Effects of different organic pastures on dairy heifer growth and development


by Katie Navarra

Organic producers can find it challenging to raise heifers. On non-organic operations, heifers are typically fed total mixed rations (TMR), a balanced diet that provides all the necessary nutrients. While organic producers can use TMR, organic feed ingredients are costly. Often organic dairy farmers turn to pastures to trim expenses, but grazing tends to produce lower weight gains. However, there are studies indicating that a legume-grass mix can improve weight gain in heifers on pasture-based systems.

During an eOrganic webinar, Jake Hadfield, Utah State University Extension agriculture agent, discussed the results of his master’s work, which explores how organic producers can make the most of pasture-based diets.

“These animals are very important because they’re coming in to be your milk producers,” he said. “If we look across the U.S., one-third of the average dairy herd is replaced each year. That’s a large number of animals going in and out of these herds, so it’s important that we’re focusing on making sure heifers are developed and are able to come in and handle the production load that they’re going to be facing.”

Replacement heifers are the second largest expense on an operating dairy. This group of animals is fed for two years without contributing to income until they have a calf and begin lactation.

“We want to breed these heifers at 14 months so that they can calve before or by the time they’re two years of age,” he explained. “That’s a critical thing because we want to make sure that these animals reach these endpoints, especially in a pasture-based system.”

Achieving the optimum breeding weight requires a strategic approach. The faster they achieve a mature weight, the more cost efficient they are; however, if weight gain is achieved too quickly it can be detrimental to future milk production.

“It’s kind of a balancing act to try and make sure that we can decrease cost so we’re not spending too much money while at the same time making sure these heifers maintain adequate lifetime production,” he said.

Dairies use a variety of methods to achieve weight gain. TMR is the most common because it is completely controlled, but it is costly. Other operations feed their dairy heifers a combination of hay and feed. Raising dairy heifers on pasture has advantages and disadvantages.

“In pasture settings we see a decrease in feed costs just due to the fact that we’re relying on our pastures to be able to provide that feed,” Hadfield explained. “Another advantage is that these pastures can be more simplistic. There’s less labor and time involved.”

On the flip side, pastures are seasonal and impacted by precipitation and climate, both of which can affect nutrition. There also tends to be a decrease in production gains due to the fact that there isn’t the same control as compared to TMR. Pastures can also increase the parasite load if the animals aren’t monitored carefully.

“One of the things we can do is to improve pastures,” he said. “Fertilizer is a simple way to provide nutrition to the plants. In an organic setting, only certain products can be used and they usually cost more, but it is one way to improve pastures and help increase overall quality and yield.”

Previous research has shown that legumes are able to fixate nitrogen from the air and put it into the ground, which increases pasture quality and yield, especially protein. And there’s new research showing that condensed tannins in legume forages have been shown to improve rumen efficiency.

Pasture-based systems can increase urea nitrogen levels; one study indicated that cows that had high blood urea nitrogen levels (above 19 mg/dL) had a 20% decrease in pregnancy rate, according to Hadfield. However, other research he found showed that blood urea nitrogen levels below 15 mg/dL was ideal for reproductive performance.

“Other research shows there is no difference between conception rates between animals raised on a traditional system such as a conventional system or a pasture-based system,” he explained. “So these are some things to consider and there really needs to be more research in this area.”

Hadfield and his colleagues tested their hypothesis that mixed pastures comprised of legume and grass mixes could result in improved growth and reproductive efficiency in developing dairy heifers. They observed that the heifers that received the TMR were very consistent, but also saw that the heifers receiving perennial grass plus bird’s foot trefoil had high weight gains that were comparable to what they ended up seeing with heifers that received a TMR.

“We also saw that our heifers receiving mixed pastures tended to have a higher body weight as well as have higher weight gains and blood urea nitrogen concentration than those that received the monoculture grass pastures,” he said. “That’s something to consider just due to the fact that those mixed pastures did tend to have the more protein and more nutrition value for these heifers.”

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