D. K. Revell

Feed gaps in mixed-farming systems: insights from the Grain & Graze program

A central concern of the Grain & Graze research, development and extension program has been improving the management of the feedbase on mixed farms through addressing ‘feed gaps’ – times of year during which the supply of forage is insufficient to meet livestock demand. In this review, we use the available data on pasture growth and quality, supplemented by modelling results, to describe the characteristic timing of feed gaps across the Australian cereal-livestock zone. Feedbase interventions studied during the Grain & Graze program have mainly addressed the supply side of the feed balance equation. We review these studies, paying particular attention to the time scale of the variability in the feed balance that each intervention is intended to address. We conclude that grazing of cereals (either dual-purpose or forage crops) is the most promising means of alleviating winter feed gaps in regions where they are important. Reducing feed gaps in summer by relying on unpredictable summer rainfall events will increase year-to-year variability in forage production and will therefore require more flexible livestock management systems to exploit it. The use of forage shrubs offers a practical tool for increasing the predictability of summer and autumn feed supply, but given their moderate capacity for providing additional metabolisable energy it remains important to carefully manage livestock over autumn and to manage the herbaceous inter-row pasture. Feed gaps mainly arise from an interaction between biology and economics. We find, however, that the options studied in the Grain & Graze program for addressing feed gaps require either greater complexity in pasture and grazing management or more opportunistic livestock trading; they therefore come at a cost to the manager’s limited decision-making time. Times with feed gaps are also times when particular natural resource management risks (especially erosion) need to be managed. Supply-side interventions to relieve feed gaps will generally use more soil water, which will often have positive effects on natural resource management outcomes.

Shearing ewes at mid-pregnancy is associated with changes in fetal growth and development

This study investigated the effect of mid-pregnancy shearing (at Day 70 of pregnancy, P70) on herbage intake of grazing single- and twin-bearing ewes, lamb birth weight, and cold resistance of new-born lambs. At pregnancy diagnosis on P50, 30 single-bearing and 30 twin-bearing ewes were allocated either to be shorn at P70 (n = 15 for each pregnancy rank) or to remain unshorn to serve as controls (n = 15 for each pregnancy rank). All ewes were mated over a 3-day period with synchronisation of their oestrus. Herbage intake was measured indirectly from in vitro pasture digestibility and faecal output of grazing ewes, with the use of intra-ruminal chromium slow-release capsules, over six 5-day periods from P64 to P105. The weights of placental and fetal tissues were assessed in a subgroup of 16 ewes at P140 and P141. In the remaining sheep, lamb liveweight at birth and during lactation until weaning at 103 days of age was measured, and cold-resistance of new-born lambs was assessed by measuring summit metabolic rate (SMR) by indirect calorimetry. Ewe liveweight (corrected for fleece weight), condition score, and herbage intake during pregnancy were not affected by shearing treatment. Mid-pregnancy shearing did not affect placental weight, but increased the relative weights (i.e. g/kg liveweight) of fetal thyroid gland and lungs and reduced the relative weight of adrenal glands and heart. The ratio of secondary to primary wool follicles in near-term fetal skin was about 10% higher in offspring of shorn than of unshorn ewes. The metabolic rate of fetal hepatic tissue was increased by mid-pregnancy shearing, particularly in twin fetuses, possibly indicative of an increase in placental transport of nutrients to the fetuses. This conclusion is supported by the greater birth weight (average response 0.5 kg) of lambs born to ewes shorn at mid-pregnancy. Mid-pregnancy shearing also increased the SMR of new-born twin lambs by 16%, but decreased the SMR of singleton lambs by 26%. These results indicate that mid-pregnancy shearing can increase lamb birth weight without increasing ewe herbage intake or placental weight. An increase in the efficiency of nutrient uptake by the placenta is implied, and possible effects on the activity of thermogenic tissues are discussed.

