Body weight and wool production in grazing sheep given access to a supplement of urea and molasses: intake of supplement/response relationships

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Abstract
SUMMARY: A technique for estimating the intake of liquid supplements by individual, grazing animals was used in a trial with 200 sheep grazing poor quality pasture and given access to a urea-molasses supplement (19%, w/v).A mathematical procedure was developed to estimate intake of supplement based on measurements of the accumulation of tritiated water (TOH) and its rate of turnover in the body of each animal after a TOH-labelled mixture had been available for a period of 7 days.In calculating the level of intake of labelled supplement, it was assumed that each animal ingested the mixture once daily over the 7-day period, since animals were observed to take the supplement daily and the daily loss of supplement from the dispenser was noarly constant. It was estimated that the combined intakes of the animals accounted for 87% of the known total loss of labelled supplement from the dispenser.Of the 200 sheep, 97 did not consume any supplement and among the other 103 animals, estimated intake varied from 5 to 550 ml/day.All sheep lost body weight during the trial, but those consuming the supplement lost significantly less weight, and grew significantly more wool during the period of supplementation, than did the sheep that did not consume the supplement.A small but significant amount of the variance (13%) in body-weight change and wool growth during supplementation was removed by multiple regression analysis, by including the intake of the supplement, faecal egg count (as an indication of parasite burden) and body weight at the start of the trial, as independent variables. Other factors not studied (e.g., dry matter intake) apparently accounted for a large proportion of the variance.The relationship between body-weight change and intake of the urea-molasses mixture was compatible with the hypothesis that the supplement was used largely as a concentrate feed, and not solely as a nitrogen supplement.