A few months ago we discussed both the basics of how to understand a forage analysis, and also how to select the right mineral mix for your sheep. Lambing season is just around the corner, so, today we are going to discuss two very common and completely preventable nutrition-based problems you might encounter. We will be discussing pregnancy toxemia (also called ketosis or twin lamb disease) and hypocalcemia aka milk fever. Both are derived from your ewes having poor nutrition.
Pregnancy toxemia and milk fever are two completely different conditions. However, they are both the result of insufficient nutrition in the weeks surrounding lambing. Both disorders are life threatening, and seeing a frequent occurrence of either is a clear indication that your flock’s nutrition management needs an immediate reevaluation. Preventing these conditions through appropriate nutrition is much preferable to trying to treat them after symptoms have started.
Let’s start by taking a look at pregnancy toxemia
Pregnancy toxemia (also known as twin lamb disease or ketosis) typically occurs in the last 6-8 weeks of pregnancy. It is essentially that your ewe has extremely low blood sugar similar to what might happen to a diabetic person. Symptoms you might see include a sheep that isn’t staying with the flock, or that seems dull and listless. They likely aren’t eating and won’t move away if you approach them. Left untreated they will eventually be unable to stand and will die. If you see one of your late gestation ewes behaving oddly, don’t ignore it. Left untreated, the sheep with pregnancy toxemia will die within the next few days.
Treatment is simple, administration of glucose injections, propylene glycol drenches, and trying to increase the quality of their feed. Unfortunately, while in principle treatment is simple, in practice it isn’t straight forward. It can be very difficult to bring back an ewe that has succumbed to pregnancy toxemia. Not all ewes will survive despite your best treatment efforts. This is why it is ALWAYS better to do everything you can to prevent it.
Pregnancy toxemia disease is caused by the ewe being in a negative energy balance.
The calories your ewe is consuming are below her energy requirements. The reason pregnancy toxemia is often called twin lamb disease is that the risk of pregnancy toxemia goes up as the number of fetuses increases. More fetuses mean decreased rumen space. The majority of lamb growth occurs in the last 6-8 weeks of pregnancy. Your ewe’s nutrition requirements increase while the space inside her body for her rumen simultaneously decreases. The more fetuses your ewe has, the greater her energy requirements and the smaller her rumen.
If your ewe’s feed contains insufficient calories, the ewe starts to mobilize body fat to compensate. Blood glucose levels drop, and the liver gets overwhelmed as it is breaking down fat for energy. If excessive amounts of fat are mobilized in response to the low glucose levels in the blood, the liver may struggle to keep up resulting in incomplete fat break down and increased ketones in the blood. This is all bad news for both the ewe and the lambs.
Fortunately, pregnancy toxemia is easy to prevent if you ensure your feed has sufficient energy levels. It is also worth noting that ewes that are either over or under conditioned (too fat or too thin) are more prone to developing pregnancy toxemia. Thus it is also important to know how to body condition score your ewes. Aim for ideal body condition, and watch ewes that fall outside of that range more closely in late gestation. If you aren’t sure what the body condition score of your ewes please we posted an article about how to body condition score your sheep a couple months ago.
How do I know if my ewes diet contains sufficient calories?
Since you can’t determine the energy level of your feed just by looking at it, this is where your forage analysis comes in. You also need to know what the ewe’s estimated requirements are. If we look back to the NRC requirements and our forage analysis from our discussion on understanding a forage analysis we can compare our hay to our ewes requirements. Remember the NRC requirements are MINIMUM requirements.
Higher TDN = higher quality feed.
There are a variety of different measurements of the quality of our forage present on the analysis. Today we are mainly going to concern ourselves with TDN, DE, and ME. Total digestible nutrients (TDN), is a measurement of the quality of the feed. The TDN of low quality hay is typically 45-52%. Good quality hay is 58% or greater. DE is the digestible energy, and ME is the metabolizable energy. All 3 are measurements of the energy level in your feed. Not all forage analysis reports will show all 3 measurements, however, as you can see in the red circles above, the NRC provides a column for each.
