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

Abstract

Lupins were treated by either heat (115°C for 1 h) or by formaldehyde (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 degradability 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. Concentration of acid detergent insoluble nitrogen in lupins was not enhanced by treatment. A 3 × 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 methionine (3 g methionine per day, yes or no). The diet contained (kg −1) 620 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 approximately 8 MJ per day ME. Seventy-two sheep were fed the diet containing untreated lupins without methionine supplementation during a 4 week pretreatment period and were subsequently allocated to one out of the six treatments according to pretreatment wool growth rate ( n = 12 sheep per treatment). Treatment lasted for 8 weeks. Comparative clean wool growth rate was determined 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 with six sheep per treatment. Both body weight gain and clean wool growth were not significantly effected by either treatment of lupins. Supplementation of rumen protected methionine significantly increased both body weight gain (by 27%) and clean wool growth. The effect of supplementary rumen protected methionine on clean wool growth was twice as high in sheep fed either heat- or formaldehyde-treated lupins (37 and 36%, respectively) as compared to sheep fed untreated lupins (19%). Sulphur, but not nitrogen concentration in clean wool was significantly increased by supplementation of rumen protected methionine. The efficiency of utilisation of metabolisable protein (defined according to [AFRC, 1993. Energy and protein requirements of ruminants. CAB International, Wallingford]) for N retention was improved by 13, 22 and 27% for diets containing untreated, heat- and formaldehyde-treated lupins due to supplementary rumen protected methionine. Organic matter digestibility and daily faecal N excretion were unaffected by lupin treatment and by supplementation of rumen protected methionine, indicating an equal ME supply to all sheep. Correspondingly, the ratio of total purine derivatives to 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 recommended as a means to improve the lupin protein quality for wool production unless extra rumen protected methionine is supplemented.