The effect of feeding formaldehyde-treated casein to sheep on nitrogen retention and wool growth

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Abstract
The effect of treating supplementary casein with formaldehyde on nitrogen (N) digestion, N retention, and wool growth was studied in two experiments with young Romney sheep. In vitro tests showed that untreated casein was rapidly digested by rumen micro-organisms. Formaldehyde-treated casein was protected from ruminai degradation and was digestible in acid-pepsin conditions. Supplements of 25, 50, or 75 g per day of each type of casein were added to a basal ration predominantly of roughage fed at an energy intake close to maintenance. Formaldehyde treatment of casein reduced the concentration of ammonia in rumen fluid, reduced urinary N excretion, and increased N retention. Urea N in peripheral blood plasma was decreased by formaldehyde treatment of casein, but increased with increasing level of casein intake. Live-weight gains were small, but were increased by formaldehyde treatment of casein and by level of casein intake. Wool growth rate and fibre diameter were increased by formaldehyde treatment of casein, the mean increase in wool growth rate being 32%. Both parameters also increased with increasing level of casein intake. There was evidence that wool growth and fibre diameter showed greater increases with increasing intake of formaldehyde-treated casein compared with untreated casein, but this difference did not attain significance. After supplementation ceased there were residual effects of previous type and level of casein on wool growth and fibre diameter for 5 weeks. Due to seasonal effects, wool growth and fibre diameter decreased linearly with time. The seasonal effect was not influenced by either type or level of intake of casein.