The value of stubbles and chaff from grain crops as a source of summer feed for sheep

Key messages

• Sheep can consume a higher quality diet through selective grazing, but the overall low quality of stubble and chaff means that farmers need to ensure higher quality feeds are also available, e.g. spilled grains, green pick and providing supplementary feed to meet nutritional requirements.
• Wheat chaff alone provided less than half of the maintenance requirements of ewes. By comparison, barley chaff contained seven times the amount of spilled grain, on average, and other barley chaff components were of higher feeding value.
• Offering a 200g/day lupin supplement improved ewe energy intake additively, i.e. did not affect the amount of chaff eaten.
• Understand current use of stubbles in Western Australia as part of the seasonal feedbase.
• Measure the nutritive value of components of chaff and standing stubble from winter crops.
• Investigate the intake and component selection of wheat chaff by sheep.

Aims

• Understand current use of stubbles in Western Australia as part of the seasonal feedbase.
• Measure the nutritive value of components of chaff and standing stubble from winter crops.
• Investigate the intake and component selection of wheat chaff by sheep.

Introduction

Crop stubbles provide an important year-round supply of forage on mixed farms in the Mediterranean-type climate regions of southern Australia. New crop cultivars, alternate crop species, modern harvesters and a reduction in the density of volunteer pasture plants and weeds have affected the nutritional value of modern crop stubbles for livestock. The increased aggregation of chaff in piles, lines and windrows may have increased the ability of sheep to select the higher-quality chaff components but has also provided the option to transport chaff for sale or use on-farm for confinement feeding.

Crop stubbles are notoriously variable in their value for sheep feed. For example, Thomas et al (2021) estimated the feeding value of wheat stubbles ranged between 60 and 190 sheep grazing days per hectare of stubble. Stubble components, (e.g. main stem and leaf) also vary widely in their feed value, and non-cereal crops such as canola and lupins are more variable in feed value due to higher likelihood of grain losses during harvest. Ewes typically graze stubbles during mating and early pregnancy, when access to high quality feed, (e.g. spilled grain) is critical for good reproductive performance. Stubbles also have an important role for finishing lambs to market specifications and/or feeding ewe lambs during summer before integration into the breeding flock.

Traditionally, farmers have relied on building up feeding knowledge through observation or trial and error for mob rotations and providing supplementary feed when grazing sheep on stubbles. This paper presents updated information on the feeding value of components of stubble harvested for the main winter crops grown in WA, which to our knowledge has not been measured extensively in 20 years (Roberts and Paterson 2001). Results of an animal house study to investigate the intake of wheat chaff by young and mature ewes are also reported.

Method

The research activities carried out to evaluate the value of stubbles for grazing by sheep included i) a farmer survey ii) field survey of stubble paddocks and iii) an animal house study.

Farmer survey

A survey of mixed crop and livestock farmers in WA was conducted to understand the key features of their stubble management practices and to identify priority issues. The survey was conducted using the Survey Monkey web service, and a total of 41 farmers participated from 16 grower groups. Their willingness to participate is gratefully acknowledged. The online survey was authorised by the CSIRO Human Ethics Committee (Ethics Clearance 111/18).

Areas covered by the survey included the structure of the farming business, seasonal feedbase, chaff management at harvest, current stubble and grazing management practices, use of geospatial data (yield maps) and research priorities for stubble management.

Field survey

Stubble material from a wide range of crops and harvesting conditions was collected for analysis either from i) chaff lines and heaps sampled by farmers during the 2018/2019 harvest or ii) a survey of ungrazed standing-crop stubbles made from 17 to 21 December 2018. At least four quadrats (each 0.25m²) were collected from each paddock where standing stubbles were sampled. Sampling sites were selected randomly within paddocks, or randomly within specific target areas of the paddock. Further details of the collection of samples are provided in Thomas et al (2021).

