School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemDietary strategies to adapt to, and mitigate, climate change in sheep( 2023-04)Climate change and associated global warming are major menaces to the Australian sheep industry. In addition to being susceptible to the harmful effects of climate change, sheep actively contribute to it through the release of methane (CH4) into the atmosphere. The aim of this thesis was to test and identify suitable feed additives that can reduce enteric CH4 emission and improve the thermoregulatory responses, rumen and digestive functions that were impaired by heat stress in sheep. In the first experiment, sheep were exposed to 3 different durations of heat stress (1 day, 3 days and 5 days; 28 to 38oC and 40 to 60% relative humidity; RH) with thermoneutral being the control (18 to 21oC and 45 to 55% RH) and observed variations in the rumen fermentation profile and rumen microbiota. The following two studies had three different groups of sheep based on the diet; wheat based diet (WD), Bioprotect treated wheat based diet (BD) and maize based diet (MD). Sheep experienced 3 consecutive periods of varying temperature and feeding levels. Period 1 (P1) consisted of 1.7xmaintenance energy (MF) feeding level and thermoneutral conditions (18 to 21oC and 40 to 50% RH). During period 2 (P2) sheep were fed at 1.7xMF level and were exposed to heat stress (28 to 40oC and 30 to 50% RH). During period 3 (P3) sheep were held under heat stress and fed at 2.0xMF level. In the fourth experiment, sheep were supplemented with two different dosages of a sugarcane derived polyphenol (0.25PG and 1PG) and tested for their enteric CH4 mitigation potential and production responses. To explain differences in the enteric CH4 production and ascertain the influence of Polygain on rumen microbiota 16s rRNA sequencing was also explored. The final experiment reported in this thesis studied the effect of an essential oil mix, Agolin, on enteric CH4 reduction and production variables in growing lambs. Results from this thesis demonstrated that short duration heat waves particularly, 3 and 5 days of heat stress, can significantly reduce total and individual rumen volatile fatty acid (VFA) concentrations and alter the VFA profile and rumen microbial diversity indices and richness of certain microbes of second cross lambs. Treating wheat with Bioprotect can partially alleviate the effects of heat stress on the thermoregulatory responses of sheep. As Bioprotect works as a rumen bypass feed by promoting the digestion of starch and protein in the small intestine, animals experience less metabolic heat from rumen fermentation. This enables the sheep to have better body temperature control. Bioprotect can also reduce enteric CH4 from sheep without hampering diet digestibility and dry matter intake (DMI). Polygain feeding reduced CH4 emissions without compromising average daily gain (ADG) or DMI. The highest CH4 reduction (49% reduction). was achieved from the lowest dosage of Polygain (0.25% PG) used in the study. Agolin was also successful in reducing CH4 emissions from sheep. Sheep fed Agolin showed a 27% reduction in CH4 without reducing DMI or ADG. The findings from the work reported in this thesis are novel as most of the work covered in the thesis is pioneering research in the sheep industry. However, it is important to conduct follow up research over longer durations and with larger sample sizes for policymaking if these feeding strategies are to be adopted.