Asking Why? Forage specialist answers common questions

Why are my replacement heifers so thin? Why did my alfalfa hay test so low? Why? Why? Why? University of Nebraska Extension forage specialist Bruce Anderson

Why are my replacement heifers so thin? Why did my alfalfa hay test so low? Why? Why? Why? University of Nebraska Extension forage specialist Bruce Anderson takes time to answer common questions.

For instance, Anderson says it’s not unusual for calf weaning weights and replacement heifer rates of gain to be higher in dry years than in wet years – as long as it wasn’t so dry that animals went hungry. Even though the grass is lush and looks excellent, in wet years it also contains more moisture and can be what some people might call ‘washy.’

The extra growth that was stimulated by all the moisture tends to dilute the nutrient concentration in the grass. Plus, it tends to pass through the animals more rapidly so some nutrients don’t get digested.

As for low forage test values for alfalfa hay this spring, Anderson says that too might have been caused partly by this same dilution effect. But Anderson says a couple other factors also played an important role.

One factor might have been that the alfalfa was simply cut later than usual due to all the rain delays. It may not have looked more mature, but it still was older and thus contained extra fiber.

Another issue is slow drying of hay after cutting due to high humidity or cloudy weather. Until alfalfa dries down to less than 50% moisture, it continues to burn off nutrients. So, as it takes alfalfa longer to dry down, more desirable nutrients are burned away, leaving behind the less desirable fiber. Plus, cloudy weather reduces the amount of nutrients produced to begin with.

Now that summer heat has set in, how does that affect different types of forage plants? Anderson says cool-season plants suffer along with you and me. Alfalfa and clovers, bromegrass, orchardgrass, fescues, and wheatgrasses all hurt during hot weather.

Do you remember – before air conditioning – how drained you used to feel after spending a night when the temperature never dropped below 80? The same thing happens to cool-season forages, resulting in very slow growth, lower forage quality as plants burn up the good nutrients, and limited recovery of root reserves after defoliation, says Anderson.

Whereas, warm-season grasses are just the opposite. Millet, sudangrass, sorghums, and native bluestems, gramas, switchgrass, and other warm-season grasses thrive when the temperature is around 90 degrees. Their metabolism runs at peak efficiency when it is hot so they grow rapidly while maintaining reasonable forage quality and good root growth.

Of course, this assumes these plants have adequate moisture. Once they dry up, these grasses will overheat too, just like cool-season grasses do at lower temperatures, according to Anderson.

As you graze or hay, be aware of the stress weather is putting on your forage. When it’s too hot, be prepared to allow plants to recover for a longer time before next use. And don’t expect high feed values when the goodies are burned right out of the plants.
Proper expectations and management adjustments can limit the stress from stressful weather.

Rotational Value
A final question that Anderson addresses is why rotationally grazed pastures tend to do better in summer.

Anderson points out that by mid-July most years, we start to notice our grasslands suffering from a lack of water. But rotationally grazed pastures aren’t hurt quite as bad. He says that is primarily because their root systems are healthier and deeper than continuously grazed pastures due to the periodic rest they receive.As a result, they can gather more soil moisture from deeper soil depths.

Anderson suggests that if you aren't already grazing rotationally, start now, regardless of whether you have abundant rain and grass or you are in a drought.

He explains that starting rotational grazing when you have plenty of grass will rest plants and begin to improve their root system immediately.This makes them better able to gather moisture during the next dry spell.

Likewise, when you are short on grass, rotational grazing improves harvest efficiency of your pasture. By concentrating animals onto smaller pastures, grazing uniformity improves. This means your animals do less pick-and-choosing-and-trampling as they graze. They eat more of what is available to them and they waste less feed. This helps current pasture growth feed your animals longer.

So do some extra cross-fencing. You will stretch your feed supply as well as improve roots and production for next year.