Animal house study

To investigate the voluntary feed intake of header chaff, we conducted an individual pen feeding experiment with Merino ewes fed nine different wheat chaffs. Experimental treatments were ewe age (young and mature) and lupin supplement (+ or -), with the nine wheat chaffs sourced from different properties in the mixed farming region of WA. The experimental design was a split-plot with main treatments, lupins x age, allocated as a completely randomised design, and sub-treatments, chaff type, allocated as a 9 x 9 Latin square balanced for residual effects (Table 1). Each day 1500g fresh weight of wheat chaff (~1400g DM) was offered to each of the sheep on nine consecutive days, with the + lupin treatment being offered 200g fresh weight of lupins in addition. The amount and quality of material eaten by the sheep was measured daily, by collecting daily refusals for weight and nutritive value assessment. Analysis of variance for treatment effects (lupins and age) on intake and intake per unit metabolic liveweight (g DM/kg liveweight^0.75) were carried out using the R statistical computing environment (R Core Team 2020).

The CSIRO Wildlife and Large Animal Animal Ethics Committee approved the experimental work (organisational reference 2019-26). In the experiment we used 36 female non-pregnant Merino sheep (ewes), in two cohorts from the same genetic and environmental background i) 18 of 15-month ewes (young) and ii) 18 of 5-year ewes (mature). The ewes were selected from a commercial farm in the wheatbelt of Western Australia and had been grazed on stubbles during the previous summer. The young ewes were an average of 53.4kg and Condition Score 2.8, and the mature ewes were an average of 72.6kg and Condition Score 3.6 immediately before starting treatment chaff diets. Due to the short duration of the study there was little effect on body condition, despite the low quality of the feeds offered.

All animals were health checked by an experienced staff member before leaving the farm of origin, and were drenched, vaccinated and a lice treatment applied. Sheep were given an acclimatisation period of two weeks in both yard and pen environments before commencement of the treatment chaff diets. By gradually introducing the animals to the pen environment for short periods over several days, we ensured that the experimental sheep were calm and familiar with the experimental facilities and procedures. Sheep were offered oaten chaff as a base diet, which was initially supplemented with 100g/head/day of lupins to meet the protein requirements of the sheep. However, lupin feeding was withdrawn for the six days before the experimental period to ensure the intake of lupins did not influence results, given lupin supplementation was a treatment factor.

Results

Seasonal feedbase

On average, sheep produced in mixed farms spend just over 20% of time grazing stubbles, as a percentage of time spent by feedbase component reported by farmers (Figure 1). Green and dry pastures, and supplementary feed, make up the other main sources of feed.

Figure 1. Average percentage of time spent grazing on each feedbase component across 41 mixed farms in Western Australia.  

Chaff management at harvest

Farmers were asked about their chaff management practices at harvest. Approximately half of farmers spread chaff, while slightly less than half aggregated chaff in either chaff piles (from chaff carts), chaff lines or windrows (Figure 2). Collecting chaff in rows or piles was more common for cereal crops than canola or lupins.

Figure 2. Application of chaff and stubble management practices when harvesting crops by number of survey respondents.

Chaff feeding value

The composition of chaff collected at harvest varied considerably from that of standing stubbles, particularly in relation to the proportion of main stem (large) material. Figure 3 shows the differences in the fractions of chaff and stubble components in wheat chaff samples collected from heaps or lines, or samples collected from standing stubbles, either between rows (OffRow) or from paddocks where chaff had been distributed widely from the back of the header (Spread). Wheat chaff heaps and lines comprised only 10-15% main stem material, whereas standing wheat stubble samples were closer to 50% main stem and had less (>10%) small material including grains. Barley chaff from lines and heaps had approximately seven times the amount of grain, on average, compared with wheat chaff (26.2 ± 8.8 v 3.9 ± 1.5g/kg grain in chaff).

Figure 3. Proportion of chaff and stubble material collected from different sources comprised of large, medium, small and seed (grain) components.

The metabolisable energy (ME) content of chaff components (estimated from percent dry matter digestibility) varied between components and crops (Figure 4). Stem and leaf material from barley stubbles was approximately 1MJ/kg higher in ME content compared with wheat. Fine stem, leaf and pod material from lupins had the highest ME content of the different crops.

Figure 4. The estimated metabolisable energy content (MJ/kg DM) of chaff collected from winter crop stubbles in Western Australia following the 2018 growing season.

Chaff intake by sheep

The daily intake by young and mature ewes offered nine different wheat chaffs, with or without a 200g/day lupin supplement, are shown in Table 1. The daily intake of wheat chaff was the same for young compared with mature ewes (733 v 682g DM/head/day; P=0.295; Table 1), and there was no overall effect of lupin supplementation on ewe’s intake of chaff (P=0.873; Table 1). On a metabolic bodyweight basis, the DM intake of young ewes was 36% higher than mature ewes (37.7 v 27.8g DM/kg liveweight/day; P<0.001).

