Farm Table says:
Assessment of varying allocations – Part 2 (182 days on feed)
What is the problem?
Predictions from climate change models suggest that there will be more extreme thermal events and that the duration of these events will be longer. Severe heat episodes resulting in significant cattle losses (estimates in brackets) have occurred in Australia.
This study purpose was to:
- To feed 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) develop firm recommendations on the amount of shade needed to achieve the desired animal welfare outcomes, and production benefits, if they exist in a costeffective manner, and
- Compose 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).
What did the research involve?
-The study was undertaken at The University of Queensland, Gatton between 13th September 2007 (entry to feedlot) and the 13th March 2008 (exit feedlot). Cattle arrived on the 13th September and immediately entered the feedlot.
-One hundred and twenty six Black Angus (335 ± 24 kg; 17th September 2008 – induction) yearling steers were used.
-The area of shade is the shade provided at mid day (1200 h Eastern Standard Time). Shade was provided by 70% solar block shade cloth attached to a 4 m high frame (Rural pacific marketing P/L., Gatton) located in the middle of each shaded pen with a north-south orientation.
– From the 13th September to the 26th September the cattle were fed a starter 1 ration (Table 1). Low quality barley hay was available ad libitum from day 1 to day 7. From day 7 the amount of hay offered was reduced so that by day 12 the cattle only had access to starter 1.
3.4.2 Dry matter intake
-Due to the feeding method used (self feeders) dry matter intake could not be measured on a daily basis. Instead a weekly measure was made.
3.4.3 Approximate analysis
-A 500 g sample of feed was taken from each delivery. A sub-sample (approx. 100 g) was removed and the percentage dry matter.
3.4.4 Water usage
– Water usage was recorded using water meters on a pen basis. Water usage rather than intake is used due to evaporative water loss and losses due to splashing.
3.5 Climatic data
-Climatic data were obtained from two automated weather stations. Data was collected at 10 min intervals from one station (Esidata MK-3; Environdata Australia P/L, Warwick, Qld. Australia) and at 30 min intervals from the second (Vantage Pro 2; Davis Instruments, Hayward, California, USA) from the 1st November 2007 until 13th March 2008.
3.5.1 HLI thresholds
-The base threshold of 86 was adjusted by +2 (HLI threshold = 88) for both the shaded and un-shaded cattle for the first 80 days on feed 13th September 2007 – 1st December 2007. In addition the threshold was further adjusted (+5) for the shaded pens giving a threshold of 93 (88 + 5).
-Cattle were weighed at the start of the study (17th September 2007; induction into feedlot), five times during the study (1st November 2007 – Day 49, 29th November 2007 – Day 77, 20th December 2007 – Day 98, 17th January 2008 – Day 125, 14th February 2008 – Day 153) and the day before exiting the feedlot (12th March 2008 – Day 182).
3.6.2 Blood samples
-Blood samples (2 x 10 ml samples/animal) were initially collected from 4 randomly selected animals from each pen (16 per treatment) on Day 49 (1st November 2007).
3.6.3 Panting score
-Panting scores were visually assessed using the 0 – 4.5 scale, with panting score 0 being an animal under no heat load.
3.6.4 Location and posture
– In addition to panting score cattle location (and number of cattle) within a pen (at feeder, at water trough, in sun, under shade (if applicable) and posture (standing or lying) were recorded.
3.7 Animal ethics approval
-The use of animals in this study was approved (SAS/524/07/MLA) by The University of Queensland Production and Companion Animal Ethics Committee in accordance with the Queensland Animal Care and Protection Act and the Australian Code of Practice for the Care and Use of Animals for Scientific Purposes.
3.8 Statistical analysis
-The HLI was divided into 5 categories: (1) Mild, when HLI is < 70.0; (2) Moderate, when the HLI is 70.1 – 77.0; (3) Hot, when the HLI is 77.1 – 86; and (4) Very Hot when the HLI is 86.1 – 95, and Extreme when the HLI >95. The AHLU was divided into 5 heat load categories (modified from Gaughan et al 2008).
