Ciências Agrárias
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Item Performance and amino acids requirements of nellore and crossbred Angus×Nellore fed diets with different crude protein content during growing and finishing stages(Universidade Federal de Viçosa, 2016-09-23) Amaral, Paloma de Melo; Valadares Filho, Sebastião de Campos; http://lattes.cnpq.br/5061647079712333An experiment was conducted to evaluate whether a reduction in dietary crude protein and genetic group (GG) affects animal performance, feed efficiency and carcass traits of beef cattle at different stages of feedlot. Forty-four animals (22 Nellore and 22 crossbred F1 Angus x Nellore), with 8 months and initial shrunk BW (SBW) = 218.6 ± 2.15 kg (Nellore = 211.5 kg; Angus x Nellore = 225.7 kg) were used in this experiment. Eight animals (4 from each genetic group) slaughtered at the beginning of the experiment were used as baseline reference to estimate initial chemical body composition. The 36 remaining bulls were randomly assigned to one of three dietary treatments. The experiment was conducted in a completely randomized design with six replicates, in a 2x3 factorial scheme. The factors were two genetic groups (Nellore and crossbred F1 Angus x Nellore - A×N) and three crude protein contents (CP) (100, 120 and 140 g/kg DM).The experimental period lasted 224 days, being divided in 2 growing stages (GS; Growing (GR) = 112 days, and Finishing (FS) = 112 days). At the end of the experiment, all animals were slaughtered to evaluate their chemical body composition, and carcass characteristics. Crossbred A×N had a higher DMI (%BW) (19.28) compared to Nellore (18.26), and also higher ADG (A×N = 1.18; Nellore = 0.88 kg/d), regardless of growth stage or CP. Crossbred A×N had a higher intake of all nutrients regardless theCPor growth stage. Crossbred A×N ended up the experiment heavier than Nellore, since they showed a greater ADG and were more efficient when compared to Nellore animals. DMI did not differ (P> 0.05) among CP contents within growth stages, however it increased over time. Animals fed 14% CP had a lower DMI (g/BW) during growing stage, however differences were vanished on finishing stage. During growing stage, animals fed 10% CP had a lower ADG compared with animals fed 12 and 14% CP, which did not differ between them. However, during finishing stage there was no difference among CP on ADG. Differences among CP regarding efficiency were also eliminated during finishing stage. Our study found that crossbred animals have, not only greater performance, but also show better carcass traits compared to Nellore, representing an option to increase productivity. We also found that it is possible to adjust diets according to feedlot stage. During the growing stage, 12% of CP should be used, being reduced to 10% during finishing stage of feedlot, without adversely affects performance or carcass characteristics. A second trial aimed to evaluate amino acids requirements for beef cattle. It is expected to work with AA instead of CP requirements in order to provide the correct amount of essential AA to meet maintenance and production requirements. Despite the advances in determining microbial protein synthesis and AA digestibility in small intestine (Rutherfurd et al., 2016), lesser advances were done in intermediate metabolism of AA and especially in net requirements of AAs (Tedeschi et al., 2015). Furthermore, the use of crossbred animals has been increasingly, however, there is no data in the literature comparing AAs requirements between GG, or correlating efficiency with amino acids requirements. Therefore, the objective of this study was to evaluate the retention of AA in the empty body weight and also to determine net requirements of AA in purebred (Nellore) and crossbred (A×N) bulls, fed different crude protein content. Fifty-two bulls, (26 Nellore and 26 crossbred F1 Angus x Nellore) with 8 months and initial shrunk BW (SBW) = 215.0 ± 15.0 kg (Nellore = 208.0±12.78 kg; Angus x Nellore = 221.9±14.16 kg) were used in this experiment. Eight animals (4 from each genetic group) slaughtered at the beginning of the experiment were used as baseline reference to estimate initial chemical body composition. The 36 remaining bulls were randomly assigned to one of three dietary treatments. The experiment was conducted in a completely randomized design with six replicates, in a 2x3 factorial scheme. The factors were two genetic groups (Nellore and crossbred F1 Angus x Nellore - A×N) and three crude protein contents (CP) (100,120 and 140 g/kg DM).The experimental period lasted 224 days. At the end of the experiment, all animals were slaughtered to evaluate their amino acid composition in the body and also the net requirements of amino acids for gain. In the present study it is observed that some AA as lysine and phenylalanine have high correlation with muscle, however, other amino acids (e.g. methionine) have a stronger correlation with body’s composition. It is worth mentioning that this behavior is not constant among different weights, showing that more studies like this need to be conducted to determine more precisely the net requirements of amino acids.A third experiment was divided in two trials. The objective of the first trial was to the nutritional requirements of protein and energy for maintenance and weight gain and the efficiencies of use of metabolizable energy for maintenance and weight gain using the comparative slaughter technique. In the second trial, the net energy requirements for maintenance were also estimated using the heat production measured in a respirometric chamber. In trial 1, 52 animals (26 Nellore and 25 Angus × Nellore), with 8 months and initial body weight = 215.0 ± 15.08 kg (Nellore = 208.0 ± 12.78 kg; F1 Angus x Nellore = 221.9 ± 14.16 kg). The experiment was conducted in a completely randomized design with six replicates, in a 2×3 factorial scheme. The factors were two genetic groups (Nellore and cross-breed F1 Angus × Nellore - A × N) and three crude protein contents (CP, 100, 120 and 140 g / kg DM). The animals selected for voluntary consumption were randomly assigned to one of three dietary treatments. The animals in maintenance were fed with 12g DM/kg BW, with the diet of 12% CP on the DM basis. The animals assigned to the reference group were slaughtered for evaluation of initial empty body weight (EBW) and initial chemical composition of EBW. At the end of 225 days the animals were slaughtered. Trial 2 was carried out at the Federal University of Minas Gerais, where the production of heat (PC) and methane from eight animals (4 Nellor and 4 Crusaders Angus × Nellore) were measured in a respirometric chamber. Soon after, these same animals returned to the UFV, where a digestibility experiment was conducted using a 4 × 4 Latin Square. The relationship between SBW and EBW found in this study was 0.925. There was a difference (P <0.05) between GG for the ADG x EBWG ratio, with an average ratio of 0.966 for Nellore animals and 0.947 for crossbred animals. The value found for NEm was 74.6 Kcal / PCVZ0.75 / day, with no difference between the GGs. The MEm found for Nellore animals was 122 kcal / EBW0.75 / day and 119 kcal / EBW0.75 / day for crossbred animals. There was no difference between GG (P> 0.05) for NEg, and the equation was: RE = 0.0643 x EBW0.75 x EBWG0.6191. The conversion efficiencies of NEm to MEm of Nellore and crossbred animals in this experiment were, respectively, 61.1 and 62.7%. The equation obtained to estimate the net protein requirement for gain was: RP = 188.37 x EBWG - 9.39 x RE. The efficiency of use of the metabolizable protein for gain (k) was 0.3302. In trial 2, apparent digestibilities of nutrients did not differ (P> 0.05) among GG. Likewise, there was no difference for apparent digestibilities of nutrients (P> 0.05) when comparing restricted and voluntary consumption. CPI increased linearly (P <0.05) with CP levels. There was a linear effect of dietary levels of CP (P <0.05) on the apparent digestibilities of DM and OM. An NEm of 85.2 kcal / EBW0.75 / day and an MEm of 114 kcal / EBW0.75 / day were obtained using the respirometric chamber, these values being higher and lower, respectively, than those obtained by the comparative slaughter.