Abstract:
Proc. Amt. Sot. Am' Prod. 1994 Vol. 20 rn. WOOL GROWTH, FIBRE DIAMETER AND WEIGHT GAINS SHOW LINEAR RESPONSES TO RUMEN PROTECTED METHIONINE G. MATA, D.G. MASTERS and D. BUSCALL CSIRO Division of Animal Production, Private Bag, PO, Wembley, W.A. 6014 Abomasal or parenteral doses of methionine have been shown to stimulate wool growth in sheep with an optimum response from about 2.5 g/day (Reis 1979). However, the size of the response may depend on diet quality (Dove and Robards 1974) and the potential for response by the sheep (Pickering and Reis 1993). In sheep grazin, annual pastures, abomasal supplements of 3 g/day of methionine increased feed 0 intake and liveweight gain at most times of the year (Mata et al. 1992). Field application of these results however has been hampered by a lack of suitable means of delivery of methionine to grazing animals. In this study we report the results of a dose rate experiment with Lactet (Nippon Soda, Japan), a methionine formulation that is protected from degradation in the rumen and is effective in increasing the availability of methionine to sheep (Mata, unpublished). Forty-two Merino wethers with an initial liveweight of 44.0 + 1.37 kg (mean + sem) were kept in individual pens and fed 1150 g/day of a diet containing hay (85.2%) lupins (120/c), urea (2%) and minerals (O.S3%) for 12 weeks. All animals received a constant amount of feed estimated to maintain weight and to supply 9.7 MJ ME/kg dry matter (DM) and 146 g crude protein/kg DM. The experiment consisted of a pre-treatment period of 25 days, a treatment period of 63 days and a post-treatment period of 65 days at pasture. On day 25 sheep were allocated to 1 of the following treatment levels of methionine: 0, 1, 2, 3, 5 and 8 g/day. Lactet was mixed with the feed each day. Analysis of data was by regression analysis using day 25 values as covariates. Table 1. Tota 1 clean wool growth (CWG, g/100 cm2), fibre diameter f&m) and liveweight gain (LWG giday) and percentage change relative to the control group during the 63 day treatment period Growth and fibre diameter (PcO.001). The response was best Lactet significantly increased wool a described by a linear fit and resulted in production increases of up to 32% for clean wool growth (r2 = 0.58 1, df = 40) and 9.2% for fibre diameter (r3 = 0.448, df = 40) relative to the control group. Liveweight and growth rate also showed a significant linear response to Lactet (P c 0.001). Growth rate increased between 17 and 113% relative to the untreated group (r2 = 0.575, df = 40). Residual effects on wool growth were observed 65 days after the termination of treatment for the higher dose (8 g/day), but no residual effects were observed for liveweight. The observed production responses to Lactet were due to an increased efficiency of utilisation of nutrients, as intakes were the same for all sheep. Feeding Lactet is a practical method of providing methionine, protected from degradation in the rumen. Wool growth and liveweight gain increased with up to 8 g methionine/day. This work was partly funded by WRDC and Lactet was donated by Nippon Soda Co Ltd., Japan. DOVE, H. and ROBARDS, GE. (1974). Amt. J. Agric. Res., 25: 945-56. MATA, G., PETER, D.W. and PURSER, D.B. (1992). Proc. Amt. Sot. Anim. Prod. 19: 144. PICKERING, FS and REIS, P.J. (1993). Amt. J. Agric. Res., 33: 7-12. REIS, P.J. (1979). In 'Physiological and Environmental Limitations to Wool Growth', (Eds J.L. Black and P.J. Reis). pp . 223-42 (University of New England Publishing Unit: Armidale). 451