Thorn tree leaves: a nutritious grain substitute in pig feed

Smallholder pig production in Southern Africa is constrained by feed shortages and the demand for grains to feed the ever-growing human population. This makes it important to identify alternative feedstuffs for pigs.

Thorn tree leaves: a nutritious grain substitute in pig feed
A study conducted in South Africa found that leguminous leaf meals could be used to significantly lower the soya bean component in a pig’s traditional diet.
Photo: Pixabay
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Including leguminous leaf meal in a pig’s diet can reduce the proportion of soya bean normally used. Acacia leaves, for example, have a relatively high crude protein (CP) and
favourable mineral concentration.

A South African study evaluated the nutritive value of Acacia leaf meals and found that
finisher pigs fed incremental levels of Acacia tortilis leaf meal showed an increase in both
average daily feed intake (ADFI) and average daily gain (ADG).

Materials and method
Eight trees each of five dominant eguminous species, A. tortilis, A. robusta, A. nilotica, A. nigrescens and A. xanthophloea, were hand-harvested from the same grazing camp at Makhathini Research Station, Jozini.

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The leaves were harvested by cutting branches off each tree and drying under shade for three to four days to prevent damage of heat-sensitive nutrients.

The dried branches were carefully beaten by stick to release the leaves, which were then sieved through a 2mm sieve to get rid of thorns and twigs, and placed in airtight bags. The
leaf meals were evaluated for their chemical composition, and A. tortilis was selected.

Thirty finisher male F1 hybrid (Landrace x Large White) pigs with an initial average weight of 60,6kg were allotted randomly to six dietary treatments containing A. tortilis leaf meal at levels of 0g, 50g, 100g, 150g, 200g and 250g/kg dry matter (DM) respectively.

Each treatment diet was offered ad lib to five pigs in individual pens for 21 days.

A. tortilis and A. xanthophloea leaf meals had the highest CP and fat content among all the
Acacia species. The neutral detergent fibre and acid detergent fibre concentrations in the leaves varied significantly across species. ADFI, ADG and gain-to-feed ratio were measured every week.

There was an increase in both ADFI and ADG as A. tortilis leaf meal increased, before
they started to decrease. It was observed that A. tortilis leaf meal can be included up to
150g/kg DM in finisher pig diets without negatively affecting animal performance.

The ability with which pigs utilise leaf meal-based diets improves with duration of exposure
(adaptation) to such diets.

• Note: Acacia tortilis is now attributed to the genus Vachellia, and known as Vachellia tortilis.

• Source: Growth rates of pigs fed on incremental levels of Acacia tortilis leaf meal-based diets