Wool growth in Merino wethers fed lupins untreated or treated with heat orformaldehyde, with and without a supplementation of rumen protected methionine

Lupins were treated by either heat (115 degrees C for I h) or by formaldehy de (0.4 g 100 g(-1) crude protein). The fractional rate of disappearance of N from dacron bags suspended in the rumen of steers was reduced by either treatment. Assuming a rumen outflow rate of 0.03 h(-1), effective rumen deg radability was 0.96, 0.94 and 0.92 for protein and 0.84, 0.82 and 0.81 for dry matter in untreated, heat- and formaldehyde-treated lupins. Concentrati on of acid detergent insoluble nitrogen in lupins was not enhanced by treat ment. A 3 x 2 factorial experiment was performed with Merino wethers to study the effect of treating lupins on wool growth and body weight gain on a feeding level slightly above maintenance. Factors were lupin treatment (untreated, heat- and formaldehyde-treated) and supplementation of a rumen protected m ethionine (3 g methionine per day, yes or no). The diet contained (kg-l) 62 0 g chaffed oaten hay, 350 g broken lupins and 30 g mineral premix and was supplied once daily to sheep at a level of 900 g per day air dry or approxi mately 8 MJ per day ME. Seventy-two sheep were fed the diet containing untr eated lupins without methionine supplementation during a 4 week pretreatmen t period and were subsequently allocated to one out of the six treatments a ccording to pretreatment wool growth rate (n = 12 sheep per treatment). Tre atment lasted for 8 weeks. Comparative clean wool growth rate was determine d on mid-side patches of approximately 100 cm(2) shorn in 4 week-intervals. Faeces and urine were collected for 7 days at the end of the experiment wi th six sheep per treatment. Both body weight gain and clean wool growth wer e not significantly effected by either treatment of lupins. Supplementation of rumen protected methionine significantly increased both body weight gai n (by 27%) and clean wool growth. The effect of supplementary rumen protect ed methionine on clean wool growth was twice as high in sheep fed either he at- or formaldehyde-treated lupins (37 and 36%, respectively) as compared t o sheep fed untreated lupins (19%). Sulphur, but not nitrogen concentration in clean wool was significantly increased by supplementation of rumen prot ected methionine. The efficiency of utilisation of metabolisable protein (d efined according to [AFRC, 1993. Energy and protein requirements of ruminan ts. CAB International, Wallingford]) for N retention was improved by 13, 22 and 27% for diets containing untreated, heat- and formaldehyde-treated lup ins due to supplementary rumen protected methionine. Organic matter digesti bility and daily faecal N excretion were unaffected by lupin treatment and by supplementation of rumen protected methionine, indicating an equal ME su pply to all sheep. Correspondingly, the ratio of total purine derivatives t o creatinine in urine was not significantly affected by either experimental factor. 79% of total N in urine was present as urea. It is concluded, that treating lupins with formaldehyde or heat cannot be r ecommended as a means to improve the lupin protein quality for wool product ion unless extra rumen protected methionine is supplemented. (C) 1999 Elsev ier Science B.V. All rights reserved.