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 Na2SeO3); two concentrations of Cu; 6·7 and 17·0 mg Cu (Cu added as CuSO4) and two concentrations of S; 2·15 and 3·97 g S (S added as Na2SO4)/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.

An experiment was conducted to investigate the effects of supplements of sorghum grain (1·1 kg/day), sodium propionate (65 g/day) and intra-abomasal glucose infusion (200 g/day) on the liveweight gain (LWG), glucose metabolism and nitrogen utilization of Hereford steers (four per group) given molasses-based diets ad libitum (molasses 589, urea 18, sunflower meal 194, pangola grass hay 187, minerals 12 g/kg as fed). There was no significant effect of treatment on voluntary feed consumption (97–106 g dry matter (DM)/kg0·75 per day) or DM digestibility (0·564–0·579). The LWG of steers given grain supplements (899 g/day) and sodium propionate (943 g/day) were significantly (P<0·05) higher than those of steers given the basal diet (741 g/day) and basal diet plus glucose infusion (794 g/day).

All supplements decreased plasma urea concentrations and urinary N excretion and increased the efficiency of N utilization from 0·19 to 0·36–0·38 g N retained per g apparently digested N intake. The provision of grain (13% DM intake) increased ammonia and volatile fatty acid (VFA) concentrations in rumen fluid, and both grain and sodium propionate increased the proportion of propionic acid in ruminal VFA. Grain supplementation and glucose infusions significantly (P<0·05) increased glucose entry rates (g/day and g/kg0·75 per day) without affecting plasma glucose concentrations or glucose pool size and space. Sodium propionate supplements increased plasma insulin concentrations to a lesser extent than grain supplements and glucose infusion. Increased glucose availability in the present studies was associated with an improved utilization of dietary protein and, in some cases, with improved LWG.

In two experiments conducted at Badgery's Creek, NSW (Latitude 34°S) the roles of testosterone and the thyroid hormones triiodothyronine (T3) and thyroxine (T4) as possible initiators of the change in voluntary feed intake (VFI) associated with the seasonal reproductive behaviour (rut) in male fallow deer were investigated.

In Expt 1, the association between changes in these hormones with the onset of the rut was assessed in deer in which the timing of this event was manipulated by changing the photoperiod, or by melatonin administration. Groups were maintained under either natural photoperiod (n=6; control), a constant long daylength (16 h light[ratio ]8 h dark; n=9; LD group) or a constant long daylength and implanted with melatonin capsules (n=5; LD+M group) for 7 months from December until the following July. Blood samples were obtained weekly and VFI recorded.

Feed intake decreased by 94% from the last week of March for 3 weeks in the control group. Changes of a similar magnitude were measured in the LD and LD+M groups but these changes were advanced by 1 and 9 weeks respectively in these groups. In all groups, circulating testosterone concentrations increased markedly at a time corresponding with the decrease in VFI. The concentrations returned to basal levels with the resumption in VFI. A distinct decrease in plasma concentrations of T3 and T4 in all three groups was associated with the decrease in VFI, however, the relationship with T3 was less apparent.

In Expt 2, the role of testosterone in the regulation of the decline in VFI was investigated. Fallow bucks were treated with testosterone enanthate every 4 or 5 days for 28 days up to 6 weeks prior to the expected onset of the rut. Plasma testosterone concentrations, which were increased 13-fold, resulted in a decline in VFI which was comparable to that observed in the subsequent rut. Plasma free fatty acid concentrations were correlated negatively with the decline in VFI.

Thus, the seasonal increase in circulating testosterone concentrations plays an important role in initiating the fall in VFI associated with the rut. As the rut was still apparent in animals maintained under an extended photoperiod, it is possible that factors other than decreasing daylength act as the cue for the timing of the rut.

