Supplementation of sheep grazing wheat stubble with urea, molasses and minerals: quality of diet, intake of supplements and animal response

Abstract

Supplements of urea, molasses and minerals were offered for 15 weeks to mature crossbred wethers grazing wheat stubble at Condobolin in central New South Wales. The sheep were then grazed without supplements on a phalaris-subterranean clover pasture for a further five weeks. On the wheat stubble, dead crop residues amounted to more than 4000 kg DM ha-1 and constituted 95% or more of the available plant material throughout the experiment. Diets selected by the sheep contained significant amounts of grain or green plant material only during the first six weeks, while the proportion of dead plant material increased from 66% to 98% of the diet as the experiment progressed. Supplementation had no effect on diet selection. All sheep gained some weight during the first six weeks of stubble grazing, and thereafter lost weight. This loss was reduced from 0.66 kg week-1 to 0.47 kg week-1 with a mineral block supplement, and to 0.37 kg week-1 with supplements of a mineral/urea block, or molasses or molasses/urea licks. Significant differences in mean liveweight occurred between unsupplemented sheep and those offered a mineral/urea block, or a molasses lick. These differences were reduced by half after five weeks on green pasture, due to compensatory gain. Supplementation had no effect on wool production, or on the amount of dead plant material utilized for animal production, which amounted to a mean of about 10% of the quantity initially available. Mean intakes of supplement by groups were close to the desired amounts, i.e. 10 g urea or 50 g molasses sheep-1 day-1, or both, but for all supplements intake varied widely among individual sheep, with the coefficient of variation exceeding 40% in more than half of the recordings. Apart from special circumstances where reduced rates of weight loss may be important, it seems that little benefit will be gained from feeding urea, molasses or mineral supplements to sheep grazing crop stubbles.

Urea supplementation effects on the utilization of low‐quality forage and lamb production in patagonian rangelands

“…Liveweight differences between supplemented and control ewes declined during lactation (Figure 3). This observation supports the idea that the initial differences caused by undernutrition may disappear following a period of high levels of nutrition, outweighing the benefits of previous supplementation (Entwistle and Knights, 1974;Mulholland and Coombe, 1979). This hypothesis may be valid at an individual level, but not at a population level, because, even though the positive effect of supplement on ewe and lamb live weight was not sustained, its influence on total lamb production will persist.…”

“…Several experiments around the world suggest a clear effect of supplementation on the performance of pen-fed sheep; however, responses in the field have been less clear (Tudor and Morris, 1971;Mulholland and Coombe, 1979;Butler et al, 1987). This discrepancy may arise from several causes: (1) diet selectivity is more important in field experiments (Tudor and Morris, 1971), (2) diet selection may change with supplementation (Hatfield et al, 1991), (3) urea often decreases forage palatability (Bhattacharya and Pervez, 1973;Butler et al, 1987), (4) unsupplemented sheep may show compensatory growth in the more favourable season (Entwistle and Knights, 1974;Mulholland and Coombe, 1979) and (5) N-restricted sheep may markedly increase their nitrogen use efficiency by reducing nitrogen excretion and increasing N recycling (Farid, 1985;Farid et al, 1989).…”

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

“…However, if individual animal supplement consumption is measured, and there are three animals that consume no supplement, and two animals that consume .5 kg/d, then only 50% of the animals consumed at least the target amount. Mulhol-land and Coombe (1979) used disappearance of supplement to estimate intake and found this method resulted in 100% of target intake by grazing wethers for molasses and molasses-urea liquid supplements, whereas only 55 and 40% of sheep consumed the target amount or more of molasses and molasses-urea liquid supplements, respectively, when individual supplement consumption was measured.…”

“…Individual supplement intake measured using tritiated water indicated that the proportion of nonfeeders was 49%, and the CV for individual supplement intake was 52%. Mulholland and Coombe (1979) offered crossbred wethers grazing wheat crop residue access to molasses-based mineral or mineral-urea block supplements, or to molasses or molasses-urea liquid supplements in roller lick troughs. Mean supplement intake as a percentage of the target intake was 11% for the mineral block, 28% for the molasses-urea block, 55% for the molasses, and 37% for the molasses-urea liquid supplement.…”

Impact of Area Specific Urea Molasses Mineral Block on the Production Performance of Pashmina Goats

“…ASUMMB provides all essential nutrients . However, Mulholland and Coombe (1979) have found no improvement in wool production on urea molasses mineral block supplementation in sheep.…”