Modification of pen microclimate to improve the productivity and welfare of feedlot cattle

Megan Sullivan (2011). Modification of pen microclimate to improve the productivity and welfare of feedlot cattle PhD Thesis, School of Agriculture and Food Sciences, The University of Queensland.

       
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Author Megan Sullivan
Thesis Title Modification of pen microclimate to improve the productivity and welfare of feedlot cattle
School, Centre or Institute School of Agriculture and Food Sciences
Institution The University of Queensland
Publication date 2011-09
Thesis type PhD Thesis
Subjects 07 Agricultural and Veterinary Sciences
Abstract/Summary Australia and the globe are experiencing rapid climate change and since the middle of the 20th century, Australia‟s temperature has, on average, risen by about 1°C, with an increase in heatwaves and the number of very hot days (> 35 °C). Feedlot cattle are highly susceptible to heat stress and as a result there are frequent losses in productivity, compromised welfare and unfortunately a number of heat stress related deaths. There have been numerous studies investigating the benefits of shade for feedlot cattle, but there is limited information indicating the specific amount of shade that is beneficial to the productivity and welfare of feedlot cattle. There is also limited information on the biological effects of heat stress on feedlot cattle, in particular heat shock proteins. To investigate the hypothesis that; ‘shade will improve the productivity and welfare of feedlot cattle in proportion to shade allocation and as heat load increases average daily gain, feed efficiency, biological markers, physiological responses and panting score will change accordingly’, two shade studies were conducted to investigate the amount of shade that is beneficial to the productivity and welfare of feedlot cattle and a third study investigating the specific effects of heat stress on the biological and physiological parameters of Bos taurus beef cattle was conducted. Experiment one was conducted in the summer of 2007 using short fed (119 d) black Angus heifers and experiment two, was conducted in the summer of 2007/2008 using medium fed (177 d) black Angus steers. Four shade allocations were used in both experiments one and two; 0 m2/head, 2.0 m2/head, 3.3 m2/head and 4.7 m2/head. Individual panting score and pen location were collected, blood sampling and weighing occurred approximately every 30 d and dry matter intake monitored weekly. Results indicated that the performance of the unshaded were noticeably impaired compared with the shaded cattle. The unshaded cattle had the poorest average daily gain and feed efficiency and subsequently the lowest profit margin. The unshaded cattle were also subject to increased heat load and were unable to seek relief from the direct solar radiation. The results from experiment one indicated that any amount of shade over 2.0 m2/head improved the performance of short fed feedlot cattle but this improvement does not increase as shade allocation increases. However, in experiment two as shade allocation increased, so in turn did animal performance. This may suggest that a higher shade allocation is more beneficial for medium fed cattle. Results from blood sampling indicated creatine kinase was the most reliable indicator of heat stress with the unshaded cattle having the highest concentration of this biological marker in both experiments. Welfare was also improved in the shaded cattle. The results from experiment one suggest that any amount of shade over 2.0 m2/head has a positive impact on animal welfare (reduction in mean panting score). However further reductions were not evident as shade area increased to 3.3 or 4.7 m2. In contrast to experiment one, the results from experiment two suggest that as the shade allocation increased, animal welfare is further improved by continual reductions in mean panting score. Overall, from both experiments one and two it can be concluded that shade improves the productivity and welfare of feedlot cattle and that any area of shade over 2.0 m2/head allows for this improvement. A third study was conducted investigating the before, during and after heat event effects on physiological parameters and biological markers (heat shock protein 70) of beef cattle. The study was conducted in a climate controlled facility and the cattle were subject to a temperature regime of 2 d thermoneutral (THI 65-71), 5 d hot (THI 71-85) and 3 d thermoneutral (THI 65-72) and were unacclimatised to the conditions. Physiological observations and blood sampling occurred periodically throughout the experimental period and dry matter intake was monitored daily. Results indicated that as hot conditions were imposed the physiological parameters responded as expected; respiration rate, rectal temperature, skin temperature and panting score increased with these parameters been significantly correlated. A strong individual animal response was detected for all parameters, but in particular heat shock protein 70. A lag was detected with heat shock protein 70 and rectal temperature and it was shown that heat shock protein 70 lagged rectal temperature by up to 360 minutes. It was also shown that recovery from heat events occurs for both physiological parameters and biological markers when hot conditions abate. Results of these studies showed that shade is beneficial to productivity and welfare and any amount of over 2.0 m2/head allows for this improvement, as indicated by changes in animal performance, panting score and biological markers. Recovery from heat stress occurs as hot conditions abate, supporting the implementation of shade that was shown to reduce heat load.
Keyword beef cattle, heat stress, shade, welfare, productivity

 
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Created: Fri, 23 Sep 2011, 09:34:32 EST by Ms Megan Sullivan on behalf of Library - Information Access Service