Dairy farmers might be able to fill their milk tanks faster if they feed hay that was cut in the afternoon instead of the morning.

In a recent 10-week study, early to mid-lactation dairy cows fed a total mixed ration (TMR) containing 40% afternoon-cut alfalfa produced 10% more milk than cows fed a TMR with 40% morning-cut alfalfa.

Cows fed the ration with afternoon-cut alfalfa also ate 10% more feed and gained body weight, explain Henry Mayland, a USDA-ARS soil scientist in Kimberly, ID, and D. Kim, a Utah State University graduate student.

The lactation study followed previous ARS studies that showed cattle, sheep and goats had a significant preference for both alfalfa and tall fescue hay cut in the afternoon vs. the morning. In fact, they sometimes ate up to 50% more of the afternoon hay, says Mayland.

"Afternoon-cut forage is a few percentage points higher in total non-structural carbohydrates and simple sugars than morning-cut forage because plants accumulate sugars during the day via photosynthesis, but incur a net loss at night via dark respiration," he says.

The afternoon-cut alfalfa in the latest study was slightly lower in neutral detergent fiber and acid detergent fiber, thus was slightly higher in relative feed value.

The differences between morning- and afternoon-cut forages are retained during swathing, field drying and storage, says Mayland.

To humans, morning- and afternoon-cut hays can look, smell, feel and taste the same, but ruminant animals are very sensitive to slight differences.

"They can sense a difference between hays that vary in carbohydrates by as little as one percentage point," notes Mayland.

For the lactation study, irrigated alfalfa in Cache Valley, UT, was cut around 6-8 a.m. and 4-6 p.m. on Aug. 1. It was field-dried, baled, stored and tested at the Caine Dairy Research Center at Utah State. Then 10 cows were fed the ration with afternoon-cut alfalfa, and 10 ate the one with morning-cut hay.

Based on their newest findings, the researchers figure cutting in the afternoon instead of the morning could add about $15/ton to alfalfa's value.

"Hay growers can add value to their product by cutting in the afternoon, and dairymen can boost production by feeding afternoon-cut hay," points out Mayland. "It's a win-win situation for everyone."

The researchers plan further studies to learn the differences in crude protein and dry matter digestibility between morning- and afternoon-cut forages.