Assessment of varying allocations of shade area for feedlot cattle (Phas e 2)

Summary

This study reports the results of the second of two studies that were undertaken to examine the impact of shade provision on different classes of feedlot cattle.

The objectives of this project were to:

• Provide a scientific basis for shade usage for feedlot cattle by: (i) studying the impact of the provision of various shade area (m2/animal) on production and welfare of feedlot cattle, and (ii) developing 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 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 13th September 2007 and the 13th March 2008 using 126 Angus steers (335 ± 24 kg at induction on 17th September 2007). The steers were on fed for 182 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 data collection period was from 1st November 2007 to the 13th March 2008 (134 days; NB: feed and water data were collected from day 1).

Key findings

Climatic summary

Five major heat load events occurred during the data collection period of the study (1st November 2007 – 13th March 2008), mainly as a result of high humidity. During this period rain was recorded on 64 days. The majority of the rain fell during February (237.1 mm; 16 days of rain) and was characterized by occasional localized storms and general widespread rain. The February rainfall was 105 mm above the long term averages. Rainfall during the remainder of the months were close to the long term averages. During the study period mean monthly maximum temperatures reported by the Bureau of Meteorology were slightly below the long term averages for the Gatton area. Based on long term (1913 – 2007) climate averages for Gatton the mean number of days exceeding 30^oC for the period 1st November to 13th March is 79 days. For the period 1st November 2007 – 13th March 2008, a maximum of 30^oC was recorded on 43 days, and exceeded 35^oC on four days. The highest ambient temperature recorded were: November (37.4^oC), December (33.1^oC), January (32.6^oC), February (38.4^oC) and March (29.1^oC; 13 days only). Over all the maximum mean temperature for November was -1.7^oC below average, December -2.2^oC below average, January -3.1^oC below average, February -1.7^oC below average, and March -1.4^oC below average (13 days only). Based on ambient temperature alone the summer period was mild with a few intermittent hot days.

HLI and AHLU

HLI: The maximum HLI < 86 occurred on 16 of the 134 days data was collected, and HLI>86 for 86 days. Of the 86 days, maximum HLI>90 for 82 days, >96 for 45 days, >100 for 32 days, and >110 for 3 days. The minimum HLI was below 60 units 34/134 days.

AHLU: Shaded cattle ~ The AHLU for the shaded cattle was greater than 0 and less than 10 on 34 days; was between 10 and 25 on 9 days; between 25 and 50 on 14 days; between 50 and 100 on 9 days; and exceeded 100 on 3 days. The highest AHLU recorded for the shaded pens was 127.6. There were 3 carry over heat events during the study. AHLU: Un-shaded cattle ~ The AHLU for the un-shaded cattle was greater than 0 and less than 10 on 29 days; was between 10 and less than 25 on 16 days; was between 25 and 50 on 20 days; was between 50 and 100 on 16 days; and was greater than 100 on 16 days. The highest AHLU recorded for the un-shade pens was 294.1. There were 5 carry over heat events during the study ranging from 2 – 6 days duration.

Panting Score

Panting score (PS) was used as an indicator of the stress imposed on the animal by the climatic conditions as measured by HLI. Panting scores were similar between treatments under cool, moderate and hot conditions. When conditions were classified as very hot (HLI 86 – 95) or extreme (HLI >95) differences were seen. Under very hot conditions the mean panting score was greatest (P < 0.001) in the un-shaded cattle. A mean PS (MPS) greater than 1.2 is indicative of excessive heat load and high levels of stress (Gaughan et al. 2008). The MPS of the cattle in the un-shaded pens was 2.14 when HLI × AHLU was classified as extreme. Under the same classification the MPS of the shaded cattle were lower (P < 0.001) at 1.97, 1.92 and 1.82 respectively for 2.0, 3.3 and 4.7 m2.

Blood Parameters

The concentration of creatine kinase may be a useful indicator of welfare status. Exposure to stress (physical or disease) often leads to tissue damage in animals. When this happens there are changes in serum enzyme activity. Creatine kinase (CK) levels in the blood are associated with muscle damage. In the current study the CK levels were highest (P<0.01) in the un-shaded cattle (365.3 U/L). The values in the shaded cattle were similar across the treatments (134.7 – 154.7 U/L).

Cattle Performance

There were no between treatment differences (P<0.05) for liveweight at the commencement of the study (Table 5). By the completion of the study the cattle with access to 4.7 m2 were the heaviest (P<0.05) at 622.3 kg. The cattle with access to 4.7 m2 shade had the best (P<0.01) ADG (1.62 kg/d). There were no differences (P>0.05) between the 0, 2.0 and 3.3 m2 treatment groups.

There were no treatment differences for marbling score, hot standard carcass weight, P8 fat depth, fat colour or meat colour. However, the cattle with access to 4.7m2 of shade had a lower (P<0.05) dressing percentage compared to the other 3 treatments. The reasons for the differences in dressing percentage are not known. There was no differences in carcass value between treatments.