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Assessment of varying allocations of shade area for feedlot cattle - Part 2 (182 days on feed)
The objectives of this project were to provide a scientific basis for shade usage for feedlot cattle through:
(i) studying the impact of the provision of various shade area (m2/animal) on production and welfare of feedlot cattle, and
(ii) develop firm recommendations on the amount of shade needed to achieve the desired animal welfare outcomes, and production benefits, if they exist, in a cost-effective manner, and Make recommendations, based on both a review of the scientific literature and the study outcomes, on changes required to the thresholds for the various shade areas used in the Risk Analysis Program (RAP).
The study was conducted between the 23 December 2006 and the 30 April 2007 using 126 Angus heifers (350 kg at induction). The heifers were on feed for 119 days. Four shade areas were used: 0.0, 2.0, 3.3 and 4.7 m2/animal (the shade area represents the amount of shade available at 1200 h (EST). The following data were collected:
Ambient temperature (C) Relative humidity (RH; %) Wind speed (WS; m/s) Wind direction Solar radiation (w/m2) Black globe temperature in the sun (BG; oC) Black globe temperature under shade in pen 6 (BG; oC) Rainfall (mm)
From these data the heat load index (HLI) and the accumulated heat load units (AHLU) were calculated. The relationships between the animal data (see below) and the HLI/AHLU were determined by categorizing the HLI and AHLU.
The HLI was divided to 4 categories:
(3) Hot and
(4) Very Hot.
The AHLU was divided into 4 heat load categories:
(1) Low heat load
(3) High and,
(4) Very High when the AHLU > 50. In addition HLI and AHLU were combined to produce 4 risk categories.
The following categories were used:
Low (low: HLI < 70; AHLU < 1), Moderate (mod: HLI 70.1 77; AHLU 1 - 10), High (high: HLI 77.1 86; AHLU 20 50) and Extreme (ext: HLI > 86; AHLU > 50).
Individual panting score ~ collected at 0600, 1200 and 1800 h on cool days, and every 2 h between 0600 and 1800 h on hot days. Location and posture in yard (standing or lying in shade or sun, eating or drinking) ~ collected at 0600, 1200 and 1800 h on cool days, and every 2 h between 0600 and 1800 h on hot days. Liveweight (start, 3 occasions during the study, end of study) Blood samples (3 occasions during study corresponding with weighing) Feed intake (weekly) ~ pen basis Feed to gain ratio ~ calculated from liveweight and feed intake (treatment basis) Carcass weight P8 fat depth
Three major heat events occurred during the study. Rain was recorded on 26 days. Most rain fell during January which was characterized by localized storms. The maximum ambient temperature was greater than 35oC on 18 days. There were 13 days during January when maximum ambient temperature exceeded 35oC. The highest ambient temperature recorded during January was 39.9oC. During February the maximum ambient temperature was 34.7oC. During March, 35oC was exceeded on 5 occasions, with a maximum of 38.8oC being recorded.
During the study period mean monthly maximums reported by the Bureau of Meteorology were slightly above the long term averages (1913 2007; January +1.7oC, February +1.4oC, March +2.9oC and April +2.1oC). Overall the summer period was mild with a few intermittent very hot days. HLI: The maximum HLI > 85 on 100 of the 119 days (84.0%) the cattle were in the feedlot; HLI > 90 on 58/119 (48.7%) days; HLI > 95 on 31/119 (26.1%) days; HLI > 100 on 5/119 days (4.2%) (Figure 3).
The minimum HLI was below 60 units each day. AHLU: Shaded cattle ~ The AHLU for the shaded cattle were greater than 0 and less than 10 on 28 occasions, were between 10 and 25 on 7 occasions and exceeded 25 on 6 occasions. The highest AHLU recorded for the shaded pens was 36.2. Un-shaded cattle ~ The AHLU for the un-shaded cattle were greater than 0 and less than 10 on 29 days; were greater than 10 and less than 25 on 12 days; were greater than 25 and less than 50 on 16 days; and were greater than 60 on 11 of the days. On 4 days the AHLU > 60 < 80, on 2 days the AHLU > 80 < 100, on 2 days the AHLU > 100 < 120, and on 3 days the AHLU >120.
Panting Score Panting score (PS) was used as an indicator of the stress imposed by the climatic conditions. Panting scores were similar between treatments under cool, moderate and hot conditions.
When conditions were classified as very hot or extreme (HLI >86) differences were seen. Under very hot conditions the mean panting score was greatest (P < 0.001) in the un-shaded cattle. There were no differences (P > 0.05) between the shaded treatments under any of the HLI categories. A mean PS (MPS) greater than 1.2 is indicative of excessive heat load and high levels of stress.
The MPS of the un-shaded pens exceeded 1.7 on very hot - extreme days. The MPS of the shaded pens did not exceed the high heat load or moderate stress category (MPS = 0.8 1.2).
There were no statistical differences in terms of carcass quality or carcass weight. However the mean carcass weight of the un-shaded cattle was 12 kg lighter than the mean for the 4.7m2 group. The un-shaded cattle had a feed efficiency of 11:1 compared to approximately 8:1 for the shaded treatments (mean of all shade treatments). The ADG of the un-shaded cattle was lower (P
This page was last updated on 24/07/2017
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