Long term cow feeding study with Bt corn

Citation:

Steinke K, Guertler P, Paul V, Wiedemann S, Ettle T, Albrecht C, Meyer HH, Spiekers H, Schwarz FJ. Effects of long-term feeding of genetically modified corn (event MON810) on the performance of lactating dairy cows. J Anim Physiol Anim Nutr (Berl). 2010 Jun 22 [Epub ahead of print]. PMID: 20579187

Content Summary

The goal of this study was to "evaluate the effect of Bt-corn on feed intake, milk production, milk composition and body condition in lactating dairy cows" compared to genetically similar non-Bt corn over a 25 month period.

The two corn types were grown under the same conditions in the same location in Germany. The feed was designed to maximize the amount of Bt protein that the cows would consume. Previous experiments have shown that certain types of processing can degrade the Bt protein, so the corn was processed immediately after harvest at low heat levels. Feed included silage as well as kernels, because leaves and cobs contain more Bt protein than kernels. The amount of corn in the feed was at the maximum recommended by the EFSA GMO Panel Working Group on Animal Feeding Trials. The components of the food was analyzed regularly during the study. The researchers found that the components of the two feed types were similar throughout the experiment, indicating compositional equivalence between Bt corn and the genetically similar non-Bt corn.

Eighteen genetically similar cows were in the two feeding groups for a total of thirty six cows, but nine cows in each group were removed from the study and replaced with different (but genetically similar) cows due to illness or infertility. Most of the cows experienced two full lactations during the 25 month feeding study, but some of the replacement cows were already lactating when they entered the study. The cows were milked twice daily and the milk yield was measured each week on two consecutive days. On days that milk yield was measured, milk samples were analyzed for fat, protein, lactose, urea, and cell count. The cows' body weight, body condition score, and backfat was measured on those days as well. Milk yield was similar in both groups during the first and second lactation, as shown in Figure 2, below.

Food was available ad libitium for both groups, meaning that the cows were able to eat as much feed as they wanted during the study, and the amount that each cow ate was recorded daily. Each week, a sample of the Bt-corn feed was analyzed for Bt protein content, and the Bt protein intake per cow was calculated based on their daily feed intake. The average Bt protein intake for the Bt group of cows was 6.0 mg for the first lactation and 6.1 mg for the second lactation and was consistent throughout the trial. The cows' food intake was the same for both groups during the first and second lactation, as shown in Figure 1, below. On average, the cows in the non-Bt and Bt feeding groups ate 18.7 vs 18.9 kg / day during the first lactation and 21.0 vs 20.4 kg/day during the second lactation.

There were some differences in milk composition and body condition between the Bt and non-Bt groups. During the first lactation, the Bt group had significantly higher milk fat, protein, and urea concentrations while other measurements were not significantly different. During the second lactation, the Bt group had significantly lower lactose concentrations and higher body weight, body condition scores, and backfat thickness while other measurements were not significantly different. All of these measurements within both groups during both lactations fall within normal levels and the differences were small, as shown in Figure 3, below, for milk fat and protein.

The researchers conclude that there are no consistent effects of feeding MON810 Bt corn to dairy cows. The Bt corn and non-Bt corn are compositionally and nutritionally equivalent and have equivalent effects on the performance of dairy cows.

Impact Summary

The Journal of Animal Physiology and Animal Nutrition is ranked 18 / 49 in Agriculture, Dairy & Animal Science and 44 / 141 in Veterinary Sciences. Its impact factor is 1.229, according to ISI Journal Citation Reports in 2009. This article has not been cited as of 29 June 2010.

Abstract

A long-term study over 25 months was conducted to evaluate the effects of genetically modified corn on performance of lactating dairy cows. Thirty-six dairy cows were assigned to two feeding groups and fed with diets based on whole-crop silage, kernels and whole-crop cobs from Bt-corn (Bt-MON810) or its isogenic not genetically modified counterpart (CON) as main components. The study included two consecutive lactations. There were no differences in the chemical composition and estimated net energy content of Bt-MON810 and CON corn components and diets. CON feed samples were negative for the presence of Cry1Ab protein, while in Bt-MON810 feed samples the Cry1Ab protein was detected. Cows fed Bt-MON810 corn had a daily Cry1Ab protein intake of 6.0 mg in the first lactation and 6.1 mg in the second lactation of the trial. Dry matter intake (DMI) was 18.8 and 20.7 kg/cow per day in the first and the second lactation of the trial, with no treatment differences. Similarly, milk yield (23.8 and 29.0 kg/cow per day in the first and the second lactation of the trial) was not affected by dietary treatment. There were no consistent effects of feeding MON810 or its isogenic CON on milk composition or body condition. Thus, the present long-term study demonstrated the compositional and nutritional equivalence of Bt-MON810 and its isogenic CON.