PIRSA was informed in early May 2010 about suspicious deaths in calves that had been occurring over a period of time on the Fleurieu peninsula, possibly associated with feeding milk containing Bronopol preservative.
Bronopol (“Acticide L” tradename - 2-bromo-2-nitro-propane-1,3-diol) is a commonly used preservative in milk that is added to fresh milk prior to storage and testing for a range of production parameters. In some large testing facilities, after the milk has been tested, it is collected by farmers who feed it to livestock, typically young calves or pigs.
This report describes a case of possible Acticide poisoning that occurred in the Fleurieu peninsula in early 2010.
Approximately 2 yrs ago, some calves owned by a farmer who collected waste milk containing Bronopol started getting sick, staggery & dying. The farmer "lost a few" over a period of time, and stopped receiving the milk. Two other farmers then started getting the milk and10 of 30 calves died with similar symptoms.
In early May 2010 a worker at a milk processing facility took some milk (containing Bronopol at recommended rates) home to feed some calves and the next day three 3 week old calves were dead and older calves around 4-6 weeks were affected (scours & staggery), but survived. A local Veterinarian, Dr Simon Edwards, investigated on 29/4/2010 & submitted some samples from a PM of a calf. A range of cultures and tests were performed on the samples, with no conclusive results or diagnosis. Histopathology indicated a toxic enteritis or “toxic shock” syndrome in the small intestine. Unfortunately no milk samples of that batch were stored, but other samples were collected and frozen at the factory.
At the time, milk was removed by a waste disposal company, and the factory was keen to have the problem investigated and resolved.
Bronopol was used in sister factories in Vic & NSW (the same compound- ACTICIDE L) with apparently no problems, and fed to local calves.
The symptoms appearing in affected calves, as reported, appeared to be ataxia and sudden death, sometimes associated with diarrhea. Some of these cases may have involved other agents, for example Salmonella spp, but experienced farmers noted that losses ceased when the milk containing Bronopol was removed. The last case involved sudden death of apparently healthy calves overnight, following one exposure to the milk. In this case, three 3 week old calves were found dead in the morning and 5 other calves of varying ages from 7-9 weeks of age were scouring, and staggery. The older calves appeared less affected than younger ones and all affected live calves recovered after a few days. No more milk containing the preservative was given to the calves.
Since the only management factor to change in this event was feeding milk containing the preservative, an investigation was commenced into the toxicity of Bronopol fed to calves.
A number of samples were tested from both the dead and scouring calves, and no significant pathogens were detected. Following this, frozen samples of milk that had been treated as normal and contained ACTICIDE L (98% Bronopol) at recommended mixing concentrations were tested.
The preservative solution is mixed by adding of 1.5kg of ACTICIDE L per 10 L ( 150gm /L) of warm water, then diluted to 1mL per 200mL milk, giving a solution of 0.75gm/L. The samples tested contained 0.15% or (1.5gm/L) Bronopol.
Based on the manufacturer's recommendations of 0.01% to 0.1%, tested samples of milk contained higher than the recommended amount of preservative.
However, these recommendations are for preservation of industrial and personal care products, not for food stuff for consumption. In the EU maximum recommendation is 0.02% for use in oral personal care products for human use.
There does not appear to be any studies in the literature documenting toxicity in ruminants, or young ruminants. The majority of studies appear to use laboratory species of rats, dogs and rabbits as experimental animals and the toxicology of Bronopol describes an oral LD50 of 254mg/kg for rats, although higher doses are reported as safe in rats (Bryce, Croshaw et al., 1978)
Calves younger than 6 weeks of age may be more sensitive to bronopol than older calves - as appears to have occurred in this case - and ruminant species may be more sensitive than other species by oral ingestion.
Based on the oral LD50 for rats, a 50kg calf would need to consume 12.7gm bronopol to reach the level at which 50% would be expected to die. (254mg x 50kg). However a 30kg calf might need only 7.6gm.
If milk contains 0.15% bronopol (1.5gm/L), then a 50kg calf would need to consume 12.7/1.5 = 8.5L of milk for toxicity to occur, based on LD50 for rats, or 5L for a 30kg calf.
The amount of milk consumed individually by the calves in this case is unknown, but may have been around 4-6 L, thus a small calf may have been able to consume a toxic amount, based on rat studies.
Contact was made with 3 other factories that also use Bronopol as a preservative in milk samples, to compare dilution rates and to survey any effects in livestock. Results are shown in the table below. The dilution rates are described as kg/ 20L as this is the common method of measuring and diluting this compound in practice.
|Factory 1||4kgs in 20L (200gm/L diluted 1ml in 200ml milk)||Only fed to pigs- no problems observed|
|Factory 2||2.4 - 3.2 kg in 20L||Diluted when fed to calves, occasional symptoms in some calves|
|Factory 3||3kg in 20L||Lost calves with a stronger solution previously|
In summary, it appears that industry standards vary, and solutions of 2.4kg (winter) to 4kgs , or 120gm /L to 200gm /L mixed in 200ml milk are being used, and some deaths in calves have been observed, but none in pigs.
One farmer reported that the milk containing Bronopol is diluted when fed to calves initially, for about 3 weeks. Any calves with symptoms are taken off the milk and fed powdered milk until recovered, then slowly reintroduced to the milk.
Caution should be used when feeding milk containing Bronopol to calves younger than 6 weeks
When feeding to young calves the milk should be diluted 50% with normal or powdered milk for a transition period of 2 to 3 weeks
Calves should be carefully monitored in the first week of feeding the compound, and if any symptoms seen, removed from the source and fed another source of milk until recovered. Calves should then be slowly introduced back to the milk using only diluted sources.
Factories could consider lowering the concentrations of Bronopol preservative in the milk, and this may vary according to season. It may be that a considerably lower concentration may still provide the required preservation of milk.
Manufacturers of Acticide L could consider trials to investigate the required minimum concentration of Bronopol in milk to achieve the necessary preservative function.
Scales measuring the Bronopol powder should be regularly checked.
Farmers receiving milk containing Bronopol should be given written recommendations for use.
This case was referred to PIRSA by a local veterinarian puzzled by a syndrome of sudden death in some calves for which no satisfactory diagnosis could be made. Government veterinary officers have an opportunity to assist practitioners in investigations where aetiology may be complex and require a lot of detailed and time consuming enquiry. This has the benefit of providing a satisfactory diagnosis to clients and vets, and feedback to Industry about possible adverse effects of products in some cases. A copy of this report was sent to the manufacturing source, the milk testing facility, affected producers and the private veterinarian.