Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/15/2013
Publication Date: 5/15/2013
Publication URL: http://handle.nal.usda.gov/10113/56881
Citation: Faciola, A.P., Broderick, G.A. 2013. Effects of feeding lauric acid on ruminal protozoa numbers, fermentation, and digestion and on milk production in dairy cows. Journal of Animal Science. 91:2243-2253. Interpretive Summary: Dairy cows have a generally beneficial relationship with the microbes living in the rumen, the first compartment of their stomach. Cows harbor three major microbes: bacteria, protozoa, and fungi. All three are involved in digestion of fibrous feeds, allowing cows to extract much of the energy from forages and other materials that are of no benefit as human food. Also, bacteria provide more than half of the protein that the cow uses to meet her protein needs for maintenance and to produce milk. On the other hand, protozoa feed off of bacteria and actually reduce the supply of bacterial protein to the cow. Despite this effect, the protozoa play a positive role in digestion, so complete elimination of protozoa may be undesirable. The goal of this research was to find a practical way for farmers to control the protozoal population and consequentially increase bacterial protein supply to the cow without harming digestion. Previous research showed that dosing the rumen with small amounts of lauric acid, a fatty acid that makes up nearly half of the fatty acids in coconut oil, was found to suppress protozoa without negatively affecting digestion. Our goal this time was to determine the amount in the diet that would be equivalent to dosing lauric acid straight into the rumen. In the first experiment, two Holstein cows were fed lauric acid in amounts that increased stepwise from 0 to 480 g/d. We found that 480 g/d of lauric acid was highly effective in reducing the protozoal population by 80%; this dose also reduced rumen ammonia concentration, indicating improved protein utilization by the cows. We also found that it took 12 days for protozoa to return to their original numbers after withdrawing of lauric acid from the diet. In the second experiment, 48 Holstein cows were fed one of four diets in which lauric acid was added in stepwise increments, increasing from 0 to 720 g/d. Lauric acid again was found to be effective in reducing ruminal protozoa when fed in the diet; however, it was also found that lauric acid decreased feed intake and consequentially milk production. The one positive was that feeding lauric acid improved feed efficiency—the amount of milk produced per unit of feed consumed. Results of these two experiments indicate that reducing protozoal numbers improved protein utilization and feed efficiency in dairy cows. However, feeding lauric acid in amounts sufficient to adequately depress protozoa also decreased the cow’s feed intake, and thus milk production, to too great an extent to be a practical technique for use by U.S. dairy farmers. Further studies may identify ways to reduce protozoa and improve feed efficiency without loss of milk production; but, at this time, feeding lauric acid cannot be recommended.
Technical Abstract: The objectives of this study were: (1) to determine the level of lauric acid (LA) addition to the diet necessary to effectively suppress ruminal protozoa (RP) to the extent observed when a single dose was given directly into the rumen; (2) to assess its effects on production and ruminal metabolism; and (3) to determine the time needed for RP to re-establish themselves after LA is withdrawn from the diet of lactating dairy cows. In experiment 1, two Holstein cows fitted with ruminal cannulae were used in a split-plot design pilot study. Both cows consumed the same level of LA, starting with 0 g/d and increasing to 129, 270, and 438 g/d mixed into the diet. Diets were fed as TMR and contained (DM basis) 30% corn silage, 30% alfalfa silage, and 40% concentrate. Intake of 270 g/d of LA in the TMR suppressed RP by 70%; increased ruminal propionate, valerate, and total VFA concentration; and decreased ruminal ammonia and TAA concentration, suggesting improved N utilization. After withdrawing the highest LA dose from the diet, RP returned to their original numbers in 12 days. In experiment 2, 48 multiparous Holstein cows (8 with ruminal cannulae) were blocked by DIM into 12 blocks of four cows (2 blocks of cannulated cows) and were randomly assigned within replicated 4x4 Latin squares to balanced dietary treatment sequences. Diets were fed as TMR and contained (DM basis) 36% corn silage, 29% alfalfa silage, and 35% concentrate; and LA intake levels were 0, 220, 404, and 543 g/d mixed in the TMR. In experiment 2, LA was effective in reducing RP, ruminal ammonia and TAA concentration when consumed in the TMR; however, dietary LA also linearly decreased DM intake. Intake of LA higher than 220 g/d reduced ruminal total VFA concentration, digestibility, milk production and milk components. Therefore, LA does not appear to be a feasible RP suppressant for feeding in practical diets.