Developments on the Enviropig File

C.W. Forsberg and colleagues in the Department of Molecular and Cellular Biology at the University of Guelph report on progress breeding pigs that secrete the enzyme, phytase, in their saliva and thus require supplements of neither inorganic phosphorus nor phytase. The results - in terms of physical and financial performance and manure phosphorus - are promising, they told delegates to the 28th Centralia Swine Research Update.

17 June 2009

5 minute read

The Cassie line of Enviropig^TM is a transgenic line of pigs that secrete phytase enzyme in the saliva. This unique trait enables the pigs to digest plant phosphorus more efficiently than conventional pigs. Therefore, it is unnecessary to include either supplemental phosphorus or phytase in the diet. In growing Cassie pigs, there is up to a 60 per cent reduction of phosphorus in the manure compared to age and gender matched conventional Yorkshire pigs. The trait is inherited in a Mendelian fashion through seven generations without loss in salivary phytase activity. Seventh generation Cassie finisher barrows retained 35 per cent more cereal grain phosphorus than conventional Yorkshire barrows receiving 750 units of phytase per kilo of feed.

Tissue analysis of third generation Cassie and conventional University of Guelph Yorkshire pigs maintained at the Arkell Swine facility demonstrated similar compositions. To assess the health of the pigs we have analyzed hematology, clinical chemistry and urology. These data for third, sixth and seventh generation pigs did not revealed any substantive differences, except improved phosphorus retention by the Cassie pigs.

A submission has been made to the Food and Drug Administration (FDA) in the United States under the New Animal Drug legislation to obtain regulatory approval of Cassie pigs for human food consumption. At this time over 2000 pages of data has been submitted covering aspects including, development of the Cassie pigs, location and DNA sequence of the phytase transgene in the genome, stability of the phytase transgene through generations, meat cuts and tissue composition, lack of allergenicity and toxicity of the novel phytase, swine health and performance. Several components of the submission have been reviewed and approved. If clearance were obtained this would permit both production and sale of Cassie pigs in the United States. A similar application is in preparation for the Canadian Regulatory Authorities including Health Canada, Canadian Food Inspection Agency and Environment Canada.

The objective of this report is to present data on the growth and conformation of Cassie pigs through the second to seventh generation assessed on a yearly basis by the Sire Line Index (SLI). The numbers of pigs used are listed in Table 1, and this included all Cassie pigs raised to maturity. The SLI is an estimate of the economic breeding value of a pig and a higher number indicates a more valuable pig. The SLI is calculated by an algorithm using the Estimated Breeding Values (EBVs) for age (days to reach 110 kg), lean muscle yield, loin eye area and feed conversion ratio (FCR).

Cassie pigs were fed a cereal grain diet without supplemental phosphorus or added phytase. At Arkell Swine the conventional Yorkshire pigs were fed a similar diet but with a combination of added phosphorus and phytase, except for finisher phase conventional pigs that were fed a diet with phytase in the place of supplemental phosphorus.

The authors comment that although they do not have information on the diets of Canadian breeder pigs, they would be similar to the conventional Arkell Swine diets.

Table 1. Numbers of pigs including males and females used to derive SLI and adjusted breeding values for each year from 2000 to 2007
Year	2000	2001	2002	2003	2004	2005	2006	2007
Cassie Hemizygotes	2	-	-	16	23	70	49	21
Cassie Homozygotes	-	-	-	-	9	2	3	5
Arkell Yorkshire	1,842	438	845	520	466	495	759	1057
Canadian Yorkshire	44,465	40,030	41,597	41,821	38,609	42,018	48,455	-

The Sire Line Index (SLI) of the Cassie hemizygous pigs was on average 20 per cent higher than that of the conventional pigs in the Arkell breeding herd during 2004 to 2007, and 26 per cent higher than that of Canadian Yorkshire breeding pigs during 2004 to 2006 (Figure. 1). The SLIs were significantly higher for the Cassie hemizygous pigs in 2004, 2006 and 2007 and the homozygous pigs were significantly different from the Yorkshire pigs in 2006 and 2007. However, the number of homozygous Cassie pigs was insufficient for a strong statistical comparison, but it is obvious that they performed similar to the Cassie hemizygous pigs. There were no differences in SLI between the boars and gilts of either the Cassie or the Arkell Yorkshire pigs, except that in 2007 the hemizygous boars had a higher SLI than the homozygous gilts. The higher SLI of the Cassie pigs as compared to the Arkell and Canadian Yorkshire pigs was due to a combination of fewer days to market weight (4.4 days less than for the Arkell Yorkshire pigs and 10 days less than for the Canadian Yorkshire pigs; Figure 2) and increased lean yield (Figure 3) which was inversely related to a reduced back fat.

As stated above, these results were achieved with Cassie Enviropig diets lacking supplemental phosphorus and supplemental phytase in contrast to diets for conventional pigs that contained these supplements.

Conclusion

This growth and conformational data demonstrates that the Cassie Enviropigs are healthy, grow rapidly, have highly desirable marketing characteristics (high protein content), are marginally cheaper to produced, and exhibiting lower manure pollution potential.