Feeding Ruminants Frozen Feed

Depending on the year and location, Ontario can be quite cold with variable precipitation across the province. Feeding out forages in the winter months certainly comes with some challenges. One challenge is the potential to feed snow and ice along with the forages that are being prepared for feeding.

In recent winters, the question 'does frozen feed affect ruminants?' has come up in discussion. If so, what does it affect? Looking at research that has been done with regards to feeding frozen feed, or allowing animals to obtain their water intake from snow or ice, we noticed the lack of data on this topic, especially for goats but also for ruminants such as sheep and cattle. This article presents a summary of research conducted on this topic.

For a rumen to function properly, it is important that the temperature remains consistent, as rumen microbes are more efficient in a consistent environment. Studies show that ingestion of frozen feed and water can cause the rumen temperature to drop rapidly but not return to a normal temperature for several hours. The ingestion of frozen feed not only affects the ruminal temperature, but the overall body temperature of the animal itself, as demonstrated by a decreased rectal temperature. These same studies show that even if the ruminant is kept in a warm barn but only given access to frozen water sources, they can be observed shivering and bellowing to express discomfort. This indicates that ingestion of frozen water or feed can cause a "cold shock", a rapid decrease in internal temperature and induction of shivering, regardless of other factors. The long term effects on the health and production of the animals experiencing such cold shock has not been evaluated. Suggested methods to reduce this cold shock include providing dry roughage along with frozen feed to buffer the rumen, or providing warm water to counteract the effects of the frozen feed.

Studies show that another concern associated with feeding frozen feed to ruminants is that it decreases their dry matter intake (DMI). The exact reason why DMI drops with frozen feed is unknown, although there are a few theories. One researcher concluded that DMI decreases due to the increased effort needed to break off and chew frozen feed compared to thawed feed. Simply chopping the feed into more manageable pieces could be a solution to this problem. Another researcher came up with a more complex theory. If feed has poor digestibility, the animal will spend a significant amount of energy warming it up and digesting it with little energy available for maintenance or gain. For this reason, ruminants decrease their feed intake to conserve energy. This theory highlights the importance of providing ruminants with high quality feed, especially in the winter months when the feed is expected to be cold or frozen. It has been demonstrated that supplementing frozen feed with unfrozen roughage can result in a normal level of DMI. Therefore, studies suggest when frozen feed must be fed, there are several ways to maintain DMI, including chopping the feed into manageable chunks, providing highly digestible feed, and supplementing frozen feed with unfrozen roughage.

The upkeep of the body temperature, regardless of external influences, is called thermoregulation. Once the body temperature falls below the lower critical temperature, the animal must increase its metabolic heat production to sustain itself. When ingested feed or water is frozen, the ruminant must first warm the feed to the ruminal temperature before it can begin to digest. This warming of feed increases the ruminant's metabolic heat production. The feed begins to be warmed by the mouth and esophagus when it is being chewed and then swallowed. Once it has reached the rumen, blood flow to the rumen is increased and energy is diverted towards the rumen. Some of the energy that was once stored as fat or used for other processes such as lactation is now diverted to the rumen. It is unknown exactly how much energy is needed to heat frozen feed as it varies by rate of feed intake and quality of diet, but it is known that this extra energy requirement increases the maintenance energy demands of the animal. For this reason, it is important to ensure that all animals are in good body condition and have access to energy-dense feed when feeding frozen feed or water.

Other questions that arise when feeding frozen feed include "is the quality of the feed being affected?" and "are ruminants capable of extracting the same amount of nutrition from frozen feed as they do thawed feed?". Unfortunately, there is not a lot of research in this area. However, the research that we do have suggests that frozen feed has lower crude protein content than thawed feed. This study noted that frozen feed also appears to have increased lignin, the indigestible portion of plants, therefore suggesting a decrease in the digestibility of the frozen feed. However, this is only one single study and more research is needed to conclude exactly how feed quality is affected by freezing.

Managing the feeding of frozen feed to ruminants can be a challenge in Ontario winters. Of course, it should never be the sole source of feed the animal has access to. Research has been conducted to illustrate the short term effects the ingestion of frozen feed has on ruminants. Although some studies have concluded that there are negative effects of feeding frozen feed to ruminants, these negative effects can be easily overcome. By simply providing ruminants with unfrozen roughage and high quality feed we can counteract the drop in both body temperature and DMI. Ensuring all animals are in good body condition prior to the winter months also aids in counteracting these negative effects. The long term effects on the health and production of feeding ruminants frozen feed have not yet been evaluated. More research is needed to investigate these long term effects and their possible mitigation.

References for this article are available upon request.

*A version of this article also appeared in the December issue of the Livestock Alliance magazine.

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