Triiodothyronine influences digesta kinetics and methane yield in sheep

Abstract

Methane yield from ruminants is positively correlated with mean retention time (MRT) of digesta, which is known to be influenced by the hormone triiodothyronine (T3).We hypothesised that a decrease in the MRT in the rumen in response to administration of a T3 solution to sheep would reduce their methane yield. To test this hypothesis, 10 mature Merino wethers were injected with T3 (300 µg) on two different protocols (daily; n = 5 and every second day; n = 5) and the effect on daily methane yield, digesta MRT, DM digestibility, rumen volatile fatty acid concentrations, microbial protein output and plasma T3 concentrations studied. Compared with when injected with saline (control), injection of sheep with T3 every second day resulted in decreased methane yield (P < 0.05) and lower acetate (P < 0.001), butyrate (P < 0.001) and propionate (P < 0.01) concentrations in the rumen. MRT of digesta, derived from faecal excretion of CoEDTA and Cr-mordanted fibre, were reduced in the total tract (P < 0.001) and hindgut (P < 0.01) but not in the rumen (P > 0.05). DM digestibility was not affected by injection of T3 every second day but water intake (P < 0.05) and urine output (P < 0.01) were increased. When sheep were injected with T3 daily, changes were only observed in plasma T3 concentration (P < 0.001) and volume of CO2 produced (P < 0.05). The results indicate that increasing plasma concentration of the thyroid hormone T3 within physiological levels reduces digesta retention time, especially retention time in the hindgut and leads to a reduction in enteric methane yield. Further work is warranted to assess whether plasma T3 concentrations may be indicative of enteric methane yield.

Low ambient temperature elevates plasma triiodothyronine concentrations while reducing digesta mean retention time and methane yield in sheep

“…Results from this experiment also indicated that colder ambient temperatures can induce a natural decrease in MY and MRT, with MRT reduction being recorded in both the ruminal and post‐ruminal regions of the GIT. This corresponds with a previous study showing administration of exogenous T 3 reduces post‐ruminal and total MRT and MY when the T 3 concentration is within physiological ranges (Barnett et al., ). While our results support the notion that exposure to cold ambient temperatures elevates plasma T 3 concentrations, it is unclear whether this elevated T 3 concentration is the main instigator of change in MRT and MY, or whether other physiological mechanisms triggered by exposure to cold temperatures have an important role.…”

Invited review: Large-scale indirect measurements for enteric methane emissions in dairy cattle: A review of proxies and their potential for use in management and breeding decisions

“…Apparent totaltract digestibility did not differ between high-and low-MeY groups in that study, suggesting potential for postruminal digestion to compensate for reductions in rumen fermentation. This is in line with Barnett et al (2012), who also demonstrated that a reduction, induced by injections of triiodothyronine, in whole-tract mean retention time reduced MeY, and identified the possibility that blood triiodothyronine concentration may be a factor by which animal genotype affects mean retention time and thus a possible indicator of MeY. Several other studies have used treatments to increase fractional passage rates from the rumen, with corresponding reductions in MeP.…”

“…Although gene-centric metagenomics is not low cost or high throughput, these results point to potential future proxy approaches using inexpensive gene chips. 5 the size of the rumen and its retention time are related to CH 4 emission (Pinares Patiño et al, 2003;Barnett et al, 2012;Goopy et al, 2014). Rumen volume was determined by X-ray computed tomography scanning in the study by Goopy et al (2014), which demonstrated that low-MeY sheep had smaller rumens.…”

Effect of Simulated Heat Stress on Digestibility, Methane Emission and Metabolic Adaptability in Crossbred Cattle

“…Barnett et al (2012; 2015) reported a positive correlation of ambient temperature and a negative correlation of triiodothyronine (T 3 ) with MRT of digesta. In present study, although the T 3 level did not alter but the decline in thyroxin levels at 35°C and 40°C exposure suggested that the MRT of digesta was comparatively higher at theses temperatures.…”

“…Reduced gut motility, rumination, ruminal contractions and passage rate of digesta during high ambient temperature are major factors which influences CH 4 by ruminants. CH 4 emission from sheep is positively correlated with mean retention time (MRT) of digesta, which is known to be influenced by the hormone triiodothyronine (Barnett et al, 2012; 2015). …”