Desempenho produtivo e exigências nutricionais de fêmeas Nelore em crescimento

• Autor(a) principal: Gionbelli, Mateus Pies
• Data de Publicação: 2010
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/5671
• topic: Crescimento; Novilhas Nelore; Requerimentos; Growing; Nellore heifers; Requirements; CNPQ::CIENCIAS AGRARIAS::ZOOTECNIA::NUTRICAO E ALIMENTACAO ANIMAL

This work was developed based on three experiments conducted aiming to evaluate animal performance and determine the nutritional requirements of growth in Nellore female cattle. The first two experiments aimed evaluate the dry matter intake (DMI) and nutrients, average daily gain (ADG), feed efficiency (FE), diet digestibility, microbial efficiency and cold carcass yield (CCY) and primal cuts (PC) of young Nellore heifers receiving two levels of concentrate. Nineteen heifers with initial average weight of 165.6±29.8 kg were used. Three animals were used in a trial to determine the digestibility and microbial efficiency of the two levels of concentrate diet (22.5 and 45%) and also including treatment with a restricted intake maintenance level. The remaining 16 heifers were confined for 168 days for evaluation of performance and intake, divided into two levels of concentrate, being 22.5 and 45% concentrate diet. Every 42 days, four animals, two from each level of concentrate, were slaughtered to determine carcass characteristics, making a factorial arrangement 2 × 4. The digestibility and microbial efficiency were not affected (P>0.05) by concentrate level and not by the level of intake, ad libitum or restricted. Heifers fed 45% concentrate diet had greater ADG (P<0.05) than those fed 22.5% concentrate, and the CMS and EA did not differ (P>0.05) between levels of concentrate. ADG (kg / day), DMI (% body weight/day) and EA were higher (P<0.05) in the first period of feedlot (0-42 days) compared to the other (42 to 168 days). It can be conclude that heifers fed 45% concentrate had greater ADG than those fed 22.5% concentrate, and that Nellore heifers, feedlot after weaning and slaughtered young, have appropriate CCY and PC and can reach the point of slaughter (more than 3 mm subcutaneous fat) from 274 kg of body weight, or 10 @ of carcass weight. The third experiment was carried out aiming to determine the nutritional requirements of protein, energy and macro minerals (Ca, Mg, P, Na and K), verify the variations in the retention of energy as protein and fat as well as evaluate the efficiencies of protein and energy deposition and the efficiency of metabolizable energy utilization for maintenance and weight gain of growing Nellore heifers. A comparative slaughter experiment was conducted using 24 heifers with an average initial weight of 168.9±27.1 kg. At the beginning of the trial four heifers were slaughtered, constituting the reference group. The 20 remaining animals were confined for 168 days, and harvest every 42 days for determination of body composition by chemical analysis of tissues. Several methods for determination of metabolizable and net requirements of energy for maintenance (NEm and MEm), protein for maintenance (NPm and MPm), energy to gain (RE), protein to gain (RP) and macro minerals to gain were evaluated. The requirements NEm and MEm obtained were respectively 77.58 and 119.74 Kcal/EBW0,75/day, and the models obtained for ER and PR were: ER (Mcal/day) = 0.0701 × EBW0,75 × EBG1,1216 and RP (g/day) = EBW × (256 to 25.71 × ER ÷ EBW), respectively. The requirement of MPm obtained for heifers was 3.61 g/PC0, 75/day. The efficiency of use of metabolizable protein for gain was 0.42 and the efficiency of energy deposition as protein and fat were 0.25 and 0.83, respectively. It can be concluded that requirements per kg net weight gain of protein and minerals decrease while the energy increases with increasing body weight, and that the efficiency of utilization of metabolizable energy for gain (kg) decreases as a function of energy retained as protein in the gain in Nellore heifers. We also developed a study aiming to develop equations to estimate the chemical composition of noncarcass components (head, feet, blood, skin and organs and viscera) of Nellore females from the empty body weight (EBW) of body composition and the proportion of components in EBW. Data from 24 heifers weighing between 126 and 304 kg, derived from a comparative slaughter experiment were used. It was developed a multiple regression equations for selection of predictor variables by stepwise technique. The EBW was the predictor variable that most influenced the chemical composition of non-carcass components. It was observed an influence of carcass chemical composition on the percentage of crude protein (CP) of the head, legs and leather. The percentage of potassium (K) in the head, feet and blood can be estimated using the EBW. The chemical composition of all chemical constituents of blood, except the magnesium (Mg) can be estimated using the EBW of the animal. Since the chemical composition of organs and viscera cannot be estimated, except the fat, taking the statement that the chemical composition of this body component hardly lead to results with good accuracy. It can be concluded that the chemical composition of the head, feet and the blood of cattle can be estimated from empty body weight and body composition, being not necessary a complete dissection of the head and feet. However, further studies should be conduct to build models using a larger database in order to improve the precision and accuracy of the models as well as identify other possible variables and also the effects of gender and breed type.