Browsing by Author "Genis, Maria Petronella"

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    The effect of dietary energy content and the provision of a β-adrenergic agonist in the diet, on the production and meat quality of South African Mutton Merino feedlot lambs
    (Stellenbosch : Stellenbosch University, 2014-12) Genis, Maria Petronella; Hoffman, Louwrens C.; Brand, T. S.; Stellenbosch University. Faculty of AgricSciences. Dept. of Animal Sciences.
    ENGLISH ABSTRACT: Two studies were conducted on Elsenburg Experimental Farm, Western Cape, South Africa. The aim of these trials was to determine the following: 1) the effect of dietary energy as well as the inclusion of a β-adrenergic agonist (β- AA) on the production of South African Mutton Merino (SAMM) feedlot lambs 2) the effect of the trial diets on the rumen pH 3) the effect of varying dietary energy levels and the inclusion of a β-AA in the diet on the relationship between slaughter weight, commercial cut yield and bone:fat:muscle ratio of SAMM feedlot lambs 4) the effect of dietary energy as well as the inclusion/absence of a β-AA on the meat quality of SAMM feedlot lambs 5) the effect of dietary energy as well as the inclusion/absence of a β-AA on the sensory, physical and chemical characteristics of SAMM feedlot lambs. To quantify the effects of these parameters the study was conducted in two separate experiments. In the first experiment one hundred and eight (108) SAMM lambs, weaned at ca 120 days of age of different gender (rams and ewes) were housed in individual pens for approximately 6 weeks. The treatments consisted of three different dietary energy level diets (high – 12.7 ME MJ/kg, medium – 12.0 ME MJ/kg and low 11.3 ME ME/kg) with either the inclusion or absence of a β-AA (Zilpaterol hydrochloride, at 8.6 g/ton) in the diet. The experiment was arranged as a 2 x 2 x 3 factorial design with gender (rams or ewes), β-AA (provided or not) and dietary energy level (low, medium or high) as main factors. In the second experiment one hundred and twenty (120) SAMM lambs, weaned at ca 120 days of age of different gender (wethers or ewes) were housed in individual pens for approximately 6 weeks. The treatments consisted of three different dietary energy level diets (low – 11.3 ME MJ/kg, medium – 12.0 ME MJ/kg and high – 12.7 ME MJ/kg). The experiment was arranged as a 2 x 3 factorial design with gender (wethers or ewes) and dietary energy level (high, medium or low) as main factors. Where no interaction occurred the data is presented as the effect of dietary energy level, β-AA and gender on parameters. Three ruminally cannulated sheep were used for measuring the rumen pH. No differences were found between the three experimental diets on the rumen pH. Overall a gradual decline in pH from the time the animals were fed was observed. Dietary energy level only affected the dressing percentage in the first experiment, while it affected several parameters in the second experiment. The β-AA had no significant (P>0.05) effect on any parameters. While gender significantly (P<0.05) effect several of the production and carcass yield parameters. Main effects dietary energy and gender affected the leg yield and fat percentage in the bone:muscle:fat relationship respectively. While positive correlations between slaughter weight and the following parameters were observed: carcass weight, leg yield, shoulder yield, neck yield, flank yield and cranial fat thickness. Beta-adrenergic agonists are commonly used in livestock production to enhance meat production and decrease the fat content of the body. Beta-adrenergic agonists normally improve growth performance and enhance a leaner carcass. The factors β-AA and dietary energy level had no effect on the proximate composition of the loin, fat thickness or the tenderness of the meat. The ewes had a significant higher fat content than the ram lambs. The meat of the ram lambs was less tender than the meat from the ewe lambs. The acceptability of meat is dependent on the toughness (chewiness and resistance), flavour (aroma and taste) and succulence (juiciness) of the meat. It is known that dietary energy as well as the inclusion of a β-adrenergic agonist may influence the sensory, physical and chemical characteristics of the meat. No significant differences (P>0.05) due to dietary energy level or the inclusion of the β-AA were found for the physical characteristics of the meat. There were, however significant (P<0.05) differences found during the sensory testing for tenderness between gender (76.2% for ewes vs 72.9% for rams) and between the β- agonist groups (75.4% vs 72.9% for the inclusion of the β-AA). Sustained juiciness was also affected (P<0.05) by gender (68.0% for ewes vs 65.7% for rams) and the inclusion of a β- agonist groups (67.9% absent vs 65.8% included). Overall it was concluded that, of all three main effects, gender had affected the meat attributes the most.