The use of different anabolic agents in gilts

[摘要] 24 Crossbred gilts (Large White x Landrace) purchased as weaners were randomlyallocated to four treatment groups (n = 6) and submitted for an observation period ofthree phases: Phase I, in which the animals were treated with anabolic agents(nandrolone, clenbuterol, zeranol); Phase 2, could be seen as the anabolic agentclearance period; and Phase 3, in which certain carcass characteristics and meat qualityparameters were measured. The trial was aimed to compare the effect of the differentanabolic agents zeranol (implants of 36 mg/pig, every three weeks, for 9 weeks),clenbuterol (daily oral dose of 0.5 mg/pig, for 9 weeks) and nandrolone(intramuscularly injected, 50 rng/pig, every ,3 weeks, for a period of 9 weeks), ongrowth rate parameters, carcass and meat characteristics, visceral organ growth andblood concentrations of urea, glucose, creatinine, oestradiol and the hematocrit. Thegilts were individually housed and fed a pig growth diet (16% crude protein) adlibitum, with free access to water. Body weight of all animals were recorded every 48hours to monitor the average daily gain (ADG) and the growth rate up to the targetliveweight of 85 kg. Weekly feed intake was monitored and the feed conversion rate(FCR) determined for the individual animals and the mean of the groups. Backfatthickness (P2) and eye muscle diameter were measured weekly with the aid of a sonarapparatus in all animals, to monitor the deposition of fat and lean muscle. Blood wassampled weekly from 4 specific animals per group for the determination of hematocrit,blood urea, blood glucose, blood creatinine and blood oestradiol concentrations. The clearance rate of the anabolic agents was monitored in the urine sampled every secondday from all anabolic agent treated animals following cessation of treatment. Atslaughter (85 kg liveweight), several carcass measurements were done. Visceralorgan weights were noted and meat quality parameters (water loss, cutting resistance,pH) were determined.Zeranol treatment revealed an improved growth rate (ADG of 727 g/d and 147.3 daysto attainment of 85 kg) compared to the control and the other treatment groups.None of the three anabolic agents improved the FCR significantly, although the controlshowed the lowest mean value (2.76 kg feed/kg liveweight gain). A tenclency for anincrease in this parameter was observed over time, in all the groups, the highest meanvalue being encountered in the group treated with zeranol (3.32 kg feed/kg liveweightgain). Overall average daily feed intake was significantly (P<0.05) greatest in thezeranol treated animals (2.03 kg/cl). Backfat thickness (P2) deposition assessedthrough ultrasonic measurements, showed no significant differences between thetreatments and the control. The diameter of the eye muscle, weekly monitored by thesame method, from the P2 site, showed significant (P<0.05) differences - the controlhaving the highest value (4.43 mm/week). The clearance rate of the anabolic agentswas faster in clenbuterol treated animals than in the zeranol group, while fornandrolone group this could not be. assessed, because its metabolites in swine are stillunknown. Zeranol treated animals had a significantly (P<0.05) improved cold carcassweight and dressing percentage (68.8 kg and 79.8% respectively). Mean values forbackfat thickness were generally high in carcasses from zeranol treated animals (PI = 13.5 mm; Pi = 14.8 mm; P3 = 16.6 mm) which leaner carcasses were obtained in theclenbuterol group (PI = 6.7 m; P2 = 7.4 mm; P3 = 8.6 mm). The eye muscle area(physically measured) was significantly (P<0.05) higher in the nandrolone group (34.3cm2) compared to the Zeranol group (30.6 cm2), but not statistically different from thecontrol and the nandrolone group. Zeranol, clenbuterol and nandrolone treatmentsdid not significantly alter carcass conformation indicators. However, carcass weightwas recorded to be positively (P< 0.05) correlated to ham circumference (r = 0.52);chest depth (r = 0.64) and chest diameter (r = 0.56).With the exception of cutting resistance values, in which the zeranol treatment groupproduced more tender meat (3.74 kg shear force) than the control and the other twotreatments, the rest of meat quality parameters measured (muscle pH; cooking loss ofwater holding capacity) were not affected by the treatment with anabolic agents. Nosignificant differences in the weights of digesta, digestive tract and the visceral organs(liver, kidneys, lungs, heart and spleen) were found following anabolic agent treatment. Suppressed ovary growth (0.6 g of weight) and over-growth of the reproductive tract(134 g uterus weight) and increased size of the vulvas were observed following zeranolimplantation of gilts. The reproductive organs from clenbuterol and nandrolonegroups were functional and apparently unaffected.The determination of blood urea, blood glucose, blood creatinine and blood oestradiollevels using specific kits to assess the concentrations of the metabolites and hormonesgenerally did not result in definite trends of increases or decreases over time. Thesedeterminations could thus not be accurately used as possible indicators of themetabolic status following the use of zeranol, clenbuterol and nandrolone in gilts.It was concluded that the use of clenbuterol and nandrolone in gilts yielded noimprovements in the growth parameters. In gilts treated with zeranol, overall growthrate was higher. Ultrasonic measurements of backfat thickness and eye musclediameter proved to be an inaccurate and unreliable predictor of fat thickness orleanness of the carcass. A longer withdrawal period is necessary after an implantationof pigs with zeranol compared to the rapid clearance realised after an oral dose ofclenbuterol. The faster growth rate obtained following the use of zeranol implants iscounteracted by higher feed costs of lean meat production and the yield of poorer ratioof lean-to-fat content in the carcass when compared to the clenbuterol and nandrolonetreatments. The growth of the digestive tract, liver, heart, kidneys, spleen and lungswere not affected by anabolic agent treatment, and thus the anabolic effect of zeranolconcerning growth characteristics is not through an increased gastrointestinal capacity.The assessment of growth performance and feed utilisation efficiency through bloodlevels of glucose and urea appear to be time consuming and not always practical.Further investigations regarding blood biochemistry, ideal doses of the anabolic agents,their metabolism and clearance rate in swine, as well as the margin of consumer'ssafety, is still of crucial importance for the future legal and safe use of anabolic agentsin the pig industry. From the results obtained, it would seem that the use of theseanabolic agents for the respective treatment periods and doses in gilts are not justified.

[发布机构] University of the Free State