Effect of dietary inclusion of medium-chain saturated fatty acids on ammonia and methane emitting potential of dairy manure

Two experiments with lactating dairy cows were conducted to evaluate the effect of dietary inclusion of medium-chain saturated fatty acids (lauric and myristic, Exp. 1 and coconut oil, Exp. 2) on the ammonia and methane emitting potential of dairy manure. Experiment 1 was a replicated 3 x 3 Latin square design trial with 6 cows and Experiment 2 was a completely randomized block design trial with 36 cows and also involved dietary crude protein levels as a treatment. Individual cow (Exp. 1; n = 6) or composite (Exp. 2; n = 2) fecal and urine samples were combined in a 1.7:1 (w/w; feces and urine, respectively) ratio and ammonia and methane emitting potential of manure was measured in a steady-state gas emission system. In Exp. 1, the end-point cumulative ammonia emission was greater for lauric acid than for the control. Diets had marginal effect on manure methane emissions. In Exp. 2, dietary protein level had a profound effect on ammonia emissions; the low-crude protein diet had 37% lower ammonia emissions compared with the high-crude protein diet. The end-point cumulative methane emission was drastically increased by coconut oil compared with the control. Overall, individual medium-chain saturated fatty acids fed to dairy cows had biologically insignificant effects on the ammonia and methane emitting potential of manure as measured in these experiments. A larger dose of coconut oil caused a sizable increase in cumulative methane emission from dairy manure.