Two experiments have been conducted with young Lincoln, Corriedale, Polwarth, and fine Merino maiden ewes to compare the growth of fleece by these breeds and to assess relations between the growth of fleece and some factors, nutritional and non-nutritional, likely to influence its growth. In both experiments four representatives of each breed were kept in a sheep house in single pens and fed a high quality diet of constant composition. The second experiment followed immediately on the first and the same sheep were used except for necessary replacements. In the first experiment, which lasted for about one year, the intake of the diet was continuously unrestricted; in the second the intake of the diet was progressively restricted by ordered steps and was finally maintained for 12 weeks at one-fifth of the unrestricted intake of the first 4 weeks of the experiment. With few exceptions, the absolute or relative values of the characters measured formed a smooth series from the fine Merino through the Polwarth and Corriedale to the Lincoln-either in ascending order (e.g. food and water intake; liveweight and chest dimensions; fibre thickness, length, and volume; clean wool, suint, and total skin products output; clean wool and suint output per unit food intake) or descending order (e.g. total and primary follicle density; ratio of secondaries to primaries; wax output and wax output per unit food intake) or showed little or no difference between the breeds (e.g. body length and height; food intake per unit net liveweight; total skin products per unit food intake). The relative positions of the breeds as shown in the first experiment mere generally maintained in the second as food intake was progressively reduced. The results of the two experiments were combined for the individuals and a series of partial regression analyses were undertaken to determine the regression of some variables of fleece production on the level of food intake, atmospheric temperature, fleece weight, and experimental time. Self-selected food intake decreased with increase in fleece weight and less obviously with increase in experimental time (or, possibly, with deposition of subcutaneous fat). Water intake increased with both increase in food intake and rise in atmospheric temperature. Wool weight produced, and fibre thickness, length, and volume growth, all increased with increase in food intake, and within the limits of observed food intake the relation between wool growth and food intake was adequately represented by linear regression. Increase in atmospheric temperature exerted no significant influence on wool growth, except by the Lincolns (through fibre thickness). A positive regression of wool growth rate on fleece weight, acting through fibre length growth, was found, but change in fibre thickness was not related to increase in fleece weight. Wax production was positively related to increase in food intake and negatively to rise in atmospheric temperature. Suint production was positively related to both food intake and fleece weight. Wool, wax and suint production per unit food intake decreased with increase in food intake. Wax per unit food intake decreased with rise in temperature and suint per unit food intake increased with increase in fleece weight.
