Low emission feed : opportunities to mitigate enteric methane production of dairy cows

Abstract

As global demand for high-quality food originating from animal production is expected to rise due to an increasing human population and consumer income level, the expected role of ruminants in meeting this demand brings multiple challenges. Ruminant production needs to adapt to environmental changes and, at the same time, reduce its impact on the environment. Ruminants production systems have a major impact on the environment through the emission of greenhouse gases such as methane (CH4), nitrous oxide and carbon dioxide. Microbial fermentation of feeds in the gastrointestinal tract, known as enteric fermentation, is the main source of CH4 emissions from dairy production. Enteric CH4 emission is strongly related to the amount of feed fermented in the rumen, which depends on feed intake, feed composition and rumen fermentation conditions associated to the intrinsic characteristics of these feeds and the characteristics of the whole diet. Important gaps in knowledge remain however. The prime aim of this thesis was to investigate the effects of various feeding strategies to mitigate enteric CH4 emissions of dairy cows. First experiment was conducted to investigate the effects of type and level of starch in the concentrate. Inclusion of a high level (53%) of starch in the concentrate that accounted for 40% of the total mixed ration dry matter (DM) produced lower CH4 per unit of estimated rumen fermentable organic matter (eRFOM) than a low level (27% of DM) of starch (43.1 vs. 46.9 g/kg of eRFOM). Methane production per kg of eRFOM also was lower for diets based on rapidly fermentable starch (gelatinized maize grain) compared to diets based on slowly fermentable starch (native maize grain) (42.6 vs. 47.4 g/kg of eRFOM). However, inclusion of 53% of starch in the concentrate from both types of starch did not affect CH4 emission intensity (CH4 Ei) (CH4 emission per kg of fat- and protein-corrected milk; FPCM). In a subsequent experiment, maize silage was prepared from whole-plant maize harvested at a very early (25% DM), early (28% DM), medium (32% DM) and late (40% DM) stage of maturity and fed to dairy cows as an alternative to concentrate as starch source. Diet consisted of (on DM basis) 75% maize silage, 20% concentrate and 5% wheat straw. Increasing harvest maturity of maize silage linearly decreased CH4 yield (21.7, 23.0, 21.0 and 20.1 g/kg of DM intake) and CH4 emission as a fraction of gross energy intake (6.3, 6.7, 6.3 and 6.0%). Methane Ei tended to decrease linearly with maturity (13.0, 13.4, 13.2 and 12.1 g/kg FPCM). In another experiment grass silage as roughage source was tested. This experiment was designed to investigate the effects of N fertilisation of grassland and maturity of grass at cutting on CH4 emission in dairy cows. Two N fertilisation rates (65 vs. 150 kg of N/ha) were examined in combination with three stages of grass maturity (early, 28 days of regrowth; mid, 41 days of regrowth; and late, 62 days of regrowth). Diet contained 80:20 ratio (on DM basis) of grass silage (mainly ryegrass) and concentrate. Dry matter intake decreased with N fertilisation and maturity, and FPCM decreased with maturity but was unaffected by N fertilisation. Methane Ei (mean 15.0 g/kg of FPCM) increased by 31% and CH4 per unit digestible OM intake (mean 33.1 g/kg of DOMI) increased by 15% with increasing maturity. Methane yield (mean 23.5 g/kg of DM intake) and CH4 as a fraction of gross energy intake (mean 7%) increased by 7 and 9% with maturity, respectively, which implies an increased loss of dietary energy with progressing grass maturity. Rate of N fertilisation had no effect on CH4 Ei and CH4 yield. Despite the importance of in vitro gas production technique for evaluating feeds, in vitro study as a stand-alone approach was considered inadequate to fully evaluate the potential effect of feeds and rumen fermentation modifiers on CH4 production, because in vitro studies are frequently performed separately rather than in parallel with in vivo studies. To test this hypothesis, both in vitro and in vivo CH4 measurements were measured simultaneously using cows in the first experiment that were fed (and adapted to) the same dietary material used as a substrate for in vitro incubation, as donor for microbial inoculum. It was found that 24-h in vitro CH4 (mL/g of incubated organic matter) correlated well with in vivo CH4 when expressed per unit of eRFOM (R2 = 0.54), but not when expressed per unit of organic matter ingested (R2 = 0.04). In the same experiment, results showed that incubation of the same substrate with rumen inocula obtained from donor cows adapted to different diets produced a variable amount of CH4 suggesting that it is important to consider the diet of the donor animal when collecting rumen inocula for in vitro incubation. Even though the in vitro technique has limitations to represent in vivo conditions, it is useful for screening of large sets of animal feeds or feed additives to be used as a CH4 mitigation strategy. In this thesis, two in vitro experiments were conducted to examine the effects of variation in structural composition of condensed tannins (CT) in sainfoin accessions collected from across the world on CH4 production, and CT extracts obtained from a selected sainfoin accessions on CH4 production. Results revealed substantial variation among CT in their effect on in vitro CH4 production and this variation was attributed to differences in chemical structure of CT. Condensed tannins evaluated in this thesis showed to have potential to reduce in vitro CH4 production, but require further investigations to fully evaluate their in vivo effects. In conclusion, results from the research work conducted in this thesis show that changes in the basal diet of dairy cows and in roughage production management can substantially reduce the amount of enteric CH4 produced and thereby influence the impact of dairy production on the environment