Tannins in feed may offer production boost for dairy cattle

In-silage tannins may make dairy cattle more efficient without the need for additional dietary protein, says researcher.

A team of researchers from the US Department of Agriculture’s US Dairy Forage Research Center examined the use of Lotus corniculatus L.​ or birdsfoot trefoil (BFT) as a forage alternative to alfalfa in terms of protein production in milk and attempted to find the optimal amount of dietary condensed tannin (CT), they said. The group published its results in the Journal of Dairy Science​​.

“We were pursuing the condensed tannin [level], because of our hope that it would improve production and the environmental footprint of dairy,”​ said Glen Broderick, USDA researcher and corresponding author. “And it does, but the plants are not as good.”​

It can be more of a challenge to grow a tannin-containing plant like birdsfoot trefoil (BFT) because not as much work has been done to establish strains of the plant that are resistant to concerns like drought and cold weather, he told FeedNavigator. “The extension of this is that through genetic engineering, it looks like it would be possible to have the trait expressed in alfalfa,”​ he added.  

“Birdsfoot is a good source of forage with dairy cows it would work somewhat better in a dairy ration that alfalfa,”​ he said. “If you can grow it; and you might have sufficient land and are not worried about a yield knock.”​

The team found that cows getting diets containing condensed tannins, produced less milk urea nitrogen (MUN) and that there was little variation in the level of milk true protein, said the researchers. However, additional work is needed to pinpoint the amount of CT needed for the diet as results were somewhat inconclusive.

“Compared with AS diets, diets containing BFT reduced MUN and urinary excretion of urea and total N [nitrogen], which would be expected to reduce ammonia emissions from manure; however, little improvement was made in conversion of feed CP [crude protein] into milk true protein,”​ said the researchers. “Although earlier work suggested that milk and component yields were optimal at 1.0 to 1.6% CT, feeding BFT silage containing 0.5% CT gave rise to the greatest yields of milk, ECM [energy corrected milk], milk protein, and other components in the current trials.”​

Why birdsfoot trefoil?​

Several legumes contain levels of condensed tannins that are involved in hydrophobic interactions and hydrogen bonding with the proteins in conserved forages, said the researchers. Those activities limit protein degradation and the formation of non-protein nitrogen (NPN) during ensiling.

When a silage is created, it also can contains enzymes that will digest the protein in the feed, said Broderick. For ruminants, this means that over time the usefulness of the proteins dwindles.

Previous research has found that the presence of CT improved the growth and milk production of ruminants, said the researchers. Using a forage that included CT also limited the output of urinary urea and ammonia.

However, the interaction of CT with proteins in forage and the chemical properties vary based upon which legume produced them, they said. It has been suggested that the tannins found in birdsfoot trefoil is particularly effective for boosting ruminant performance.

In previous research using fresh-cut forage, feeding BFT improved milk production in cows and ewes, when compared to production results from animals getting a diet where the CT had been inactivated, they said.

“Our hypothesis was that the presence of CT in BFT would, relative to the AS [alfalfa silage] control, improve protein utilization for milk production in lactating dairy cows,” ​said the researchers. “Moreover, we wished to identify the CT concentration that would optimize cow performance.”​

Study details​

Researchers ran two separate feeding trials to examine the feed ingredient.

In the first feeding trial, 32 cows were given one of four diets for a four-week period, and then rotated to the next diet, said the researchers. Diets included an alfalfa-based diet, and one with a low, medium and high amount of condensed tannins.

Samples were taken of the silages, total mixed ration, orts and analyzed for dry matter, total nitrogen (N), neutral detergent fiber (NDF), and acid detergent fiber (ADF), they said. Milk yield was recorded and samples were taken to check for fat, true protein, lactose, solids-not-fat (SNF), MUN ECM and the efficiency of feed conversion, N utilization and body weight (BW) change were established.

Fecal matter and urine were collected to test for dry matter (DM), organic matter (OM), NDF, ADF total N and indigestible ADF, they said.

In the second study, 50 cows were given one of five diets for 12 weeks, said the researchers. “Diets were fed as TMR and contained (DM basis) 48% AS (covariate and AS control diet), 16% AS plus 32% of 1 of the 3 BFT silages with varying levels of CT, or 48% of a mixture of equal DM from all 3 BFT silages,”​ they added.

Diet samples were collected and tested for DM, ash, OM, total N, NDF and ADF, while milk collected was checked for protein, lactose, SNF, MUN and ECM, they said. Body weights were noted and urine and fecal matter were collected and analyzed.  

Results​

In the first study, the alfalfa diet had more ash and crude protein, while the mid-level birdsfoot diet had the most ADF and NDF, said the researchers.

Dry matter intake was higher for diets with BFT, and cows on the AS diet lost weight, they said. Milk yield was similar for all diets, but there tended to be more milk protein concentration and true protein yield in the BFT diets.

MUN was reduced linearly with increased BFT and apparent N-efficiency was higher, they said. Apparent digestibility of DM, OM (organic matter), N, NDF and ADF were larger for the alfalfa diet, but fiber digestion did not decline linearly with an increase in CT.

In the second feeding trial, the diet with the most tannins was found to have the most NDF, ADF, neutral detergent insoluble nitrogen (NDIN) and acid detergent insoluble nitrogen (ADIN), with less N and NPN than the other diets, they said. Cows getting the BFT diets tended to have more DMI and milk yield.

“The DMI responses were reflected in linear effects on yield of milk, ECM, fat, true protein, lactose, and SNF, indicating reductions with increasing CT concentration,” ​said the researchers. “Milk concentrations of fat, lactose, and SNF were not affected by diet; however, milk true protein was lower on the mixed BFT diet versus the other three BFT diets.”​

MUN was larger for the AS diet, but apparent N-efficiency was not altered, they said. However, the apparent digestibility of DM, OM and ADF was similar among all diets.

“There was a generally positive use from the birdfoot rather than the alfalfa,”​ said Broderick on the results. But, the team was unable to pinpoint the best level of dietary tannin, he added.

However, there could be several reasons for the results found, he said. “You have to have cows that are in a position to use the extra protein, if they’re later in lactation or the requirements are met on the control diet, when you increase the supply of metabolizable protein you may not see much response,” ​he added.

“If you had access for birdsfoot trefoil forage and you were getting appropriate yield, you’d have improved protein utilization and somewhat improved protein yield of the cows with the same amount of protein in the diet,”​ he said was the overall takeaway.