H. Dove

Diet selection, herbage intake and liveweight gain in young sheep grazing dual-purpose wheats and sheep responses to mineral supplements

Young crossbred sheep grazed dual-purpose wheat crops in three experiments evaluating the factors affecting variability in liveweight gain. All crops had high crude protein contents [22–33% dry matter (DM)] and in vitro DM digestibilities (0.754–0.876), which would not have limited liveweight gains. Digestibilities measured in vivo in grazing animals were even higher (0.839–0.854). No significant differences were found in preference of sheep for six different wheat cultivars. The diet composition and herbage intake of the sheep were measured in all experiments using plant wax marker profiles. Wheat forage made up 0.88–0.98 of the diet in sheep supplemented with unchopped oaten hay and 0.97–0.99 of the diet in unsupplemented sheep. Total intakes in the first two experiments were ~1380 g DM/day (3.7–4.0% of liveweight). Intakes in Experiment 3 were lower (960–1180 g DM/day; 2.6–3.1% of liveweight) because drought conditions reduced the amount of forage available. There were marked liveweight gain responses (30–50%) to mineral supplements based on NaCl, CaCO3 and MgO. Evidence is presented that these were mainly due to the Na and Mg, since the consumed diet was more than adequate for Ca. Relative to the requirements of young sheep for growth, wheat forage had high K levels (6–8 times requirement) and very low Na levels (as low as 0.02–0.03 of requirement) and thus very high K : Na ratios. Since high dietary K : Na ratios can greatly reduce Mg absorption from the rumen, the response to Na may have been partly mediated through improved Mg absorption. The liveweight gain responses to Na/Mg were large and economic, so it is recommended that young sheep grazing dual-purpose wheat be routinely supplemented with a 1 : 1 mix of NaCl : MgO.

Effects of a spring-sown brassica crop on lamb performance and on subsequent establishment and grain yield of dual-purpose winter wheat and oat crops

We evaluated the integration of a spring forage brassica crop (Brassica campestris cv. Hunter) into a cereal–pasture rotation, as a means of assessing the effects of this practice on the subsequent establishment and grain yield of wheat and oat crops. A brassica crop was grown for lamb production on 0.2 ha plots prepared for dual-purpose cereals, in spring 2003 near Canberra, ACT, Australia. Mackellar winter wheat and Blackbutt oats were sown in the following autumn on the previously sown brassica plots and on plots left fallow over the spring–summer period. A factorial experiment was used to determine the effects of (i) cultivar, (ii) brassica v. fallow, and (iii) grazing on cereal establishment and grain yield. Lamb liveweight gains on brassica over 33 days were rapid (294 g/day) and provided 2141 grazing days/ha and 637 kg lamb weight gain/ha. Average grain yield of Mackellar on plots following brassica (2.8 t/ha) was reduced by 29% compared with plots following fallow. Average grain yield on grazed plots (2.6 t/ha) was reduced by 38% compared with ungrazed plots. In both Mackellar and Blackbutt, reduced numbers of kernels per spike and reduced kernel weight accounted for the reduction in grain yield under grazing. Two other experiments were conducted at a separate site to obtain data on the nutritive value of the cereal forages and to record phenological development of the two cereals and compare grain yield responses to cutting before and after stem elongation stages. In vitro and in vivo measurements of digestibility in the vegetative phase were similar in the two cereals (91–94%). Grain yield was significantly reduced following cutting at the post stem elongation stage in Mackellar and Blackbutt and, in Mackellar, was attributable to reduced kernel number per spike and kernel weight. The overall economic return, combining actual returns from lamb production on the forage brassica, and estimated returns from grazing and grain production, after variable costs of each phase were accounted for, were

Faecal alkane recoveries from multi-component diets and effects on estimates of diet composition in sheep.

1117/ha for Mackellar wheat and

Using the alkanes and long-chain alcohols of plant cuticular wax to estimate diet composition and the intakes of mixed forages in sheep consuming a known amount of alkane-labelled supplement.

