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More Sugar In The Hay, More Milk From The Cow

“We would recommend they think about cutting late in the day, around 6 p. m.”


The person who sang “Make hay while the sun shines” had the time of day wrong.

Dairy cows perform better eating alfalfa cut later in the day rather than early in the morning, researchers at Agriculture and Agr i -Food Canada in Quebec have found.

The reason? Sugar.

A plant photosynthesizes sunlight to produce sugar. The sugar content of a plant rises along with the sun in the sky, peaking at sunset and decreasing during the night. In the morning, the cycle begins all over again.

So alfalfa cut at the end of the day contains more sugar than if harvested earlier. As a result, cows will consume more of it, utilize protein more efficiently and produce more milk, the AAFC research team found.

The idea that sugar content in feed affects an animal’s performance seems so simple it’s surprising nobody thought of it before. Although similar research had been done on other herbivores, this was the first time it was tried on dairy cattle, said research scientist Robert Berthiaume, one of the team leaders.

But the cows have known all along. Berthiaume said dairy cows will prefer to graze late in the day when sugar content in plants is highest. They will also systematically go for alfalfa hay mowed later rather than earlier in the day, given a choice.

It probably has to do with taste and smell, Berthiaume said from AAFC’s Dairy and Swine Research Centre in Sherbrooke, Que.

“They go for it even if they don’t know what’s in it. So we assume that, if they go for it, it’s because they either smell it or taste it.”

Because the higher sugar content encourages cows to eat more, their dry matter intake is higher and their milk production is greater. Berthiaume said dairy cows fed late-day alfalfa consumed five to 10 per cent more feed and increased milk production by about the same amount.

Their digestion was more efficient, too. Because high-sugar alfalfa produces more energy, bacteria in the rumen make better use of the protein in the feed. Low-sugar alfalfa causes bacteria to misuse the protein, producing ammonia in the rumen and nitrogen urea in the cow’s urine. Urea can produce nitrous oxide, a greenhouse gas more potent than carbon dioxide.

So, besides improving performance, alfalfa cut late in the day produces less greenhouse gas from cattle, although only about five per cent. Not enough to prevent global warming, Berthiaume acknowledged.

He said other studies show a similar effect on beef cows. The breed of cattle doesn’t seem to have much to do with it. All prefer sweeter grass, whether grazed or harvested.


The AAFC study, published in the Journal of Dairy Science, involved late-lactating cows. Preliminary data from another study with early-lactation cows suggests the advantage may not be quite as great, although it’s too early to tell, said Berthiaume.

Although not recommending a wholesale switch to late-day mowing (it’s not practical), Berthiaume farmers should consider the practice when it fits into their management practices.

“If they want to harvest haylage and/or dry hay from alfalfa fields, we would recommend they think about cutting late in the day around 6 p. m. instead of cutting early in the morning.

“I would definitely rethink my cutting regime if I were a farmer, try to start a little later and gear up towards that.”

AAFC is currently studying the phenomenon in other forages. Berthiaume said sugar in timothy is not the same as in alfalfa, but results so far appear similar. [email protected]

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