Citrus paradisi

Grapefruit, sweet orange

Useful reference: 22

Both are small trees or shrubs about 3 m high that grow in the same habitat. The orange has long been cultivated in all warm climates, especially in the subtropics but also in many tropical countries. The grapefruit has not been cultivated commercially as long as the orange. The grass in citrus orchards can be grazed by calves and sheep.

FRESH CITRUS

Useful reference: 497

Oranges and grapefruits, as well as lemons, sometimes go to waste if they are not marketed. Cattle can consume large amounts of these fruits (up to 40 kg a day have been reported) with no apparent harmful effects. Cows with access to fresh oranges have produced more on this feed than on clover pasture. Fresh oranges should be offered to dairy cows only after milking so as to avoid flavoured milk. When feeding fresh citrus, protein and mineral supplements should be provided as fresh citrus contains little protein, calcium or phosphorus. Pigs prefer oranges and tangerines to grapefruit. Free-choice feeding of citrus fruits together with a protein supplement has given good results. To avoid the danger of whole citrus fruits getting stuck in the gullet, they should be sliced. This can easily be done by throwing the fruits through a frame in which saw blades are mounted parallel with a few centimetres of space between them.

CITRUS PULP

Useful reference: 50

When oranges or grapefruits are processed into juice or sections, 45-60% of their weight remains in the form of peel, rag and seeds. This waste is palatable to cattle. Mature cattle accustomed to this feed will consume 6-10 kg a day. Intakes of up to 120 kg a day have been reported for mature cows in hot climates. Because of the high water content and perishable nature of the waste, it can only be used economically close to the processing plant. The feed is rather difficult to handle, ferments and sours quickly, and can be a fly-breeding nuisance if allowed to spoil. Large amounts are available in the harvest seasons and the material can be ensiled for year-round feeding. As citrus pulp is rather moist, a firmer silage is obtained if the pulp is pressed before ensiling or mixed with grass or hay. The ensiling process takes less than fifty days, and the silage is eaten readily by cattle.

Fresh citrus pulp is useful as an ensiling additive to tropical grasses that do not ferment easily by themselves. The addition of 20% fresh citrus pulp to a tropical grass silage will lower the pH and increase lactic and acetic acid fermentation. Pure citrus-pulp silage has a much higher weight per volume than grass or maize silage; therefore, silos in which it is to be placed should be more strongly reinforced than average. This problem does not apply to trench silos. Citrus pulp can easily be ammoniated by direct contact with ammonia at atmospheric pressure. The citrus pulp is loaded into a long polyethylene sleeve, and ammonia gas from a bomb is let into one of the ends. The progress of the ammonia is easily followed because ammoniation turns the pulp brown and heats it up. When the ammonia reaches the open end of the sleeve, the gas is turned off and the excess ammonia is aired off from the pulp before feeding.

DRIED CITRUS PULP (CITRUS MEAL)

Useful reference: 51

To increase the use of citrus pulp, it can be preserved by drying. Direct drying cannot be used, however, because of the slimy consistency of the waste. It has been found that the hydrophillic nature of the pectin in the waste can be destroyed by adding lime. The dried pulp can be stored for year-round feeding and deteriorates less in storage than many other feeds. Rodents and birds are not so attracted to dried citrus pulp as they are to other feeds. Dried citrus pulp is slightly hygroscopic and should therefore be stored dry. The machinery for drying is expensive, and the process is economical only where large amounts of waste accumulate. The first step in processing is the addition of 0.5% calcium in the form of limestone or calcium hydroxide to the shredded skins to neutralize the free acids and combine with the fruit pectin. Following this, there are two ways of further processing the citrus pulp:

1. The excess moisture is removed in a press before drying the pulp. The press liquor may then be discarded or concentrated under reduced pressure to 60-70% dry matter and used in animal feed, known as citrus molasses.

2. All the wet material is dried directly in a rotary drier. This method is practical in areas with access to natural gas where fuel costs are low.

Dried citrus pulp that has been pressed before drying is some 10% lower in nitrogen-free extract. Only the contents of ash, fibre and water are consistent, whereas protein and nitrogen-free extract vary according to the season, the proportion of oranges and grapefruits, and the quantity of seeds in the fruits.

No distinction is made between dried pulp from oranges and dried pulp from grapefruits. The dried material is sometimes screened into citrus meal. Citrus pulp and fines, but often the whole mixture is ground and sold as citrus meal.

Dried citrus pulp has been used as the main energy source for beef cattle and pregnant heifers and has constituted up to 45% of calf rations; however, the results have indicated that the pulps should not be used at high levels for milking cows as milk production tends to decrease. Urinary calculi have been observed in steers fattened with rations of more than 30% citrus meal.

Because of the processing method, citrus pulp is a good source of calcium, but it contains little phosphorus. Owing to this imbalance there is a very real need to ensure that calcium and phosphorus levels are adequate and in the right ratio. As citrus pulp has a low content of vitamin A, green leafy roughage is an important ingredient in rations with high levels of citrus pulp.

Substances toxic to swine and especially to poultry are present in dried citrus pulp that includes seeds; also, the high fibre content restricts its use in pig and poultry rations. Dried citrus pulp at the level of 10% in chicken diets reduces growth and at about 30% may be toxic. When added to the diets of layers, even at a level of 2.5% dried citrus pulp adversely affects yolk colour. Dried citrus pulp has been used as deep litter for poultry and subsequently as livestock feed (see I21). Citrus pulp has been ammoniated to increase its nitrogen contents but the method seems to offer little advantage over the separate feeding of a source of nonprotein nitrogen.

CITRUS MOLASSES

Useful reference: 209

The liquid obtained from pressing citrus waste contains 10-15% soluble solids, of which 50-70% are sugars. This material, which may amount to more than half the total weight of the waste, can be concentrated into citrus molasses. Citrus molasses is normally thick viscous liquid, dark brown to almost black, with a very bitter taste. This bitter taste does not diminish its usefulness in cattle feeding, and citrus molasses can be used in the same way as sugar-cane molasses. It may be mixed with pressed pulp prior to drying, thus increasing the ratio of total digestible nutrients (TDN) to crude fibre in the dried product without lessening the keeping quality of the pulp. When fed free-choice to cattle, they consume up to 3 kg per day. It is less readily accepted by pigs. It has been found that citrus molasses can replace 10-40% of the maize in the pig ration, depending on the age of the pig.

CITRUS SEED MEAL

Useful reference: 136

Citrus seeds are sometimes collected separately at the canning plants for oil extraction. The resulting oilcake, called citrus seed meal, compares favourably with many sources of vegetable protein. However, it contains limonin, which is toxic to pip and especially to poultry. Citrus seed meal is therefore unsatisfactory for these animals. At 5% inclusion it reduces growth and at 20% causes mortality in growing chickens. It is acceptable to ruminants and is comparable to cottonseed oil cake, having the same percentage of crude protein. There is no restriction on its inclusion in diets for ruminants. The toxic factor can be extracted under laboratory conditions, but the process is too expensive for application on a commercial scale.