Exigências nutricionais de cordeiros deslanados e validação do modelo Small Ruminant Nutrition System (srns)

Abstract

The objective of this study was to determine the nutritional requirements of energy and protein in Morada Nova lambs. Initially it was evaluated the effects of metabolizable energy (ME) levels were evaluated on intake, nutrient digestibility and carcass traits in 40 Morada Nova lambs with initial weight of 12.2 ± 2.05 kg. To determine the energy requirements and protein was realized a comparative slaughter trial was conducted with 48 Morada Nova lambs, non-castrated and 2 months of age, with initial body weights averaging 12.05 ± 1.81 kg (BW). Eight animals were slaughtered at the beginning of the trial as a reference group, in order to estimate initial empty body weight (EBW) and body composition. The remaining animals were assigned to a randomized block design with eight replications per block and five diets with increasing metabilizable energy contents (0.96, 1.28, 1.72, 2.18 and 2.62 Mcal/kg DM). The chemical composition was determined using the composition of the right half carcass as well as using a sample between the cutting of 9th and 11th ribs (section HH) of the half left carcass, where we sought to evaluate the accuracy of this indirect method for determination of body composition. Was estimate efficiencies of the utilization of metabolizable energy for maintenance (km) and weight gain (kg), the requirements of metabolizable energy (ME), total digestible nutrients (TDN) and metabolizable protein (MP) for maintenance and weight gain of Morada Nova lambs, as well as evaluate the Small Ruminant Nutrition System (SRNS) model for predict dry matter intake (DMI)and average daily gain (ADG). To determine the nutritional requirements the animals were slaughtered when the average body weight (BW) group reached 25 kg. It was detected crescent linear effect of levels of ME for intake of dry matter (DM), organic matter (OM), crude protein (CP), total carbohydrates (TC), non fibrous carbohydrates (NFC) and total digestible nutrients (TDN) in g/day. Quadratic effect was observed for neutral detergent fiber (NDF) intake and fibrous carbohydrates (FC) with the maximum point equal to 1.56 and 1.44 Mcal/kg DM (p<0.017) (p<0.003). Linear effect was observed for coefficient of digestibility of DM, OM, EE, CP, NDF, TC, FC and NFC. Daily weight gain (DWG) presented linear increase (p<0.0001) with the levels of ME. The greatest DWG observed was 135.98 g/day for the level of 2.62 Mcal/kg DM. Characteristics of evaluated carcass (hot carcass weight, cold carcass weight, loss by cooling in kilogram, and biological yield) did not vary in function of levels of ME (p>0.05) with average values of 11.52; 11.03; 0.48 kg and 57.25%, respectively. Protein content of the EBW of the animals increased from 161.67 to 175.28 g/kg of EBW when the BW of the animals increased from 15 to 30 kg. The net energy requirement for maintenance obtained was 52.36 ± 1.34 kcal/kg EBW0.75/day. The energy and fat contents of the EBW of the animals increased from 1.64 Mcal/kg and 79.38 g/kg, to 2.11 Mcal/kg and 123.73 g/kg of EBW, respectively, as the BW increased from 15 to 30 kg. The net energy equirements for EBWG increased from 2.15 to 2.78 Mcal/kg EBWG for body weights of 15 and 30 kg. Daily nitrogen excretion was 293.17 ± 0.07 mg/kg BW0.75/day and the net protein requirement for maintenance was 1.83 g/kg BW0.75/day. The amount of protein deposited during the gain increased from 177.84 to 192.93 g/kg of EBWG with the increase in body weight of the animals from 15 to 30 kg. The efficiency of ME utilization for the maintenance level (0.96 Mcal/kg DM) was 0.24, and for the other treatments decreased with increased kg of feed energy (0.60 to 0.40). The ME requirement for maintenance of an Morada Nova lamb of 20 kg BW is 0.56 Mcal/empty body weight, while the total metabolizable protein and total digestible nutrient requirements of an animal of 20 kg BW and ADG of 200g/day is 74.86 g/day and 0.32 kg/day, respectively. The DMI and ADG predicted by the model SRNS did not differ (p≤0.05) from the observed values. The chemical composition of the housing through the use of cutting of 9th and 11th ribs showed high Pearson coefficients of correlation (r), when to estimate the percentage of protein (r = 0.89), fat (r = 0.81) and minerals (r = 0.83). Based on the observed and predicted values by cutting of 9-10-11th ribs equations were developed to estimate the percentage of protein, ether extract and ash of the carcass from these components in cutting of 9th and 11th ribs:% EE in carcass = -6.443 +2.879 *% EE (R ² = 0.76); % CP in carcass = -21.05 + 3.052 *% EE (R ² = 0.83);% Ash in carcass = 4.52 to 0.362% * Ash (R ² = 0.15). The cutting of 9-10-11th ribs satisfactorily estimated the contents of protein and ether extract of the empty body, with r = 0.84 and 0.78 for protein and lipids, respectively. . Increment of energy level in the diets maximized intake and nutrient digestibility. There was increase of daily weight gain of the animals but without changing carcass characteristics. The net energy and protein requirements for maintenance and gain in Morada Nova lambs is lower than values commonly recommended by the main evaluation systems for feed and nutritional requirements for lambs. The crude protein and ether extract of empty body can be satisfactorily estimated from the chemical composition of the cutting of 9th and 11th ribs.