A preliminary examination of the nutritive value of four saltbush (Atriplex) species.

Abstract

Proc. Aust. Soc. Anim. Prod, Vol. 18 A PRELIMINARY EXAMINATION OF THE NUTRITIVE VALUE OF FOUR SALTBUSH (ATRIPLEX) SPECIES B.E. WARREN*, C.J. BUNNY* and E.R. BRYANT* Four saltbush (Atriplex spp.) and two hay-based diets were fed to individually Sheep fed the saltbush diets generally penned sheep over a three week period. lost weight (about 200 g/day) and had an elevated water intake relative to the hay-fed group. Mean dry matter (DM) intake on all the saltbush diets increased over the term of the experiment. Intake of a diet containing equal proportions of hay and one of the saltbushes was much greater than any of the other diets. Digestibility of dry matter from the saltbushes was 0.53 to 0.62, nitrogen 0.70 to 0.81 and fibre 0.26 to 0.45. INTRODUCTION The increasing importance of saltbush (Atriplex spp.) in revegetation programs on saline soils makes a detailed evaluation of this species essential as Pol (1980) reviewed the nutritional data are limited and quite variable. literature on saltbush and found nitrogen levels of between 22 and 34 g/kg, crude fibre contents of 90 to 140 g/kg and total ash of from 90 to 380 g/kg. None of these data relate to species commonly grown in Western Australia (WA). More recently Malcolm et al- (1988) reported relatively high in vitro DM digestibilities of from 0.62 to 0.75 for leaf material of five saltbush species grown in central WA, and digestibilities of stem material about half that of leaf. The five species also had crude protein contents of about 100 g/kg but quite high oxalate levels; A, amnicola and A. undulata had levels of 59 and 66 g/kg oxalate respectively. These levels are cause for concern as oxalates can be toxic in ruminants. Much of the ash content of saltbush is sodium and potassium chloride and sheep grazing saltbush consume large amounts of these elements. This may lead to a decrease in feed intake and an increase in water consumption (Hamilton and Webster, 1987), although Wilson (1966a) found that addition of sodium chloride to hay diets only reduced feed intake at high levels (>5%), perhaps due to reduced palatability. Wilson (1966b) found a proportional increase in water intake with increasing salt ingestion and Pol (1980) showed elevated water Most of the ingested sodium (>90%) is intakes by sheep on saltbush diets. excreted in the urine but even at high levels of intake the concentration in the urine remained relatively constant due to the high water intake (Wilson, 1966b). The objectives of this experiment were to examine the nutritive value in sheep of four saltbush species commonly grown in WA and the relationship between water intake and saltbush consumption and the effects on short term weight changes. Twenty eight adult Merino wethers (49-62 kg) were allocated on body weight, using a stratified scale, to six treatment groups; five of five animals and one of three. They were housed in individual pens indoors, with individual feed and water containers. The sheep were weighed, after fasting overnight, at the commencement of the experiment and every seven days thereafter. * Sheep and Wool Branch, Dept Agriculture, Katanning, W.A. 6317. 424 Proc, Aust. Soc, Anim, Prod. Vol. 18 Foliage, consisting of leaf and stem material to about 5-6 mm diameter, of four saltbush species (A. undulata, A. lentifonnis, A. amnicola, A. cinerea) was collected during early May, 1989, from two year old plantation-grown bushes and dried at 60�C in a forced draft oven for 48 hours to allow long-term storage, The dried material was then chopped through a chaff-cutter (20-30 mm length) and sealed in plastic bags until used. Oaten hay was similarly chopped and stored. The chopped oaten hay and four saltbushes were offered to the 5 groups of five sheep and a mixed diet containing 500 g/kg oaten hay and 500 g/kg A. undulata to the group of three. All diets (D) were offered for 21 or 14 (D6) days at All feed residues were collected about 10% above the previous days intake. daily, dried, weighed and retained for analysis. Sub samples of about 50 g were taken daily from the feed material and bulked over each seven-day period. Water containers were replenished with a measured amount of rain water twice daily and intake recorded. After the first seven days of the experiment, total faeces were collected and weighed. A 10% sub-sample of the wet faecal material was taken, dried at 65OC and bulked over each seven day period. At the completion of the experiment feed samples and feed residues from each seven day period were dried to a constant weight at 65OC. These and the faecal samples were then ground through a 1 mm screen in a laboratory hammer mill and stored in sealed plastic containers to await analysis. Standard analytical procedures were used to determine neutral detergent fibre (NDF), acid detergent fibre (ADF), lignin, ash, Kjeldahl nitrogen (N), inorganic phosphorus (P), sodium (Na) and potassium (K). Crude protein was calculated as N x 6.25. Analysis of Chemical composition of the diets (Dl to D6) is shown in Table 1. variance was used to examine differences between means. Table 1 Chemical composition (g/kg DM) of the two control diets (oaten hay and oaten hay/A, undulata) and four saltbushes RESULTS The results are summarised in Table 2. Feed intake during week 1 of the experiment was significantly (P<O.Ol) lower for three of the saltbush diets (D3-D5) than the other diets and this was reflected in the