Organic Broadcaster

Research compares fatty acids, meat of dairy steers grazing two cover crop systems

By Hannah Phillips and Brad Heins, U of MN

Editor’s note: This research poster took first place at the recent Organic Research Forum at the MOSES Organic Farming Conference.

It is well established that winter cover crops, when used in rotation with other crops, improve soil health. Cover crops are commonly used as a “green manure” or harvested for grain and straw; however, they could potentially be grazed with livestock in the early spring and summer. In addition, grazing is a low-input method to feed livestock, which could improve soil health by adding fresh manure to the field or pastures. Farmers who want to improve soil health and utilize a low-input grazing system may benefit from integrating crops and livestock in their system.

Consumers of organic products identify the health benefit of food as one of their selection criteria. There has been substantial research in the past several years involving omega-6 and omega-3 fatty acids (FAs) in human health and disease prevention. Although omega-6 FAs are important for health, they act as a pro-inflammatory in the body, and chronic inflammation in the body can lead to a range of diseases. On the other hand, omega-3 FAs act as an anti-inflammatory. This is why it is important to have a balanced omega-6/3 FA ratio in a human diet. The average American diet is a ratio of 15 – 16.7:1, but the ideal goal is to be as close to 1:1 as possible.

Crossbred steers graze winter rye at the University of Minnesota West Central Research & Outreach Center.

In this project, we explored the feasibility of grazing crossbred dairy steers on two types of cover crops as a method of utilizing a low-input system. In addition, we wanted to evaluate if beef from crossbred dairy steers would add value to the organic beef market by improving taste and health benefits.
The University of Minnesota West Central Research and Outreach Center grazed crossbred dairy steers on winter wheat and winter rye because they are two common cover crops in the Upper Midwest. Thirty bull calves were born at the organic dairy in Morris, Minn. from March to May 2015 and assigned to 1 of 3 replicated breed groups at birth. Breed groups were: purebred Holstein (HOL), crossbreds comprised of Montbéliarde, HOL, and Viking Red (MVH), and crossbreds comprised of Jersey, Normande, and Viking Red (NJV). Dairy steers grazed either winter wheat (WW) or winter rye (WR) cover crops that had been planted in September 2015 on two adjacent 10 acre plots. In April 2016, each breed group was randomly assigned to either cover crop and grazed rotationally until June 2016 with supplemented minerals for a total of 7 weeks.

When cover crops matured, steers were moved to a barn with outdoor access to a forage diet or were placed on perennial pasture based on forage availability. Steers were slaughtered in 2 groups, 9 weeks apart at an average age and weight of 16 months and 1,036 lbs.

Strip loin steaks from each dairy steer were collected. The steaks were evaluated for sensory attributes at the University of Minnesota Sensory Center. All 108 participants consumed cubes of cooked steak from each of the 6 groups in a double-blind study. Participants ranked the first cube on a scale of 0 to 120 for texture, flavor, and overall liking, and the second cube on a scale of 0 to 20 for juiciness, toughness, and off-flavor for all groups. In addition, a back fat sample was collected from each steer and analyzed for omega-6 and omega-3 FAs.

For cover crop differences, beef from steers grazing WW had higher flavor, texture, juiciness, and overall liking, and lower toughness and off-flavor compared to beef from steers grazing WR. For breeds, the NJV steaks had a higher texture liking and lower toughness compared to steaks from both MVH and HOL. Furthermore, NJV and MVH steaks had higher juiciness than HOL steaks (P < 0.05). The NJV steaks had a higher overall and flavor liking than HOL steaks.

The omega-6 and omega-3 FAs (Table 1) were not different between steers that grazed WW compared to WR. From this study, cover crops did not influence FA concentration in the fat of beef. The omega-3 FA concentration was higher in fat from MVH steers compared to HOL fat. The omega-6/3 ratio was higher in HOL back fat compared to NJV and MVH back fat. Although these steers were finished on a forage diet, they received grain during the pre- and post-weaning stages. This may have influenced the higher omega-6/3 ratio in this study than steers fed a no-grain diet throughout their lifetime.

In summary, the NJV steaks were preferred to HOL steaks, with MVH steaks falling in between. To complement this, the steaks from steers grazing WW were preferred to steaks from steers grazing WR. A lower and healthier omega-6/3 ratio was found in NJV and MVH back fat compared to HOL back fat.
Both cover crop and breed influenced sensory attributes, but omega-6 and omega-3 FAs were only influenced by breed. Fat in the diet is broken down into free FAs in the rumen by microbes and built back up into long chain fatty acids for deposition in adipose tissue. Differences in omega-6 and omega-3 FAs in back fat for breeds could be due to a number of factors, including differences in rumen microbial ecology and rumen pH.

In this study, the wheat and rye cover crops were ready to graze three weeks earlier than other perennial pastures on the farm. This study not only applies to grazing steers, but to grazing dairy cows as well. By grazing cover crops, we were able to start grazing three weeks earlier in the grazing season and graze the system three times through with about 16 days of rest between grazing periods. Grazing winter wheat and winter rye are both feasible to graze in the early spring and summer.

Hannah Phillips is a graduate student at the University of Minnesota pursuing a master’s degree focused on organic dairy systems. Brad Heins is an associate professor in the Department of Animal Science.


From the May | June 2017 Issue

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