J.B.J. van Ryssen

Nitrogen and phosphorus concentration in faeces: an indicator of range quality as a practical adjunct to existing range evaluation methods

Vegetation monitoring, currently complemented by climatic data in particular rainfall areas, does not always supply sufficient information to provide reliable guidelines for appropriate stocking densities on ranch or reserve scale. This paper considers how the nutrient status of animals may be used to improve the setting of management guidelines by reflecting how wild herbivores perform under differing environmental and management conditions. Faecal nitrogen concentrations of between 13 and 16 g kg−1 are above a threshold level that indicates a dietary deficiency which may precipitate nutritional stress in animals (such as happened during the 1991/1992 drought). Faecal phosphorous concentrations of between 1.9 and 2.0 g kg−1 over a long period of time would indicate a deficiency that may lead to low reproductive rates. Faecal analysis could therefore be used to assess whether applied stocking densities will allow grazers, and probably mixed feeders such as impala too, to select for a diet of sufficient quality for maintenance.

Contribution of dietary sulphur to the interaction between selenium and copper in sheep

The effect of concentration of sulphur (S) in a diet on the interrelationship between copper (Cu) and selenium (Se) metabolism was investigated in sheep. The animals received a sheep finishing diet in individual feeding pens for a period of 74 days. The minerals were included in the diets according to a 3×2×2 factorial experimental design. The final mixtures contained three concentrations of Se; 0·35, 0·88 and 1·34 mg Se (Se added as Na 2 SeO 3 ); two concentrations of Cu; 6·7 and 17·0 mg Cu (Cu added as CuSO 4 ) and two concentrations of S; 2·15 and 3·97 g S (S added as Na 2 SO 4 )/kg dry matter (DM). An increase in dietary Cu resulted in a significant ( P <0·01) increase in liver Se concentration; 2·30 v . 3·43 mg Se/kg DM for the low v . the high Cu treatments. The addition of S reduced the hepatic Se concentration significantly ( P <0·01). This was most pronounced at the high Cu intake, resulting in a significant ( P <0·05) three-way interaction between the three minerals, i.e. the hepatic Se concentrations were 2·53, 2·08, 4·07 and 2·79 mg/kg DM for the low Cu–low S, low Cu–high S, high Cu–low S and high Cu–high S treatments, respectively. Dietary S reduced ( P <0·01) the concentration of Cu in the liver from 678 mg/kg DM at the low S to 305 mg/kg DM at the high S intakes. Dietary Se did not change the concentration of Cu in the liver significantly. Adding S to the diet caused a reduction ( P <0·01) in the Se concentration of rumen bacteria, i.e. from 3·48 mg/kg DM in the low S to 1·96 mg/kg DM in the high S treatments. Selenium concentrations in rumen bacteria and the liver were the most sensitive to changes in Se intake, followed by the heart, muscle, plasma and whole blood. It was concluded that an increase in S intakes would decrease the accumulation of both Cu and Se in the liver of sheep, resulting in a diminishing degree of interaction between Cu and Se.

Metabolism of selenium and copper in sheep with and without sodium bicarbonate supplementation

The interrelationship in metabolism between dietary selenium (Se) and copper (Cu) was investigated in sheep receiving a diet with or without sodium bicarbonate (NaHCO 3 ). A sheep finishing diet, containing 0·3 mg Se/kg DM and 7·4 mg Cu/kg DM, and supplemented with 1·0 mg Se (as Na 2 SeO 3 ) and/or 15·0 mg Cu (as CuSO 4 ) and/or 40 g NaHCO 3 per kg feed, was fed to young ewes for a period of 64 days. Hepatic Cu concentration and net accumulation were not affected by NaHCO 3 supplementation. Furthermore, no evidence was found in blood, tissues or faeces to show that NaHCO 3 influenced Se metabolism. However, hepatic Cu concentration was raised from 354 to 422 mg/kg DM ( P <0·05) when the diet was supplemented with 1 mg Se/kg DM, independent of the level of dietary Cu. Furthermore, hepatic Cu retention was significantly ( P <0·05) influenced by a Se × Cu interaction, namely when the diet was supplemented with 15·0 mg CuSO 4 or 1·0 mg Na 2 SeO 3 /kg DM or both, 0·084, 0·081 and 0·088 of the dietary Cu respectively was retained in the liver, compared to 0·047 in the sheep on the basal diet. In addition, supplementation with Se and Cu together increased hepatic Se concentration to a greater extent ( P <0·001) than when Se alone was added to the feed (3·65 v . 5·17 mg Se/kg DM respectively). The concentration of Se in both muscle tissue and in rumen bacteria was raised ( P <0·001) by Se supplementation, but more so ( P <0·05) in both cases when Cu was not added to the diet. Interactions between Se and Cu were not influenced by NaHCO 3 supplementation in the conditions of this study.

