More Information on Animal Performance

Companies and independent academic scientists have completed dozens of animal performance studies, many of which have been published, on a wide variety of species including beef and dairy cattle, broiler and layer chickens, swine, sheep and catfish. Below is a summary of the results of these published studies.

Animal performance studies are designed to demonstrate whether or not feed from transgenic crops is nutritionally equivalent to feed from non-transgenic crops by measuring growth traits such as feed intake, body weight gain and feed efficiency of the animals that consume the feed. Any unintended health effects would also be observed if they occur. The U.S. and several international regulatory agencies now require a wild or domesticated fowl growth study for regulatory approval. Additional studies with other species are conducted voluntarily to provide the livestock industry with information on the nutritional quality of transgenic crops. Unexpected changes in nutritional quality and safety are assessed through sensitive biochemical tests when the regulatory agencies determine whether or not a crop is substantially equivalent to its non-transgenic counterpart.

Transgenic and conventional corn, soybeans, canola and sugar beets have been compared in feeding studies to assess animal performance, and no differences have been found in feed derived from transgenic and non-transgenic crops. These feeding studies support the claim that feed derived from transgenic grain can be considered substantially equivalent to feed derived from non-transgenic grain.

In reviewing the animal feeding studies, the focus will be on corn and soybeans because they make up the main ingredients in most livestock rations. Specifically discussed are studies involving transgenic corn containing a gene from Bacillus thuringiensis (Bt), which protects the corn from the European corn borer and transgenic soybeans that are tolerant to the herbicide glyphosate.

Transgenic Corn

In a five-day study, Aulrich et al. (1998) fed Bt and non-Bt corn grain to laying hens and measured no differences in nutrient composition, body weight, digestible organic matter and protein as well as energy available for metabolism. Brake and Vlachos (1998) conducted a 38-day broiler study comparing Bt and non-Bt corn and measured no differences in mortality, body weight, or feed intake while measuring an improvement (p<0.05) in feed conversion. Carcass data did not differ between groups with one exception; breast meat yield was higher (P<0.05) in broilers fed Bt corn. However, slight differences in overall composition of the diets may have been the cause for these improvements with the Bt corn. In a third study, Halle et al. (1998) fed Bt and non-Bt corn to broilers for 35 days and found no differences in body weight gain, feed intake, feed conversion or protein digestibility. Mireles et al. (2000) conducted two studies to compare nutrient composition and availability in Bt and non-Bt corn. The first study measured true metabolizable energy (TME) and amino acid digestibility and found no difference between the two corn sources. The second study was designed to measure the performance of broiler chickens fed starter feeds. No differences in weight gain and feed efficiency were seen in chickens fed Bt or non-Bt corn. Finally, Sidhu et al. (2000) found no difference in growth, feed efficiency and fat pad weight between broilers fed diets containing glyphosate-tolerant corn and diets containing conventional corn.

Faust and Miller (1997) fed green chop from Bt or non-Bt corn to lactating cows for 14 days. No differences were measured in feed intake, milk yield, milk composition or udder health. Mayer and Rutzmoser (1999) fed cows diets containing either Bt or non-Bt corn silage with grass silage and supplement in a five-week crossover test. They found no differences in food intake, milk production and milk composition (fat, protein, lactose, urea).

Folmer et al. (2000b) utilized a 4 X 4 Latin square design to compare the lactational performance and ruminal fermentation parameters of cows fed one of four balanced diets containing Bt or non-Bt corn silage from either early maturity or late maturity hybrids. No differences were measured between Bt and non-Bt diets at either maturity for milk production, milk composition or rumen fermentation characteristics (in-situ fiber digestibility, rumen volatile fatty acid [VFA] concentration and rumen pH). The animals fed early maturity hybrids (Bt and non-Bt) had improved (P<0.005)   total rumen VFA and efficiency of production when compared to later maturity hybrids (Bt and non-Bt).

Donkin et al. (2000) fed lactating dairy cows either glyphosate tolerant and non-glyphosate tolerant corn silage and corn grain in identical mixed rations. They found no differences in dry matter intake, milk production, milk protein yield, lactose yield or milk fat yield between the two treatment groups. Likewise, no differences were found in milk composition as measured by percentage of fat, protein, lactose and non-fat solids; somatic cell count; and milk urea nitrogen.

A common practice is to graze cornfields after harvest with animals that have a lower nutrient requirement such as beef cows. Cows are turned out to graze the stalks and leaves that are left in the field after the combine has harvested the corn grain. Another practice is to harvest and precision chop the entire corn plant and store the chopped forage in a large silo that is relatively air-free. Over the period of a couple of weeks, the forage ferments resulting in the production of lactic acid, which preserves the forage as silage for future use.

