Sérgio Raposo de Medeiros

Mathematical models in ruminant nutrition

Mathematical models can be used to improve performance, reduce cost of production, and reduce nutrient excretion by accounting for more of the variation in predicting requirements and feed utilization in each unique production situation. Mathematical models can be classified into five or more categories based on their nature and behavior. Determining the appropriate level of aggregation of equations is a major problem in formulating models. The most critical step is to describe the purpose of the model and then to determine the appropriate mix of empirical and mechanistic representations of physiological functions, given development and evaluation dataset availability, inputs typically available and the benefits versus the risks of use associated with increased sensitivity. We discussed five major feeding systems used around the world. They share common concepts of energy and nutrient requirement and supply by feeds, but differ in structure and application of the concepts. Animal models are used for a variety of purposes, including the simple description of observations, prediction of responses to management, and explanation of biological mechanisms. Depending upon the objectives, a number of different approaches may be used, including classical algebraic equations, predictive empirical relationships, and dynamic, mechanistic models. The latter offer the best opportunity to make full use of the growing body of knowledge regarding animal biology. Continuing development of these types of models and computer technology and software for their implementation holds great promise for improvements in the effectiveness with which fundamental knowledge of animal function can be applied to improve animal agriculture and reduce its impact on the environment.

Effects of dietary supplementation of rumen-protected conjugated linoleic acid to grazing cows in early lactation

Conjugated linoleic acids (CLA) are potent anticarcinogens in animal and in vitro models as well as inhibitors of fatty acid synthesis in mammary gland, liver, and adipose tissue. Our objective was to evaluate long-term CLA supplementation of lactating dairy cows in tropical pasture on milk production and composition and residual effects posttreatment. Thirty crossbred cows grazing stargrass (Cynodon nlemfuensis Vanderyst var. nlemfüensis) were blocked by parity and received 150 g/d of a dietary fat supplement of either Ca-salts of palm oil fatty acids (control) or a mixture of Ca-salts of CLA (CLA treatment). Supplements of fatty acids were mixed with 4 kg/d of concentrate. Grazing plus supplements were estimated to provide 115% of the estimated metabolizable protein requirements from 28 to 84 d in milk (treatment period). The CLA supplement provided 15 g/d of cis-9,trans-11 and 22g of cis-10,trans-12. Residual effects were evaluated from 85 to 112 d in milk (residual period) when cows were fed an 18% crude protein concentrate without added fat. The CLA treatment increased milk production but reduced milk fat concentration from 2.90 to 2.14% and fat production from 437 to 348 g/d. Milk protein concentration increased by 11.5% (2.79 to 3.11%) and production by 19% (422 to 504 g/d) in the cows fed CLA. The CLA treatment decreased milk energy concentration and increased milk volume, resulting in unchanged energy output. Milk production and protein concentration and production were also greater during the residual period for the CLA-treated cows. The CLA treatment reduced production of fatty acids (FA) of all chain lengths, but the larger effect was on short-chain FA, causing a shift toward a greater content of longer chain FA. The CLA treatment increased total milk CLA content by 30% and content of the trans-10,cis-12 CLA isomer by 88%. The CLA treatment tended to decrease the number of days open, suggesting a possible effect on reproduction. Under tropical grazing conditions, in a nutritionally challenging environment, CLA-treated cows decreased milk fat content and secreted the same amount of milk energy by increasing milk volume and milk protein production.

Conjugated linoleic acid (CLA) effects on pups growth, milk composition and lipogenic enzymes in lactating rats.

Conjugated linoleic acid (CLA) has a range of biological properties, including effects on lipid metabolism, milk and body composition in animals. This study investigated the effects of dietary CLA on lactating rats and development of the suckling pups. Dams were fed either a control diet or the same diet supplemented with 25 g/kg of a fat supplement containing 540 g CLA/kg (final concentration of 13.5 g CLA/kg diet) from parturition to the 15th day post-partum. The CLA mixture used in this study contained the following isomers (per 100 g): cis-9, trans-11 (24 g); cis-10, trans-12 (35 g); cis-8, trans-10 (15 g); cis-11, trans-13 (17 g) and others (9 g). On d 15 post partum, CLA supplementation reduced milk fat content by 33% and pup growth by 21%. The milk fatty acid profile, with decreased content of short and medium chain acids, suggests CLA inhibition was more pronounced for de novo lipid synthesis. Consistent with these results, activities of fatty acid synthase, glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were reduced by CLA treatment in the mammary gland and liver. In contrast, the activity of NADP-malate dehydrogenase was unchanged.

Calcium and potassium content in beef: Influences on tenderness and associations with molecular markers in Nellore cattle

Calcium (Ca) and potassium (K) are essential nutrients in animal nutrition. Furthermore, the Ca content can influence meat tenderness because it is needed by the proteolytic system of calpains and calpastatins, major factors in postmortem tenderization of skeletal muscles. K content, which is needed for muscle contraction, can also affect meat tenderness. This study showed that K positively affects the Warner-Bratzler shear force (WBSF), measured at 14days of meat aging, which means that higher levels of K are related to lower meat tenderness. Additionally, a significant effect (P≤0.015) of a SNP in the calcium-activated neutral protease 1 (CAPN1) gene on Ca content was observed. Metal content in beef can affect not only nutritional values but also meat quality traits. Part of this effect may be related to variation in specific genes.

