It might not seem like much when you walk through the barn and notice an empty feed bunk. The feed truck eventually comes through to drop a pile of feed, the cows in the pen dive in to eat and everything seems right with the world.

That may be the perception, but the reality is that the digestive system in the cow has just been through a stressful situation. That period of low feed intake probably did more harm than you realize.

Remember that cows are creatures of habit and prefer as little excitement in their day as possible. That goes for the rumen and the microbes contained within. In the ideal rumen world a steady flow of feedstuffs enters the rumen, maintaining a constant equilibrium, or homeostasis, between all bodily functions.

When that flow of feedstuffs shuts off, that homeostasis is interrupted and important functions, especially within the rumen and for the immune system, are thrown into chaos.

A drop in feed intake can be the result of several factors:

• Empty bunk. It sounds simple, but keeping fresh feed in front of cows can be an issue on dairy farms. The cause varies: change in dry matter, increase in pen size without changing ration amounts, a mistake by a feeder, equipment malfunction, etc. Realize that the issue is greater for over-stocked pens. Those cows that aren’t aggressive enough to fight their way to the bunk will have a larger off-feed deficit than the average of the pen.
• Pre-calving cows. Feed intake in cows during the three weeks before calving can drop 33 percent, and as much as 88 percent in the last week before calving (Hayirli, et al. 2002). This can have a dramatic impact on rumen function and makes it critical to be cautious during early fresh period feeding.
• Environmental stressors. Heat stress can be especially hard on feed intake. It’s important to have heat abatement measures in place to reduce impact.
• Diseases and disorders. Cattle impacted by BVD can have as much as 80 percent reduction in feed intake. Cows with mastitis or metritis can drop intake by as much as 50 percent.

GI Function.

To understand how reduced feed intake can be disruptive it’s important to understand the roles played by the gastrointestinal tract. Optimal gut health involves maximum digestion and absorption of nutrients while maintaining a protective barrier and allowing communication between the cow and microbes.

First and foremost is digestion of feedstuffs. This includes nutrient absorption of short chain fatty acids (SCFAs), minerals and other components contained within the ration.

A second function involves creating a protective barrier that stands as the first line of defense for the immune system. This barrier regulates transmission of materials, keeping undesirable molecules outside of the animal and allowing movement of desirable materials through cells.

A third function involves communication between the host and microbes. This includes nutrient sensing and signaling from the diet or from microbes to the cow to regulate body functions.

Research shows that a drop in feed intake has a negative impact on one or all of these functions.

• A study in Germany (Gabel. et al. 1993) exposed animals to 48 hours of complete feed withdrawal. Compared to animals who were not subjected to this treatment, absorption SCFAs and volatile fatty acids was reduced by 50 percent.
• A University of Saskatchewan study (Zhang, et al. 2013) showed the impact over different levels of reduced intake. In the study 18 Angus heifers were fed diets at 75, 50 and 25 percent of free choice feed access. The heifers were all fed the same diets and recovery was tracked once the animals were back on full feed over three weeks. Heifers in the lowest intake group had the following reaction:
  • Production of short-chain fatty acids was lowest
  • pH was highest in the lowest intake group and pH levels were lower in full-feed diets.
  • The ability of the rumen and small intestine to absorb nutrients was lowest
  • The function of the protective barrier inside the gut was affected the most in the lowest intake diets. This indicates that the tight junction between cell walls was negatively impacted, suggesting barrier degradation.
• In another University of Saskatchewan study (Kvidera, et al. 2017) off-feed events changed microbial structure and increased release of pro inflammatory molecules, and a short-term exposure to reduced feed intake changed the morphology of bacteria inside the intestine.

Long Recovery.

Studies also show that recovery after an off-feed event can be extensive. In the study where Angus heifers were exposed to various levels of feed reduction, recovery was more severe in the lowest feed intake diets. While rumen pH levels were highest in the 25 percent intake group, pH levels plunged to the lowest levels once heifers went back on full feed. This indicates these heifers are more susceptible to subacute rumen acidosis and fatty liver issues. A study by Pederzollie, et al. in 2018 showed a reduction in the absorptive surface of the rumen by over 50 percent, which could explain why volatile fatty acid absorption drops and why cattle are exposed to rumen acidosis when they go back on feed.

Based on these research results, low feed intake can have a significant impact on the long-term health of dairy cows. Implementing management tactics to avoid off-feed events can pay dividends. Following strict feeding protocols to ensure feed bunks always contain feed is an important step. Avoiding overcrowding so all animals within a pen have access to feed is another action.

One opportunity lies in the transition period. Cows that are placed on highly fermentable fresh cow diets are especially susceptible to sub-acute rumen acidosis. Cows close to calving experience a significant drop in intake at calving and spike in ruminal pH. If facilities allow, producers should offer a short-term fresh pen where cows could be fed a high forage diet for two or three days to establish a good rumen fill before transitioning to a full fresh cow diet.

For further discussion around conditions that can cause cattle to inadvertently go off feed – and strategies for mitigating impacts and accelerating recovery – check out this recorded webinar, presented Dr. Greg Penner from the University of Saskatchewan.