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Transgenic goats engineered to secrete the human protein cholinesterase into their milk produced less milk, with lower fat and lactose levels and unusually high white blood cell counts.

Manipulated Organism: Goat (Capra aegagrus).

Inserted Transgenes: Human butyryl-cholinesterase gene, which produces a protein with pharmaceutical applications. Gene expression was controlled by the promoter for goat beta-casein (a milk protein).

Goal of These Studies: Compare the lactation of goats expressing the transgenic protein with half-siblings that do not contain the transgene.

Intended Effect: High levels of the transgenic protein (1 to 5 g/L) were produced in the goat milk.

Unintended Effects:
  • Milk production in the GM goats began to deteriorate in both quantity and quality beginning in the second week of lactation. Over the course of the 70-day study, the average daily milk production of the transgenic goats was only half that of the non-GM goats (0.9 versus 1.9 kg/day).

  • After one week of milk production, the amount of fat in the transgenic goat milk dropped from 4-5% to 1-2% and remained at that level, while the non-GM goats continued to produce milk with 5% fat for another four weeks.

  • The lactose content of the GM goat milk began to steadily decline after three weeks of milking, but the non-GM goat milk lactose concentration remained constant.

  • As lactation progressed, the amount of sodium in the GM milk increased while the potassium concentration decreased. Because milk is enriched in potassium and impoverished in sodium relative to the interstitial spaces of the mammary gland, these changes indicated a deterioration of the membrane that separates the milk space from the interior of the mammary gland.

  • Unusually large numbers of white blood cells were detected in the GM goat milk, and this problem increased over time. Although high cell counts normally indicate a mammary gland infection (mastitis), physical examination of the udder and bacterial testing of the milk revealed no indication of an infection.

Source: Baldarasse, H., D. K. Hockley, M. Dore, E. Brochu et al. (2008). "Lactation Performance of Transgenic Goats Expressing Recombinant Human Butyryl-Cholinesterase in the Milk," Transgenic Research vol. 17, pp. 73-84.

Author Affiliations: PharmAthene Inc., Montreal, Canada; University of Montreal, Canada; McGill University, Canada.

Funding: Not mentioned.

Product Status: Not on the market as of 2009.

Copyright 2009 The Nature Institute.

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