Maternal constraint and the birthweight response to mid-pregnancy shearing

Pregnancy shearing has been shown to increase lamb birthweights. However, results have been variable between studies. It has been suggested that the birthweight response to pregnancy shearing is greatest in conditions in which the unshorn dam gives birth to lambs of low birthweight. This study was designed to examine the birthweight response under 2 differing maternal treatments (one designed to restrict fetal growth and the other designed not to limit fetal growth), with the aim of explaining the variation observed in pregnancy shearing studies. Mixed aged Romney cross ewes were either shorn during mid pregnancy (n = 55) or left unshorn (n = 50). At shearing, ewes were split into either a ‘maintenance’ group (64 kg at shearing and fed to permit total ewe liveweight gain equivalent to expected conceptus growth during mid- to late-pregnancy) (n = 52) or a ‘low’ group (54 kg at shearing and fed to permit total ewe liveweight to increase at half the expected conceptus growth during mid- to late-pregnancy) (n = 53), respectively. Mid-pregnancy shearing was found to increase the birthweights of singletons (5.6 v. 4.9 kg, P < 0.05) but not twins, and of lambs born to maintenance group ewes (by 0.6 kg, P < 0.05), but not low group ewes. Additionally, mid-pregnancy shearing had no effect on the thermoregulatory capacity of twin-born lambs. When the results of this study are considered with those of previous New Zealand pregnancy shearing studies, they suggest that there are 2 criteria (and not one, as previously suggested) that must be met to achieve a response to pregnancy shearing. Firstly, the dam must have the potential to respond [i.e. have been destined to give birth to an otherwise lightweight lamb(s)], and secondly, the ewe must have the means to respond (i.e. an adequate level of maternal reserves and/or level of nutrition to partition towards additional fetal growth).

Mid-pregnancy shearing can increase birthweight and survival to weaning of multiple-born lambs under commercial conditions

In several field studies, mid-pregnancy shearing has increased lamb birthweight, which may be associated with an increase in lamb survival. However, animal numbers have been too low in these studies to accurately examine any effects on survival rates to weaning. This study was designed to investigate the effect of mid-pregnancy shearing on the birthweight of multiple-born lambs and their survival rates to weaning under commercial farming conditions at 2 different sites. At Riverside, 657 twin- and 47 triplet-bearing ewes were either shorn at mid-pregnancy (n = 347) or left unshorn (n = 357). Similarly, at Tuapaka, 532 twin-, and 60 triplet-bearing ewes were either shorn at mid-pregnancy (n = 291) or left unshorn (n = 301). Mid-pregnancy shearing significantly (P<0.05) increased the birthweights of lambs at each site (by 0.44 and 0.13u2009kg at Riverside and Tuapaka, respectively). Mid-pregnancy shearing significantly (P<0.05) increased lamb weaning weights (by 1.07u2009kg) and survival rates to weaning (by 5.5%) at Riverside, but not at Tuapaka. These findings show that mid-pregnancy shearing under commercial farming conditions can increase the birthweight of multiple-born lambs and, when the birthweight response is large enough to reduce the numbers of otherwise lightweight lambs, it is associated with an increase in survival rates to weaning.

In vitro screening of selected feed additives, plant essential oils and plant extracts for rumen methane mitigation

BACKGROUNDnRuminants produce large quantities of methane in their rumen as a by-product of microbial digestion of feed. Antibiotics are added to ruminant feed to reduce wasteful production of methane; however, this practice has some downsides. A search for safer and natural feed additives with anti-methanogenic properties is under way. The objective of this research was to examine selected feed additives, plant essential oils and plant extracts for their anti-methanogenic potential in the rumen using an in vitro batch fermentation system.nnnRESULTSnA significant reduction (Pu2009<u20090.05) in methane production was observed with nine feed additives (up to 40% reduction), all eight essential oils (up to 75% reduction) and two plant extracts (14% reduction) when compared to their respective controls. Amongst these, only an algal meal high in docosahexaenoic acid, preparations of Nannochloropsis oculata, calcareous marine algae, yeast metabolites and two tannins did not inhibit microbial gas and volatile acid production.nnnCONCLUSIONSnThe current study identified some potent dietary ingredients or plant compounds that can assist in developing novel feed additives for methane mitigation from the rumen.

