versão impressa ISSN 0375-1589
S. Afr. j. anim. sci. vol.39 no.5 Pretoria 2009
A.N.M. Nour El-DinI; S.Z. El-ZarkounyI,#; H. GhobashyII; E.I. Abdel-GawadII; D.J. KeslerIII
IDepartment of Animal Production, Faculty of Agriculture, Alexandria University, Alexandria, Egypt
IIAnimal Production Research Institute, Agricultural Research Center, Ministry of Agriculture, Cairo, Egypt
IIIDepartment of Animal Sciences, University of Illinois, Urbana, 61801, USA
Physiological and productive responses to recombinant bovine somatotropin (rbST) injection and calcium soap of fatty acids (CSFA) supplementation were studied in post-weaning male Rahmani lambs. Male lambs (n = 20) of similar initial body weight (27.9 kg) and age (162 d) were divided randomly into four equal groups. The first was fed the injected with 100 mg of rbST biweekly; the third (basal diet and served as control; the second (GH) was CSFA) was supplemented with 50 g/d of CSFA and the fourth (GH + CSFA) was injected with 100 mg of rbST biweekly plus 50 g/d of CSFA. Treatments increased the average daily gain and final body weight. Concentration of insulin-like growth factor-1 (IGF-1) in lambs treated with (GH) and (GH + CSFA) was higher than that of CSFA and control groups. Haematological parameters (RBC, WBC, and haemoglobin concentrations) did not change. Animals injected with rbST had higher serum total protein than other treated groups and controls. Control lambs showed the least serum albumin concentration. Injection of rbST and supplementation of CSFA increased serum glucose in treated lambs compared to controls. Serum urea concentration was not affected by injection of GH, while CSFA supplementation decreased serum urea concentration compared to the control. Serum triglycerides concentration decreased in rbST-injected lambs than other treatment groups. Lambs supplemented with CSFA only or combined with rbST had higher concentration of serum cholesterol than control or rbST-injected lambs. The results of the present study suggest that rbST and CSFA may increase the average daily gain and improve the physiological status of growing lambs.
Keywords: rbST, CSFA, average daily gain, IGF-1, cholesterol
Exogenously administered somatotropin is one biotechnology tool that increases growth rate, improves feed efficiency, and increases the proportion of lean to fat tissue in the carcasses of lambs (Mclaughlin et al., 1991. Growth hormone exerts some of its actions on skeletal muscles growth via IGF-1, thus the concentration of IGF-1 in blood is generally increased by somatotropin treatment (Vestergaard et al., 2003; Govoni et al., 2004). Commercial products based on calcium soaps of fatty acids (CSFA) are widely used in dairy rations, while these products are less used for growing steers or growing lambs diets (El-Bedawy et al., 2004). Bypass fats are hydrolyzed to their polyunsaturated fatty acids and glycerol, a precursor for glucose (Morsy, 2008). Moreover, Moallem et al. (1997) reported that plasma urea concentrations were decreased in high producing dairy cows fed calcium soaps of fatty acids, reflecting the better utilization of amino acids as reviewed by Etherton & Bauman (1998). The objectives of this study were to determine the separate and combined mechanisms by which rbST administration and calcium soap of fatty acids affect growth rate, serum IGF-1 concentration, haematological parameters as well as serum biochemical parameters in growing Rahmani lambs.
Materials and Methods
Twenty weaned crossbred lambs (initial live weight 27.9 ± 1.8 kg) of 162 ± 5 days of age were assigned randomly to four equal treatment groups, five animals each. Groups were balanced for mean age and body weight. Animals were offered berseem hay ad libitum and commercial concentrate mix containing at least 140 g crude protein/kg. Animals had free access to fresh drinking water. Animals were housed in shaded barns in separate groups. The first group was fed the basal diet and received no further treatment and served as a control. The second group was fed the basal diet plus 50 g/head/day of protected fat (calcium soaps of fatty acids; CSFA; Megafat, Alfa Chemical Co, Alexandria, Egypt). The third group was fed the basal diet plus biweekly injections of 100 mg/head of sustained release formulation of recombinant bovine somatotropin (rbST; Somatec, Elanco-Eli Lilly export, S.A. Geneva). The fourth group was fed the basal diet plus 50 g/head/day of CSFA and received an injection of 100 mg/head/14 days of rbST.
