Producing Low Sugar Hay - Some Considerations

By Amy Barkley, Livestock Specialist, SWNYDLFC

"I have a client who needs me to produce low sugar hay… what's a foolproof method?" I hear this question quite a bit from folks who are producing hay for critters that have a low energy demand. Many of these farmers' clients feed pleasure or pet horses, that are generally easy keepers and require forage with a low sugar density. Some highly conditioned livestock like beef cattle, sheep, or goats may also need low energy forage to help them shed some pounds before breeding season to decrease the risk of breeding issues and gestational metabolic disease. So, this begs the question: how do you produce low sugar forage?

Many folks strongly believe that harvesting forage at a certain time of day impacts the sugar content, and there's truth to that. The theory is that there is a significant difference in free sugars in forage that is harvested in the early morning vs the late morning or afternoon. It makes sense: the plant conducts photosynthesis during the day, producing food for the plant and increasing free sugars. In the early morning, it's gone through the dark cycle of photosynthesis and used up those sugars, so the free sugars in the plant should be lowest. So, does this make a significant difference, and should farmers harvest forage heavy with dew and slugs to achieve a more desirable nutrient profile?

This topic has been on the minds of scientists for some time. In 1969, a pair of researchers looked at the variation in water-soluble carbohydrates in forage over the course of the day and found that while they did increase from morning to noon, a significant portion was used by the plants to conduct respiration and protein building. The increase in carbohydrate concentration during the daylight hours that this study found is consistent with similar, previous studies. Researchers in 2010 had comparable findings, and reiterated others' results that species has a more significant influence on the sugar content of forage than the impact of time of day.

Species influence is confirmed through various studies and data collected from NYS farms. According to the 20-year averages from Dairy One's Forage Testing Library, legume pastures have a tendency to be higher in total digestible nutrients and ESC (simple sugars) with values of 65.9 and 7.80, respectively, vs a grass pasture, which is lower in TDN and ESC at 60.7 and 6.79, respectively. So, pastures with a lower portion of legumes are going to reliably make for a lower sugar hay when harvested at the same maturity. That said, keep in mind that there is also individual variation between species of the same forage class, too.

Forage maturity also has a great impact on how much free sugar is available in hay. As forages age and start developing their seedheads, they divert more of their easy-to-digest sugars into those that add structure to the plant. These structural carbohydrates are not very digestible or are indigestible. During this maturation process, simple sugar concentration decreases, as does TDN. From my experience reviewing forage tests from SWNY farms, I can confirm that the nutritional content of forages drops steeply the more mature they get. Young forage that has not yet developed seedheads is what I like to call "rocket fuel". This is dairy animal or performance animal chow; it has more energy and protein than what most meat-type ruminant livestock and horses need. While more mature forage doesn't have the pretty green color or soft texture of a less mature forage, which can be a selling point for some, it's the nutrition that counts. Getting your forage tested and sharing those results with potential customers is a value-added service that can help you match your forage with the right end user.

While time of day, species, and maturity influence the sugar content of forage, it's hard to develop an exact estimate of what the TDN or ESC will be before it's put up. There is variation from field-to-field, day-to-day, and even in harvesting and baling techniques. On top of that, any rain that the forage may get on it once cut can impact how much sugar is conserved. The best way to understand if your management is getting you a forage that meets your goals is to test it. The cost is usually around $30 per sample and it takes about a week or so for the test results to come in once the sample is submitted. If you need assistance with taking samples or interpreting test results, you can reach out to your local extension specialist.

Hold, D. A. and A. R. Hilst. 1969. Daily Variation in Carbohydrate Content of Selected Forage Crops. Agronomy Journal. Volume 61, issue 2, 239-242.

Pelletier, S. et al. 2010. Forage Nonstructural Carbohydrates and Nutritive Value as Affected by Time of Cutting and Species. Agronomy Journal. Volume 102, issue 5, 1388-1398.

The Dairy One Forage Composition Library can be accessed at: https://apps.dairyone.com/feedcomposition/