1081/ha for Blackbutt oats. These returns were

Effect of roughage species consumed on fecal alkane recovery in sheep, and effect of sample drying treatment on alkane concentrations

583/ha and

Mineral supplementation of lambing ewes grazing dual-purpose wheat

910/ha more than the estimated return from the fallow, ungrazed treatments for wheat and oats, respectively.

Intake and productivity of lambs grazing leafy or stemmy forage rape and the effect of energy or protein supplements

In a feeding trial with sheep, four animals each were fed one of the three roughages (perennial ryegrass (PR), meadow fescue (MF) and red clover (RC)) or one of the four different mixtures (g/day 250 : 250 : 250, 375 : 75 : 300, 525 : 187.5 : 37.5 and 75 : 525 : 150, respectively) of those three roughages, both with and without the inclusion of 100 g of beeswax-labelled barley. Further, four sheep received a pure lucerne diet to enlarge available data on single species faecal recoveries. All sheep except those fed single-component diets and the 250 : 250 : 250 roughage mix were administered intra-ruminal alkane controlled-release devices (CRD). The aim of the study was to investigate the effect of diet composition on faecal alkane recoveries, and to assess the accuracy of the alkane-based estimate of diet composition and intake based either upon a general set of faecal recoveries across diets or upon dietary recoveries and dietary samples more specifically attributable to individual dietary treatments. For each roughage component independently, the accuracy of diet composition estimates was assessed using linear regression across all diets. The estimates of the proportion of barley were analysed further using mean differences and mean prediction errors. Faecal alkane recovery increased with increasing chain length and was affected by diet composition. RC had a significantly higher faecal recovery for alkanes C25, C27, C29 and C31 than at least one of the other single-roughage diets. When considering mixed diets consisting of PR, MF, RC and barley, the composition of the roughage component significantly affected faecal recovery of all alkanes except C30 and C33. The inclusion of beeswax-labelled barley caused a decrease in faecal recovery of alkanes up to C29. This effect was attributable to the beeswax rather than the barley itself. By contrast, the decrease of faecal recovery of synthetic dosed alkanes from the CRD in diets containing barley, compared with the corresponding diets without barley, was attributable to the supplement itself. It was concluded that synthetic dosed alkanes behaved differently during gut transit from natural alkanes. The proportions of individual dietary components were estimated well over a wide range of proportions. Generally, the more information available, the more accurate the estimates achieved. However, a general set of faecal alkane recoveries and bulked samples of dietary components yielded estimates of diet composition sufficiently accurate for a large number of studies, especially in situations where groups of animals are of concern and not the individual animal.

New perspectives on the mineral nutrition of livestock grazing cereal and canola crops