Animal performance of beef cows grazing Bt or non-Bt corn crop residue was compared over a two-year period (Russell et al., 2000; Russell et al. 1999). There was no difference in animal performance in either year of the two-year study.

Two trials were conducted to evaluate the use of corn silage and corn residue by Folmer et al. (2000). An absence of significant European corn borer pressure resulted in similar grain yield and residue corn between Bt and non-Bt corn. In trial 1, 23 acres of Bt corn residue and 21 acres of non-Bt were divided into 3 pastures each and stocked with eight or nine steers per pasture to result in equal stocking rates. Average daily gain (avg. 0.28 kg/d) was similar between both corn sources. In addition, 16 steers were allowed access to either seven acres of Bt or non-Bt corn residue. No preference was show for grazing either field.

In trial 2, 128 steers were fed silage diets containing either Bt or non-Bt versions of two hybrids as corn silage at a 90% inclusion rate with 10% supplement. The steers were fed in a 2 x 2 factorial design and performance parameters were measured. Dry matter intake was higher (P<0 .05) for steers fed Bt than non-Bt corn silage (8.61 vs. 8.32 kg/d respectively). An interaction (P< 0.05) was observed between genotype and the Bt trait for daily gain and feed efficiency. For hybrid A, steers receiving the Bt version had improved daily gain over those receiving the non-Bt version. For hybrid B, there was no significant difference in daily gain between the steers fed the Bt vs. the non-Bt version. Steers fed both versions of hybrid A had improved (P< 0.05) feed efficiency when fed the Bt version than when fed the non-Bt version. No differences were measured in feed efficiency between steers fed the Bt and the non-Bt versions of hybrid B. Improved (P< 0.01) daily gain and feed efficiency were measured for steers fed hybrid B compared to hybrid A, although an interaction was present. The authors concluded that while hybrid genotype appeared to affect performance, there was no consistent effect on performance of growing steers due to the presence of the Bt trait.

Daenicke et al. (1999) compared the digestibility and animal performance of sheep and growing bull calves that were fed Bt corn silage or non-Bt corn silage. There were no differences in the digestibility of organic matter, fat, fiber or nitrogen free extract. Likewise, there were no differences in intake, body weight gain, feed conversion, hot carcass weight, dressing percentage and abdominal fat.

The feeding value of whole plant corn silage and crop residues over a two-year period was compared between Bt and non-Bt corn by Hendrix et al. (2000). Three studies were conducted each year: 1) performance of steer calves fed corn silage, 2) performance of beef cows grazing corn residue and 3) grazing pattern of beef cows when given a choice between Bt and non-Bt residue. There were no differences between steers fed the two corns silage sources for average daily gain or dry matter intake. Feed/gain was greater (P<0.05) for Bt vs. non-Bt corn silage. There was no difference in weight change between cows grazing the Bt and non-Bt residues. Over the entire observation period, no differences were measured in preference for one corn residue over the other between grazing cows.

In another study conducted by Russell et al. (2000), the nutritive value of the crop residues from Bt and non-Bt corn hybrids and their effects on performance of grazing beef cows was studied. No differences were measured between the residues from Bt and non-Bt residues for dry matter or organic matter composition. Over the grazing season, no differences were measured between residues for rates of change of residue composition.

In further work, Russell et al. (2001) studied the effects of grazing crop residues from Bt-corn hybrids on the performance of pregnant beef cows. Four hybrids planted on duplicate fields were utilized in the study that was conducted over 2 consecutive years. One hybrid was non-Bt while three hybrids contained the Bt gene from two different sources. Thirty Angus x Charolais x Simmental cows in midgestation were allotted between to two drylots or the eight crop residue fields to strip-graze for 126 days. Biweekly visually estimated body scores were taken with dry alfalfa hay supplemented to maintain a mean body condition score of 5 out of a 9-point scale. Crop residue yields were determined monthly from a 4 square-meter location in each grazed and ungrazed area paddock. On two consecutive days following 2 weeks of grazing, forage selected during a two-hour grazing period by one fistulated steer per field or drylot was harvested from via the rumen cannulae. Dry matter intake (DMI) was calculated from the digestibility of the forage and the fecal output in two cows per field or drylot during the same 2-day period. There were no effects on yields of harvested grain, dropped ears or grain, residue dry matter (DM) or organic matter (OM) over the 2 years. At grazing initiation, in-vitro organic matter digestibility (IVOMD) as well as acid detergent fiber (ADF) and acid detergent lignin (ADL) differed (P<0.05) by base genetics but not by Bt vs. non-Bt hybrids. Rates of change in NDF, ADF, ADL, crude protein (CP) and IVOMD over winter did not differ between hybrids. There were also no differences between hybrids for intakes of forage digestible OM, NDF and ADF. No differences were seen in the amount of hay required to maintain body condition score between hybrids.