Lambs were weighed biweekly in the mornings before access to feed and water. Blood was collected by jugular vein puncture one week after each rbST injection. Blood samples were immediately collected in heparinised tubes for fresh haematological blood analysis. Remaining blood was centrifuged at 3000 rpm for 20 min and serum was harvested and stored at -20 ºC for later analysis. Concentrations of serum insulin-like growth factor (IGF-1) were determined using a commercial kit (IGF-1-ELISA, Biosource, Europe SA, B1400 Nivelles, Belgium). Serum concentrations of total protein, albumin, glucose, urea and cholesterol were determined using commercial enzymatic colorimetric kits (Diamond Diagnostics, Egypt). Serum triglyceride concentrations were determined using Commercial kit (BioSystems S.A. Costa Brava 30, Barcelona, Spain). Globulin concentrations were calculated as the difference between total protein and albumin. Data was analyzed by the general linear model (GLM) procedure using SAS statistical package (SAS, 1999). The model included rbST and CSFA as main effects and their interaction. Duncan's Multiple Range Test was used to test variations between means.
Initial age and weight of lambs were similar among treatment groups. Mean final weights were 41.5, 46, 48 and 47 kg in control, GH, CSFA and GH plus CSFA lambs, respectively (Table 1). Average daily gain increased (P <0.05) in all groups. Serum concentrations of insulin-like growth factor-1 (IGF-1) in lambs treated with GH and GH + CSFA were higher (P <0.01) than those receiving the CSFA and the controls (Figure 1).
Haemoglobin concentrations (Hb), red blood cells count (RBCs), white blood cells count (WBCs), and packed cells volume (PCV) did not differ among treatment groups and the control (Table 2). Serum total protein in the GH group was higher (P <0.05) than the other groups (Table 3). The Control had lower (P <0.05) serum albumin concentrations than the treated groups. Moreover, CSFA group alone had higher (P <0.05) albumin concentrations than the GH or GH + CSFA groups. However, serum globulin concentration was extremely variable among all groups; and the GH group had the highest concentration of serum globulin. Glucose concentrations were increased (P <0.05) by GH injection and CSFA supplementation. Serum urea concentrations were not affected by the CH injection, while CSFA supplementation decreased (P <0.01) serum urea concentrations compared to the control. On the other hand, serum triglycerides concentrations were lower (P <0.01) in GH lambs than in the remaining groups. Lambs supplemented with CSFA only or combined with GH had higher (P <0.05) concentration of serum cholesterol than the control or GH lambs.
Average daily gain of growing lambs was improved by treatment with GH and CSFA either alone or combined. The current findings are in agreement with those reported by McLaughlin et al. (1991) and Beermann et al. (1990) who reported 16 - 18% increase in growth rates of growing lambs treated with rbST. However, growth performance of Pelibuey lambs was not influenced by the inclusion of different levels of calcium soaps of tallow in diets (Salinas et al., 2006). Moreover, treatment with GH alone or combined with CSFA increased serum concentrations of IGF-I similar to Govoni et al. (2004) and Godferson et al. (1990) who reported that administrations of exogenous forms of GH increased serum IGF-I in Herford calves and growing wethers, respectively. No marked changes were found in haematological parameters in the current study, which is consistent with previous results reported by Sallam et al. (2005).
In the current study GH-treated lambs had elevated serum total protein, albumin, globulin, and glucose concentrations compared to controls. Serum urea and cholesterol concentrations were not affected by GH injections, while serum triglycerides concentrations were decreased. The present results are in part similar to those reported by McLaughlin et al. (1991) where lambs treated with rbST had greater serum glucose and albumin concentrations than controls while urea concentrations were decreased in rbST-treated lambs. GH dramatically reduced fatty acids synthesis in adipose tissue and decreased adipocytes hypertrophy (Dunshea et al., 1992). This may illustrate the cause of reduction in serum triglycerides concentration in lambs treated with rbST. However, the current results showed that CSFA increased serum cholesterol. Fat supplementation markedly increases lipoprotein cholesterol export by the intestine, the major site of de novo cholesterol synthesis in ruminants (Noble, 1981). Similar data were reported by Espinoza et al. (1997) where cholesterol was elevated in Pelibuey ewes fed CSFA. Further, CSFA supplementation alone or combined with GH decreased serum concentrations of urea which is consistent with previous findings by Moallem et al. (1997) and Metwally et al. (2006) in dairy cows fed protected fats. This decrease in urea may be explained by improved efficiency of amino acids utilization and increased protein accretion.
In conclusion, injection of rbST and supplementation of CSFA improved average daily gain and serum IGF-1 of growing Rahmani lambs. CSFA-supplementation decreased serum urea concentration indicative of increased protein utilization, while rbST-injection decreased serum cholesterol and triglycerides concentrations. Therefore, GH injections either alone or combined with protected fats can be used to improve growth performance in growing lambs.
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