Effect of ionophores on the accumulation of copper in the livers of sheep

Lambs were allocated to three treatments: control (C), monensin (M) and lasalocid sodium (L) in a concentrate diet containing 36 mg copper per kg food. After 2 months deaths from copper toxicity occurred and the trial was terminated. All lambs were slaughtered. The mean liver copper concentration (mg/kg dry matter) of 1907 in the M treatment was higher than the mean concentrations of 1342 and 1229 in the C and L groups respectively ( P

Factors affecting the voluntary feed intakes of sheep grazing Pennisetum clandestinum (kikuyu) pastures: observations in the animal

Abstract Two experiments designed to establish possible reasons for the often‐observed low voluntary feed intake of animals grazing kikuyu pastures were conducted at two widely differing locations. Low digestibility and low rate of digestion limited feed intake only when sheep were grazing dry, wilted kikuyu. At other times, rumen contents were relatively low, and voluntary intakes appeared to have been controlled by other factors. The foaminess of the rumen under circumstances of a low rumen fill seems to suggest that a high saponin content could have limited intake. However, the fact that a high rumen fill coincided with a high in vitro foam production in one instance may imply that a high saponin content was not instrumental in limiting intake. Only the rumen ammonia concentration and the total nitrogen content of the leaves showed a consistent relationship with voluntary intake.

Factors affecting the voluntary feed intake of sheep grazing Pennisetum clandestinum (kikuyu) pastures: Observations from forage analysis

Abstract Sheep were used in two investigations to study factors which could limit voluntary intake of Pennisetum clandestinum (kikuyu) pasture. Possible reasons for the low intakes were found in the high soluble nitrogen and nitrate content of the pasture, its high oxalate content, and its considerable potential for foaming, the latter suggesting the presence of sapbnins. The high fibre content of the material could also have limited intake in wilted, dry or stemmy kikuyu. The relative importance of these factors appears to change with growth stage, the amount of nitrogen fertilizer applied, stocking rate and moisture supply. The factors which are detrimental to forage quality such as oxalates and nitrates are higher in the young and actively growing material than in older material, while the in vitro production of foam seems unrelated to forage quality and remained high, despite changes in other factors which detrimentally affected forage quality.

The accuracy of indirect methods for predicting feed intake of sheep at steady-state intake and following abrupt changes in intake

Abstract Four indirect methods for estimating feed intake were compared with actually measured feed intake when intake was uninterrupted, and also when intakes were changed abruptly. Intakes were estimated from: marker infused into the rumen and collected at the abomasum of faeces, marker infused into the ileum and collected at the faeces, faeces collection using faecal bags and a method which does not use markers, but uses the kinetics of rumen digestion and passage. During uninterrupted intake all methods gave relatively accurate estimates of intake provided digestibility was estimated accurately. With abruptly changing intakes, longest delays were observed with the marker based methods. The faecal collection method and the method based on rumen digestion kinetics had the shortest delay before giving the same value as actually measured intake. It was concluded that with rapidly changing intakes, the indirect methods will lag behind actually measured intake by about two days.

Copper and Molybdenum Levels in Tissues of Hypercuprotic Sheep during and after being Fed Different Levels of Molybdenum

High levels of molybdenum (Mo) fed for short periods of time can reduce the level of accumulated copper (Cu) in the livers of sheep (1). This results in elevated levels of Cu and Mo in plasma and other tissues (2,3), including the liver (4). Such liver Cu levels will not be a reliable indication of the Cu status of the animal since some time is required after withdrawal of Mo to resume “normal” levels. Plasma Cu was found to reach an elevated level within 12 days of feeding Mo and return to normal within a similar period after withdrawal of Mo (5). The effect of high levels of dietary Mo and the withdrawal of the Mo on Cu and Mo levels in plasma and tissues of sheep was investigated. Two sheep breeds which differ in ability to accumulate hepatic Cu were used.