Forage grass growth under future climate change scenarios affects fermentation and ruminant efficiency

Abstract

With an increasing human population access to ruminant products is an important factor in global food supply. While ruminants contribute to climate change, climate change could also affect ruminant production. Here we investigated how the plant response to climate change affects forage quality and subsequent rumen fermentation. Models of near future climate change (2050) predict increases in temperature, CO₂, precipitation and altered weather systems which will produce stress responses in field crops. We hypothesised that pre-exposure to altered climate conditions causes compositional changes and also primes plant cells such that their post-ingestion metabolic response to the rumen is altered. This "stress memory" effect was investigated by screening ten forage grass varieties in five differing climate scenarios, including current climate (2020), future climate (2050), or future climate plus flooding, drought or heat shock. While varietal differences in fermentation were detected in terms of gas production, there was little effect of elevated temperature or CO₂ compared with controls (2020). All varieties consistently showed decreased digestibility linked to decreased methane production as a result of drought or an acute flood treatment. These results indicate that efforts to breed future forage varieties should target tolerance of acute stress rather than long term climate.

Figure 1

DFA analysis of grass variety based on FTIR analysis, showing no distinct clustering between varieties (AC Aber Clyde, AD Aber Dart, AE Aber Echo, AG Aber Glyn, AN Aber Niche, AZ Aber Zeus, B Barolex, BX Aber Root, DV Da vinci, P Premium (A); climate scenarios (B), showing distinct clustering between environmental conditions (DFA circles around the mean group centres with 95% confidence circles for DF1 vs DF2; HS heat shock).

Figure 2

Effect of climate scenario on total gas production (A), total CO₂ production (B) and total methane production (C) at 48 h fermentation as affected by climate change scenario (all corrected for starting weight of dry matter); HS heat shock). Raw data points are overlaid on boxplots, coloured by replicate experiment. Notches represent 95% confidence intervals. Lower case letters indicate significant difference based on ls means with Tukey adjustment (P < 0.05).

Figure 3

DFA analysis of liquid (A) and pellet (B) FTIR as affected for each climate scenario at the end of 48-h fermentation (DFA circles around the mean group centres with 95% confidence circles for DF1 vs DF2; HS heat shock).

Figure 4

MDS ordination of VOC profiles of grass varieties exposed to rumen fluid, based on proximity values from random forest classification by (A) climate scenario; (B) biological replicate; and (C) variety of grass.

Figure 5

Comparisons between VOC profiles from grass varieties exposed to rumen fluid, broken down by climate scenario. Compounds are classified into hierarchical classes, and every node represents on the heat trees one compound or parent class. Node size is proportional to relative abundance for that class/compound. Each of the small heat trees represents a comparison between two climate scenarios. Node colour is on a scale representing the mean abundance change between conditions as a proportion of the total abundance of that compound: orange indicates that the compound had higher relative abundance in the ‘column’ treatment, grey indicates no difference, and blue indicates higher relative abundance in the ‘row’ treatment. Relative abundance is on an arbitrary scale where each sample sums to 100. For ease of viewing, compounds are only included if their relative abundance at least doubled in at least one comparison. For this reason, in some cases a node will show a different direction of change to its parent nodes (i.e. other compounds, not included in the plot, contribute to the parent node’s direction of change).