|PARIAN-KHAJEHDIZAJ, FARHAD - University Of Tabriz|
|NOEL, SAMANTHA - Aarhus University|
|JOHANSEN, MARIANNE - Aarhus University|
|WEISBJERG, MARTIN - Aarhus University|
|HELLWING, ANNE LOUISE - Aarhus University|
|HOJBERG, OLE - Aarhus University|
|Hall, Mary Beth|
|LUND, PETER - Aarhus University|
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2022
Publication Date: 4/5/2023
Citation: Parian-Khajehdizaj, F., Noel, S., Johansen, M., Weisbjerg, M., Hellwing, A., Hojberg, O., Hall, M., Lund, P. 2023. Methane emission, nutrient digestibility, and rumen microbiota in Holstein heifers fed 14 different grass or clover silages as the sole feed. Journal of Dairy Science. 106(6):4072-4091. https://doi.org/10.3168/jds.2022-22638.
Interpretive Summary: One of the goals of feeding cattle is to reduce the methane emissions produced by their rumen microbes in order to reduce the contribution to the greenhouse gas load related to climate change. In this study, two types of clover and three grasses from different cuttings were fed as silages to dairy heifers to evaluate the impact of the forage type on methane emissions. It is likely that much of the digestion of the forages was carried out by rumen microbes. A key finding was that daily methane emissions were not closely related to the amount of fiber consumed or digested, but to the amount of total organic matter digested. The latter is affected by the digestibility of the feed and the amount the animal consumes. Because the animal meets its nutrient requirements using the nutrients released during digestion, reducing feed digestibility is not a good solution for reducing methane emissions. Alternatives could include supplementing with some feeds that are digested by the cow and not by rumen microbes, or by determining approaches to divert digested organic matter from methane production by the microbes. These finding provide information that could help producers choose the best forages with respect to nutrient digestibility and methane emissions.
Technical Abstract: This experiment investigated the variation in enteric methane (CH4) production and associated gas exchange parameters, nutrient digestibility, rumen fermentation, and rumen microbiome when a range of silages based on two different forage types (grass or clover) and different species within the two types, were fed as the sole feed to heifers. Three grass species (perennial ryegrass, festulolium, and tall fescue) and two clover species (red clover and white clover) were included. Perennial ryegrass was harvested at two maturity stages in the primary growth, white clover was harvested once in the primary growth, four cuts of festulolium and tall fescue, and three cuts of red clover were harvested during the growing season, giving 14 different silage batches in total. Sixteen Holstein heifers 16-21 months old and 2-5 months in pregnancy were fed the silages ad libitum as the sole feed in an incomplete cross-over design. Each silage was fed to four heifers, except for the two perennial ryegrass silages which were fed to eight heifers for a total of 64 observations. The CH4 production was measured for three days in respiration chambers. Heifers fed clover silages had higher dry matter intake (DMI) compared to heifers fed grass silages, and heifers fed tall fescue silages had the numerically lowest DMI. Compared to grass silages, feeding clover silages led to higher crude protein digestibility, but to lower neutral detergent fiber (NDF) digestibility. Though differences between silages were seen in organic matter and NDF digestibility, the digestibility of potentially digestible NDF was similar across forage types and species. Rumen pH was higher in heifers fed clover silages compared with those fed grass silages. Based on composition analysis, the rumen microbiota of the heifers clustered clearly according to forage type and species. More specifically, seven of the 34 dominating rumen bacterial genus-level groups showed higher relative abundances for the clover silages, whereas seven genus-level groups showed higher abundances for the grass silages. Replacing grass silages with clover increased CH4 production per kg NDF digested, but reduced proportion of gross energy (GE) lost as CH4 from 7.5 to 6.7% of GE intake. Enteric methane intensity varied from 26.9 liters (L) /kilogram (kg) DMI for third cut red clover silage to 37.0 L/kg DMI for late-harvested first cut ryegrass silage. This 38% difference in methane intensity pinpoints that choice of forage type and optimal forage quality is important, and the present study gives the outlines for choosing the optimal forage type and forage species with respect to nutrient digestibility and enteric methane emission in ruminants.