Requerimentos nutricionais e aspectos quantitativos do crescimento, desenvolvimento e digestão de vacas Nelore gestantes e não gestantes

Vários desafios ocorrem no status fisiológico normal da vaca para suportar a formação de um novo indivíduo da espécie. Dados sobre exigências nutricionais e aspectos quantitativos do crescimento, desenvolvimento e digestão de vacas Bos indicus são limitados. Objetivando preencher pelo menos uma parte da lacuna existente, foi conduzido um experimento de abate comparativo com vacas gestantes e não gestantes. Os resultados são aqui apresentados em quatro capítulos. No primeiro capítulo, quarenta e nove vacas Nelore (32 gestantes e 17 não gestantes) com peso médio inicial de 451 ± 10 kg foram usadas num experimento para avaliar o crescimento e desenvolvimento de tecidos maternos e fetais durante a gestação em vacas zebuínas. As vacas foram divididas em dois grupos de acordo com o nível alimentar, que foi ALTO (ad libitum) ou BAIXO (alimentação restrita a 1,2 vezes a mantença, segundo o NRC). As 32 vacas gestantes foram separadas em 4 grupos com 8 vacas em cada e abatidas aos 136, 189, 239 e 269 dias de gestação para coletas de tecidos e análises. Vacas do alto nível alimentar tiveram maior ganho de peso (P0,10). Vacas do nível alimentar alto aumentaram o peso do úbere após 239 dias de gestação (P 0.10). HIGH-fed cows increased the weight of fresh udder after 239 d of gestation (P 0.10). LOW-fed cows had proportionally (g/kg of EBWnp) lower liver, visceral fat and mesentery (P < 0.01) and greater heart (P < 0.10) than HIGH-fed cows. The proportional weights of rumen- reticulum, omasum and total stomach were affected (P &#8804; 0.05) by pregnancy and were lower at 269 d than in early gestation. HIGH-fed cows had greater fetuses at 269 d of gestation than LOW-fed cows. Fetuses from HIGH-fed cows had greater carcasses (P = 0.03) but did not differ from fetuses from LOW-fed cows in organs and viscera (P = 0.27). Placenta weight was greater in HIGH-fed cows (P < 0.01) and the relationship between placenta and fetus weight was different between feeding levels (P < 0.01). The weights of the gravid uterus and fetus, as well as their contents of energy and N, were lower in this study compared to previous studies with Bos taurus cattle. In the second chapter, data from the same 49 cows used in the first chapter were used to develop a set of equations and relations for BW adjustments in pregnant or not pregnant beef cows, improving the options and the reach of the research in the area. Cows were weighed every 28 d (0700 h, before feeding) to obtain the BW, and reweighed at the same time the following day after 16 h of fasting to obtain the shrunk body weight (SBW) values. Pregnant cows were separated into four groups of eight cows each and harvested at 136, 189, 239 and 269 d of pregnancy to obtain the empty body weight (EBW) and the weight of components related to pregnancy. To establish the relationships between the BW, SBW and EBW of pregnant and non-pregnant cows as a function of time of gestation, a set of general equations was tested, based on theoretical suppositions. The pregnant compound (PREG) was defined as the weight that is genuinely related to pregnancy, that includes the gravid uterus minus the non-pregnant uterus plus the accretion in udder related to pregnancy. The PREG was deducted from the SBW or EBW of a pregnant cow to estimate the non-pregnant SBW and EBW (SBWnp and EBWnp) and to calculate the body gain of only maternal tissues (rSBG and rEBG). The overall equation to predict SBW from BW was 0.8084 × BW 1.0303. The equation to predict gravid uterus weight in function of days of pregnancy (DOP) was 0.2106 × e((0.03119 0.00004117 × DOP) × DOP) . There was no accretion of weight in udder up to 238 d of pregnancy and the accretion after 238 d was exponentially correlated with DOP. We conclude that the weight related to the pregnancy can be estimated in a live cow allowing estimating the non-pregnant EBW and SBW of a pregnant cow. This allows estimate and compare the weight gain of tissues not related to the pregnancy and the comparison of weight gain of a pregnant and non-pregnant cow. The objective of the third chapter was to evaluate the effects of pregnancy and feeding level on intake, digestibility and efficiency of microbial N production in Nellore cows. Forty-four