-Blood data were analysed using PROC Mixed (SAS). The effects of treatment and treatment × collection period (i.e. 1st – 5th collection) were determined. Carcass data were analysed using PROC GLM (SAS).
What were the key findings?
4.1 Climatic conditions
Rainfall during the period of data collection. The daily black globe temperature, relative humidity and wind speed.
4.2 Heat Load Index
-The maximum HLI was less than 86 on 16 of the 134 days of data collection. The maximum HLI exceeded 86 on 118 days (72.9%), 82 of which the HLI>90.
4.3 Accumulated Heat Load Units
4.3.1 Shaded cattle
– The AHLU for the shaded cattle was greater than 0 and less than 10 on 34 occasions (Figure 5). It was between 10 and 25 on 9 occasions, and between 25 and 50 on 14 occasions.
4.3.3 Heat waves
-The first heat event occurred from 5th December until the 13 December. During this period the cattle were under heat load from the 7th December (0700 h) until 13 December (2300 h).
4.4 Pen surfaces
4.4.1 Pen surface temperatures
-Direct sunlight penetration under the shade was 72% lower than un-shaded areas. The mean unshaded pen surface temperature was 44.6o C (range 36.8 – 53.4o C). In the shaded pens the mean pen surface temperature in the sun was 44.7o C (range 33.3 – 54.8o C).
4.4.2 Pen surfaces
-General It was planned that the pens would be cleaned approximately every 28 days.
4.5 Panting score
4.5.1 Heat Load Index
-There were inconsistent but small changes in mean panting score when conditions moved from moderate to hot and larger increases when conditions changed from hot to very hot.
4.5.2 HLI × AHLU risk categories
-During the study period, humidity and low air speed were the main influencing factors when conditions were classified as very hot or extreme.
4.6 Dry matter intake, feed efficiency, water usage, growth performance and carcass data
4.6.1 Dry matter intake
-As it is not valid to statistically analysis mean daily intakes from whole pen intakes all DMI data are presented with no statistical analysis.
4.6.2 Feed efficiency
-Feed efficiency (feed to gain) has a major influence on feedlot profit. Based on the age and breed of cattle used in the study, and the feeding methods used a feed to gain ratio of 7:1 was expected.
4.6.3 Water usage
– Rainfall contributed to the volume of water in the troughs so this was added to the total amount of water used.
4.6.4 Growth performance and carcass traits
-There were no between treatment differences for liveweight at the commencement of the study.
4.6.5 Carcass value less feed costs and cost of gain
-When the cost of feed used was subtracted from the value of the carcass the cattle with access to 4.7m2 of shade had a margin of $648.61 compared to $482.58 for the un-shaded cattle.
4.7 Animal posture/shade usage in relation to HLI x AHLU
-The use of shade by cattle is influence by climatic conditions. The major climatic factors are to a combination of ambient temperature and solar radiation (basically black globe temperature), and relative humidity.
4.8 Blood parameters
-The mean (pooled for all bleeds) serum concentrations of creatine kinase, glucose, insulin, lactate dehydrogenase, sodium, potassium and chloride.
4.8.1 Creatine kinase
-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.
-The serum concentrations of glucose, chloride, sodium, and potassium are within the normal range for cattle (Fraser et al. 1991; Doornenbal et al. 1988; Yokus and Cakir 2006).
4.8.3 Lactate dehydrogenase
-Lactate dehydrogenase is the last enzyme of the glycolytic pathway and catalyzes the conversion of pyruvate to lactate (when O2 is not available in muscle cells) or lactate to pyruvate (when O2 is available) (Doornenbal et al. 1988; Looper et al. 2008).
-The serum insulin values obtained from the cattle in the present study were lower than values reported by Borger et al. (1973) for feedlot steers.
During there is general agreement that provision of shade improves the welfare of Bos taurus feedlot cattle when they are exposed to hot weather there is little scientific evidence showing a production response.