Looking at our forage analysis where it is underlined in blue, you can see that our grass hay comes up short for meeting the energy requirements of our late gestation ewes. For example, TDN is only 52% whereas the NRC says our ewes need a minimum of 65%. If we don’t change our feed or supplement more nutrient dense feeds, we would likely see pregnancy toxemia in our flock.
This is a very common scenario, and also one very easy to remedy if you are aware that it’s likely to be a problem. Many forages do not contain sufficient energy to meet the needs of a late gestation ewe carrying multiple fetuses. If you look at your forage analysis and it comes up short on energy levels as compared to what your ewes need, you can supplement a concentrated feed for the last few weeks of pregnancy. It’s much better to know this ahead of time so that you can compensate before your ewes start going down.
Another very common condition seen in sheep is milk fever.
Milk fever is a calcium deficiency in the blood. As your ewes are growing their fetuses and starting to make milk to feed their lambs they need a lot of calcium. If their diet is insufficient in calcium, then you run the risk of them developing milk fever. Milk fever can occur in roughly the same time frame as pregnancy toxemia—the last 6-8 weeks of pregnancy—and also during early lactation.
Symptoms present similar to those described above. Progression is much more rapid though. Ewes might experience muscle tremors, be lethargic, and will eventually be unable to stand. Left untreated ewes can die in just a few hours. Fortunately, if caught in time, milk fever is easy to treat with a calcium injection. However, given how rapidly ewes can deteriorate and die from milk fever, this is far from an ideal scenario.
Just like pregnancy toxemia, milk fever is a result of poor nutrition.
And once again, just like you cannot know the energy level of your forage by looking at it, you cannot determine the calcium level either. Mineral status is even less predictable than energy from a visual inspection of a forage. It is not at all uncommon for forages to be calcium deficient. A basic forage test can save you a lot of headache.
Looking back at our example forage test above, we can compare calcium levels to requirements (underlined in red on our analysis). Once again you can see that our grass hay comes up short. It is only 0.34% calcium, and our ewes need a minimum of 0.4%. Based on this information, we now know that feeding this hay without feeding alfalfa or a mineral mix with added calcium, would be setting our sheep up for trouble.
If your feed tests low in calcium you have a couple options. You can provide extra calcium in your mineral mix and/or feed a high calcium forage. Feeds vary widely in their calcium levels. Legumes like clover and alfalfa are usually high in calcium. Grasses are typically lower in calcium. High energy feeds like corn are high in phosphorus and low in calcium.
This is important to keep in mind. Are you adding grain to your ewes’ diets during the last few weeks of gestation to meet their energy requirements? If so, you need to make sure you are compensating with sufficient calcium. You not only need to compensate for them eating less hay and more grain, but also for the high phosphorus levels in the grain.
Based on our typical forage conditions, our preference is to feed high calcium alfalfa and offer calcium in our mineral mix.
The grass hay here is often sufficient or borderline sufficient in both energy and calcium for the majority of gestation. Thus, we feed a mineral mix containing some calcium throughout gestation. Then during the last couple months of gestation, we switch from grass hay to a high quality, leafy, 2nd or 3rd cut alfalfa. Feeding alfalfa ensures that our ewes start to consume extra calcium as their requirements increase. This is something that a free choice mineral supplement cannot guarantee. For our flock switching to alfalfa also usually meets their increased energy needs in late gestation creating a win- win situation for our ewes.
Pregnancy toxemia and milk fever are just a couple examples of how the nutrition status of your flock and the quality of your forages can cause or save you a lot of headache and potential heartache. Knowing as much as you can about the nutrition of your flock can help you to make informed decisions. This will allow your sheep to be as productive and profitable as possible. Remember, nutrition is one of the foundational blocks upon which every shepherd’s success is built.
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