Faculty of Veterinary Science
Department of Production Animal Studies
Selected Highlights from Research Findings
Bovine respiratory disease (BRD) is the most economically important disease of feedlot cattle worldwide. The objectives of this research project entitled: Use of treatment records and lung lesion scoring to estimate the effect of respiratory disease on growth during early and late finishing periods in South African feedlot cattle, were to estimate the effect of BRD on growth during the early (processing to day 35) and late (day 35 to slaughter) finishing periods in two South African feedlots, to investigate the effects of lesion type and severity on growth rate and to quantify the hidden economic cost of reduced growth due to BRD.
This was the first time that such a study had been done in South Africa, and also the first time that both treatment records and lesion scoring had been combined in order to more fully account for the total impact of the disease.
Slaughter data of 2 036 animals were analyzed during the normal course of operations of two well-managed feedlots. Records were kept of clinical disease and treatments, and at slaughter after a mean feeding period of 137 days; lungs were examined for lesions of respiratory disease.
Findings indicate that:
· The peak incidence of respiratory disease occurred on day 18 after arrival. Management in the first four to six weeks after arrival is critical;
· The overall incidence of BRD, including sub clinical disease, was 52,5% - fewer than half of the BRD cases were clinically detected and treated;
· Lung lesions was found in 43% of the calves at slaughter, 8,6% had parenchymal lesions and 38,8% had pleural adhesions; both lesion types resulted in reduced growth rate, but were indicative of losses occurring at different times during the feeding period;
· After day 35, animals treated for BRD tended to grow faster than those with sub clinical BRD, indicating that treatment was generally successful in reducing economic losses; and
· Overall, BRD reduced daily weight gain by 143 g over the entire feeding period. The hidden cost of reduced growth rate due to BRD amounted to approximately R25 per calf with clinical or sub clinical BRD, or R13 per animal entering the feedlot.
Dr PN Thompson
Production Animal Studies
+27 (0) 12 529 8290
peter.thompson@up.ac.za
BRD is largely a single clinical entity of bronchopneumonia with a multifactorial aetiology as a result of complex interactions between environmental factors, host or animal factors and pathogens, which include bacteria, viruses and mycoplasmas.
The presence of Mycoplasma species has been shown to increase the severity of respiratory disease and the aim of the study was to identify the isolation rates of Mycoplasma in feedlot cattle in South Africa.
Transtracheal aspirate samples were collected from sick and healthy animals from the majority of the bigger feedlots in South Africa (other than Western Cape) for the period 2000 to 2004. Researchers were able to show a statistical increase in Mycoplasma isolations in animals with pneumonias/respiratory disease complex.
It has always been suspected that Mycoplasmas played a role in the pathogenesis, but it had never been quantified in South Africa (nor in US feedlots in the manner this study was conducted). Future research will include the development of a vaccine.
Dr CAP Carrington
Production Animal Studies
+27 (0) 12 529 8453
chris.carrington@up.ac.za
This research project entitled: Vanadium mining and cattle health, was started several years ago when Professor Bruce Gummow at the Department of Production Animal Studies was approached by a referring veterinarian to find answers to an "illthrift" problem that was occurring among dairy cattle adjacent to an alloy processing plant.
The investigation found that animals between four – 18 months showed signs of emaciation, chronic diarrhoea and in some instances rhinitis, conjunctivitis and recumbence. Many of the animals showing these symptoms eventually died.
The epidemiological investigation, backed by post-mortem and clinical pathology findings, showed that the symptoms and deaths could probably be attributed to chronic vanadium poisoning. Vanadium is a transition element derived in South Africa primarily from iron ore.
As a result of the findings of the initial study, Xstrata, one of the biggest vanadium mining companies in the country, approached Gummow to study the long-term effects of vanadium exposure in cattle. Cattle, placed on the mine for the study, acted as a sentinel system and are now being used to warn the mine of breaks in their pollution monitoring and as a risk communication tool for surrounding farmers.
The integration of cattle farming into the management of vanadium mine has been a revolutionary step by the vanadium mining industry and one applauded by environmentalists and surrounding farmers. During the study a novel stochastic exposure model was developed to estimate the composite external dose of vanadium taken in by cattle over the five-year period of exposure. This was estimated at between 0.05 and 23.96 mg Vanadium/kg body weight/day for cattle farmed adjacent to the processing plant (High exposure group) and between 0.01 and 12.72 mg/kg/d for cattle farmed a few kilometers from the mine (Low exposure group).
Samples taken from live animals as potential biomarkers for vanadium exposure included caudal coccygeal vertebrae, tail hair, milk, urine, faeces, rib-bone biopsies and a wide range of clinical pathology and hematological parameters. In addition tissue samples were taken from 42 adult cattle slaughtered during the course of the project.
