds of milk on the farm and at conservative milk stimulation of only eight percent, a Holstein cow producing 50 pounds of milk per day, and a seven cents electric cost per cow per 16 hours of light, her extra milk income would be 46 cents a day against costs, including increased feed consumption of 30 cents, or a new income gain of $16 per 100-head herd a day. Furthermore, it has been calculated that at that level of return, new or additional lighting equipment would be paid back in less than 345 days of use.

It seems the time has come even for dairy cattle farmers to take photobiology seriously as a source of potential farm net income. Who knows, seeing red or blue colors in the dairy barn might be positive and lead to even more profits in the future.