Cows are in negative energy balance (NEB) when their energy requirements (i.e., maintenance, gestation, production) are not met by their energy intake.
Days before calving, cows enter into an NEB period: Dry matter intake drops, driven by hormonal changes, but the energy requirements for calf growth and colostrum yield increase. Postpartum, the energy demands of milk yield progressively increase, but energy intake falls short, resulting in an NEB period that lasts up to six weeks.
Cows are able to overcome periods of NEB through metabolic adaptations. They can mobilize fat depots to synthesize non-esterified fatty acids and ketone bodies (i.e., beta hydroxybutyrate). These can be used as alternative energy sources by the mammary gland.
Despite the negative connotation of NEB, it is important to remember high-genetic-merit cows are only able to express their production potential because they get into an NEB period. However, in some instances, the mechanisms designed to cope with NEB fail, and cows develop fatty liver, a metabolic disorder that compromises liver function.
Optimum liver function is essential for gluconeogenesis, ketogenesis, ammonia detoxification, metabolism of steroid hormones, immune function and others. Thus, one of the major goals for a successful transition period – defined as three weeks before and three weeks after calving – is preventing fatty liver.
This can be achieved through minimizing fat mobilization from adipose tissue (reducing NEB) or increasing fatty acid exportation from the liver. However, this last strategy is challenging, as a cow’s ability to export fat from the liver is very limited compared to other species.
Over the past decades, researchers have emphasized the importance of prepartum and postpartum dietary strategies to minimize NEB and favor fat exportation from the liver.
Some of the strategies evaluated were the inclusion of various levels of starch, fiber or energy concentration in pre- and postpartum diets. The inclusion of glucose precursors, vitamins and choline supplementation were also studied. However, other strategies also have a critical influence to minimize NEB effects.
One key factor to the success of dietary strategies during the transition period is feeding management practices. Below are some considerations for nutritionists and dairy producers.
Microbiological quality of feeds
A good starting point to ensure a successful transition period is evaluating the microbiological quality of high-moisture feeds (i.e., silages, cull fruits). During times of low milk prices, some dairies try to minimize the cost of feeding by offering spoiled feed to dry cows and even to lactating cows.
However, spoiled feed is more likely to be contaminated with molds and mycotoxins that will reduce intake and nutrient absorption, alter endocrine responses and suppress the immune system. Some tips to minimize spoiled feed are:
- Reduce the surface spoilage of silage by covering it with double plastic or oxygen-barrier technologies.
- Feed seasonal high-moisture byproducts (i.e., pomegranates, peaches) fast before spoilage takes place. Dairy producers should buy according to their needs. Don’t buy tons just because it’s cheap; it will spoil.
- Clean out refusals daily, especially during the summer, to avoid residual feed undergoing secondary fermentation.
Performance of feeders
Poor feeder performance may challenge the onset of lactation. This was observed in situations where feeders were not able to differentiate between regular alfalfa hay and dietary cation-anion difference alfalfa hay or between bags with minerals for dry cows or close-up cows.
It is important to assess whether the feeder properly identifies each commodity, whether he follows the recipe as indicated by the nutritionist, or whether he is feeding the cows at the same time every day. Feeders should be carefully trained and empowered to make decisions.
For example, if the feeder knows what forage particle length should look like for close-up and fresh cows, he should report any problems or seek solutions (i.e., sharpening the knives, changing the mixing time).
Another important feeding management issue is deciding the amount of feed that should be delivered to close-up and fresh cow pens. Those are very dynamic pens with ever-changing cow numbers. Therefore, in most instances, some guessing is applied on cow numbers.
We have noticed some feeders opt to underfeed those pens to minimize refusals and feedbunk cleaning. Nutritionists and managers should walk those pens and evaluate feedbunks several times a day. We have visited a dairy where close-up cows were underfed and, even though the dietary cation-anion difference was adequate, urine pH was not acidic.
Despite the important role of the feeder, oftentimes the nutritionist and the manager have limited interaction with the feeder. Data from the feeding management software can help to evaluate feeders’ performance based on loading errors, feeding time, time between ingredients, etc.
However, it is the one-on-one interaction that will be most productive. I find it very useful to ask for the feeder’s opinion on what needs to be changed to improve feeding at the dairy.
Preparation of the TMR
When preparing the close-up TMR recipe, large dairies face an important challenge: The volume of the close-up recipe is 20 to 40 percent of the mixer box capacity. This may compromise the efficiency of mixing.
If it is safe, managers and nutritionists should climb to the top of the mixer box and evaluate the efficiency of the mixing process. Is the feed moving and mixing? Is there feed stuck on the top of the augers? The problem of mixing efficiency will be solved if a smaller mixer box is acquired.
A less costly strategy can be to prepare premixes. Based on our research, a total of 68 percent of dairies in California were preparing a close-up premix, but on 24 percent of dairies, feeders were still emptying anionic salts bags directly into the mixer.
In summary, each dairy faces its own challenges coping with NEB. If you are concerned about how your fresh cows are performing, just get involved with management. One starting point is to discuss your ration with the nutritionist and understand what is your feeding strategy for transition cows. Also evaluate if feeding management practices are properly implemented on your dairy. And don’t forget: Talk to your feeder. 
PHOTO 1: Talk with your feeder often to ensure they are following the correct diet formulation set by you and your nutritionist.
PHOTO 2: Anionic salts sitting on the auger blades after mixing a close-up TMR ration. Photos by Rúbia Lopes.
