Parliamentary Research Branch

PRB 98-1E

THE IMPACT OF rbST ON HEALTH

Prepared by:
Frédéric Forge
Science and Technology Division
October 1998

The effects of rbST on human and animal health are still controversial. The following facts are generally accepted.

• Where the overall composition of milk is concerned (mineral, vitamin, protein and lactose content, for example), no difference has been observed between milk from rbST-treated cows and milk from untreated cows. Nor has a higher concentration of rbST been observed in the milk of rbST-treated cows. Thus the quantity of rbST contained in milk is the same whether or not the cows have been given rbST. Furthermore, most rbST is destroyed by pasteurization.

• In cows, rbST influences the production of Insulin-like Growth Factor 1 (IGF-1), a hormone occurring naturally in humans and cows’ milk. A slightly higher concentration of IGF-1 has been observed in the milk of rbST-treated cows. According to the 1992 conference of the Joint FAO-WHO Expert Committee on Food Additives, the higher concentration of IGF-1 in milk after rbST treatment is still within the range of concentrations among a test group of cows. However, according to the 1993 Monsanto submission in the United Kingdom, IGF-1 concentrations in the milk of rbST-treated cows could be five times higher than concentrations in the milk of untreated cows. Although IGF-1 is not destroyed by pasteurization, heating milk for the production of baby foods reduces its concentration by 50%; rbST and IGF-1 are both destroyed during yogurt production.

The following organizations have concluded that milk from cows treated with rbST in accordance with sound veterinary practices does not constitute a risk to human health:

• the United States National Institute of Health, in December 1990;

• the Joint FAO-WHO(1) Expert Committee on Food Additives, in February 1992;

• the Commission of the European Community, in January 1993;

• the Center for Veterinary Medicine of the United States Food and Drug Administration, in November 1993;

• the Joint FAO-WHO Expert Committee on Food Additives, in February 1998.

Also, the Human Safety Division (HSD) of Health Canada initially recommended that rbST be registered, judging that it did not constitute a risk to human health.

Nevertheless, some points are worth considering, particularly the activity of rbST and IGF-1 in the human body.

Some observers claim that rbST, like any other protein, is broken down in the digestive tract where, since it is specific to cattle, it is inactive in humans. It is also claimed that IGF-1 is broken down in the digestive tract and thereby becomes biologically inactive.

According to the Health Canada internal report entitled "rbST (Nutrilac) Gaps Analysis Report," dated 10 June 1998, however, the theory that neither rbST nor IGF-1 is biologically active when given orally does not appear accurate in all circumstances. A 90-day study on sub-chronic exposure in rats was submitted by Monsanto; it showed that, after high doses were given orally, rbST could be absorbed intact from the digestive tract and cause an immune response. The consequences of this observation have not been fully assessed by the HSD.

Also according to the Health Canada report, recent experimental data indicate that IGF-1 can survive in the digestive tract and be absorbed intact, particularly when ingested with milk proteins. The report asks that the local effects of IGF-1 residues present in the milk of rbST-treated cows be studied in greater depth and that the findings on IGF-1 submitted in February 1998 to the Joint FAO-WHO Expert Committee on Food Additives be verified among newborns.

In February 1998, the FAO-WHO Committee on Food Additives concluded that the higher concentration of IGF-1 in the milk of rbST-treated cows was in fact lower than the concentration found in the digestive tract and other parts of the human body. IGF-1 absorption after milk consumption should not increase IGF-1 concentration in the body or its organs, even if all the IGF-1 present in the milk is absorbed within the digestive tract.

The effects of the increased use of antibiotics for cows to counter the increased incidence of mastitis caused by rbST use are also a subject of concern (see the section entitled Animal Health). In February 1998, the Joint FAO-WHO Expert Committee on Food Additives studied the possible contamination of milk as a result of the increased incidence of mastitis and the resulting increased use of antibiotics for cows. It concluded that the use of rbST does not increase the risk to human health when antibiotics are used to treat mastitis, and that possible higher concentrations of antibiotic residues in milk can be managed using existing dairy industry practices.(2)

According to the Health Canada internal report, however, the apparent link between rbST use and increased incidence of mastitis (as pointed out on Monsanto’s product labels) could have effects on human health. The possibility of emerging resistance to antibiotics in pathogens transmissible to humans has not been studied.

The Health Canada study continues. At present, two groups of experts, one with respect to animal health, under the auspices of the Canadian Veterinary Medicine Association and the other, with respect to human health, under the auspices of the Royal College of Physicians and Surgeons of Canada, are assessing rbST. Their assessment will be part of the decision-making process.

The most important negative effect on the health of rbST-treated animals is the possibility of increased incidence of mastitis.(3)

A number of factors can promote mastitis: lactation, the environment, the herd, the season and so on. Studies have shown that there is a connection between the level of milk production and the incidence of mastitis, whether or not the cattle have been treated with rbST. Since rbST-treated cows produce more milk, it has been suggested that the increased incidence of mastitis could be due to this higher level of production, rather than to the hormone treatment.

It is difficult to determine the role of the rbST treatment in the increased incidence of mastitis. In the United States, the Food and Drug Administration (FDA)(4) has concluded that the use of PosilacÒ (the rbST-based product marketed by Monsanto) is not biologically significant in the incidence of mastitis per unit of milk produced since, when compared with mastitis caused by other major factors, the effects of rbST were not great. On the other hand, the European Union Committee on Veterinary Medications has concluded that classical statistical techniques do not allow us to conclude that the rbST treatment has no direct impact on the incidence of mastitis.

Monsanto does acknowledge that the use of rbST can increase the risk of mastitis but points out that other factors, which can be managed, may also play a role. The product label carries a message recommending that farmers assess their mastitis-prevention practices before using the product.

On the other hand, in a study published in 1997, the Virginia Polytechnic Institute and State University questioned the method used by the FDA to assess the impact of rbST on the incidence of mastitis. The University stated that the findings of the FDA contradicted the results analyzed in this study and suggested that the labelling indicating that good management practices were effective in preventing mastitis should be reviewed. The University study also noted the weakness of certain conclusions in the scientific literature used to assess the effect of rbST on the incidence of mastitis in the United States. This effect is therefore still open to discussion.

Where other effects of rbST on animal health are concerned, Monsanto’s proposed product label indicates a number of undesirable effects including digestive problems, lameness and other foot problems, and reproductive problems. These effects were confirmed by the Health Canada internal report dated 10 June 1998, which concludes that the first assessments of the risks of rbST to cows, although of poor quality, indicate that rbST can have results including congenital defects, reproductive problems, and increased incidence of lameness.

(2) Each Canadian province has monitoring programs. Before a producer's milk is pooled, it must be certified free of antibiotic residues.

(3) Mastitis is an inflammation of the teat.

(4) In the United States, the FDA is responsible, among other things, for assessing and approving veterinary products for animals intended for use as food.