Gravedad API

Sheep fed chicory in this study had 17% lower CH4 yields compared with

pasture (chicory, 29.5 vs. pasture, 36.1 g CH4/kg DMI). This is consistent with, although smaller than, previous findings of Waghorn et al. (2002) who found a 37% reduction of CH4 yield when sheep were fed chicory, compared with those fed pasture (16.2 vs. 25.7 g CH4/kg DMI). The reasons for a reduction in CH4 yield in response to chicory are not known. Factors influencing CH4 yield include DMD, passage rate, and the chemical composition of the diet (Moss et al., 2000; Boadi et al., 2004); differences between chicory and pasture in these factors may help to explain the lower CH4 yield from chicory fed sheep.

Models that have been developed in an attempt to describe and/or predict CH4 yield (Blaxter & Clapperton, 1965; Holter & Young, 1992; Ellis et al., 2009; Yan

et al., 2009) and relationships derived from these models generally indicate that

an increase in DMD, which coincides with a decrease in the proportion of dietary fibre, relates to a decrease in CH4 yield. Nevertheless, these models describe and predict CH4 yield with mixed success, and many of these models are based on data from ruminants fed TMR type diets. Blaxter and Clapperton (1965) reported that the CH4 emissions of ruminants decreased in response to

137 increasing diet apparent digestibility when fed above maintenance energy requirements. The in vitro DMD of chicory in the current study was 12% greater than pasture (68.1 vs. 79.8%). This difference is somewhat larger than the 7% in previous in vivo reports with sheep (79.3 vs. 74.0%, Waghorn et al., 2002) and red deer (75.2 vs. 68.5%, Hoskin et al., 1995; 78.5 vs. 72.7%, Kusmartono

et al., 1997). Chicory in this study had a greater concentration of pectin, a

higher ratio of readily fermentable carbohydrates to structural carbohydrates and lower cellulose and hemicellulose concentrations compared with pasture, which agrees with previous reports (Hoskin et al., 1995; Barry, 1998).

From models developed to predict CH4 yield (Blaxter & Clapperton, 1965; Holter & Young, 1992; Ellis et al., 2009; Yan et al., 2009), the greater DMD and concentration of readily fermentable carbohydrates supports the finding that sheep fed chicory yielded less CH4 than pasture-fed sheep. Nevertheless, the analysis of the New Zealand CH4 database of sheep and cattle fed fresh forage diets found no significant relationship between DMD or chemical composition

and CH4 yield (Waghorn & Woodward, 2006; Hammond et al., 2009).

Therefore, it is difficult to speculate what contribution the differences in diet DMD and/or chemical composition between chicory and pasture would have made to the differences in CH4 yield reported in this study and further research is required to elucidate this.

The above models are predominantly based upon conserved forage diets that are high in structural fibre, and the proportion of readily fermentable carbohydrates is often in the form of starch sourced from grains. In contrast, the readily fermentable carbohydrates in fresh forage diets contain very low amounts of starch and normally consist of differing types of fructans (Chalmers

et al., 2005). The effect of differing types of readily fermentable carbohydrates

on the rate of fermentation and CH4 yield is not understood.

The wet chemistry analysis of chicory only accounted for 860g of the chemical components per kilogram of DM. This implies that a proportion of the chemical components of chicory were not identified and the impact of this proportion on CH4 yield is unaccounted for. In addition, the chicory fed to sheep in this study had a greater ash concentration than pasture. Therefore the reduced CH4 yield

Chapter 4: Potential CH4 mitigation technologies

138

of sheep fed chicory could simply be a result of these animals consuming less fermentable material compared with pasture fed animals.

The 31% reduction in CH4 when expressed per kg digestible DMI, from sheep fed chicory compared with pasture, suggests that differences in apparent DMD between chicory and pasture cannot fully explain the reported difference in CH4 yield. This implies that there may be a modification of the microbial fermentation pathways affecting methanogenesis in sheep fed chicory. This is supported by 18% greater propionic acid (23.8 vs. 20.2% molar % of total VFA) and 3% lower acetic acid (69.1 vs. 71.2% molar % of total VFA) concentrations found in the rumen fluid of sheep fed chicory compared with pasture. Moss et al. (2000) reported that a greater production of propionic acid is associated with a reduction in methanogenesis. However, VFA concentrations from rumen fluid have been shown to have no clear relationship with CH4 yield (Robinson et al., 2010).

Pinares-Patiño et al. (2003b) and Okine et al. (1989) demonstrated that CH4 yield is inversely related to the rumen fractional outflow rate (FOR) of the particulate phase of the digesta. The passage rates of chicory or pasture through the digestive tract were not determined in this study. Nevertheless, previous studies with red deer reported particulate FOR of chicory (4.08%/hour) from the rumen to be twice that of pasture (2.78%/hour; Kusmartono et al.,

1996; 1997), which was attributed to the rapid breakdown of chicory in the rumen (Kusmartono et al., 1996). Sun et al. (2007) identified that the rapid degradation of chicory, compared with pasture and white clover, was due to a unique cell wall structure, which is rich in pectin (Sun et al., 2007). Both the rapid breakdown and increased fractional outflow of chicory in the rumen compared with pasture could limit the amount of time feed particles are exposed to microbial fermentation, thus contributing to a reduction in CH4 yield.

In this study, it was intended that all sheep were offered the treatment diets at the same feeding level (1.5), but the actual feeding level of animals fed chicory (1.45) was lower than those fed pasture (1.58). The difference in feeding level reflected a mean difference of 0.18 kg DM/day between chicory and pasture fed sheep (0.70 vs. 0.88 kg DM/day), which could have impacted upon CH4 yield.

139 The reduction of CH4 yield and reported superior nutrient value of chicory for grazing ruminants (Barry, 1998) suggests that chicory as a CH4 mitigation tool that could be successfully implemented into grazing systems, with appropriate climate, topography and soil types for growing chicory. In this study, chicory was fed as pure culture forage, but farm practices often result in multiple forage species on offer to animals at the same time. The proportion of chicory required in the diet to achieve significant reductions in CH4 yield is not known and needs further investigation if chicory is to be proven as a useful on-farm mitigation tool. Additionally, the testing of diets and their relative effects on the ruminant animal and associated digestive processes, including CH4 yield, are mostly conducted over a relatively short period of time. There have been no long term investigations to ascertain if adaptation to the diet may occur and if differences in CH4 yield changes over time.

4.5.2 Potential mitigation agents