Relações metionina + cisteína : lisina na dieta de bezerros mestiços lactentes

Abstract

The study aimed to evaluate effects of amino acid profile modification in crossbred calves diet fed milk replacer on nutrient digestibility, performance, body composition, gain composition of body components, and determine nutritional requirement for calves up to 60 days fed milk replacer. First part of the study aimed evaluating effects of four different dietary relationship of methionine + cysteine:ysine for crossbred calves on animal performance and body composition for two different ages’ groups. Thirty-six Holstein-Gyr male calves were separated in two groups: sixteen newborn calves (NBC), which were slaughtered at 30 days-old, representing a physiological phase from 8 to 30 days-old; and twenty pre-weaned calves (PWC), which were slaughtered at 60 days-old, representing a physiological phase from 30 to 60 days-old. At eight days of age, the animals were randomly distributed among the experimental treatments: four methionine + cysteine: lysine dietary ratios (MCLR: 44; 48; 52; and 56%), that were provided by an amino acid supplement added to 1.0 kg (wet basis) of commercial milk replacer reconstituted at 13.8% (dry matter basis). The effect of MCLR on the digestibility of nutrients was not observed, as well as no significance was observed regarding the interactions between physiological phase and MCLR. For the NBC group, there were no responses observed in performance according to different MCLR. PWC responded positively to higher methionine + cysteine: lysine ratios; In conclusion, an optimal MCLR to allow the best performance and protein gain should be between 52.33 and 53.93%. The second part aimed presenting information on the estimates of energy and protein requirements for crossbred calves fed milk replacer. In addition to the 43 calves described in the first part of the study, there were introduced to the database studied, seven calves that made up the maintenance group, that were slaughtered at 30 days of age. The diet and the experimental treatments were the same used in the first part of the study; however, Chagas, J.C.C. Relações metionina + cisteína:lisina na dieta de bezerros mestiços lactentes the animals were distributed in a completely randomized design between MCLR and were evaluated as compound group. Different MCLR were tested for models and there was no significant effect on the energy and protein requirements (P > 0.05). The net energy requirements for maintenance were 75.2 kcal/EBW0.75/day, energy utilization efficiency for maintenance of (km) 67.38%. The prediction equation of net energy requirements for gain (Mcal/day) was: RE = 0.0879 x EBW0.75 x EBWG0.7380, as energy utilization efficiency for gain of (kg) 47.74%. The requirements estimated for metabolizable protein for maintenance were 4.83 g/EBW0,7.5/day. The equation for the estimated requirements for liquid protein to gain (g/day) was: NPg = EBWG x 246.73 x EBW-0.1204, as protein utilization efficiency for gain of (k) 71,55%. The requirements of energy and protein reported presented are higher than the values reported for calves fed with milk. It suggests that milk replacers are used, for calves up to 60 days, less efficiently when compared with whole milk.