As the transition cow enters negative energy balance, no longer meeting her nutritional requirements, there is a huge demand on the liver to continue to make glucose to drive milk production.
At the time of calving, the fresh cow mobilizes fat or milks off of her back. Fat is mobilized as non-esterified fatty acids (NEFAs) and glycerol, which is not optimal because while the glycerol can be used to make glucose, the NEFAs can lead to ketosis or fatty liver, said Dr. Heather White from the University of Wisconsin – Madison at the Vita Plus Dairy Summit, Dec. 9-10, in Baraboo, Wisconsin.
White offered three strategies to nutritionally help a cow deal with the mobilized fat and make more glucose to support milk production.
1. Spare energy and milk components
Of the energy the cow is consuming that is not used to meet her needs, 97 percent goes into the milk. Of that milk energy, 50 percent is milk fat. “So even though milk fat is only 3.5, 4, 4.5 percent of the milk, it is half of the energy that it takes to make milk. It’s a very energetic, expensive component of milk,” White said.
White and her fellow researchers considered marginally reducing milk fat – not enough to affect the farm’s premium, but enough to free up that energy for the cow to make more milk.
It is known that trans-10, cis-12 conjugated linoleic acid (CLA) reduces milk fat. Therefore, White looked at supplementing a protected CLA to decrease milk fat and increase milk production. The supplement was fed on a commercial dairy to the pre-fresh pen 21 days prior to calving. It was then individually fed through the milking robot to multiparous cows for 30 days and first-calf heifers for 70 days (since heifers peak a little later in lactation).
During the supplementation, multiparous cows produced an average of 5.5 pounds more milk per day per cow. Post-supplementation, the cows continued to produce 3.5 more pounds per day on average.
“Even after supplementation ended, milk yield maintained significantly greater than controls,” White said.
Milk fat in multiparous cows did decrease significantly (0.2 percent), but quickly returned to the same level as the control group after the 30-day supplementation was over.
“The important thing here is you are only supplementing for fresh cows, so we never changed the bulk tank milk fat percentage when we were doing this study,” she said.
For first-calf heifers, CLA cows produced slightly more than 2 pounds more milk per day during supplementation, which they maintained through 150 days in milk. Milk fat was decreased, which held through the lactation, yet it did not influence bulk tank milk fat.
White also looked at the cows’ ability to rebreed. There was no change in multiparous cows, but primiparous cows significantly improved their conception rate. Primiparous cows fed the CLA supplement had a 53 percent conception rate compared with a 35 percent conception rate seen in the control group.
Therefore, transition period CLA supplementation may spare energy from milk fat synthesis and allow the cow to put it into milk volume. Milk yield can increase 5 to 7 pounds per day without changing overall fat yield, bulk tank fat, protein yield, body weight, health incidences or rumination minutes.
“The caveat here is this [CLA supplement] is not yet FDA-approved for general use in the U.S., but it is approved for use in Canada, Mexico and EU,” White said.
2. Protect the liver from fat accumulation
As fat accumulates within the liver, it can lead to health disorders and makes the cells less efficient at what they need to do. So getting fat out of the liver is important. One way to do that is feeding rumen-protected choline. A meta-analysis of all the studies that fed a rumen-protected choline revealed it decreases fat in the liver and increases milk production 5 pounds per day, likely through improved liver function, White said.
To better understand how that is happening, White used a cell culture model to expose liver cells to four different concentrations of choline representative of what would be circulating in the cow, whether she was supplemented or not. She also mimicked a transition cow by adding a NEFA load to some of the cells. White reported they did, in fact, see an increase of very low density lipoprotein (VLDL) export by giving choline.
“The other thing we know decreases the liver’s efficiency is that there is a charge for oxidizing fatty acids in the liver,” she said. Oxidizing the NEFAs that come to the liver causes oxidative stress and results in reactive oxidative species (ROS), which accumulate and decrease the liver’s efficiency. She found that cells supplemented with choline also tended to reduce the amount of ROS accumulating in the liver.
3. Optimizing amino acid balance
In addition to exporting VLDL and reducing ROS, choline can be used in the liver to donate methyl groups to help regenerate methionine. As methionine is increased, it decreases endogenous methionine regeneration, but does not change VLDL export or ROS. “I think that methionine wasn’t used for those because the cell and the cow have priorities for methionine that exceed these pathways,” she said.
Within the cow, methionine is required for milk protein synthesis, DNA methylation, the start codon of every protein generated in the body, creatinine synthesis and regenerating tetrahydrofolate (THF). “It’s required for a lot of pathways that it has to meet before it can be used for other things like being used to export VLDL,” White said.
Since methionine is important to the cow, White wanted to know if it mattered what form was fed. She did a similar cell culture model to see if methionine needs of the cells could be met either by dietary sources or regeneration. The liver can only use L-methionine, but it is able to convert D-methionine and HMB to L-methionine. “If you give a synthetic analog, the liver can use it just the same as if you give a DL-methionine,” she concluded.
Even though methionine does not decrease ROS, it does increase glutathione, which is an antioxidant.
Overall, White said, there is a biological priority for methyl donor use – for the whole animal and at the cellular level. The lack of interaction supports separate roles for methionine and choline. Lipid accumulation, oxidative stress and methyl donors all decrease how well the liver can make the glucose it takes to support the demands of lactation.
In conclusion, White said, the negative energy balance associated with the transition to the lactation period can be mitigated by a few nutritional strategies. CLA supplementation spares energy from milk fat to milk production and improves conception in heifers. Choline increases VLDL export, decreases fatty liver, increases milk production, decreases ROS and can serve as a methyl donor for methionine regeneration. Methionine plays many roles in the cell and supports protein synthesis and milk production. PD
PHOTO: Staff photo.