multiparous Nellore cows (32 pregnant and 12 non-pregnant) with average initial body weight of 451 ± 10 kg were fed either HIGH (ad libitum) or LOW (restricted feeding 1.2 times maintenance according to the NRC) feeding level. The diet consisted of corn silage (85%), ground corn, soybean meal, urea and mineral mixture. The intake was controlled daily and the DM intake (DMI) was evaluated weekly. In vivo apparent total digestibility was estimated using indigestible NDF as an internal marker and microbial N synthesis was estimated from the technique of the purine derivatives in urine. The voluntary feed intake reduced as the pregnancy advances in Nellore cows and can be calculated as DMI (kg/d) = (16 0.0093 × days in pregnancy) / 1000 × SBWp or DMI (kg/d) = (16.4 0.0093 × days in pregnancy) / 1000 × SBWnp. The average DMI of LOW-fed cows corresponded to 102, 98 and 67% of the amount of energy necessary to attend the maintenance and pregnancy energy requirements suggested by NRC for a cow at 0, 135 and 270 d of pregnancy, respectively. LOW-fed cows had 0.26 kg/d of average shrunk body gain indicating that the nutrient energy requirements of Zebu cows are likely lower than those suggested by NRC. The interaction between the feeding level and days of pregnancy was significant (P<0.05) for the digestibility of DM, OM, N, EE, NDFap and GE, and the values of TDN. In all these cases there was a reduction in digestibility with increasing gestation age in HIGH-fed cows, while the digestibility OM, N, EE, NDFap and GE increased as function of days of pregnancy in LOW-fed. The reduction in the digestibility of neutral detergent fiber occurs faster than in dry matter digestibility. These data suggests that the reduction of the digestibility as pregnancy increases is caused by an increase in the rate of passage as compensation factor for the ruminal volume reduction. There were no direct effects of pregnancy on microbial N production in Nellore cows. In the fourth chapter 49 adult Nellore cows (32 pregnant and 17 non-pregnant) with average initial body weight of 451 ± 10 kg were used in a comparative slaughter study aiming to describe equations and relationships for prediction of net, metabolizable and dietary energy and protein requirements for adult, pregnant and non-pregnant, Bos indicus cows. Feeding control was measured individually and cattle were fed either HIGH (ad libitum) or LOW (restricted feeding 1.2 times maintenance according to the NRC). The 32 pregnant cows were separated at random into 4 groups of 8 cows each (4 cows per each feeding level) and harvested at 136 ± 1, 189 ± 1, 239 ± 1 and 269 ± 1 d of pregnancy. The non-pregnant cows were harvested at different times of the experiment (85 to 216 days of feeding control) in order to keep them in experiment for a similar amount of time as the pregnant cows. The digestible energy and N and losses of energy as methane and urine were directly measured to establish the relations between GE, DE and ME. Energy and N content were analyzed in empty body and pregnant compounds and a set of relationships and equations based in the factorial method from ARC was used to estimate the nutrient requirements of energy and N. The net energy and protein requirements for pregnancy (NEp and NPp) estimated in this study were about 3&#8260;4 of those estimated by NRC. When estimated by a logistic model, the daily requirements for pregnancy showed an exponential increase up to approx. 250 days of gestation and then decreased. However, when an allometric model was used to estimate the daily requirements for pregnancy, the maximum daily requirements were at birth. There were no differences in the dynamics of energy and protein (P=0.388 and 0.137, respectively) in the cow s empty body weight pregnant free (EBWnp) suggesting that the pregnancy does not affect the requirements for accretion of body reserves in cows. The partial efficiencies for use of metabolizable energy for maintenance, weight gain and pregnancy (km, kg and kc) were respectively 70, 53 and 12%. The partial efficiencies for use of metabolizable protein for maintenance, weight gain and pregnancy (zm, zg and zc) were respectively 22, 22 and 5%, indicating that in mature cows the major portion of metabolizable protein intake is not used for tissue accretion. The efficiency of transformation of DE in ME was 0.80

