IACUC Animal Use Budget Estimator

Understanding yield factors in animal budgeting

The fraction of pups born alive from each mating. For mice, typical values are 0.80–0.90. Factors that reduce breeding yield: advanced maternal age, inbred strain subfertility, mutant alleles affecting fertility, first-time breeders.

The fraction of live-born pups that survive to weaning (typically P21). Values of 0.90–0.98 are normal for standard mouse strains. Lower for fragile mutants, immunodeficient lines, or strains with pup cannibalism.

The fraction of weaned animals with the desired genotype. This is driven by Mendelian genetics: 50% for heterozygous $\times$ wild-type, 25% for het $\times$ het targeting homozygous, 6.25% for double-het crosses. This is usually the biggest multiplier in the budget.

The fraction of genotype-confirmed animals that complete the experimental protocol. Typically 0.85–0.95. Lower for surgical models, chronic disease models, or studies with high-mortality endpoints.

A safety margin (typically 1.1–1.2×) that accounts for unexpected losses not captured by the yield factors above. The buffer is the first thing the IACUC will question if your total animal number seems high.