Six mature Merino sheep received three treatments in a randomized block design experiment. The treatments were: chopped oaten hay diet at 90% of ad libitum intake without urea (L); the ciet offered at the same level as for L with urea infused into the rumen at 11.5 g kg-1 dry matter intake (LU); and the diet offered at 90% of the ad libitum intake achieved with urea infused at 11.5 g kg-1 dry matter intake (HU). Sheep given HU consumed 37% more (P < 0.01) organic matter (OM) than those fed L or LU, but the apparent digestibility of OM did not vary (59.2-61.8%) between treatments. The addit onal food consumption was associated with c. 20% increase (P < 0.05) in the weight of OM in the reticulorumen and significantly higher (by 10-35%; P < 0.05) fractional outflow rates of most dietary and microbial constituents of digesta. The fractional digestion rate of potentially digestible plant cell walls was not affected by urea, but the flow of microbial non-ammonia nitrogen from the abomasum was enhanced (L, 7.0; LU, 8.2; HU, 12.5 g day-1; P < 0.05). The results of this study suggest that the stimulatory effect of urea upon food intake was associated with the provision of additional microbial protein for digestion in the intestines, rather than changes in the rate or extent of organic matter fermentation in the reticulorumen.
The voluntary intake and digestion of three pasture hays of varying quality by Angora goats was compared with that by Merino sheep. The excretion and retention of nitrogen and sulfur were also measured. When a high quality hay was given, there were no differences between goats and sheep in the intake of organic matter (68 vs 61 g/kg0.75.d) or in organic matter digestibility (digestible organic matter intake) (72 vs 7 1 %). However, the goats appeared to utilize nitrogen less efficiently than the sheep as evidenced by nitrogen retention (673 vs 794 mg/100 g digestible organic matter intake.d), and there was a tendency for sheep to use absorbed energy more efficiently for body tissue synthesis. The apparent digestion of organic matter (65 vs 57%), plant cell wall constituents (67 vs 59%), nitrogen (29 vs 19%) and sulfur (40 vs 33%) in a medium quality hay low in nitrogen was greater in goats than in sheep. There were no differences in intake, but the goats were more efficient at conserving nitrogen (nitrogen retention -87 vs -200 mg/ 100 g digestible organic matter intake.d). Similar trends occurred when a poor quality hay with a higher nitrogen content was given. Goats have apparent advantages over sheep in their ability to digest fibrous feeds and conserve limiting nutrients from such feeds. Consequently, they may require less supplementary feeding than sheep in temperate areas during late summer and autumn when animals graze mature pastures.
Five sheep with simple cannulae in the rumen and abomasum were given a diet of chopped oaten hay at 95-98% of ad libitum intake from continuously moving belts. Flows of digesta from the abomasum were estimated by a double marker method by reference to 51Cr-EDTA as the fluid marker, and either 103Ru-P, lignin, or acid insoluble ash (AIA) as the particulate marker. Estimates were also made by reference to lignin as a single marker. Estimates of the weight of digesta leaving the abomasum daily were unaffected by the choice of particulate marker when used with 51Cr-EDTA, but were 25% lower when lignin was used alone. The estimated flows of dry matter and acid detergent fibre (ADF) were dependent upon the choice of markers. Compared with estimates of ADF flow given by 51Cr-EDTA and lignin, estimates given by AIA were lower (-24.6%) and those given by 103Ru-P were higher (+26.2%). Lignin alone gave estimates 1.6% higher. Observations on the distribution of 103Ru-P in digesta dry matter indicated a markedly higher concentration on fine than on large particles. It is concluded that lignin may be preferable to 103Ru-P as a particulate marker when certain coarsely chopped roughages are given to sheep, and when samples of digesta from the abomasum are obtained through a simple cannula.
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