For years I’ve recommended a very simple diet for ewes in their lambing jugs: a few pounds of alfalfa pellets in a tray hanging on the side of the pen. Nutritious, convenient and waste-free. But at various meetings over the years, shepherds have raised two reasonable concerns about this technique, and I’d like to address them here because they both involve basic concepts about forages and fiber.
Concern No. 1: A sudden switch to pellets will reduce digestion efficiency and cause problems
Reducing “digestion efficiency” means reducing feed digestibility enough to cut milk production drastically or cause health problems with the ewes and lambs. This is a complex problem, so let’s examine this situation thoroughly.
Modern nutrition laboratories analyze the dry matter of a feedstuff into two main fractions: cell contents and cell walls. The cell contents include the non-fibrous, soluble and liquid stuff inside cells. These cell contents are essentially 100% digestible. Pelleting doesn’t change this digestibility. The dry matter of medium-quality alfalfa contains approximately 54% cell contents, and none of it is affected by pelleting.
The cell wall fraction of a feedstuff is called NDF (neutral detergent fiber). NDF is not a simple substance – it’s actually a complex assortment of different fiber compounds that combine to form the rigid structure of plant cell walls. NDF contains three basic types of fibers: cellulose, hemicellulose and lignin. The common term ADF (acid detergent fiber) is a subset of NDF and is composed of only two of these fibers: cellulose and lignin.
Medium-quality alfalfa hay typically contains 26% cellulose, 10% hemicellulose and 9% lignin. These three fibers equal the 46% NDF fraction of the plant. (The 1% difference from 46% is due to other very minor components.) We’ll take a look at each type of fiber separately. Lignin is, for all practical purposes, totally indigestible, which means that all of it passes unchanged completely through the gastrointestinal tract into the manure. Numerically, this means that its digestibility is zero. Pelleting doesn’t alter this digestibility, since it’s rather difficult to reduce a zero any further. Therefore, any changes in “digestion efficiency” cannot occur in this lignin fraction.
Cellulose and hemicellulose, on the other hand, are fibers that are potentially digestible. Their digestibilities depend mostly on rumen fermentation, as in how much can the rumen microbes ferment these fibers and how long do these fibers remain in the rumen to be fermented? Any changes in “digestion efficiency” would occur in these types of fibers.
The nutritional principle here is fairly straightforward: Fiber digestibility is defined by its rumen fermentation, and the longer a fiber remains in the rumen, the more it is fermented.
This is where pelleting may have a real effect. Feeding pellets usually increases feed intake. Ewes generally eat more pelleted alfalfa than long hay alfalfa. Increased intake reduces the retention time in the rumen and therefore reduces the digestibilities of the cellulose and hemicellulose. But how much? Ah, that is the question.
Let’s see if these changes have real biological meaning for these ewes. The total amount of potentially digestible fiber is the sum of the cellulose and hemicellulose fractions of the feed, which for this alfalfa would be 36% of the total dry matter (= 26% + 10%). Any changes in “digestion efficiency” would have to occur in that 36% fraction.
If the normal digestibility of this fiber (when fed as long hay alfalfa) were 60%, then this fiber would provide 21.6% digestible nutrients (= 60% of 36%). If pelleting reduces rumen retention time enough to shorten fiber fermentation by, say 25%, that would mean that instead of a 60% digestibility, the fiber in alfalfa pellets would only have a digestibility of 45% (= 60% less the reduction of 25%). In pelleted alfalfa, the 36% cellulose/hemicellulose fraction would yield only 16.2% digestible nutrients (= 45% of 36%). Still with me?
This means that pelleting alfalfa could reduce the amount of absorbed nutrients (from the cellulose/hemicellulose fraction) from 21.6% to 16.2%. In other words, the total digestibility of the entire pellet would be lowered by 5.4% (= 21.6 - 16.2).
That’s not very much when you consider that this would occur only during the one to three days when ewes are in the jugs. After that brief period, the ewes go into mixing pens where they are fed their regular early lactation ration of grain and forage. So … a potential nutritional loss of only 5.4% for less than three days is hardly measurable and is biologically not significant.
Concern No. 2: Ewes can’t adjust to the alfalfa pellets quickly and therefore will suffer from digestive problems
Well, the obvious question is, adjust from what? Let’s examine how ewes are fed before they go into a jug.
Ewes in late pregnancy are usually kept in a drop flock or gathered near a barn. Their diet typically consists of hay or silage, plus some grain. Most current recommendations suggest that ewes with multiple fetuses should receive a daily supplement of 0.5 to 1 pound of grain (corn, barley, etc.) during the last four weeks of pregnancy. The grain provides enough extra energy to prevent the metabolic problem of ketosis. Ewes on pasture – particularly those lambing late in the spring – may or may not receive any grain during late pregnancy.
All these late-gestation diets, however, are based on forage, which is just another way of saying that they are all relatively high in fiber. For example, medium-quality alfalfa hay contains 46% NDF and 35% ADF, early-bloom grass hay contains 61% NDF and 34% ADF, and young spring grass contains 55% NDF and 31% ADF (all on a DM basis). Silages would have similar fiber levels. In contrast, shelled corn contains only 9% NDF and 3% ADF.
Some people think that alfalfa pellets are somehow very different from the alfalfa hay from which they are made. Not really. Typical medium-quality alfalfa pellets (17% protein) contain 46% NDF and 35% ADF – the same as the hay. The only major difference between pellet and hay is the physical form – the pelleting process smushes fiber into smaller pieces. (“Smush,” incidentally, is a technical term.) Sure, pellets may differ from long hay in consumption level, fermentation time, salivation amount, heat damage, etc. – but these factors don’t alter the overriding principle that alfalfa pellets contain as much fiber as other forages. Nutritional problems during diet transitions are usually caused by major differences in fiber content between the two feeds – especially going from a high-fiber diet to a low-fiber diet. Feeding alfalfa pellets to ewes in the jug is not a major switch from a late-gestation diet – it’s really just changing the form of the fiber.
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