Small ruminants such as sheep and goat play a major role in the rural economy. Animal production and reproduction depend on the feed efficiency which in turn is controlled by the appropriate interplay of hormones via enzymes in the system. Enzyme concentration in blood is proportional to the intracellular concentration and represents the metabolic activity and the physiological status of the animal. The enzyme system acts as a biocatalytic domin in the biological system. Serum enzymes are the index of metabolic profile of an animal which are subjected to reproductive physiological variation. In this book, various intracellular enzymes at different stages of reproduction in small ruminants were described. This book will help to the small ruminant rearers and breeders to improve the fertility and enhance reproductive performance in cost effective manner.