The aim of the study was to investigate the changes in renal function in late pregnant and early lactating Corriedale ewes. Compared with the non-productive state, plasma urea concentration was increased by 67% during pregnancy, whereas it decreased by 36% during lactation. Urine flow, urea clearance, renal plasma flow and glomerular filtration rate were significantly reduced (P<0·05) during both late pregnancy and early lactation. Filtered load of urea and the amount of urea eliminated were significantly reduced (P<0·05) only in lactating ewes. No changes were noted in the fractional excretion of urea, the filtration fraction and the urine osmolality during both late pregnancy and early lactation. It was concluded that, as in other breeds, Corriedale ewes can adapt to increased nitrogen requirements during late pregnancy, and especially during early lactation, by increasing the renal conservation of urea. Unlike other breeds, however, Corriedale ewes restrict the urine urea losses mainly by reducing renal plasma flow and glomerular filtration rate, without any modification of the tubular reabsorption of urea during both late pregnancy and early lactation.

Experiments were carried out at Uhříněves (Czech Republic) in 1996 and 1997 to evaluate the effects of avoparcin, bacitracin, flavomycin, tylosin and virginiamycin on in vitro fermentation of ovine ruminal contents and rabbit caecal contents. In incubations of the rumen contents supplied with starch, hemicellulose and pectin, all antibiotics at 20 μg/ml decreased production of fermentation gas and changed molar composition of fermentation products in favour of propionate. Flavomycin, tylosin and virginiamycin significantly decreased total production of volatile fatty acids (VFA). In incubations of the rabbit caecal contents, attempts to modify composition of microbial metabolites failed. Bacitracin was the only antibiotic which significantly increased the molar percentage of propionate and decreased acetate. This fermentation shift was accompanied by a decrease in total VFA production. The net production of propionate was thus similar in control and bacitracin-treated cultures. Rumen in vitro fermentation yielded more fermentation gas, methane and propionate than rabbit caecal fermentation of the same substrate. There was no apparent effect of antibiotics tested on methanogens in either microbial system, as the ratios of methane to VFA production were similar in control and treated cultures.

Growth and reproduction of the snail Helix aspersa (Müller) var. maxima were examined at four combinations of temperature and artificial photoperiod and in transparent and opaque containers at two temperatures for over 40 weeks. Effects of temperature on both processes predominated. However, following 10 weeks of oviposition at optimum temperature (20°C), absence of photoperiod inhibited egg-laying throughout a further 15 weeks. Following inhibition of oviposition, the albumen gland atrophied, indicating the storage of secretory products.

Snail growth was improved by rearing in opaque rather than transparent containers in a long-day photoperiod. Snail oviposition was unaffected by container type throughout a 28-week period, demonstrating an acute perception of photoperiodicity by snails maintained at low light intensity.

First-harvest, precision-chopped Lolium perenne grass with a dry matter (DM) content of 132·0 g/kg and water-soluble carbohydrate (WSC) and crude protein (CP) contents of 24 g/kg and 106 g/kg DM, respectively, was ensiled in farm scale silos following the addition of formic acid (FA) (2·5 l/t) or molassed sugarbeet pulp (MSBP) (50 kg/t). Mature twin-bearing ewes (n=56) were allocated to one of seven treatments and offered either FA-treated silage or MSBP silage ad libitum. The trial commenced on day 91 of pregnancy, when the ewes were offered FA-treated silage (T1), FA-treated silage+soyabean meal (T2), MSBP silage (T3), MSBP silage+soyabean meal (T4), FA-treated silage+MSBP (T5), FA-treated silage+MSBP+soyabean meal (T6) or FA-treated silage+a barley-based supplement (150 g CP per kg DM) (T7, control). Soyabean meal supplementation was only offered in the last 3 weeks of pregnancy, with the objective of achieving a total CP intake of 220 g/ewe per day. Compared with the FA-treated silage, the MSBP silage had a higher nitrogen content (P<0·01) and a lower neutral detergent fibre (NDF) content, but the two silages did not differ in DM, acid detergent fibre (ADF) or gross energy contents. Silage DM intakes (SDMI) were higher on the MSBP silage-based diets (T3, T4) than for any other treatment (P<0·05). The addition of soyabean meal significantly increased SDMI in T2 in the last week of pregnancy (P<0·05), but there was no response in SDMI to soyabean meal supplementation in any of the other treatments. Ewe liveweight changes (kg) of −0·4, 4·1, 7·8, 10·2, 7·1, 9·6 and 10·8 (S.E.±1·2), body condition score changes of −0·96, −0·59, −0·42, −0·33, −0·37, +0·01 and −0·27 (S.E.±0·1) and total lamb birth weights (kg) of 8·0, 8·7, 9·2, 9·9, 8·6, 8·0 and 10·4 (S.E.±0·5) were recorded for ewes in T1 to T7 respectively.

