Effects of feed restriction and realimentation on mohair fiber growth and tissue gain by growing Angora goats

Abstract

Angora wethers (48), approximately 6 months of age and 15.7 kg initial BW (SEM = 0.38), were used to determine the effects of the level of feed intake and realimentation on mohair fiber growth and tissue gain. There were two 12 weeks phases in which dehydrated alfalfa pellets (18% CP and 48% NDF, DM basis) were fed. In phase 1, feed amounts were intended to provide ME adequate for 0, 15, 30, 45, 60, and 75 g/day of tissue (non-fiber) gain and 0, 1.5, 3.0, 4.5, 6.0, and 7.5 g/day of clean mohair fiber growth, respectively (L1, L2, L3, L4, L5, and L6, respectively), although actual levels were slightly greater; intake was ad libitum in phase 2. DM intake in both phases increased linearly (P < 0.05) with increasing level of feed offered from 0.48 to 1.00 kg/day in phase 1 and 1.08 to 1.48 kg/day in phase 2. Tissue gain increased linearly (P < 005) with increasing level of feed offered in phase 1 from 15.3 to 72.1 g/day and decreased slightly in phase 2 from 105.6 to 97.0 g/day. Greasy mohair fiber growth was not affected by treatment in phase 1 (6.31, 6.18, 6.85, 7.14, 7.07, and 6.47 g/day; SEM = 0.431) or 2 (6.59, 6.67, 6.52, 7.21, 7.69, and 6.64 g/day for L1, L2, L3, L4, L5, and L6, respectively; SEM = 0.349). During the entire experiment, mohair fiber growth relative to DM intake decreased linearly (P < 0.05) from 8.40 to 5.37 g/kg with increasing level of feeding in phase 1. Mohair fiber diameter increased linearly (P < 0.05) from 22.4 to 23.8 μm in phase 1 and 25.4 to 27.1 μm in phase 2. Digestibility of DM components and energy utilization were determined once per phase. Digestibility of OM was similar among treatments in phase 1, whereas values in phase 2 increased linearly (P < 0.05) from 68.0 to 73.4% as the level of feed offered in phase 1 increased. Assuming the requirements of 37.2 and 157 kJ/g of tissue and clean mohair fiber gain, ME used for maintenance (ME m) in phase 1 was not affected by treatment. In phase 2, ME m was greater than in phase 1 (mean = 431 kJ/kg BW 0.75) and increased linearly (P < 0.05) as the level of feed offered in phase 1 increased (551, 599, 647, 765, 788, and 902 kJ/kg BW 0.75 for L1, L2, L3, L4, L5, and L6, respectively; SEM = 97.5). The phase difference and unrealistically high values for some treatments may have resulted from a greater requirement than assumed for tissue gain in phase 2. This may have been because levels of fat and energy in tissue gained was greater in phase 2 than 1 and increased in phase 2 as the level of feed offered in phase 1 increased. In summary, with levels of intake above maintenance, growing Angora goats partition nutrients to mohair fiber growth at the expense of tissue gain. Realimentation likewise does not affect mohair fiber growth but can increase tissue gain, the magnitude of which depends on the severity of previous intake restriction.