Betaine as a Dietary Additive for Heat Exposed Beef Cattle

Stephen Bonner (2010). Betaine as a Dietary Additive for Heat Exposed Beef Cattle PhD Thesis, School of Agriculture and Food Sciences, The University of Queensland.

       
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Author Stephen Bonner
Thesis Title Betaine as a Dietary Additive for Heat Exposed Beef Cattle
School, Centre or Institute School of Agriculture and Food Sciences
Institution The University of Queensland
Publication date 2010-12
Thesis type PhD Thesis
Supervisor Doctor John Gaughan
Professor Wayne Bryden
Doctor Judy Cawdell-Smith
Total pages 246
Total colour pages 1
Total black and white pages 245
Subjects 07 Agricultural and Veterinary Sciences
Abstract/Summary The heat stress response in cattle functions to minimise accumulation of excessive body heat, and to facilitate its removal. Prolonged and continuous exposure to high heat load can cause physiological imbalances. Nutritional strategies may be used to ameliorate the disturbance of homeostasis resulting from heat stress. The research presented in this thesis was designed to assess the potential of betaine as a dietary additive to ameliorate the negative aspects of the heat stress response in beef cattle. This was accomplished by; i) testing the effects of betaine on the heat stress response of steers exposed to hot conditions, ii) evaluating the influence of betaine within the rumen, iii) assessing betaine effects on rumen bacterial species, iv) the effect of betaine on the physiology and blood parameters of steers under hot conditions, and v) assessing the response of steers to dietary betaine on blood parameters over 120 days in a feedlot. A 5 day heating protocol was imposed on steers under controlled climatic conditions within 2 studies (Chapters 3 and 6). Steers were fed a grain ration containing 20 g of betaine (BET) or no betaine (CON) in Chapter 3. Three dietary treatments were used in Chapter 6; identical to Chapter 3, plus betaine (20 g) with buffer (BET+). DMI fell for all steers during the 5 day hot phases. The change in DMI (relative to DMI pre-heat) was larger (P<0.001, P<0.001) for betaine treatments in both studies. The rate of increase of rectal temperature (RT_slope) and respiration rate (RR_slope) for CON steers was greatest on day 3 of heat, in contrast to peaks for RT_slope and RR_slope occurring for BET steers on day 4 of heat. This may indicate that the response of CON steers to heat was more acute, particularly in day 3. During the hot days (Chapter 6), CON steers had the smallest (P<0.05) change in rectal temperature (ΔRT) compared with BET and BET+, and yet had the highest (P<0.05) increase in respiration rate (ΔRR). Conversely, both BET and BET+ steers had the highest core temperature throughout 5 hot days, while simultaneously having lower ΔRR compared with CON. Serum urea was higher (P<0.01) for BET and BET+, however, this may be influenced by dietary protein. Across all treatments, serum creatinine appeared sensitive to elevated temperatures. Creatinine was higher for hot days compared with thermoneutral days, and increased as ambient temperatures became more severe. This may indicate that creatinine expression is sensitive to hot conditions, and therefore having potential as a marker of heat stress in beef cattle. An in vivo study was conducted using sheep to evaluate the effect of betaine within the rumen. Two treatments were fed the same diet, while betaine was added directly to the rumen of the betaine treatment. Similar to other studies (Mitchell et al. 1979), betaine clearance from the rumen was rapid. The half-life of betaine within the rumen was within 0.9 - 2.1 h. Rumen ammonia concentration was lower (P<0.05) for betaine treatment at 6, 7 and 9 hours following betaine addition to the rumen. Betaine did not affect rumen VFA concentration, digestibility or protozoal counts. To evaluate betaine upon rumen bacterial species, an in vitro rumen culturing experiment was conducted using rumen fluid from sheep fed the same concentrate diet with and without betaine. All in vitro cultures contained betaine, while 2 rumen fluid inocula were taken from sheep previously receiving betaine (B), and 2 without betaine (C). Profiling rumen bacterial populations with DGGE demonstrated changes at 24 and 48 h. In particular, the intensity of band D increased at 24 and 48 h for C treatment, but was present for B treatment. This band was identified to the family level as Streptococcacae. Ammonia accumulation was lower (P<0.05) for C treatment in the 0 - 24 h culture. These data indicate that initial exposure of rumen bacteria to betaine in the in vitro cultures may increase the relative proportion of certain bacterial species. As a component of a larger study, steers fed for 120 days over summer in a sub-tropical environment and fed 0, 10, 20 or 40 g of betaine, or glycerol, with a shaded and unshaded treatment for all diets. Blood samples were collected on days 0, 30, 60, 90 and 110. Production data from this study is published elsewhere (Gaughan et al. 2010). Correlations between blood parameters and physiological measures (body temperature, panting score, DMI and liveweight) were observed for sodium, urea, glucose, haematocrit and red blood cells. These studies have highlighted the complexity of the heat stress response in cattle, and the indirect nature of employing nutritional strategies to attend to resulting imbalances. Successful nutritional strategies for heat stress may not always result in direct production benefits. These studies emphasise the impact of dietary nitrogen on the heat stress response and a likely interaction with betaine supplementation.
Keyword betaine
excessive heat load
heat stress
bovine
beef
feedlot
rumen
Additional Notes 104

 
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