Subacute Ruminal Acidosis in Dairy Herds - University of Wisconsin ...

Preconvention Seminar 7A: Dairy Herd Problem Investigation Strategies:Lameness, Cow Comfort, and Ruminal AcidosisThe degree of escape of trans fatty acids from the rumen depends largely on the amounts oftheir unsaturated fat precursors (18:2 and 18:3 fatty acids) are present in the diet. High rates ofpassage also contribute to more escape of these fatty acids to the rumen. These fatty acids do nothave detrimental health effects themselves; thus, it is possible for a herd to have milk fatdepression without cow health problems.The potential for plant source fats to cause milk fat depression depends on both their contentof unsaturated fatty acids (see Table 5) and on their rate of release in the rumen. Slowly releasedplant fat sources such as whole cottonseeds present much less risk for milk fat depression than dorapidly released plant fat sources such as wet distillers grains.Table 5. Typical Fatty Acid Analysis of Fats and OilsFatty Acid Corn Cottonseed Lard Canola Soybean TallowC14-1 (Myristic) 1.0 1.5 3.0C16 (Palmitic) 12.5 26.0 27.0 4.0 11.5 25.0C16-1 (Palmitoleic) 1.0 3.0 2.5C17 (Margaric) .5 1.5C18 (Stearic) 2.5 3.0 13.5 2.0 4.0 21.5C18-1 (Oleic) 29.0 17.5 43.4 60.0 24.5 42.0C18-2 (Linoleic) 55.0 51.5 10.5 20.0 53.0 3.0C18-3 (Linolenic) .5 .5 10.0 7.0C20 and over 4.0Unsat/Sat Ratio 5.7 2.2 1.4 15.7 5.5 1.0Animal source fats or ruminal by-pass fats pose little risk for incomplete biohydrogenationand milk fat depression (Figure 11). Rather, the risk with these fats can be reduced total tractdigestibility as they by-pass not only the rumen, but the entire digestive tract as well.Monensin supplementation may contribute to milk fat depression. Supplementing monensinon the high end of the dosage range (16 to 24 ppm – the same as 15 to 22 grams per ton)depresses milk fat percentage about .1 to .2%. The degree of depression may wane as themonensin if fed for a longer time period. Monensin feeding appears to interact with excessivefeeding of unsaturated fats and ruminal acidosis to cause milk fat depression. Interestingly,monensin helps prevent ruminal acidosis (probably by inhibiting lactate producers and favoringlactate utilizers), yet still has the overall effect of reducing milk fat percentage. If a herdexperiences noticeable milk fat depression soon after starting to feed monensin, it is better toinvestigate and correct other causes of the milk fat depression rather than to automaticallyremove the monensin from the diet.University of Wisconsin, School of Veterinary Medicine, 2015 Linden Drive, Madison, WI 53706102