In a feeding trial with 24 sheep, we used the alkanes, long-chain alcohols (LCOH) or both of these plant wax markers, to estimate the diet composition of animals offered diets comprising alkane-labelled cottonseed meal (CSM) together with up to four forages. The diets used were: Diet 1 subterranean clover (Trifolium subterraneum); Diet 2 subterranean clover + phalaris (Phalaris aquatica); Diet 3 subterranean clover, phalaris + annual ryegrass (Lolium rigidum); and Diet 4 subterranean clover, phalaris, annual ryegrass + wheat straw (Triticum aestivum). Estimates of diet composition were made following correction of faecal alkane or LCOH concentrations for incomplete faecal recovery, using recovery estimates derived from individual animals, mean recoveries for a given dietary treatment or grand mean recoveries. Estimated dietary proportions of CSM and known intakes of CSM were used to estimate forage intake. The LCOH concentrations of the diet components were much higher than their alkane concentrations, especially for phalaris. Multivariate analyses showed that the discriminatory information provided by the LCOH was additional to that provided by the alkanes, and that a combination of (LCOH + alkanes) discriminated better between diet components than either class of marker alone. Faecal recoveries of LCOH increased with increasing carbon-chain length; there were no differences in recovery attributable to diet. The most accurate estimates of diet composition were obtained with the combination of (LCOH + alkanes). Estimates of diet composition based on LCOH alone were not as good as alkanes alone, due to the high correlation between the LCOH profiles of phalaris and ryegrass. Total grass content of the diet was very accurately estimated using LCOH. Diet composition estimates provided estimates of whole-diet digestibility, which did not differ from the measured values. Trends in the accuracy of forage intake estimates reflected those found with diet composition and almost two-thirds of estimates based on (LCOH + alkanes) had lower error than those found with alkanes alone. The results confirm that supplements labelled with plant wax components can be used to estimate forage intake, and also show that the LCOH are useful markers for estimating diet composition. Intakes were also computed using a combination of natural LCOH concentrations in the diet and the daily dose rate of even-chain alkanes administered by intra-ruminal device. Differences between intakes so estimated and the measured intakes were closely related to the difference in faecal recovery between the LCOH/alkane pair used to estimate intake, by an amount close to that expected on theoretical grounds. It is concluded that the use of plant wax LCOH, especially in combination with alkanes, will result in improved estimates of diet composition and intake in grazing animals.

Responses to grain : sunflower meal supplements by weaned calves grazing mature pasture or eating hay in pens

The effect of roughage species on fecal alkane recoveries (the proportion of ingested alkane recovered in feces) and the effect of sample drying treatment on alkane concentrations in samples of dietary components and feces were studied in 2 experiments conducted with sheep. In experiment 1, 6 single-species diets (2 different batches of lucerne (Medicago sativa) hay, Phalaris aquatica hay, oaten straw, wheaten straw, Trifolium subterraneum hay) were fed to 6 animals each in a crossover design. A further 3 animals were fed a mixed diet of Trifolium subterraneum and beeswax-labelled cottonseed meal. In experiment 2, fecal samples from sheep fed 4 different mixtures of pelleted lucerne and ground wheat grain (lucerne : wheat 360 : 270 g/day; 360 : 450 g/day; 600 : 270 g/day; 600 : 450 g/day; 4 animals per diet), a fixed amount (270 g/day) of which was labelled with beeswax, were dried in 1 of 3 ways: freeze drying, oven drying at 65°C for 48 h or oven drying at 105°C for 24 h. Differences in fecal alkane recoveries between various roughage species were not statistically significant, due in part to high between-animal variation in recovery. The fecal recovery of odd-chain alkanes increased in a curvilinear manner with carbon-chain length. The fecal recoveries of even-chain alkanes were highly variable, due to their low concentrations, and also differed from those expected given the recoveries of the adjacent odd-chain alkanes. The results indicate that oven drying fecal samples at 65°C for 48 h could replace freeze drying, but drying at 105°C significantly reduced fecal alkane concentrations. Further studies are necessary to investigate the effect of drying treatment on the alkane concentration in fresh roughages.

Nutrient requirements of domesticated ruminants.

Lambing ewes were grazed on dual-purpose wheat in two experiments in 2010 and 2011 with or without access to a mineral supplement. The calcium, magnesium and sodium content of wheat forage was below the requirements of ewes during late pregnancy and lactation; however, no clinical cases of hypocalcaemia or hypomagnesaemia were observed in either experiment. Blood serum assays identified eight hypocalcaemic ewes and one hypomagnesaemic ewe in Experiment 1, and one hypocalcaemic ewe in Experiment 2, and the provision of a mineral supplement comprising of magnesium oxide, calcium carbonate and coarse salt had no effect on blood magnesium, total calcium, phosphorus or sodium. Lamb birthweight and survival were not affected by provision of the mineral supplement in either experiment; however, the growth rate to marking (mean 38 ± 10 days of age) of twin-born lambs was higher in Experiment 1 when the supplement was provided to ewes grazing wheat (259 vs 243 g/head.day; P = 0.002).