Cattle losses due to bloat, particularly ‘frothy bloat’, are generally associated with lush legume pastures and more productive seasons. This paper describes three cases of mortalities in beef cattle investigated across the Forbes region in the drought year of 2019 where a diagnosis of ‘bloat’ was made. Two of the cases were attributed to ‘frothy bloat’, and losses in the third case were due to ‘feedlot bloat’.
In the first case, a producer rang in May to request an investigation into cattle deaths on a local property. He was confident that the animals had died from bloat but required veterinary confirmation. Nine hundred and forty weaners had been moved late the afternoon before, from lucerne, into a paddock where vetch from the previous year’s crop had emerged. They had been checked that morning at 7.30am, but by 8.30am five animals were dead and a number of others were visibly bloating.
The bloat diagnosis was straightforward. A deceased animal with a hugely distended and drum tight abdomen was examined. The eyes were slightly bulging and the tongue protruded from the mouth. There was anterior venous congestion, and the massively distended rumen had caused extreme compression of the thoracic cavity. The rumen contained a huge volume of very lush green, foamy ingesta to confirm ‘frothy bloat’. There was no clear ‘bloat line’, although there was subtle blanching of the thoracic oesophagus.
The paddock was inspected, and while some very short clover was also present, the vetch (variety unknown) at 10-15cm high was in the majority and overgrowing the clover, and most likely to be the cause.
In case number two, a producer reported sudden death in four unweaned calves being managed in a drought lot in late November. The 115 cows with their calves were being fed a ration of barley and cattle pellets in commercial feeders, with barley stubble in hay rings. There was negligible pasture available, and both bore and dam water were supplied. The calves had not yet been marked or vaccinated. The deaths had been sporadic over the last week, and the owner had just found the fourth one.
On inspection the carcase appeared freshly deceased and was notably distended. Blood had oozed from the eye and anus, but was dried and clotted. An anthrax ICT test kit yielded a negative result so a post-mortem was conducted.
Subcutaneous emphysema was present on the uppermost side, and there was significant anterior venous congestion. The rumen was large and gas filled, and a tear was apparent on the medial surface, likely to have occurred at or soon after death.The rumen was well developed and contained lush green ingesta, with frothy bubbles present in a stable foam. The liver was slightly pale and had subtle rib imprints on its surface. Although there was no distinct 'bloat line', there was a slight change in colouration of the oesophagus to indicate congestion of the extra-thoracic portion.
The owner had recently noticed the odd calf squeezing through a gap in the fence into a small adjacent paddock of marginal lucerne. Two weeks prior there had been a minor rain event with 13mm rainfall recorded, which had ‘slightly’ freshened up the lucerne stand. This rain event appeared to stimulate enough growth to cause a problem for these calves, and after repairing the fence to prevent access no further losses occurred.
In the third case, a producer rang in December following two unexpected deaths out of a group of 20 calves being yard weaned. Weaning had commenced ten days prior. Pellets were available in a commercial feeder and there was wheaten hay in a rack, as had been used for the cows and calves when out in the paddock. One animal had died suddenly two nights earlier, and the second was found deceased that morning. These calves were two of the biggest three of the group.
The second deceased calf had severe abdominal distension, and on opening the carcase significant anterior congestion was evident. The diaphragm had ruptured and there was cranial displacement of the thoracic organs by the large, distended rumen. The liver was pale and tan in colour. The rumen contained a large amount of moderately dry ingesta - mostly digested pellets with some roughage. A particularly distinct 'bloat line' was also present in the oesophagus.
The drought of 2019 has been very significant in the Forbes district, however isolated rain events have occurred in some areas, allowing variable pasture growth at times, across a locality, a single property, or even just a paddock or two.
The property in the first case had received decent rainfall earlier in the year to allow reasonable germination of vetch seed and good early plant growth. While vetch is a legume, it is not usually considered particularly high risk for bloat when compared to other legumes such as clover and lucerne, but clearly proved to be an issue for these cattle. On the second property, a minimal rain event provided enough fresh growth on drought-affected lucerne to cause the loss of four calves.
The third case of bloat was attributed to ‘feedlot bloat’, the type we are much more likely to see in times of drought, when cattle are mostly maintained on grain diets with low to no roughage provided. It is related to the rumen micro-organism imbalance associated with grain feeding and consequent proliferation of certain types of bacteria. This effect is exacerbated when the ration contains a large amount of fine grounds. Some of these bacteria species produce mucopolysaccharides, or slime, which increase the viscosity of rumen fluid and can create a stabilise foam, inhibiting eructation. Low rumen pH can also impair rumen motility and further contribute to problems with eructation. In the animal examined the rumen was distended mostly with ingesta, rather than fluid and gas or bubbles. Foam was not present, although may have dispersed since death. Two of the larger calves of the group had been affected, so it is likely that bullying behaviour at the feeder, leading to overeating and subclinical acidosis also contributed to the mortality.