Ruminal methane emission and lactational performance of cows fed rapeseed cake and oats on a grass silage-based diet

Abstract

The objective of this experiment was to investigate the effect of lipid from rapeseed cake and oats on ruminal CH₄ emission and lactational performance of dairy cows. Twelve lactating Nordic Red cows, of which 4 primiparous, and averaging (±SD) 48 ± 22.9 DIM, 37.8 ± 7.14 kg/d milk yield were enrolled in a switch-back design experiment with 3 periods of 4 wk each. The cows were assigned into 6 pairs based on parity and days-in-milk, milk yield, and body weight at the beginning of the experiment. The experimental treatments were 1) rapeseed cake and oats (RSC+O), and 2) rapeseed meal and barley (RSM+B) as the concentrate feeds. Cows in each pair were randomly assigned to one of the 2 groups, which received the treatments in 2 different sequences, i.e., group 1 received RSC+O in period 1 and 3, and RSM+B in period 2, whereas group 2 was fed RSM+B in period 1 and 3, and RSC+O in period 2. The diets consisted of a partially mixed ration with grass silage mixed with either oats or barley, according to the treatment sequence, and the rapeseed cake or meal being mixed into a pellet with either oats or barley according to the treatments, and a mineral mix. The pellet was delivered at a fixed amount (i.e., 6 kg/d for multiparous and 5 kg/d for the primiparous cows) from the milking robot. The actual forage to concentrate ratios for RSC+O and RSM+B were 51:49 and 52:48, respectively, with NDF concentrations of 41.5 and 36.0% and CP concentrations of 17.0 and 16.7% of diet DM. Dry matter intake, milk yield, and gas exchange (with a GreenFeed system attached to the milking robot) were recorded daily, and milk composition and spot fecal samples were collected during the last wk of each period. Based on feed analysis, and dry matter intake of the cows during the experiment, the total fat content of the experimental diets was 4.1 and 2.7% of DM for RSC+O and RSM+B diets, respectively. Dry matter intake was 1.5 kg/d lower, and milk yield tended to be 1.0 kg/d greater for RSC+O vs. RSM+B. There were no differences in energy-corrected milk yield and milk composition between the treatments, while milk metabolizable energy efficiency was greater for cows fed RSC+O than RSM+B. Methane yield (g/kg dry matter intake) did not differ between treatments, but CH₄ production (g/d) was 9.4% and CH₄ intensity as g/kg energy-corrected milk was 11.7% lower for RSC+O vs. RSM+B. The lower CH₄ production was likely caused by the lower DMI and fiber digestibility, observed with the RSC+O diet. In addition, the greater lipid intake also contributed to lower rate of fermentation and subsequent decrease in CH₄ production. Overall, feeding rapeseed cake with oats in a grass silage-based diet increased feed efficiency while decreasing CH₄ emission intensity in lactating cows. This provides a practical way of mitigating ruminal CH₄ emission from dairy operations while maintaining milk production with commonly utilized feed stuffs in Nordic conditions.

Keywords: Ruminal methane emission; dairy cow; oats; rapeseed cake.