Approaches for assessing some attributes of feed-base systems in mixed farming enterprises

Improving the feed-base to better balance livestock demands with the variation in feed supply can improve the sustainability and productivity of livestock enterprises. This paper outlines some approaches and tools that can be applied to the assessment of new feed options and/or potential changes to the feed-base in mixed farming systems. Demonstrations of strategic aspects of designing feed systems include: whole-farm feed planning using simple tools, such as the MLA Feed Demand Calculator, that enable iterative changes to the balance between feed supply and demand to be considered simultaneously; assessing production and environmental risks of different feed-base systems using simulation models (e.g. APSIM, GRAZPLAN); and using bio-economic models (e.g. MIDAS) to investigate the impact of a new feed source on whole-farm profitability and the optimal balance of other feed sources and livestock production system. Also included is an example of an approach to identifying opportunities and seasonal triggers for a tactical response for utilising an alternate feed source (e.g. grazing a grain crop). The importance of economics and risk as factors for assessing feed-base systems is demonstrated. In particular, the marginal value of extra feed supply is a critical element driving the whole-farm economics of the feed system. Some approaches consider seasonal averages, but the risk of year-to-year and within-year variations in the timing and amount of feed supply should also be assessed. Several tools of varying complexity exist to investigate attributes of the feed-base, but it is important that the correct approach is applied to the particular question in mind. A range of approaches could be applied concurrently to fully explore a range of aspects of the performance of a feed-base system.

Nutrition during mid to late pregnancy does not affect the birthweight response to mid pregnancy shearing

This study was designed to determine whether dam nutrition during mid to latepregnancy influences birthweight responses from pregnancy shearing.Romney-cross ewes were either shorn during mid pregnancy(n = 68) or left unshorn (n= 66). Ewes were offered either a maintenance level of feed (a level ofnutrition that enabled the dam to maintain conceptus-free liveweight) or aed to apparenthomogeneity by using various biochemical fractionation procedures, such assolubilization with Triton X-100, sephadex gel filtration chromatography,concanavalin A–sepharose affinity chromatography anddiethylaminoethyl–cellulose ion-exchange chromatography. The isolatedPPase has a molecular mass of approximately 36 kDa and an isoelectric point of5.95. Sperm surface topography of the enzyme was investigated usingfluorescein isothiocyanate-conjugated antibody of the purified PPase. Theimmunofluorescent studies have demonstrated that the isolated PPase islocalized on the external surface of viable sperm. Immunocytochemical studiesalso revealed a marked topographical alteration of ecto-PPase duringepididymal transit of the male gametes. Immunoreactivity was observed all overthe surface of caput sperm, but was restricted primarily to the anterior tipof the head in the corpus sperm and to the posterior part of the head in caudasperm cells. The maturation-dependent decrease in PPase activity was alsoconfi

Adaptation behaviour of local and rangeland cattle relocated to a temperate agricultural pasture