Performance and nutritional requirements of growing Nellore heifers

O presente trabalho foi desenvolvido a partir de três experimentos conduzidos com o objetivo de avaliar o desempenho produtivo e determinar as exigências nutricionais de fêmeas Nelore em crescimento. Nos dois primeiros experimentos objetivou-se avaliar o consumo de matéria seca (CMS) e de nutrientes, ganho médio diário (GMD), eficiência alimentar (EA), digestibilidade das dietas, eficiência microbiana e rendimento de carcaça (RC) e de cortes básicos (RCB) de novilhas Nelore jovens recebendo dois níveis de concentrado. Foram utilizadas 19 novilhas Nelore com peso médio inicial de 165,6±29,8 kg e 9 meses de idade. Três animais foram utilizados no primeiro experimento, para determinação das digestibilidades e eficiência microbiana dos dois níveis de concentrado da dieta (22,5 e 45%) e incluindo também um tratamento com consumo restrito em nível de mantença. No segundo experimento, as 16 novilhas restantes foram confinadas por 168 dias para avaliação de consumo e desempenho, divididas em dois tratamentos, sendo 22,5 e 45% de concentrado na dieta. A cada 42 dias, 4 animais, sendo dois de cada tratamento, foram abatidos para determinação das características de carcaça, perfazendo um esquema fatorial 2×4. As digestibilidades e a eficiência microbiana não foram afetadas (P>0,05) pelo nível de concentrado na dieta e nem pelo nível de consumo, ad libitum ou restrito. Novilhas recebendo 45% de concentrado na dieta apresentaram maior GMD (P0,05) entre os dois tratamentos. O GMD (kg/dia), CMS (% do peso corporal/dia) e EA foram maiores (P0.05) by concentrate level and not by the level of intake, ad libitum or restricted. Heifers fed 45% concentrate diet had greater ADG (P0.05) 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.Coordenação de Aperfeiçoamento de Pessoal de Nível Superio

Uso de técnicas de regressão na avaliação, em bovinos de corte, da eficiência de conversão do alimento em produto: proposição de método e significância nutricional

Objetivou-se neste estudo propor e discutir método de avaliação da eficiência de conversão do alimento em produto em bovinos de corte com base na utilização de técnicas de regressão. Os procedimentos matemáticos e estatísticos foram desenvolvidos a partir de banco de dados formado pela mensuração do consumo de matéria seca e do ganho médio diário em 380 bovinos zebuínos puros ou mestiços em 15 diferentes experimentos constantes na base de dados do sistema BR-CORTE. Foram propostas duas aproximações baseadas no ajustamento de modelos de regressão linear e não-linear, tendo o ganho médio diário como variável independente e o consumo de matéria seca como variável dependente. A utilização do alimento pelo animal foi estratificada em demanda para mantença e eficiência real de conversão em produto. O parâmetro demanda para mantença possui interpretação similar em ambas as aproximações. Na solução linear, assume-se que a eficiência real de conversão em produto seja fixa e independente do ganho médio diário. Por outro lado, na solução não-linear, assume-se que a eficiência real de conversão em produto seja variável e dependente do ganho. O critério de informação de Akaike foi proposto como ferramenta para escolha entre os modelos linear e não-linear. A avaliação da eficiência de transformação do alimento em produto em bovinos de corte por meio de técnicas de regressão possibilita o entendimento mais amplo da eficiência de uso do alimento em sistemas de produção, pois permite estratificar as demandas em mantença e produção. Muitos inconvenientes associados ao uso de índices baseados em razões, como a conversão alimentar, são eliminados, ampliando a acurácia e a precisão das inferências nutricionais

Uso de técnicas de regressão na avaliação, em bovinos de corte, da eficiência de conversão do alimento em produto: comparação entre grupos experimentais

Objetivou-se neste estudo propor e discutir um método de avaliação comparativa da eficiência de conversão do alimento em produto entre dois grupos experimentais de bovinos de corte baseado na utilização de técnicas de regressão. Os procedimentos matemáticos e estatísticos foram desenvolvidos a partir de banco de dados formado pela mensuração do consumo de matéria seca e do ganho médio diário em 380 bovinos zebuínos puros ou mestiços em 15 experimentos constantes na base de dados do sistema BR-CORTE. Foram selecionados dois grupos constituídos por animais Nelore (n = 156) e animais F1 Europeu × Nelore (n = 139). Foram propostas duas aproximações baseadas no ajustamento de modelos de regressão linear e não-linear, tendo o ganho médio diário com variável independente e o consumo de matéria seca como variável dependente. A utilização do alimento pelo animal foi estratificada em demanda para mantença e eficiência real de conversão em produto e as diferenças entre grupos foram avaliadas por intermédio de variáveis dummy. O critério de informação de Akaike foi proposto como ferramenta para escolha entre os modelos linear e não-linear. A avaliação comparativa da eficiência de transformação do alimento em produto entre dois grupos experimentais de bovinos de corte por meio de técnicas de regressão permite, caso pertinente, a estratificação dos grupos em função da eficiência de uso da dieta para suprimento de demandas para mantença e para produção