A study was conducted to examine whether oilseed cakes (cottonseed cake (CSC) or noug (Guizotia abyssinica) cake (NSC)) are complementary to the bird-resistant (BR) and non-bird-resistant (NBR) varieties of sorghum stover and whether sheep select against morphological fractions containing high concentrations of tannins or proanthocyanidins (PA). Either 24 (growth study) or 16 (metabolism study) Ethiopian Menz sheep were used in a randomized complete block design to study the interaction of variety of sorghum stover with type of oilseed cake on feed selection, intake, digestibility, microbial protein synthesis, nitrogen (N) retention and growth. The degradability of the feeds and refusals was also determined. The NBR variety was more degradable than the BR variety during the early hours of incubation. NSC degraded faster, although to a lesser extent than CSC. Stover variety had no effect on ruminal ammonia concentration (RAC) while CSC induced a higher RAC than NSC did. Sheep given the NBR variety had more dust, less heads, less leaf, less sheath and more stem in their ingesta than those fed on the BR variety. It was seen that the sheep discriminated against the stems, since the ratio of stem in ingesta to stem on offer was <1. Since PA are more highly concentrated in the sheath than in any of the other plant fractions, it appears that the choice of the morphological composition of the ingesta by sheep was not determined by PA. Sheep selected a diet which was 2–5% or 5–11% more degradable than the offered or refused feeds, respectively. Relative to NSC, CSC enhanced the intake of N, N bound to neutral detergent fibre (NDF), digestibility and N retention and tended to increase (P<0·06) liveweight gain (LWG) and organic matter (OM) intake but had no effect on microbial protein synthesis. Compared with the NBR variety, the BR variety depressed N digestibility and N retention, had no effect on microbial protein synthesis and on LWG, but depressed the efficiency of LWG by c. 30%. Sheep given the BR+NSC diet had the lowest daily gain but excreted copious amounts of urine, probably in an attempt to eliminate toxic waste substances. Since sorghum is a crop of the semi-arid regions, it is quite likely that, although the bird resistance trait increases crop yield, it has resulted in a feed that is rather less suitable for livestock in this production environment, where water shortages are frequent. In-depth studies on the consequences of water shortage on the utilization of bird-resistant sorghum stover are required.

Increasing the dietary intake of K reduces the Mg absorption from the forestomachs of ruminants by decreasing the apical membrane potential and increasing the transepithelial potential difference (Vt). To evaluate genetic variations in the dependence of Mg absorption on K intake, we performed Ussing chamber experiments and studied the effect of Vt on 28Mg fluxes across rumen epithelium from different breeds of sheep. All breeds showed net absorption of Mg (JMgnet) in the absence of electrochemical gradients. JMgnet of Skudde was lower compared to Merino or Schwarzkopf sheep. Increasing Vt decreased mucosal to serosal Mg flux (JMgms) and increased serosal to mucosal Mg flux. The effect of Vt on JMgnet was almost identical in all breeds of sheep (−30 to −45% for a 25 mV increase in Vt). The effect of Vt on JMgms revealed a Vt-dependent and a Vt-independent component of transcellular Mg absorption in all breeds. Considering the driving forces for these two Mg transport mechanisms, the effect of K on Mg absorption will mainly depend on the feeding regimen, i.e. dietary K must have a relatively higher effect on Mg absorption at low Mg intake levels, which explains the correlation between pasture quality and tetany frequency as well as the missing effect of K on Mg status in some older studies.