Beef production, quality and fatty acid composition of non-descript crossbreed steers fed natural pasture-based diets

Dezah, Tatenda (2018-12)

Thesis (MScAgric)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: The broad objective of the current study was to assess beef production and quality of steers fed diets formulated using locally available feed resources in communal areas of Eastern Cape Province, South Africa. A survey to identify locally available feed resources was conducted using pretested structured questionnaires administered to 47 and 48 participants from Ncorha and Gxwalibomvu communities, respectively. Crop residues (65% of all respondents), maize stover in particular, were common in both areas, with more farmers from Ncorha (70%) using crop residues than those in Gxwalibomvu (59%). Few farmers (<5%) from both communities used cereal grains and exotic herbaceous legumes (i.e., lucerne) as feed supplements. Farmers also mentioned that cattle browsed indigenous and exotic leguminous tree species, especially Acacia mearnsii (Black wattle) during the dry season. Most abundant feed resources in Ncorha and Gxwalibomvu communities were collected in two seasons and their nutritional composition analysed. Lucerne hay and A. mearnsii had the overall highest protein in both seasons while maize grain and natural pasture hay were the overall best energy sources. Cultivated pasture hay had the highest neutral detergent fibre (NDF), acid detergent fibre (ADF) and acid detergent lignin (ADL) and consequently had the least in-vitro dry matter digestibility (IVDMD) compared to feed ingredients. Among the crop-based feed resources, Glycine max-based commercial ration had the highest crude protein content followed by maize grain. The growth performance, carcass attributes, meat quality and fatty acid composition of crossbred steers fed Acacia mearnsii-based, Medicago sativa-based and Glycine max-based diets were assessed. Thirty-six 12-month-old steers were randomly allocated to the three diets (n = 12 per treatment) under feedlot conditions for 120 days. The steers fed A. mearnsii-based diet had lower (P < 0.05) average daily feed intake and average daily gain (ADG) than steers fed M. sativa-based and G. max-based diets. Steers fed the A. mearnsii-based diet, however, had a higher (P < 0.05) feed conversion ratio than steers fed M. sativa- and G. max-based diets. Steers fed M. sativa-based diet had the highest (P > 0.05) warm and cold carcass weights followed by those fed the G. max-based and A. mearnsii-based diets, respectively. The G. maxbased and M. sativa-based diets had positive effects on growth performance and carcass characteristics of the steers compared to the A. mearnsii-based diet. Diet had no effect (P > 0.05) on meat colour (L*, a*, b*, chroma and hue), pH, temperature, drip loss, shear force, crude protein and fat. Meat from steers finished on A. mearnsii-based diets had higher (P ≤ 0.05) moisture and ash content than meat from those finished on G. max-based and M. sativabased diets. Meat from steers fed A. mearnsii-based diets had the highest cooking losses followed by those fed and M. sativa- and G. max-based diets, respectively (P ≤ 0.05). Meat from steers fed the M. sativa-based diet had higher (P ≤ 0.05) proportions of individual and total SFA and (n-) 3 PUFA and lower (P ≤ 0.05) proportions of linoleic acid and total n-6 PUFA than G. max and A. mearnsii- based diets. Steers finished on A. mearnsii-based diet had lower feedlot performance, greater gross margins, better n-3 PUFA profile and comparable meat quality to those finished on M. sativa- and G. max-based diets. The M. sativa-based diet had better potential to be used as alternative feeding resources for finishing cattle in a conventional feedlot system than the A. mearnsii-based diet.

AFRIKAANSE OPSOMMING: Geen opsomming

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