Abstract: Zona pellucida is useful for growth stimulation in animals and especially in female ruminants such as heifers. Immunization of heifers with Zona pellucida obtained from young pig ovaries leads to increased weight gains that are comparable to, or exceed the weight gain achieved with by other growth stimulants given to cattle, such as steroids, antibiotics or ionophores. Zona pellucida treatment results in longer-lasting weight gain response than that achieved with conventional growth stimulants and results in less frequent cattle handling and decreased production costs.