Kerley et al. (2001) compared Bt and non-Bt corn fed to beef steers for the last 49 days of the finishing period. Thirty-six crossbred steers were allotted to six pens and fed a 75% corn diet. Growth performance and carcass parameters were measured. There were no differences in corn composition, average daily gain, feed efficiency, yield grade or quality grade between Bt and non-Bt corn hybrids.

Petty et al. (2001) compared Bt vs. isogenic non-Bt corn fed as whole plant silage (WPS) and dry rolled grain over a two-year period. Each year corn was grown under isolation and harvested as grain and WPS. A feeding study was performed each year utilizing 56 Angus and Simmental sired steers, blocked and randomly allotted by weight and breed type one month postweaning into eight pens of seven steers each. Growing diets comprised primarily of WPS were fed for 89 and 85 days in years 1 and 2 respectively and were followed by finishing diets comprised of 75% dry rolled corn, 15% WPS and 10% supplement for 101 and 84 days in years 1 and 2 respectively. During the grower phase in year one, there were no differences (P>0.05) in average daily gain or dry matter intake but feed efficiency was improved (P<0.05) for the steers fed non-Bt corn, however this difference was not measured in year 2. There were no differences (P>0.05) in average daily gain, dry matter intake or feed efficiency during the finishing phase for either year. Steers were harvested each year when they were estimated to be 75% USDA choice as a group. There were no differences (P>0.05) in carcass characteristics in either year. The investigators summarized that there were no major differences in the feeding value of the Bt-corn compared to its isogenic counterpart.

Petty et al. (2001) also evaluated herbicide resistant and non-herbicide resistant corn fed as whole plant silage (WPS) and dry rolled grain. A total of 56 Angus and Simmental sired steers were blocked and randomly allotted to treatments by weight and breed type. The grower diet of 90% WPS and 10% supplement was fed for 85 days followed by the finishing diet comprised of 75% WPS, 15% dry rolled corn and 10% supplement for 84 days. Average daily gain, dry matter intake and feed efficiency were not different (P>.05) during the grower phase, the finishing phase or over the total duration of the feeding study. Steers were harvested when it was estimated that 75% of the steers would grade USDA choice. There were no differences (P>.05) in carcass characteristics.

Weber et al. (2000) compared grower-finisher performance and carcass characteristics from pigs fed Bt corn, the non-Bt isogenic counterpart or commodity-sourced (CS) corn. For animal performance, no differences were found in average daily gain, average feed intake, or feed efficiency between pigs fed any of the three corn varieties. Pigs fed Bt and non-Bt corn did not differ in carcass weight; however, pigs fed CS corn had heavier carcass weights and higher dressing percentages than the other two groups (P<0.05). Pigs fed the non-Bt isogenic control had smaller lean percentages and greater backfat depth at the 10th rib and P2 location than pigs fed diets containing Bt or the CS corn (P<0.05). Pigs fed the non-Bt corn had greater backfat depth at the last lumbar vertebrae than pigs fed CS corn (P<0.05). Marbling scores were highest for pigs fed Bt and non-Bt corn (P<0.05). The researchers concluded that Bt corn had no adverse effects on swine growth performance or carcass characteristics.

Herbicide tolerant and non-herbicide tolerant corn were compared in swine metabolism studies by Böhme and Aulrich (1999). The results showed no differences in protein digestibility, nitrogen free extract (NFE) digestibility or metabolizable energy (ME).

In studies designed to simulate digestion in the lower intestine, Faust (1999) compared in-vitro digestibility between corn silage derived from Bt and non-Bt corn that were ensiled at two different stages of maturity. No differences were measured in true digestibility or the digestibility of cell walls or dry matter regardless of stage of maturity.

Russell et al. (2000b) studied the nutritive value of the crop residues from Bt and non-Bt corn hybrids. No differences were measured between the residues from Bt and non-Bt residues for dry matter, organic matter composition or in-vitro digestible dry matter. Over the grazing season, no differences were measured between residues for rates of change of residue composition. The researchers also compared the performance of grazing beef cows and found no differences in the in-vitro organic matter digestibility of Bt and non-Bt residues selected by steers.

Hammond et al. (1996) reported results from feeding trials comparing soybean meal derived from glyphosate-tolerant soybeans and soybean meal from the conventional counterpart in broilers, catfish and dairy cows. No differences were measured in feed intake, body weight gain, feed efficiency, breast meat composition and fat pad thickness in broilers. Catfish fed diets comparing both soybean meals exhibited no differences in weight gain, feed efficiency or meat composition. Finally, no differences were measured in feed intake, milk yield, milk composition, dry matter digestibility, and rumen fermentation end products between dairy cows fed diets containing either soybean meal.