I’ll never forget my gray-haired neighbor Emily, who had grown up during the horrors of World War II in Germany. Emily’s grandmother had taken on the job of raising Emily and her sister, while their father was drafted into the army and their attractive mother was purportedly imprisoned for – how do I put this delicately? – being less than cooperative with a German officer.
I responded with horror – frying potatoes in motor oil? How awful. Why would you do that? And Emily said, “Because that’s all we had and, don’t ya know, your system needs a little grease to help it work.” Then she added, “And rabbits don’t have much grease in them.”
Well, I learned a lesson that day. Her explanation, while rudimentary, brings up a good point. Human digestion does indeed need grease and oil to work, and so does a cow’s. And it doesn’t just help things slide down either, it also provides a valuable energy source.
In the dairy diet, fats are contained in three sources: about 3 percent is contained in the basal ration (forages and grains), and the remainder (about 5 – 5.75 percent in total diet) is added by way of oilseeds (cotton seed or soybean), and animal fats (grease or tallow) or granular (inert) fats.
Digestibility
When we decide which fat to include in the dairy diet, the foremost consideration should be digestibility. Obviously, it wouldn’t do much good to have a high-energy fat that isn’t available or can’t be utilized by the body.
Palatability
A secondary consideration, but still very important, is palatability of the fat. Fish oil is a good example; while fish oil can be used in small amounts to increase energy, too much can make the feed offset appetite, thus decreasing dry matter intake. Therefore, energy may be increased from the fat itself but the decrease in dry matter may offset any gain.
Saturated versus unsaturated
Third, different fats may affect rumen fermentation (or ruminal inertness) in varying degrees. If a fat inhibits fiber digestion, then the energy available to the cow decreases as well. Many of these characteristics are affected by the relative amount of saturated versus unsaturated fatty acids contained in the fat source.
So before we go any further, let’s have a very basic discussion on saturated versus unsaturated. And forgive me if this is too basic for you, but this is how I remember it: saturated fat is solid at room temperature, which reminds me of plump Aunt Freeda as she sat in her overstuffed easy chair. She’s larger than a linebacker planted in a bulldozer, and if I were actually going to tackle her, I definitely wouldn’t do it while she’s sitting in that fortress with her center of ample gravity so close to the ground.
No siree, I’d wait until she’s unsaturated (or not sitting), because if she ever stood up her fluidity would change and I’d have at least a fair chance of toppling her. Similarly, unsaturated fats are liquid at room temperature and more fluid. While this really doesn’t have any correlation to how the body uses fat, it at least helps me remember which is which.
Highly saturated fats (or highly hydrogenated fats) are common among inert fats. Hydrogenation is simply the process of taking an unsaturated fat, adding hydrogen to the double bond by rumen microbes or infusing hydrogen gas into it at high pressure to create a more stable saturated fat (solid at room temperature; the process, for instance, by which vegetable oil is made into margarine). Tallow, for instance is about half saturated and half unsaturated, which makes it more rumen friendly.
But let’s not lose focus among the details – the important thing to remember is that the more unsaturated the fatty acid, the more likely it is to inhibit fiber digesting microorganisms in the rumen. Ideally, in the dairy diet total fat supplied by unsaturated sources should be kept to less than 1 pound per day (less than 500 grams of PUFA – polyunsaturated fatty acids).
Cost and ease of handling
A fourth consideration for choosing dietary fats would be cost and ease of handling. Oil seeds are a popular choice because they also provide other key nutrients like protein or digestible fiber, are economical and relatively easy to handle. Whereas, saturated fats need to be heated to liquefy them and get them to mix consistently. In addition, oil seeds, although containing highly unsaturated fats, have a slow-release function into the rumen, which minimizes rumen fermentation effects.
Feed-grade fats
Several feed-grade commodity fats are available, from tallow (hard, white), yellow grease (various restaurant and waste greases), to various blends of animal and vegetable fats. The advantages of these fats in a dairy ration include their relative low cost, acceptability of rumen inertness and high digestibility. Disadvantages include handling.
These fats must be handled as liquids for mixing, which requires heated storage tanks. Additionally, there is little quality control or uniformity. Finally, the lower quality fats can disrupt digestion and decrease feed intake, and are least stable and can go rancid fastest. Therefore, in general, the more saturated, the better.
Granular fats
Several granular fats are available commercially, and they are easy to handle and mix into rations. Quality control is regulated with fairly rigid standards, so uniformity is consistent. These granular fats were specifically developed for minimal rumen effect, making them desirable; however, costs are higher than feed-grade fats and can be limiting. And some might be less digestible than other fat sources.
Summary
When selecting fats for the dairy diet, keep these factors in mind: what ruminal fermentation effects will it have, how does its digestibility rate, what form does it come in, how easy is it to handle, and what is the cost? But for crying-out-loud, don’t use motor oil. PD
Many universities with dairy programs also offer easy to follow presentations on CD Roms that you can watch at your leisure. Here’s one.
Lynn Jaynes
Editor
Progressive Dairyman
