Evaluation of the SF6 tracer technique for estimating methane emission rates with reference to dairy cows using a mechanistic model

Tithonia diversifolia as a Supplementary Feed for Dairy Cows

The objective of this study was to examine the effects of Tithonia diversifolia as a supplementary forage on dairy cow performance and methane production. Nine lactating Holstein × Zebu dairy cows (519 ± 53.3 kg of body weight and 66 ± 13.3 d in milk) were paired by milk yield (21.3 ± 2.34 kg/d) and body weight and randomly assigned to three dietary treatments in a Latin square design with 21-d experimental periods (14 d for diet adaptation and 7 d for measurements and sample collection). The dietary treatments included the control diet consisting of fresh sugar cane plus concentrate (44:56, % of diet DM), and two treatment diets containing different levels of fresh T. diversifolia (6.5 and 15.4%, DM basis) which partially replaced both sugarcane and concentrates. Methane production was measured using the sulphur hexafluoride (SF₆) technique from d 16 to d 21 of each experimental period. Analysis of the gas samples was performed by gas chromatography. The inclusion of T. diversifolia at 15.4% DM had no effects on DM intake, milk production, nitrogen balance or methane production. There was no effect on the concentrations of total saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA) in milk fat (P ≥ 0.28), though individual milk fatty acids were affected. Serum concentrations of glucose, urea nitrogen (BUN), triglycerides, β-hydroxybutyrate (BHBA), and cholesterol were unaffected by the dietary treatments (P ≥ 0.13). There was a time (2 and 6 h post-feeding) and dietary treatment effect (P < 0.01) on the acetate to propionate ratio in the rumen. A denaturing gradient gel electrophoresis analysis of the archaeal community showed distinct clustering of the archaea populations for control and treatment diets. Taken together, our results indicate the potential of T. diversifolia as a supplementary forage for dairy cattle in the tropics.

Effects of Tithonia diversifolia on in vitro methane production and ruminal fermentation characteristics

The present study examined the effects of Tithonia diversifolia on in vitro methane (CH4) production and ruminal fermentation characteristics. The experiment was conducted as a completely randomised design (CRD) using a control (0% T. diversifolia) and three treatment groups with different concentrations (6.9%, 15.2%, 29.2%) of T. diversifolia, which replaced up to 15.2% and 14% dry matter (DM) of fresh sugarcane and concentrates, respectively. Ruminal fluid was obtained from two ruminally cannulated non-lactating Holstein × Zebu heifers maintained on a diet consisting of T. diversifolia, fresh sugarcane and 4 kg of concentrates. The inclusion of T. diversifolia had no effect (P ≥ 0.15) on cumulative gas production (mL, mL/g incubated DM, mL/g digested DM) or in vitro DM disappearance (%). Carbon dioxide (%, mL, mL/g incubated DM) linearly decreased (P ≤ 0.001) and CH4 (%, mL, mL/g incubated DM) quadratically increased (P ≤ 0.01) with increasing concentrations of T. diversifolia replacing fresh sugarcane and concentrates. The total volatile fatty acids (mM) and acetate (A) proportion of total volatile fatty acids (mmol/100 mmol) linearly increased (P < 0.01) with the increasing inclusion of T. diversifolia. Butyrate (mmol/100 mmol) increased quadratically (P ≤ 0.02), while propionate (P; mmol/100 mmol) decreased quadratically (P < 0.02). The A : P ratio increased linearly (P < 0.0001) with increasing amounts of T. diversifolia in the diet. These results indicated that increasing the amount of Tithonia diversifolia in the substrate DM increased the A : P ratio, which resulted in a six-fold increase of CH4 production when fresh sugarcane and concentrates were replaced at up to 15.2% and 14% (DM basis), respectively.