Protein requirements of growing lambs.

I . The protein requirements of lambs were established by measuring nitrogen balance in seventy-four animals given liquid diets which passed direct to the abomasum. Four groups of lambs weighing approximately 8 kg (group I), 13 kg (group z), 21 kg (group 3) and 30 kg (group 4) received diets in which 0-10, 0.15, ozo,o'z5, 0 . 3 0 , 0 3 5 or w4oof thedigestibleenergy was provided as protein (DPE:DE ratio) and a gross energy intake of from 1.30 to 1.42 MJ/kg0'73 per d. z. When the protein requirements were taken to correspond to the protein intake at the point of intersection of the line describing the increase in N balance with increase in protein intake and the line representing the maximum N balance, values of 0.25 ,023 , 017 and 012 DPE: DE ratio were obtained for groups 1-4 respectively. The requirements expressed in these terms can be applied only to lambs fed on liquid diets which contain milk proteins and escape fermentation in the rumen. To enable the results to be applied to lambs given other diets, the requirements were expressed as g reference-protein (defined as a theoretical protein with the ideal pattern of amino acids) per MJ net energy and were I 1.6, 104, 8.0 and 6.2 for groups 1-4 respectively. The relationship between protein requirement ( Y, g reference protein/MJ net energy) and live weight (X, kg) was: Y = 13.4-0.24zX. 3. The influence of energy intake on protein requirements in lambs is discussed and it is concluded that the results obtained are applicable to lambs given a metabolizable energy intake of more than about 1.75 times their maintenance requirement. 4. Application of the estimated requirements to ruminant lambs and methods of formulating diets to supply the required quantity of reference protein/M J net energy are discussed.