weight change of the animals. In week 2, feed intake increased markedly for all diets except Dl and there were no significant differences in intake between the saltbushes and Dl. All animals Intake of D2 was much higher (P<O,Ol) than the other diets. increased in weight in week 2 and there were no differences between diets. In week 3 all the sheep from D6 were removed due to exhaustion of the feed One animal from each of the other saltbush diets (D3, D4 and D5) was supply425 Proc. Aust. Soc. Anim, Prod. Vol. 18 also removed because of continuing excessive weight loss or scouring. Differences were still apparent in feed intake with D3 and D4 being lower (P<O.Ol) than the other diets. Animals on all diets lost weight. When examined over the 21 days of the experiment animals on the saltbush diets (D3-D6) lost more weight (P<O.Ol) than those fed hay (Dl) or hay/A, undulata (D2) - Sheep on the saltbush diets always drank more (P<O.Ol) water than those on the hay diet. There were few differences in water consumption between the saltbush diets (D3-D6). Table 2 Mean feed (g DM/day) and change (g/day) over three week 2 for dry matter nitrogen (N) in sheep fed diets water intake (ml/day) and liveweight (LW) weeks, and coefficients of digestibility at (DM), neutral detergent fibre (NDF) and chopped hay, hay/saltbush or four saltbush * ** s-e.1 should be used for examination of differences between treatments with five reps (Dl,D3-D6); s-e.2 for examination of differences between the treatment with three reps (D2) and the other diets Means within a row with the same (a-c), or without, a superscript do not differ significantly (P>O.O5) Dry matter digestibility on all diets was greater than 0.50 (Table 2), however, digestibility of A. amnicola and A. undulata was significantly lower (P~0.01) than Dl and D2. Digestibility of NDF was also lower (P<O.Ol) for A. undulata. The N content of saltbushes (14.4 to 19.8 g/kgDM, corresponding to 90 and 124 g CP/kgDM) t had co-efficient8 of digestibility varying (P<O.Ol) between 0.70 and 0.81. The hay was of relatively low quality with a N content and N digestibility much lower (P<O.Ol) than that of the saltbushes although the 426 Proc. Aust. Soc. Anim. Prod. Vol. 18 sheep were able to maintain weight on this diet. DISuJsSIoN Feed intake and weight gain of the sheep generally improved in week 2 as the animals adapted to the feed; this improvement was not continued in week 3. As indicated, several sheep that had been consuming saltbush refused their diets during week 2 and early in week 3 and this led to the removal of some animals from the experiment. The reason for this is not clear. Oxalate levels can be high in some salt tolerant species and this may have contributed to the problem; analysis of the diets for oxalates is currently being undertaken. The Na+K and total ash levels were respectively about 8 and 30 g/kg higher in A. amnicola and Ai cinerea than in the other two saltbushes and, although differences were not always significant, water intake was generally higher for the sheep fed A. amnicola and A. cinerea. For both diets N digestibility was also significantly lower. This may have related to a more rapid flow rate from the rumen due to the higher salt intake as suggested by Pol (1980). The N content of the saltbushes examined here was lower than those reviewed by Pol (1980) and the fibre relatively high; these analyses would be influenced by the material sampled and the season of growth. Much of the data of Pol (1980) may have been for leaf material, or for material containing a higher proportion of leaf. For this experiment leaf and. stem material, similar to material sheep had been observed to eat in the field, was collected and fed to just above appetite. Analysis of the feed and residues showed that the animals did not select from the ration they were given. The low intake of the saltbush diets led to the marked weight loss of the sheep fed this material. To maintain body weight, sheep need to consume about 900 g DM/day of 55-60% digestible material. This intake of saltbush was rarely achieved and yet even when it was (D5, week 3) the sheep still lost weight. In week 1 of the experiment consumption of A. cinerea (D6) and hay (Dl) was similar yet those fed D6 lost significantly more weight than those fed hay. In week 2 intake of D6 was second only to the hay/A. undulata (D2) diet but body weight gain was the lowest of all diets. While the high salt (ash) content of the saltbushes influences intake of digestible DM, these data may indicate that there are also other antinutritive factors associated with A. cinerea. Atriplex undulata when fed alone (D3) was consumed at a lower level than the other saltbushes but in a mixed diet with hay it was readily accepted. Intake of hay/A. undulata (D2) was frequently twice that of the the other diets and liveweight change reflected this when examined over the whole measurement period. This may indicate a potential use for saltbush as a supplement to dry pasture and stubble, and further work should be undertaken to examine the effects of mixed grazing of saltbush and dry pasture on sheep performance. REFERENCES HAMILTON, J-A. and WEBSTER, M.E.D. (1987). Aust. J. Agric. Res. 38:187. MALCOLM, C.V., CLARK, A-J., D'ANTUONO, M-F. and SWAAN, T.C. (1988). Agric. Ecosystems Environ. 21:265. POL, J.E. (1980). Hans. Thesis, University of Western Australia, Perth, W.A. WILSON, A.D. (1966a). Aust. J. Agric. Res. 17:147. WILSON, A.D. (1966b). Aust. J. Agric. Res. 17:155. 427