In April 1997, Buchholz entered into a written contract with Schneider's Milling to provide between 500 and 590 segregated early weaned (SEW) pigs every three weeks beginning October 15, 1997. The parties agreed to a price of $36.50 per pig. The contract was to continue for a period of 48 months. Because Buchholz was just starting a SEW pig program, the parties recognized that the number of pigs could vary in the first four months. Even after the first four months passed, however, Buchholz was unable to provide at least 500 pigs every three weeks. At the same time, the market price for pigs decreased significantly. In September 1998, a representative of Schneider's discussed reducing the price to $28 per pig. After some discussion, Buchholz proposed a price of $30 per pig. On October 8, 1998, the parties agreed to a price of $30 per pig and that Buchholz would produce at least 500 pigs every three weeks until April 1, 1999, or the contract would be terminated. Buchholz had two deliveries of over 500 pigs, but the other deliveries were less than 500 pigs. In February 1999, Schneider's terminated its agreement with Buchholz. Buchholz filed suit against Schneider's for breach of contract, claiming Schneider's had failed to pay the full contract price for the pigs, which was $36.50 per pig. Schneider's asserted that the contract had been modified in October 1998 to reduce the price to $30 per pig. Was this modification enforceable?