Updated April 2013
In the summer of 2006, a severe cattle welfare problem was first observed at three slaughter plants. Large numbers of fed feedlot cattle were lame and a few animals had severe heat stress symptoms. I have worked with cattle for over 30 years and this is the first time I have seen severe heat stress in crossbreds which were part Brahman (Bos Indicus) genetics. The cattle came from three different feedlots. All of the cattle were healthy looking feedlot cattle and their feet looked completely normal. All the animals were clean and came from dry feedlots with no mud. Foot rot can be ruled out because the animals came from lots in an area experiencing a drought. None of the cattle were overweight or over fat. Their estimated live weight was between 450 to 540 kg (1000 to 1200 lbs). At the first plant the temperature was over 38 degrees C (100 F) and the animals were in a lairage equipped with sprinklers. About one third had mild to moderate lameness and no heat stress symptoms. At the second plant, there were a few lame cattle and two healthy feedlot steers refused to get up. The third plant had the worst heat stress problems. The temperature was in the 32 to 34 degrees C (low 90's F) range. The sprinklers were off. Ten to 25% of the animals were mildly to moderately lame. About 5 to 10% were panting and one or two animals from each truck load were lying down and panting hard. Their tongues were hanging out. One animal was sitting like a dog and acted stiff and arthritic when the driver made him get up.
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In the summer of 2011 I observed fed steers arriving at a plant in over 100 degrees F (38 degrees C) temperatures with severe heat stress and stiff type lameness. These animals walked with a stiff hesitant gait and were definately clinically lame. The percentage of lame steers varied from 5 to 10% on a truck load to 50%. Some animals had open mouth breathing. The hooves had no signs of pathology such as foot rot. It is highly likely that the lameness and open mouth breathing was related to an unknown dose of either Ractopamine or Zilpaterol, which are beta-agonist drugs used for growth promotion. All steers were unloaded promptly at the plant.
Research conducted by Kurt Vogel at Colorado State University as part of doctoral dissertation has shown that certain combinations of beta-agonists and hormone ear implants increased heat stress while other combinations reduced it. In steers, Zilpaterol combined with a Revelor implant was a safer treatment from a heat stress standpoint compared to Zilpateral alone. When Ractopamine was fed, the opposite effect occurred. Ractopamine alone increased susceptibility to heat stress. Difficulty mixing small amounts of beta-agonists into the feed may explain why the beta-agonists used in this study had little effect on weight gain. In the meat plants, I have observed odd, uneven effects where a small percentage of the cattle were severely heat stressed and lame and the others were normal. Official feed testing parameters from the manufacturers of beta-agonists have a wide range of permissible error from 125% to 75% of the correct dose. A single initial feed test showed that the dose was low in our study. Handling the cattle frequently may also have had an effect on the lack of weight gain. This is very preliminary data and this experiment will need to be replicated. Due to a severe illness, some of the feed samples that should have been collected by feed lot management to monitor the dose was not collected. It was important to get information out on the possible beta-agonist/implant interactions and their effect on heat stress.
I recommend measuring outcomes instead of inputs. Fed feedlot cattle that arrive at slaughter plants should be scored for lameness and heat stress symptoms. Feedback should be provided back to the feedlots so that the problem can be corrected. Terry Mader from the University of Nebraska states that when cattle are open mouth panting they have severe heat stress. The first symptom of heat stress is drooling. Cattle that show signs of heat stress must be provided with either sprinklers or shades. When normal cattle breath, the head will remain still. When they are in a pre-heat stress state, their heads will start to bob up and down. Cattle that start to head bob should be carefully watched for further signs of heat stress.
In hot weather, 95 degrees F (35 degrees C), the severerly affected animals had open mouth panting and a few animals became non-ambulatory. The lame cattle were sore footed on all four feet and they were reluctant to walk quickly down the truck unloading ramp. Normal cattle will run or trot down the ramp. During cooler weather, stiffness has been observed in steers fed Zilpaterol. They act like they have muscle cramps. I have observed one group of cattle fed Zilpaterol that walked normally. They came from a feedlot with a sophisticated mill that would have mixed the feed evenly. There has also been a report of a "statue steer" which walked off the truck and when it was time to be moved to the slaughter line he stood and refused to move. He acted like he was too stiff or sore to move. These observations indicate that there are severe welfare problems in some animals fed beta-agonists. Poor feed mixing may be part of the problem. Cattle arriving at the plant should be evaluated for lameness, heat stress (open mouth breathing), and stiffness. From an animal welfare standpoint, lameness, open mouth breathing, and a stiff gate are not acceptable.
There is also a need for research on a genetic interaction and beta-agonists. I observed a pen of cattle that contained many different breeds. A Simmental steer had become very big and stiff and a Hereford steer appeared more normal. Possibly cattle with a greater genetic potential for muscle growth have more effects.
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