Citrus pulp in formulated diets: an MIA by-product put to work on farm

Why a citrus waste stream became a feed question#

Most oranges grown around the world end up as juice, and the paper puts current world orange production at 43 million tonnes, with 65% going to juice extraction. Brazil and the U.S.A. dominate this trade, each producing well over 10 million tonnes, with a large share processed for juice. Australia is a minor player by comparison, producing around 650 thousand tonnes of citrus fruit in total, most of it oranges grown in the South-east, with a large share concentrated around Leeton and Griffith in the Murrumbidgee Irrigation Area.

Juicing leaves behind peel, segment pulp and seed, collectively called wet citrus waste. The paper explains that this material has been fed to livestock for over 60 years, because it is readily eaten, but that fresh wet waste ferments quickly, draws flies, smells strongly and is awkward to store or move any distance. Drying solves those handling problems, and the paper credits a dedicated processing operation at Griffith, run by a rice growers' co-operative, with building up commercial dried citrus pulp production from what had previously been dumped MIA waste.

A detail that gives the MIA operation a particular local logic is the heat source: rice hulls, another regional by-product that had itself caused disposal difficulties. The paper states that burning a given quantity of rice hulls yields enough heat to dry a slightly smaller quantity of citrus pulp, and that the leftover silica ash has industrial uses, including as a refractory agent in steelmaking and as a filter aid in glucose syrup production. This pairing, in effect, turns two waste problems into one integrated feed and by-product operation.

What is actually in dried citrus pulp#

Citrus pulp is described in the paper as a low-protein, high-energy feed with a carbohydrate profile unlike the cereal grains that dominate most formulated rations. It contains essentially no starch, and the paper likens its nutritional character to forage, sugarbeet pulp or root crops rather than grain. This matters for ration formulation, because it offers digestible energy through a different pathway to starch-based ingredients.

Composition data summarised in the paper, drawn mainly from research in the U.S.A. and compared against the MIA's own locally produced pulp, show the material is not markedly different from Florida pulp, and that Spanish dried citrus pulp tested similarly as well. Neutral detergent fibre, linked to rumination time in ruminant diets, was measured at around 27.28% in dried citrus pulp in overseas work and confirmed under Australian conditions. On protein, the paper notes that roughly half of the nitrogen present is not true protein at all, a point that matters when nutritionists try to credit citrus pulp against other protein sources.

Like most by-product feeds, citrus pulp varies in chemical composition, palatability and nutritive value depending on the source material and how it was processed. The paper is explicit that this variability is typical of by-product feeds generally, not a particular fault of citrus pulp, and that assessing any batch properly requires chemical analysis backed up by digestibility and feeding trials rather than analysis alone.

Checking the waste stream is safe to feed#

Before recommending any by-product for livestock destined for human food chains, the paper argues it is necessary to understand the full production and processing history of the raw material, to rule out concentrated toxins, spray residues, rancidity products or mould and mycotoxin contamination. It draws a direct line between what happens in the orchard and packing shed and what eventually turns up in meat, milk or eggs.

Applied to MIA citrus, the paper works through the relevant spray program under the New South Wales Department of Agriculture's Orchard Spray Calendar. Nutrient sprays wash off with rain and are judged unlikely to be a problem; fungicides are mostly used only in post-harvest packing, so fruit destined for juicing carries little fungicide residue; and although the calendar lists around 13 pesticides, most MIA growers routinely use only white oil for scale control, which the paper judges to pose no danger to stock or consumers. Chlordane, used on young non-bearing trees and applied to the ground rather than the fruit, is treated as a separate, manageable case.

The paper also points to processing practice as a safeguard: citrus destined for juice is thoroughly washed and scrubbed, sometimes through a sorbate bath, and at the processing plant all wet waste is converted into dried pulp within 12-24 hours of juicing, which the paper says keeps rancidity and mould growth close to zero. Its underlying argument is straightforward: fruit fit for human juice is unlikely to produce a by-product unfit for livestock feed.

Pigs, poultry and horses: patchy evidence, cautious use#

The paper reports very little published data on citrus pulp in poultry diets, aside from a metabolizable energy figure of 5.52 MJ/kg. Pullets and laying hens were said to tolerate 5% dried grapefruit pulp without affecting growth or egg production, though young poultry responded unfavourably even at that level, and broiler trials found that lifting citrus pulp meal from 20 to 40% increased feed consumption and feed conversion while depressing weight gain. Australian trials with 5% MIA dried citrus pulp found no clear effect on yolk pigmentation but noted a tendency toward reduced egg production, egg weight and feed intake, a result the paper flags as cause for some caution. Its overall assessment is that this feed ingredient has found little place in Australian poultry rations.

Pig data is similarly thin. A digestible energy figure was determined using pigs in metabolism cages, equating to a total digestible nutrients figure the paper gives as 58, higher than a quoted swine feedstuffs reference figure of 45. Despite limited published work on amino acid availability, the paper notes dried citrus pulp is used commercially, with sow feeds including it at 5% for many years, reportedly helping prevent constipation around farrowing and improving pellet quality.

