Utilization of urea and molasses supplements by sheep grazing oat stubble

Abstract

Mature crossbred wethers, grazed for 11 weeks on oat stubble at a stocking rate of 20 sheep ha-1, were unsupplemented or offered supplements of a urea-mineral block, a molasses lick or a urea-molasses lick. Following rain in the fourth week, half of the area was sprayed with desiccant herbicide to establish weed-free stubbles. The stubble initially yielded c. 2600 kg DM ha-1 of dead crop residues plus 900 kg DM ha-1 of fallen grain; after 11 weeks this had fallen to c. 1400 kg DM ha-1 of dead crop residues. Initially the sheep selected diets of 0.03-0.22 grain and 0.78-0.97 dead herbage and, during this time, urea-supplemented sheep selected diets lower in grain and nitrogen (N) content than those selected by unsupplemented sheep. On weedy stubbles, where green herbage yielded more than 100 kg DM ha-1, sheep selected a diet containing c. 0.78 green herbage (N content 2.6%), ate more digestible organic matter (DOM) and gained more weight than those on weed-free stubbles, where the diets consisted of 0.98 dead crop residues (N content 1.1 %). All sheep ate some of the urea-mineral blocks throughout, but 100% acceptance of the licks only occurred by the 6th week. Mean intakes reached desired levels (10 g urea and/or 50 g molasses sheep-1 day-1) thereafter, but individual intakes varied widely on all supplements, with the coefficient of variation generally > 50%. In most periods, supplementation had only small effects on the intake of DOM. During the first 4 weeks, sheep lost weight except those offered the urea-mineral blocks. Over the whole experiment, urea-supplemented sheep lost less weight than unsupplemented sheep, but this was mainly due to higher weight gains on the weedy plots. Mean concentrations of rumen volatile fatty acids (VFA) were < 80 mmol l-1 throughout, and fell to <40 mmol l-1 on the weed-free plots in the latter stages of the experiment. Mean rumen ammonia levels, which were < 100 mg N l-1 in unsupplemented sheep, were generally increased by urea supplements, and by grazing weedy stubbles. Responses to supplementation are discussed in terms of the quality of the available plant material, the diet selected, the levels of rumen metabolites and the intake of supplements.

Delivery method and supplement consumption by grazing ruminants: a review.

“…Sixty-one percent of the wethers did not meet target consumption, and the CV of individual supplement intake was 83%. Coombe and Mulholland (1983) found the CV of individual supplement intake by sheep grazing oat stubble to be 62% for molasses-based blocks, 66% for molasses-urea liquid supplement in a lick tank, and 86% for molasses delivered in a lick tank. Mean supplement intake as a percentage of the target supplement intake was 41% for blocks, 76% for molasses-urea liquid, and 80% for molasses.…”

“…The neophobic eating pattern exhibited by feedlot cattle lasts less than 2 wk (Hicks et al, 1990). Individual supplement intake variation usually decreases with time, as animals progress through the neophobic eating pattern found with unfamiliar supplements Coombe and Mulholland, 1983). However, neophobia may last longer with novel supplements than with entire diets.…”

“…Nolan et al (1975) found that 48% of sheep did not consume any supplement after exposure to molasses-urea liquid supplement for a period of 7 d. reported that the percentage of sheep not consuming molassesurea blocks decreased from 14% in the 1st wk to 4% after the 3rd wk of the study. In another experiment, it took 8 wk of exposure to molasses-urea liquid supplement before all sheep were consuming supplement (Coombe and Mulholland, 1983). Chapple and Lynch (1986) summarized that sheep were not only neophobic to feeds, but also to feed delivery devices, and as a result, variation in supplement consumption may be caused by unfamiliarity with the feeding equipment.…”

“…Coefficients of variation of supplement intake usually decrease with increased exposure time to supplements. Coombe and Mulholland (1983) examined individual intake of a block, molasses, or molasses-urea liquid supplements by grazing sheep during five successive 2-wk periods. During the first 6 wk, the CV of individual supplement intake averaged 80%, and levels of supplement consumption by most Molasses-5% urea Graham et al (1977) Cattle 9% Molasses Sheep 18% Molasses-urea 0% Oats Kendall et al (1983) Sheep 0% Molasses-urea, confinement 6%…”

“…Molasses-urea Entwistle and Knights (1974) Sheep 15% Molasses-urea 22% Molasses Nolan et al (1975) Sheep 49% Molasses-urea Coombe and Mulholland (1983) Sheep 3% Mineral-urea 23%…”