Objetivou-se avaliar as exigências nutricionais de proteína e energia de vacas nelores em lactação no período de 0 a 180 dias. Foram utilizadas 20 vacas primíparas com peso corporal médio ao parto de 362±25 kg. Quatro vacas foram abatidas logo após o parto e foram consideradas grupo referência. Do parto aos 90 dias, quatro vacas receberam alimentação restrita na proporção de 1,5% do peso corporal (PC), em porcentagem da matéria seca (MS), e 12 foram alimentadas à vontade. Aos 90 dias do pós-parto, foram abatidas oito vacas (quatro de cada oferta alimentar). Dos 90 aos 180 dias, quatro vacas foram realocadas para mantença (1,8% PC em MS) e quatro continuaram em consumo voluntário, sendo todas abatidas ao final do período. Os conteúdos corporais de proteína e energia foram estimados pelo equação Y = a . Xb, em que X é o peso de corpo vazio (PCVZ) e a e b os parâmetros da equação. Foram obtidas relações médias de 0,894 para PCVZ/PC e de 0,936 para ganho de PCVZ (GPCVZ)/ganho de PC (GPC). As exigências líquidas de energia para mantença (ELm) foram de 97,84 kcal/PCVZ0,75 e as de energia metabolizável para mantença (EMm), 140,17 kcal/PCVZ0,75. As eficiências de utilização da energia para mantença e ganho de peso foram 0,70 e 0,44, respectivamente. Os conteúdos corporais de proteína diminuíram com o aumento do PC, enquanto os de energia aumentaram. No leite das vacas, foram determinados teores médios de 3,71; 3,88; e 4,74%, respectivamente, de proteína bruta, gordura e lactose. A exigência de ELm para lactação de vacas nelores é de 97,84 kcal/PCVZ0,75, enquanto a de EMm é de 140,17 kcal/PCVZ0,75 e a de proteína metabolizável, de 52,8 g. Para produzir 1 kg de leite com 4% de gordura, vacas nelores necessitam de 0,300 kg de NDT.

This study was conducted to evaluate the nutritional requirements of protein and energy of primiparous lactating Nellore cows from 0 to 180 days after calving. A total of 20 lactating primiparous cows with average body weight at calving of 362±25 kg were used. Four cows were slaughtered soon after calving and were considered as reference group. From calving to 90 days post partum four cows were fed restricted at 1.5% of body weight (BW) in dry matter (DM) basis and 12 were fed ad libitum. At 90 days post partum eight cows were slaughtered (four from each feeding system). From 90 to 180 days, four cows were realocated for maintenance (1.8% BW in DM) and four remained in voluntary intake, and all were slaughtered at the end of the period. The contents of protein and energy were estimated by the equation Y = a. Xb, in which X is the empty body weight (EBW), and a and b are the parameters of the allometric equation. Ratios obtained for empty body weight (EBW)/BW and empty body gain (EBWG)/BWG were 0.894 and 0.936, respectively. The net energy for maintenance (NEm) were 97.84 kcal/EBW0.75 and the metabolizable energy for maintenance (MEm) were 140.17 kcal/EBW0.75. The efficiencies of energy use for maintenance and gain were 0.70 and 0.44, respectively. The content of protein and minerals, except calcium, decreased with the increase in BW while the energy increased. The milk of cows had average contents of 3.71, 3.88 and 4.74%, respectively, for crude protein, fat and lactose. The NEm requirement for lactating Nellore cows is 97.84 kcal/EBW0,75, while MEm is 140.17 kcal/EBW0,75 and metabolizable protein requirement is 52.8 g. To produce 1 kg of milk with 4% fat Nellore cows need 0.300 kg TDN.

The objective of this study was to evaluate intake, digestibility and nitrogen (N) compounds use efficiency in F1 Holstein × Zebu grazing cows. Eighteen crossbred cows (six Holstein × Gir, six Holstein × Guzerat, and six Holstein × Nellore) were used in the experiment, constituting three experimental treatments in simple random samples, under the same feeding conditions. At the estimation of individual intake at grazing, titanium dioxide was used for estimating fecal excretion and indigestible neutral detergent fiber, in order to determine pasture intake. There was effect of the lactation period on nutrient intake, except for the intakes of dry matter (DM), organic matter (OM) and total digestible nutrients (TDN) in % of body weight (BW), as well as those of non-fibrous carbohydrates (NFC), in kg. The digestibility coefficients of crude protein (CP), neutral detergent fiber corrected for ash and protein (NDFap) and the contents of TDN varied in function of the lactation period, whereas the coefficients of digestibility of DM, ether extract (EE) and OM did not present such effect. The total milk production projected at 305 days of lactation for Holstein × Gir cows was superior in relation to Holstein × Guzerat and Holstein × Nellore cows. The excretion of urea into urine and of urea N into the milk and the plasma presented quadratic behavior in function of the lactation period. The utilization of the genetic group from Holstein × Zebu grazing cows does not cause alterations in intake, nutrient digestibility or nitrogen use efficiency; however, there is variation in function of the lactation period. Holstein × Gir cows presented greater accumulated production during lactation and persistence, followed by Holstein × Guzerat and Holstein × Nellore cows.

The objective of this study was to determine the energy nutritional requirements for females of Nellore, Nellore × Angus and Nellore × Simmental fed on two levels of concentrate. Sixty heifers from three genetic groups were used: 20 Nellore, 20 Nellore × Angus and 20 Nellore × Simmental. Twelve belonged to the reference group (four of each genetic group) and were slaughtered at the beginning of the experiment. Another 12 heifers (four of each genetic group) were fed on the maintenance level and 36 heifers (12 animals of each genetic group) were kept in feeding system ad libitum with 30 (six in each group) or 50% (six of each group) dry matter concentrate. Animals were randomly assigned to six treatments in a 3 × 2 factorial arrangement (three genetic groups and two diets) with six replicates per treatment. Nine more heifers were used in a parallel experiment to estimate the apparent digestibility coefficients (three from each genetic group). Net energy requirements were estimated by the equation of retained energy as a function of metabolic empty body weight (EBW0.75) and empty body weight gain (EBWg). Requirements of metabolizable and net energy were estimated for maintenance by the equation of heat production as a function of metabolizable energy intake. Using the combined equation RE (retained energy; Mcal/day) = 0.0703 × EBW.75 × EBWg1.128 to predict net energy requirements for weight gain is recommended. The requirement of metabolizable and net energy for maintenance of all groups is 70.55 and 106.53 kcal/kgEBW0.75/day, respectively. Use efficiencies of metabolizable energy for gain and maintenance are 36.41 and 66.23%, for the three genetic groups respectively.