Horses show the clearest acceptability limits. University of Florida work found dried citrus pulp could replace oats without harming energy digestibility, though protein digestibility fell, and concluded pelleted diets could include up to 15% citrus pulp. Victorian trials with high-fibre pellets containing 10% dried citrus pulp performed well in police horses over four months. But later field trials with 15% and 7.5% citrus pellets found a meaningful minority of horses, including several yearlings, rejected the feed, some described by trainers as tasting bitter, leading the company involved to avoid citrus pulp in branded horse rations despite clear milling benefits such as doubled throughput and improved pellet durability.

Beef and dairy cattle: the strongest case for inclusion#

Cattle feeding studies form the bulk of the evidence the paper reviews, starting with Florida work by Neal and colleagues in 1935, who measured digestibility coefficients in steers fed dried grapefruit refuse and found it palatable, with favourable effects on coat condition and flesh thickness. Texas Agricultural Experiment Station work by Jones and colleagues found dried citrus pulp could replace up to 25% of ear corn chop with husk with equal gains and slightly better finish, though replacing 60% reduced palatability, feed consumption, gains and finish; a mixture of 75 parts corn chop to 25 parts citrus pulp gave satisfactory results.

Multiple later studies, including work from Florida, Texas and California, reported consistently favourable results and a reduction in digestive upsets on full feed including citrus pulp. The paper highlights an interesting fermentation pattern: citrus pulp favours acetate production over propionate in the rumen, which Cabezas and colleagues linked to harder carcase fat over the ribs in citrus-fed cattle compared with corn-fed cattle, and which other work found interacted predictably with monensin regardless of whether corn or citrus pulp supplied the primary energy.

The paper's own MIA trial data, described as limited, found young Red Poll cattle at 8-12 months and 2500350kg gaining 1.25kg per head per day on winter pasture with 3kg hay and a smaller daily allowance of protein pellets built around a quarter dried citrus pulp, a rate it compares favourably with feedlot performance. On dairy cattle, the paper leans on a near 60-year review from the Florida Agricultural Experiment Station by Harris and colleagues, concluding citrus pulp can be included at levels up to 40% of the total ration provided calcium-phosphorus ratios are managed, and that it has roughage-sparing properties that help maintain rumen pH and milk fat on fibre-deficient diets. A South Australian trial, by contrast, found higher citrus pulp intakes reduced solids-not-fat and protein percentages in milk and produced an abnormal cream flavour at 3.4kg intake, concluding citrus meal could replace up to 2kg of rolled barley without detriment but was not a suitable substitute where lifting milk solids-not-fat and protein was the goal, a question also examined in another record in this index on dried citrus pulp or barley as dairy energy concentrates.

Sheep trials across several countries#

Work in Italy by Maymone and Dattilo found citrus waste digestibility broadly similar to cattle data from elsewhere, though dried material showed carbohydrate digestibility around 10 percentage units lower than fresh material. In Trinidad, Devendra reported high digestibility of diets containing up to 50% dried citrus meal in the concentrate portion, with digestibility maximised at 20% inclusion, while cautioning that growth trials were needed to confirm the significance of those digestibility figures.

Lebanese work with Awasi lambs, using citrus pulp dried at a lower-than-commercial temperature, found an average digestible energy of 14.63 MJ/kg calculated by difference, palatability comparable to corn-based rations, but a decline in feed intake and energy digestibility once citrus pulp exceeded 40% of the ration. A detailed Spanish study by Pascual and Crlrmona examined fattening lambs on isoproteic rations containing lucerne hay and a concentrate mixture with citrus pulp levels from 0 to 90%, using wethers for digestibility and nitrogen balance work and growing lambs for a second feeding experiment, though the paper's account of those results is incomplete in the text available. A separate study in this index, on fresh citrus pulp fed to Merino wethers, looks at wool growth responses rather than lamb fattening.

Weighing up the case for citrus pulp in formulated diets#

Taken together, the evidence the paper assembles is strongest for ruminants, particularly beef and dairy cattle, where decades of American work plus the paper's own MIA observations point to citrus pulp behaving as a reliable, palatable energy source once calcium-phosphorus balance and inclusion rates are managed. The picture is much thinner for pigs and poultry, and genuinely mixed for horses, where acceptability rather than nutrition value turned out to be the limiting factor in practice.

We would treat the pig, poultry and horse findings as indicative rather than settled, given how often the paper itself flags limited published data or contradictory results, such as the gap between Florida's controlled horse trials and the commercial feeding experience reported here. The cattle and sheep evidence, built from multiple independent research stations over an extended period, carries more weight, though the paper's own MIA trial numbers are modest in scale and described as such.

Practically, the paper frames citrus pulp's value as tied closely to its by-product origins: its cost-effectiveness against cereal grains and other energy sources, its complementary fit with urea supplementation in cattle rations by masking unwanted flavours, and its usefulness as a pelleting aid that produces higher-quality, lower-breakage pellets. For the Murrumbidgee Irrigation Area specifically, the paper's case rests as much on resource integration, turning two waste streams, citrus and rice hulls, into a saleable feed and industrial ash, as on the nutritional merits of the pulp itself, a theme the same author returns to in a separate record on rice hulls as the only roughage in feedlot rations.

Sources and further reading#

• Trove library search: find a library that holds the paper
• Meat & Livestock Australia: red meat industry research and marketing body
• Feedipedia animal feed database: an open-access database of animal feeds
• Dairy Australia: dairy industry research body

Questions#

— The Livestock Library team