Prenatal origins of productivity and quality of beef

The productive traits of beef cattle are orchestrated by their genetics, postnatal environmental conditions, and also by the intrauterine background. Both under- or overnutrition, as specific dietary components, are able to promote persistent effects on the offspring. This occurs because dietary factors act not only affecting the availability of substrates for fetal anabolism and oxidative metabolism, but also as signals that regulate several events toward fetal development. Therefore, this study aimed to summarize the gestational nutrition effects on the offspring performance and meat quality in a long term. Overall, studies have shown that many of these alterations are under the control of epigenetic mechanisms, as DNA methylation, histones modification, and non-coding RNA. The current knowledge has indicated that the fetal programming responses are dependent on the window of fetal development in which the dietary treatment is applied, the intensity of maternal nutritional stimuli, and the treatment application length. Collectively, studies demonstrated that muscle cell hyperplasia is impaired when maternal requirements were not achieved in the second third of gestation, which limits the formation of a greater number of muscle fibers and the offspring growth potential in a long term. Changes in muscle fibers metabolism and in collagen content were also reported as consequence of a dietary perturbation during pregnancy. In contrast, a maternal overnutrition during the late pregnancy has been associated with beneficial responses on meat quality. In summary, ensuring an adequate maternal environment during the fetal development is crucial to enhance the productive responses in beef cattle operation

Protected fat and variable level of protein in diets of crossbreed cows in early lactation

Current study evaluated the inclusion of protected fat and different levels of crude protein (CP) in the diet of crossbreed cows in early lactation. Twelve cows were distributed in a 4 x 4 factorial design, with four treatments (12 or 16% CP, with or without MEGALAC-E®). Statistical analyzes with ANOVA and Pearson’s linear correlation procedures were performed. Protected fat did not affect intake of dry matter (DM) and organic matter (OM) (p > 0.05). Increased CP raised consumption of CP and EE and decreased the non-fiber carbohydrates (NFC; p 0.05) on milk yield and composition due to protected fat or CP rates. Since the inclusion of protected fat and higher content of CP (16%) in the diet did not benefit the production and composition of milk in crossbreed cows, diets with 12% CP without the inclusion of protected fat are recommended.

Development of the gastrointestinal tract of newborn goats under maternal feed restriction at different stages of gestation

This study evaluated how nutritional insults applied at different stages of intrauterine development affect the growth and development of total tract organs and the mRNA expression of genes that encode growth factors, tight junction proteins, digestive enzymes, and glucose transporters in the small intestine of newborn goats. Fourteen nulliparous dairy goats were assigned to one of two nutritional plans over gestation: maintenance-restriction (M-R, n = 8) – 100% of maintenance requirement from d 8-84 of gestation followed by feeding at 50% maintenance requirement from d 85 of gestation to parturition; or restriction-maintenance (R-M, n = 6) – 50% of maintenance requirement from d 8-84 of gestation followed by feeding at 100% maintenance requirement from d 85 of gestation to parturition. Fisher’s least significant difference test was performed using SAS 9.4, considering a full fixed-effect model. When expressed per kg of body weight, the weights of the small intestine and total intestine were 18.7 and 18.1% lower, respectively, for R-M offspring. The lengths of the small intestine and the total intestine of the R-M newborns were 19.1 and 9.5% shorter, respectively. This group also had a lower villus height:intestinal crypt depth ratio. The R-M offspring tended to have lower Solute carrier family 5 member 1 (SLC5A1), Solute carrier family 2 member 2 (SLC2A2), and Occludin (OCLN) mRNA expressions. Therefore, feed restriction in the first half of gestation is detrimental to the second half of gestation, reducing the offspring’s intestinal absorptive area but enhancing their intestinal permeability