Думаю, что речь идет о рационе (корме), используемом в период перед забоем и реализацией птицы. Поскольку это понятие американского агропрома, не уверена, что есть русский эквивалент, хотя слово "предзабойный" существует (в разных сочетаниях).

Several diet formulations are typically fed to poultry from hatching to market. Prestarter and starter diets are fed to broilers for up to 19 days after hatching. These diets might contain up to three drug components: (1) a prophylactic coccidiostat, (2) a growth-promoter antibiotic, and (3) an organic arsenical compound that has both growth promoter and coccidiostat activity. A battery of grower diets are fed for the next 8 to 12 days to maintain the metabolic requirements of these fast-growing birds, and ***withdrawal diets of one or two types are fed in the remaining days before market***. Thus, the diets used in each phase are progressively reduced in drug use and cost. To comply with FDA-mandated drug-withdrawal periods, organic arsenical compounds are not used in withdrawal diets. Most poultry operations routinely monitor withdrawal feed to ensure compliance, for several reasons. First and foremost, monitoring reduces any potential risk that drug residues will remain in tissues
http://books.nap.edu/openbook.php?record_id=5137&page=27