Corn silage-based diet supplemented with increasing amounts of linseed oil: Effects on methane production, rumen fermentation, nutrient digestibility, nitrogen utilization, and milk production of dairy cows

In this study, we assessed the effects of increasing amounts of linseed oil (LSO) in corn silage-based diets on enteric CH₄ production, rumen fermentation characteristics, protozoal population, nutrient digestibility, N utilization, and milk production. For this purpose, 12 multiparous lactating Holstein cows (84 ± 28 d in milk; mean ± SD) fitted with ruminal cannula were used in a replicated 4 × 4 Latin square design (35-d period). The cows were fed ad libitum a total mixed ration without supplementation (control) or supplemented [on a dry matter (DM) basis] with LSO at 2% (LSO2), 3% (LSO3) or 4% (LSO4). The forage:concentrate ratio was 61:39 (on DM basis) and was similar among the experimental diets. The forage portion consisted of corn silage (58% diet DM) and timothy hay (3% diet DM). The proportions of soybean meal, corn grain and soybean hulls decreased as the amount of LSO in the diet increased. Daily methane production (g/d) decreased quadratically as the amount of LSO increased in the diet. Increasing LSO dietary supplementation caused a linear decrease in CH₄ emissions expressed on either DM intake (DMI) basis (−9, −20, and −28%, for LSO2, LSO3, and LSO4, respectively) or gross energy intake basis (−12, −22, and −31%, for LSO2, LSO3, and LSO4, respectively). At 2 and 3% LSO, the decrease in enteric CH₄ emissions occurred without negatively affecting DMI or apparent total-tract digestibility of fiber and without changing protozoa numbers. However, these 2 diets caused a shift in volatile fatty acids pattern toward less acetate and more propionate. The effect of the LSO4 diet on enteric CH₄ emissions was associated with a decrease in DMI, fiber apparent-total-tract digestibility, protozoa numbers (total and genera), and an increase in propionate proportion at the expense of acetate and butyrate proportions. Methane emission intensity [g of CH₄/kg of energy-corrected milk (ECM)] decreased linearly (up to 28% decrease) with increasing LSO level in the diet. Milk fat yield decreased linearly (up to 19% decrease) with increasing inclusion of LSO in the diet. Milk protein yield increased at 2% or 3% LSO and decreased to the same level as that of the nonsupplemented diet at 4% LSO (quadratic effect). Yield of ECM was unchanged by LSO2 and LSO3 treatments but decreased (−2.8 kg/d) upon supplementation with 4% LSO (quadratic effect). Efficiency of milk production (kg ECM/kg DMI) was unaffected by the 3 levels of LSO. Ruminal NH₃ concentration was quadratically affected by LSO supplementation; decreasing only at the highest level of LSO supplementation. The amount (g/d) of N excreted in feces and urine decreased linearly and quadratically, respectively, as the amount of LSO increased in the diet, mainly because of the reduction in N intake. Efficiency of dietary N used for milk N secretion increased linearly with increasing LSO supplementation in the diet. We conclude that supplementing corn silage-based diets with 2 or 3% of LSO can reduce enteric CH₄ emissions up by to 20% without impairing animal productivity (i.e., ECM yield and feed efficiency).