While it may seem that interest in early age altering is a recent phenomenon, it has not only been talked about, but it has been practiced for over 25 years in North America. Early age altering usually refers to spays and neuters done between the ages of 8 and 16 weeks instead of the conventional 5-7 months. Attention has recently focused on early age altering of animal shelter pets before adoption. Early age altering is proposed as a more reliable means of preventing shelter pets from reproducing after adoption. Surgical sterilization is recognized as the most common and effective means of reproductive control in dogs and cats. Studies show that, despite economic incentives, many cats and dogs adopted from shelters have one litter before they are sterilized. Owner compliance with sterilization programs is often under 50%, despite screening of adoptive homes, prepayment of or discounted surgery fees, contracts requiring altering and follow up by shelter personnel. In turn, about 1/3 of cats and dogs are relinquished at shelters because they are from an unwanted litter.