Effect of fat supplementation and stage of lactation on methane production in dairy cows

• Effect of fat supplementation on methane production through lactation was studied.
• Fat supplementation caused a persistent reduction of methane emission.
• The production of methane increased with days in milk.

The aim was to determine the effect of fat supplementation on methane (CH4) production and to study if the effect persists over time as lactation progresses. Rumen microbial protein synthesis and thereby milk yield may be reduced when fermentable organic matter (OM) is replaced by nonfermentable fat. Therefore the effect of concurrent supplying hydroxy-methionine-analog-isobutyrate (HMBi) to overcome this potential reduction in supply of metabolisable protein was also studied. Twelve multiparous lactating Danish Holstein cows were used in a randomised block design experiment with four treatments: Control (CON), CON supplemented with whole cracked rapeseed (WCR), CON supplemented with vegetable rumen protected fat (Lipmix 40/60, Lipitec, NLM Vantinge Aps, Ringe, Denmark) (RPF), and RPF supplemented with HMBi (MetaSmart, Adisseo, France) (RPFA). All diets contained maize silage (230 g/kg dry matter (DM)), grass clover silage (230 g/kg DM), and concentrate (540 g/kg DM). Dietary crude fat concentration was 27 g/kg DM in CON and approximately 56 g/kg DM in the three other diets. All cows were offered 3 kg per day of the same standard concentrate during milking in addition to the different mixed rations fed ad libitum. Production of CH4 was measured for four d in open-circuit respiration chambers in four periods during lactation: at 48, 125, 164, and 212 d in milk (DIM), and feed intake and milk yield were recorded at the same time. DIM did not affect DM intake (DMI). Increased DIM decreased milk yield, both measured as kg milk and kg energy corrected milk (ECM). Fat supplementation increased milk yield compared to CON, however ECM yield was not affected. Milk protein concentration decreased with fat supplementation. Methane production increased with DIM when measured in L/d, L/kg DMI and L/kg ECM. However, when CH4 production was expressed as L/kg ECM there was a tendency for interaction between DIM and treatment. Methane production also increased with DIM when expressed as % of gross energy (GE) intake. The present study demonstrates that CH4 production increases with DIM, especially when expressed as L/kg ECM. The reduction in CH4 production when fat is added to the diet persists throughout the lactation. Supplementation with HMBi tended to decrease CH4 production further.