Relocating cattle from rangeland properties to agricultural pastures in southern Western Australia allows producers to improve year-round continuity of feed supply in their beef cattle businesses, and can reduce substantially the time taken to grow animals to meet market specifications. In this study the behaviour and growth of two groups of young cattle that were sourced from different locations was evaluated after they were transferred to a new extensive grazing system. In Experiment 1, 122 Limousin-cross heifers that were raised in the agricultural region of Western Australia (AR cattle) were transferred to the experimental site from a neighbouring property (~10 km away). In Experiment 2, 95 Brahman-cross heifers that were raised in the rangelands of Western Australia (RR cattle) were transferred to the experimental site. Animal growth and behaviour were analysed across time and differences in the time-course of behavioural changes between the groups were compared. Rate of liveweight gain in the AR cattle remained consistent (~1.2 kg/day) during the experiment. There was an increase in horizontal (16%; P < 0.001) and vertical (12%; P = 0.002) head movement in AR cattle over the first several weeks after relocation, indicative of increased grazing activity, but there was little change in other behaviours over the duration of the experiment. In contrast, the RR cattle had reduced growth during the first 4 weeks after relocation (P < 0.001). From weeks 2–4 weight gain in RR cattle was 0.31 kg/day, approximately one-quarter of their average daily gain attained 4 weeks later. During the first 6 weeks, RR cattle showed behavioural changes indicative of adaptation, including a 61% increase in horizontal head movements, suggesting more grazing activity. The paddock area utilised daily by RR cattle was 32% higher in week 6 compared with week 1, and during daylight hours (0600–1900 hours) they began to travel more (23%) and spent more time active (16%). We conclude that rangeland-raised Bos indicus heifers take from 4 to 6 weeks to adapt from their previous large paddocks/natural plant environment to a new temperate agricultural environment. Our results suggest that the cause of lost productivity in rangeland cattle when they are relocated to a temperate pasture is at least in part due to initial lower grazing activity as they become familiar with the new environment.

Selecting Potential Woody Forage Plants That Contain Beneficial Bioactives

Current viewpoints on animal production systems are being challenged in many parts of the world by the importance of safeguarding their long-term environmental stability and improving productivity. Pressure for change is arising from a range of environmental problems including dryland salinity, degradation of rangeland grazing systems and desertification; the need to address growing resistance to chemical anthelmintic drugs [3] and pressure to reduce the use of antimicrobial drugs in livestock production [8]. Plants with anthelmintic properties are of special interest because of a growing problem of nematode resistance to the chemical anthelmintics. There is also concern that antibiotics used in stock feed will lead to development of resistant organisms that could harm human health. The European Union has applied a total ban on antibiotics in stock feed and producers in other countries will be under pressure to follow suit to gain entry into European markets. Global warming is also an important issue where we need to adapt to maintain productive capacity while contending with more variable rainfall patterns while reducing greenhouse gas release into the atmosphere, a particular issue with methane production from ruminant animals. These various pressures have led to an increase in the interest in exploring global plant diversity for solutions to these issues and “natural” alternatives to the chemicals used in livestock production. Financial and human resources determine the extent to which we can explore our plant diversity, which means we have to make a choice about which to include in a screening programme. In this Chapter, we have used our research programme as an example of an approach that can be taken to selecting plants for a large-scale screening programme. We acknowledge that ours is just one approach of many that can be taken and is shaped by the goals of our programme, but the principles behind our approach can be applied to more broadly to any screening programme.

Pre- and peri-pubertal feed intake: effects on age at puberty and potential litter size of replacement gilts

The effect of moderate restriction of pre- and peri-pubertal liveweight gain on puberty attainment and potential litter size was investigated. At 69 days of age, 48 Large White/Landrace crossbred gilts (28.3 ± 0.3 kg), were fed to attain a liveweight of 70 kg (LIGHT) or 100 kg (HEAVY) at 161 days of age (n = 24 gilts/treatment). At 161 days of age, half the gilts in each group were fed to gain liveweight at 0.5 (LOW) or 1.0 (HIGH) kg/day until puberty (n = 12 gilts/treatment). From 175 days of age, gilts received 20 min/day of full, physical boar contact. Gilts were artificially inseminated at the pubertal oestrus, with reproductive tracts collected 22 ± 0.1 days later, and the number of corpora lutea and viable embryos recorded. LIGHT-LOW gilts were older (P 0.05) by treatment. To conclude, puberty was delayed by chronic, but not acute, dietary restriction. Although short-term, moderate increases in feed intake increased pubertal ovulation rates, embryo numbers and survival were unaffected.