Findings indicate:
· In live animals, a difference in response was found between the two exposure groups in respect to serum albumin, monocyte and thrombocyte counts and hair and faeces vanadium concentrations. No differences could be shown for urine – the traditional occupational health biomarker. None of the other potential biomarkers examined proved to be of much value in determining or predicting vanadium exposure in bos indicus cattle;
· Average concentrations of Vanadium in the tissues of slaughtered cattle ranged from 0.08 to 2.94 mg/kg (wet-weight), while the rumen content contained 16.67 mg/kg;
· No correlation could be shown between tissue concentrations and the median exposure dose for the period an animal was in trial or the length of time exposed;
· Significant correlations were found between the exposure dose (end-dose) just prior to slaughter and the concentrations of vanadium in the coccygeal vertebrae, liver, diaphragm and rib-bone in descending order of magnitude. Other tissues showed poor correlation to the end-dose. The best tissue from slaughter animals for assessing chronic vanadium exposure is probably the liver; and
· Health risks of consuming milk and meat from cattle originating from areas high in vanadium were evaluated. Concentrations of vanadium in commonly consumed tissues ranged from <0.05 to 11.51 mg/kg (wet-weight), while the median concentration of vanadium in milk was 0.23 mg/kg.
People drinking milk were likely to consume the highest levels of vanadium because of the volumes consumed. The study however, showed that even with maximum likely consumption of meat and milk from clinically healthy cattle coming from vanadium rich areas, there was no health risk to the consumer given the current state of knowledge of toxicity in humans.
Calves have been found to be good sentinels for alerting officials to increased emission levels of vanadium around vanadium smelters, as they are very sensitive to the effects of environmental vanadium pollution.
The study has provided the vanadium mining industry with guidelines and emission targets for responsible environmentally healthy vanadium mining in South Africa. With the knowledge coming from this study it has been possible to identify many of the risks that vanadium mining may pose to cattle farming and to work out ways of minimizing these risks with the ultimate aim of providing a safe and economically viable environment for all concerned.
Prof Bruce Gummow
Production Animal Studies
+27 (0) 12 529 8257
bruce.gummow@up.ac.za
Giraffes
Researchers have made progress at unlocking some of the mysteries of giraffe biology. One such mystery, investigated over the last few years with the help of two excellent graduate students Dr Louis van Schalkwyk and Ian Bredin is how this leaf-eating giant’s skeleton supports its mass and gets the huge amount of calcium and phosphorus it needs.
This project is part of a larger project aimed at understanding the origin and evolution of giraffe, and how they have adapted to their extraordinary shape, a project started over twenty years ago by Proff John Skinner and Graham Mitchell.
The first giraffes originated over twenty million years ago in southern Spain, and over the course of their evolution migrated westwards into Asia and China (where the largest known giraffe existed until around four million years ago when climate and vegetation change killed them off), and southwards into Africa. Our familiar giraffe is the single survivor of the five or more species known to have inhabited Africa over the last six million years.
During their evolution they grew to their great height and developed their remarkable coat colours. Originally they probably had a coat colour similar to their nearest living relative the Okapi, which lives in the Ituri forest of the Congo.
The researchers have discovered that the coat colours are not just for camouflage, they are also places where the giraffes lose body heat. Their height depends on rapid elongation of their skeletons especially their lower legs and necks, and it is this aspect of their biology that is the current focus of the project.
In particular the group have analysed how the thin leg bones can support the large body mass, and why giraffes chew bones during the winter months, and when they are pregnant and lactating.
Bones are a potentially large source of calcium and phosphorus, so eating bones is a sensible strategy, and would be even more so if bones that are eaten are digested in the rumen. However bones do not seem to be digested in the rumen, so why they eat them, for the time being at least, must remain a mystery.
Hyaenas
A different aspect of bone research, namely the study of bone collection by two species of hyaenas, the brown Parahyaena brunnea and the spotted Crocuta, has confirmed differences between the two species.
Brown hyaenas are twenty kg lighter than spotted hyaenas. Being essentially scavengers, they consume seven kg of meat/bones at a time which is the capacity of their stomach.
They give birth to litters of up to six cubs and to cope with feeding large litters, carry pieces of carcasses back to the maternity dens. This results in an accumulation of bones at the maternity dens reflecting the faunal assemblage of the surrounding area at that time, a valuable assessment for archaeologists and palaeontologists.
On the other hand, the much larger spotted hyaena never have more than two cubs, they hunt and scavenge and can consume up to 35 kg of meat/bones at a sitting.
They turn the food consumed into a milk supply sufficient to satisfy two cubs, carry few pieces back to the maternity den and, when they do, these tend to be very large bones as smaller bones are crushed and eaten in their powerful jaws.
In the current project, 19 000 bone specimens have been logged into a hyena database. With the exception of 980 specimens from four spotted maternity dens in Botswana, the bulk come from six brown hyaena maternity dens from the Namib Desert in southern Namibia, confirming that brown hyaenas are prolific collectors of bones.
Prof JD Skinner
Production Animal Studies
+27 (0) 12 529 8393
john.skinner@up.ac.za
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