Desempenho, composição corporal e exigências nutricionais de bovinos Nelore de diferentes classes sexuais / Performance, body composition and nutritional requirements of Nellore bulls, steers and heifers

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

This work was comprised of two experiments that were carried out with the objective of assessing the performance, nutrients intake and digestibilities, feed efficiency, carcass traits, body composition and energy and protein requirements of Nellore bulls, steers and heifers. The first trial was carried out through July and September, 2004, using 48 animals (16 bulls, 16 steers and 16 heifers), which were individually fed for 77 days in individual pens. At the beginning of the trial, the animals were 21 months old and weighed 276.20; 265.80 and 257.30 kg, respectively, for the bulls, steers and heifers. The diet, composed of elephant grass silage, corn silage (70:30) and concentrate (roughage to concentrate ratio of 85:15, total DM basis) was offered daily. Dry matter and nutrient intakes were measured weekly, using laboratory analysis of the feed and orts. A digestibility trial was carried out at the 9th week, when spot urine samples were also taken, in order to estimate microbial protein yield and its synthesis efficiency. At the end of the experiment the animals were ultrasonically scanned using Aloka 500-V machine, equipped with a 3.5 MHz, 17.2 cm linear array transducer. Residual feed intake (RFI) was calculated by the difference between the observed dry matter intake (DMI) and the DMI obtained from linear regression of DMI on average daily gain (ADG) and average metabolic body weight (MBW) of the animals. The bulls were the heaviest, presenting superior ADG and leaner and more muscled carcasses (P<0.05). Although poorer in the performance traits, the heifers had larger carcass subcutaneous fat thickness (SF) (P<0.05), while the steers presented intermediate values. DM and nutrients intakes, but ether extract (EE), expressed as a function of the body weight (BW), were not significantly affected by sexual class. The digestibilities neither. When evaluated within the RFI groups, the animals with high RFI had the same body weight, the same growth rate and did not have any of its carcass traits affected (P>0.05), in spite of eating 11.5% more DM (P<0.05). Nutrients intakes were higher for the animals with high RFI (P<0.05), however the digestibilities did not differ from those animals that had lower RFI (P>0.05). Microbial protein yield, as well as its efficiency of synthesis, was not affected neither by sexual class nor by RFI group (P>0.05), what also was observed for the analysis of purine derivatives excreted in the urine and blood urea concentration. Excretion of urea in the urine (mg/kg BW) was only affected by sexual class, being higher for the heifers when compared to the bulls and steers (P<0.05). Sexual class affects performance and carcass traits of Nellore cattle, whereas residual feed intake does not impair carcass quality. In the second experiment, 35 animals, from a same contemporary group, were used (12 bulls 11 steers and 12 heifers). The animals were individually fed during 112 days, being slaughtered at the end of the trial, whereas the reference group was slaughtered at the beginning. The animals were randomly assigned to six treatments in a 3 x 2 factorial design, being 3 sexual classes and 2 levels of concentrate allowance (0.6 and 1.2% of BW). The parameters measured were: intake, digestibility, carcass traits, body composition, and energy and protein requirements. Bulls were more efficient, presenting higher body weight, empty body weight and carcass weight, as a result of their highest growth rate, when compared with the heifers (P<0.05), whereas the steers presented intermediate values. The relative DMI and intakes of all of the other nutrients were higher for the heifers (P<0.05) in comparison to the bulls, while the steers had intermediate values. The digestibilities, but EE digestibility, were not affected (P>0.05) by sexual class. DM and OM digestibilities were higher (P<0.05) for the diet in which the concentrate allowance level was 1.2% of BW, whereas for all the other nutrients there wasnt detected any effect due to concentrate allowance level (P>0.05). Bull carcasses were heavier and leaner (P<0.05) than heifers, while steers carcasses had intermediate values. Heifers carcasses had higher fat content than the males, due to a more pronounced subcutaneous fat depot (P<0.05). Beyond that, visceral and subcutaneous fat depots contribution, in relation to the empty body weight, was higher in the heifers (P<0.05), although the rates of fat deposition in the different depots had not been influenced by sexual class (P>0.05). Concentrate allowance level did not affected (P>0.05) the carcass traits and the body and carcass composition of the animals. Empty body protein and ether extract contents observed in the bulls were, respectively, higher and lower, when compared to the heifers (P<0.05), while it was observed intermediate values for the steers. The composition of both carcass and empty body gain was different between bulls, steers and heifers, since the rates of muscle accretion in the carcass and protein accretion in the empty body had distinct pattern, being more pronounced in the bulls (P<0.05) than in the heifers and steers. The empty body gain of the bulls was composed of more protein and less ether extract than that of the heifers and steers (P<0.05). The yield of commercial carcass cuts was not influenced by concentrate allowance level (P>0.05), but by sexual class (P<0.05). Heifers and steers had higher hind quarter yield (P<0.05), since the fore quarter of the bulls was more developed. The net energy requirement for maintenance did not differ among the sexual classes, with a mean value of 75.92 Mcal/kg EBW0,75, whereas the metabolizable energy requirement for maintenance was 108.81 Mcal/kg EBW0,75. The net energy requirement for body gain increased as the animal became heavier, being higher for steers and heifers than for bulls. For animals with body weight of 400 kg, the net energy requirements for empty body gain were 4.16; 5.34 and 5.02 Mcal, respectively for bulls, steers and heifers. The equations fitted to estimate the retained energy (RE) were: RE = 0,0515 EBW0,75 * EBWG0,9384 (bulls); RE = 0,0696 EBW0,75 * EBWG0,9250 (steers) and RE = 0,0731 EBW0,75 * EBW1,0175 (heifers). The efficiency of metabolizable energy utilization for maintenance obtained in this trial was 70%, while for body gain the efficiencies ranged from 45 to 49%. The partial efficiencies of energy utilization for protein and fat synthesis were 27.2 and 79.1%, respectively. The net protein requirements for body gain (RP = retained protein) decreased as the body weight increased, being higher for the bulls, intermediate for the steers and lower for the heifers, and can be estimated by the equations: RP = 14,78 + 175,86 ADG 2,95 RE (bulls), RP = 25,62 + 139,81 ADG 7,43 RE (steers); RP = 18,13 + 177,27 ADG 16,57 RE (heifers).

ASSUNTO(S)

nutrition nelore sex nelore sexo bovino composição corporal nutricao e alimentacao animal nutrição bovine body composition

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