GROWTH HORMONE (GH) IS SECRETED INTO THE BLOODSTREAM AND CONTROLS GROWTH IN FARM ANIMALS. THE ACTIONS OF GH ARE DEPENDENT ON A CELL SURFACE RECEPTOR CALLED THE GH RECEPTOR THAT RECEIVES THE SIGNAL FROM GH TO CAUSE CELLS TO GROW. THE GH RECEPTOR IS FOUND IN IMPORTANT TARGET TISSUES FOR GROWTH SUCH AS LIVER, MUSCLE, FAT, AND BONE. UNDERSTANDING HOW THE GH RECEPTOR FUNCTIONS ENABLES US TO UNDERSTAND HOW ANIMALS GROW. THE HYPOTHESIS IS THAT THE UNIQUE ACTIONS OF GH ON ANIMAL GROWTH DEPEND ON THE EXPRESSION OF GH RECEPTORS IN SPECIFIC TISSUES. WE WILL CREATE TWO DIFFERENT GENETIC LINES OF PIGS THAT EXPRESS THE GH RECEPTOR IN DIFFERENT TISSUES. THE FIRST GENETIC LINE WILL ONLY EXPRESS GH RECEPTOR IN LIVER AND NOT ELSEWHERE IN THE BODY. THE SECOND GENETIC LINE WILL NOT EXPRESS GH RECEPTOR IN LIVER BUT WILL EXPRESS GH RECEPTOR IN ALL TISSUES OUTSIDE OF LIVER. BOTH LINES WILL BE COMPARED WITH A CONTROL LINE (NORMAL GH RECEPTOR EXPRESSION). WE EXPECT TO FIND THAT THE EXPRESSION OF GH RECEPTOR IN LIVER IS ABSOLUTELY ESSENTIAL FOR GROWTH BECAUSE LIVER CONTROLS MANY ASPECTS OF DIGESTION AND NUTRIENT METABOLISM UNDER THE INFLUENCE OF GH. WE ALSO EXPECT TO FIND THAT THE EXPRESSION OF GH RECEPTOR OUTSIDE OF LIVER (IN MUSCLE, FAT AND BONE, FOR EXAMPLE) IS ESSENTIAL. PIGS WITHOUT GH RECEPTOR IN MUSCLE, FAT AND BONE WILL NOT GROW NORMALLY BECAUSE THEY CANNOT RESPOND TO GH. THIS RESEARCH WILL ENABLE US TO UNDERSTAND WHY SOME FARM ANIMALS GROW QUICKLY WHEREAS OTHER DO NOT. WE HOPE TO IDENTIFY THE MECHANISMS LEADING TO FAST-GROWING AND EFFICIENT FARM ANIMALS.