​Beef cattle farmers can do well to look into the economic benefits of using dried grape pomace and citrus pulp as sources of fibre when raising cattle in feedlots. So says animal science researcher Dr Tawanda Tayengwa of Stellenbosch University (SU).

Dr Tayengwa studied whether it is worthwhile for beef cattle farmers in low to middle-income countries to use dried citrus pulp or grape pomace as alternative sources of fibre for their livestock. He also investigated whether the use of these waste products could stretch farmers' rands.

Some of his findings have been published in international journals such as Meat Science and Sustainability. Dr Tayengwa recently completed his PhD in Animal Science in the SU Faculty of AgriSciences under supervision of Dr Cletos Mapiye, a senior lecturer in the SU Department of Animal Science.

Making a plan with fruit by-products

Citrus and grapes are the most widely grown fruits in the world. Up to 100 and 80 million metric tons are harvested annually worldwide, of which one-third is used for juice and wine making. In South Africa 2.9 million metric citrus and 2.0 million metric tons grapes are harvested annually. After being processed, there are around 225 000 and 280 000 metric tons of citrus pulp and grape pomace, respectively, that annually need to be disposed of in some way.

“It therefore makes economic and environmental sense to find ways to put these sources of fruit wastes to better use," says Dr Tayengwa.

He says that because of low productivity of the South African rangelands, more than 80% of all cattle are raised in feedlots to meet the demand of meat-loving consumers. The feedlot production system is however not meeting its full potential, among others because of water shortages and a limited supply of feed. As a consequence, consumers may be expected to pay higher prices for beef, and producers are not running their enterprises as profitably as can be.

“We thus need to explore alternative and underutilised feed resources such as fruit wastes that this industry can use to be more sustainable," he explains the rationale to his study.

Good source of fibre

Citrus pulp and grape pomace are both high in fibre. Dr Tayengwa therefore conducted a series of experiments to see how the use of these by products as diet components compare to the use of wheat bran, which is commonly included as a source of fibre in feedlot cattle diets. The citrus pulp and grape pomace were dried before being included in the diets. The unprocessed wet forms of these by products are characterized by a high water and tannin content, respectively, which can influence the palatability of the diet.  

Dr Tayengwa conducted feedlot study on the Mariendahl Experimental Farm of the Faculty of AgriSciences, outside Stellenbosch. A total of 24 7-month-old Angus steers were allocated to the treatment groups. Each was fed their basic daily diet, which was then either supplemented with 150 g of dried citrus pulp, 150g dried grape pomace, or 150g wheat bran per kilogram.

He among others monitored how well each animal was able to feed on and digest the alternative fibre options. In growth performance trials, he carefully noted how much weight the steers gained daily and how efficiently the feed was utilised. The chemical and physical attributes of the meat were analysed, and its fatty composition and shelf life among others ascertained. Meat was also put to a taste test.

“The steers fed a diet containing dried grape pomace and citrus pulp gained more weight each day and ultimately weighed more than those fed the wheat bran diet. They had better carcass weights and dressing percentages," Dr Tayengwa summarises the major dietary findings. “In terms of production costs, diets containing grape pomace resulted in more efficient growth, followed by citrus pulp- and wheat bran-supplemented diets."

Shelf-life aspects

Dr Tayengwa also determined whether including grape pomace or citrus pulp in beef cattle diets, influenced the shelf-life of meat when packaged in air-permeable packaging, and the eating experience once cooked.

“The findings indicated that dried grape pomace potentially is a more effective natural preservative than citrus pulp," he says. “Supplementing beef cattle diets with grape pomace improved the shelf-life of beef, when compared to diets containing citrus pulp or wheat bran."

He says this finding is of value, given that many synthetically manufactured antioxidants are currently used to extend the shelf-life of feeds and meat. Consumers are however, increasingly making themselves heard in terms of their preference for the use of natural products, and especially those that are high in fruit by product-based antioxidants.

On the downside, the sensory panel used during this phase of the research indicated that meat produced from steers raised on citrus pulp or grape pomace tended to be about 10% less tender.  

Dr Tayengwa also determined whether feeding beef cattle diets supplemented with citrus and winery by products had an influence on the fatty acid and aroma profile, respectively, of the meat produced by the trial animals. Beef from steers fed these by products was characterized by a higher level of heathy fatty acids, and a more pronounced aroma. Based on desirable flavour, consumers tended to rate meat from animals that received the by product-supplemented diets higher than meat obtained from cattle fed the wheat bran-supplemented diet.

“Overall, the results show that the use of grape pomace holds the greatest potential for beef cattle farming," notes Dr Tayengwa.

Photographs

Dr Tawanda Tayengwa in the laboratory at Stellenbosch University, busy with chemical studies on meat samples.