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

Abstract

Ruminant methane yield (MY) is positively correlated with mean retention time (MRT) of digesta. The hormone triiodothyronine (T3 ), which is negatively correlated with ambient temperature, is known to influence MRT. It was hypothesised that exposing sheep to low ambient temperatures would increase plasma T3 concentration and decrease MRT of digesta within the rumen of sheep, resulting in a reduction of MY. To test this hypothesis, six Merino sheep were exposed to two different ambient temperatures (cold treatment, 9 ± 1 °C; warm control 26 ± 1 °C). The effects on MY, digesta MRT, plasma T3 concentration, CO2 production, DM intake, DM digestibility, change in body weight (BW), rumen volatile fatty acid (VFA) concentrations, estimated microbial protein output, protozoa abundance, wool growth, water intake, urine output and rectal temperature were studied. Cold treatment resulted in a reduction in MY (p < 0.01); digesta MRT in rumen (p < 0.01), hindgut (p = 0.01) and total digestive tract (p < 0.01); protozoa abundance (p < 0.05); and water intake (p < 0.001). Exposure to cold temperature increased plasma T3 concentration (p < 0.05), CO2 production (p = 0.01), total VFA concentrations (p = 0.03) and estimated microbial output from the rumen (p = 0.03). The rate of wool growth increased (p < 0.01) due to cold treatment, but DM intake, DM digestibility and BW change were not affected. The results suggest that exposure of sheep to cold ambient temperatures reduces digesta retention time in the gastrointestinal tract, leading to a reduction in enteric methane yield. Further research is warranted to determine whether T3 could be used as an indirect selection tool for genetic selection of low enteric methane-producing ruminants.

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.…”

“…In present study CH 4 emission decreased progressively with increase in temperature up to 35°C and then increased to initial levels. Barnett et al (2015) reported a positive correlation of ambient temperature and a negative correlation of triiodothyronine (T3) with CH 4 yield. In present experiment T3 level did not alter with increase in temperature hence, no correlation was established between T3 level and CH 4 emission in crossbred cattle.…”

“…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). …”

Review: Comparative methane production in mammalian herbivores

“…Most studies on CH 4 in mammals stem from domestic ruminants, where CH 4 is, by contrast, mainly considered an unavoidable, unwelcome loss of energy and contribution to greenhouse gas emissions. As in humans, intra-specific variation in CH 4 production in ruminants has been linked to digesta retention: animals with longer digesta retention, either due to more voluminous rumens at similar intake, or due to lower intake at uncontrolled rumen capacity, generally produce more CH 4 per ingested DM (Pinares-Patiño et al, 2003;Goopy et al, 2014;Hammond et al, 2014;Barnett et al, 2015;Cabezas-Garcia et al, 2017). Here, however, it is the retention time that is considered the cause, where more time available is considered responsible for more fermentative digestion with an ensuing increased CH 4 production.…”

Decreasing methane yield with increasing food intake keeps daily methane emissions constant in two foregut fermenting marsupials, the western grey kangaroo and red kangaroo

“…In essence, a higher food intake leads to a faster passage of digesta through the digestive tract, mostly because of the limited capacity of the gut to expand. A shorter MRT, in turn, was correlated with a lower CH 4 yield in various studies with sheep (Barnett et al, , 2015Goopy et al, 2013;Hammond et al, 2014;Pinares-Patino et al, 2003). Janssen (2010) summarized these findings, creating a model for the prediction of CH 4 yield that used a range of factors, including MRT.…”