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

[摘要] 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 lambs2) the effect of the trial diets on the rumen pH3) the effect of varying dietary energy levels and the inclusion of a β-AA in the dieton the relationship between slaughter weight, commercial cut yield andbone:fat:muscle ratio of SAMM feedlot lambs4) the effect of dietary energy as well as the inclusion/absence of a β-AA on the meatquality of SAMM feedlot lambs5) the effect of dietary energy as well as the inclusion/absence of a β-AA on thesensory, physical and chemical characteristics of SAMM feedlot lambs.To quantify the effects of these parameters the study was conducted in two separateexperiments. In the first experiment one hundred and eight (108) SAMM lambs, weaned atca 120 days of age of different gender (rams and ewes) were housed in individual pens forapproximately 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 theinclusion or absence of a β-AA (Zilpaterol hydrochloride, at 8.6 g/ton) in the diet. Theexperiment 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 thesecond experiment one hundred and twenty (120) SAMM lambs, weaned at ca 120 days ofage of different gender (wethers or ewes) were housed in individual pens for approximately 6weeks. The treatments consisted of three different dietary energy level diets (low – 11.3 MEMJ/kg, medium – 12.0 ME MJ/kg and high – 12.7 ME MJ/kg). The experiment was arrangedas 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 theeffect of dietary energy level, β-AA and gender on parameters.Three ruminally cannulated sheep were used for measuring the rumen pH. No differenceswere found between the three experimental diets on the rumen pH. Overall a gradual declinein 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 thesecond experiment. The β-AA had no significant (P>0.05) effect on any parameters. Whilegender 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 thebone:muscle:fat relationship respectively. While positive correlations between slaughterweight 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 meatproduction and decrease the fat content of the body. Beta-adrenergic agonists normallyimprove growth performance and enhance a leaner carcass. The factors β-AA and dietaryenergy level had no effect on the proximate composition of the loin, fat thickness or thetenderness 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 aswell as the inclusion of a β-adrenergic agonist may influence the sensory, physical andchemical characteristics of the meat. No significant differences (P>0.05) due to dietaryenergy level or the inclusion of the β-AA were found for the physical characteristics of themeat. There were, however significant (P<0.05) differences found during the sensory testingfor 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 alsoaffected (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 threemain effects, gender had affected the meat attributes the most.

[发布机构] Stellenbosch University