Table 1. Dry Matter Digestibility (DMD), Crude Protein (CP) and Intake (g DM/ewe/day) of wheat chaff by young and mature Merino ewes, with (+ lupins) or without (- lupins) a 200g/day lupin supplement. Values are means ±standard error.

The mean digestibility of refused feed was 43.9% overall, and the digestibility of the diet eaten can be calculated at 46.3%, equivalent to 0.4MJ ME/kg higher ME in wheat chaff selected than refused. Therefore, capacity to select components from chaff is practically important, albeit modest, under the conditions of this study. This finding differs from a previous report where it was assumed that sheep did not eat selectively from chaff (Purser 1983). However, the intensity of selection from chaff observed in this study was much lower than that seen in sheep grazing standing stubbles, particularly in cases where there are substantive amounts of spilled grain, which agrees with Purser (1983). Whether sheep graze more selectively from chaff heaps in a paddock situation, compared with that observed in the current study, is yet to be determined.

The estimated ME intake from wheat chaff, based on mean nutritive value and intake values reported in Table 1, was 4.6 and 4.3MJ ME/day for young and mature ewes, respectively. Based on the liveweight of the ewes, this represents 48% and 35% of the maintenance requirements of the young and mature ewes. A further ~2.5MJ ME/day from the 200g/day of lupins increased energy intake to 74% and 55% of the maintenance energy requirements of young and mature ewes, respectively. Based on these results, while chaff is an important feed component in stubbles, sheep would require at least an amount of energy equivalent to that provided by the chaff, from a high-quality source such as spilled grain or grain supplement, to meet their typical production requirements.

Conclusion

Crop stubbles offer a valuable source of feed during a period of feed deficit in the mixed farming region of WA, with sheep spending about 20% of their time grazing on stubbles during the year. The finer stem and leaf, and other fine (< 2mm) components of chaff are about 1MJ ME/kg higher in nutritive value than the main stem, and sheep can preferentially select the higher quality components of chaff. However, even the higher quality chaff components are of relatively low feeding value and when offered ad libitum will only provide about one third to one half of the daily maintenance requirements of sheep. Therefore, farmers need to ensure that sheep have access to other high-quality feed such as spilled grains, supplements or green forage to maintain or grow sheep on wheat chaff or standing wheat stubbles. This may not be the case for barley chaff, where the proportion of spilled grain was generally much higher. This study demonstrated that provision of a supplement is additive, that is both young and mature sheep offered a supplement did not reduce their intake of chaff. However, this may depend on the overall level of feeding as the sheep in this experiment consumed substantially below their maintenance requirement. The factors responsible for variability in nutritive value seen among chaff samples remain unclear and understanding the G x E x M drivers of stubble quality would help farmers to predict livestock production outcomes more accurately when grazing stubbles.

References

Purser, D.B. (1983) The nutritional value of stubbles. In ‘Stubble utilization’. pp. 13–26. (Rural and Allied Industries: Perth, WA, Australia)

R Core Team (2020) R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria.

Roberts, D., Paterson, J. (2001) Sheep performance on cereal and canola stubbles. In ‘The good food guide for sheep. Bulletin 4473’. (Eds K Croker, P Watt) pp. 52–60. (Department of Agriculture: Perth, WA, Australia)

Thomas, D.T., Toovey, A.F., Hulm, E. and Mata, G. (2021) The value of stubbles and chaff from grain crops as a source of summer feed for sheep. Animal Production Science 61, 256-264.

Acknowledgments

The research undertaken as part of this project was made possible by the significant contributions of growers and the support of the CSIRO, MLA and AWI. This project was supported by the WA Grower Group Alliance, and many grower groups in Western Australia. Technical input by Elizabeth Hulm, Doraid Amanoel, Adam Brown, Paul Young and Josh Hendry is gratefully acknowledged.

Paper reviewed by: Roger Lawes, CSIRO Agriculture and Food.

Contact details

Dean Thomas
CSIRO Agriculture and Food
147 Underwood Ave, Floreat WA 6014
Phone: 08 9333 6671
Email: dean.thomas@csiro.au