Estimating forage intake of lactating dual-purpose cows using chromium oxide and n-alkanes as external markers

Os n-alcanos tem sido utilizados para estimar o consumo de materia seca, a digestibilidade e a composicao da dieta de animais em pastejo. O objetivo desse estudo foi comparar as tecnicas de oxido cromico e n-alcanos usadas para estimar o consumo de forragem. Vinte vacas lactantes cruzas Holandes × Gir recebendo duas fontes de gordura (tratamentos: CLA (acido linoleico conjugado) ou Megalac (controle)) mais 4 kg de concentrado foram dosadas com n-alcanos e oxido cromico para estimar o consumo de estrela-africana (Cynodon nlemfuensis Vanderyst var. nlemfuensis). A digestibilidade in vitro da materia seca da estrela africana e do concentrado foi usada para estimar o valor nutritivo da dieta. Foram quantificados n-alcanos entre C23 e C36 na dieta e fezes. A regressao entre exigencia e o consumo de energia metabolizavel (EMr, Mcal d-1) derivada da materia seca da forragem calculada usando oxido de cromo foi ConsumoCr = 19,1 + 0,62 EMr (R2 = 0,27) e a mesma relacao estimada usando a relacao C35:C36 de n-alcanos foi ConsumoC35:C36 = 9,3 + 0,77 EMr (R2 = 0,52). Houve efeito de tratamento na concentracao fecal de oxido de cromo com variacao diaria e entre turnos. Para tecnica de n-alcanos, houve efeito de tratamento e periodo e efeito linear de dia de coleta nas concentracoes fecais do C35. Para as concentracoes fecais do C36, houve efeito de tratamento e um efeito quadratico de dia de coleta. Nao houve efeito de tratamento na concentracao fecal da relacao C35:C36, mas houve efeito de turno e efeito linear de dia de coleta. As estimativas do consumo de forragem obtidas com os dois marcadores foram diferentes, mas aquela obtida com o par de alcanos C35:C36 foi mais precisa que aquela obtida com o oxido cromico e a digestibilidade in vitro. O manejo dos animais experimentais pode ter influenciado a concentracao dos marcadores nas fezes, determinando variacoes e inconsistencias que explicam parcialmente a falta de acuracia das estimativas.

Feed efficiency indexes and their relationships with carcass, non-carcass and meat quality traits in Nellore steers.

Five hundred and seventy-five Nellore steers were evaluated for residual feed intake and residual feed intake and gain and their relationships between carcass, non-carcass and meat quality traits. RFI was measured by the difference between observed and predicted dry matter intake and RIG was obtained by the sum of -1*RFI and residual gain. Efficient and inefficient animals were classified adopting ±0.5 standard deviations from RFI and RIG mean. A mixed model was used including RFI or RIG and contemporary group as fixed effects, initial age as covariate and sire and experimental period as random effects, testing the significance of the regression slope for each evaluated trait. RIG was positively related to longissimus muscle area. Efficient-RFI animals had lower liver and internal fat proportions compared to inefficient-RFI animals. Efficient-RFI and efficient-RIG animals had 11.8% and 11.2% lower extracted intramuscular fat, compared to inefficient-RFI and inefficient-RIG animals, respectively. Efficient-RFI animals had tougher meat compared to inefficient-RFI animals.

Identification of KCNJ11 as a functional candidate gene for bovine meat tenderness

The potassium inwardly rectifying channel, subfamily J, member 11 (KCNJ11) gene was investigated as a candidate for meat tenderness based on the effects reported on muscle for KCNJ11 gene knockout in rat models and its position in a quantitative trait locus (QTL) for meat tenderness in the bovine genome. Sequence variations in the KCNJ11 gene were described by sequencing six amplified fragments, covering almost the entire gene. We identified single nucleotide polymorphisms (SNP) and validated them by different approaches, taking advantage of simultaneous projects that are being developed with the same Nelore population. By sequencing the KCNJ11 in Nelore steers representing extreme phenotypes for Warner-Bratzler shear force (WBSF), it was possible to identify 22 SNPs. We validated two of the identified markers by genotyping the whole population (n = 460). Analysis of association between genotypes and WBSF values revealed a significant additive effect of a SNP at different meat aging times (P ≤ 0.05). In addition, an association between the expression levels of KCNJ11 and WBSF was found, with lower expression levels of KCNJ11 associated with more tender meat (P ≤ 0.05). The results showed that the KCNJ11 gene is a candidate mapped to a QTL for meat tenderness previously identified on BTA15 and may be useful to identify animals with genetic potential to produce tender meat. The effect of KCNJ11 observed on muscle is potentially due to changes in activity of KATP channels, which in turn influence the flow of potassium in the intracellular space, allowing establishment of the membrane potential necessary for muscle contraction.

Association of polymorphisms in the leptin and thyroglobulin genes with meat quality and carcass traits in beef cattle

The objective of the present study was to estimate the allelic and genotypic frequencies of the polymorphisms E2FB (AY138588.1: c.305C> T), located in the leptin gene (LEP), and TG5 (X05380.1:g.-422C>T), located in the thyroglobulin gene (TG), and evaluate the association of these polymorphisms in crossbred cattle of seven distinct genetic groups with the following traits: slaughter weight (SW), hot carcass weight (HCW), hot carcass yield (HCY), carcass fat thickness (CFT), ribeye area (REA), marbling (MARM) and shear force (SF). The animals were genotyped using the PCR-RFLP (Polymorphism Chain Reaction-Restriction Fragment Length Polymorphism) technique, using 201 products obtained from F1 Caracu × Nellore, Angus × Nellore and Valdostana × Nellore cows, mated to Canchim, Caracu and Red Angus bulls (only Caracu × Nellore cows were used with Red Angus bulls). The allelic and genotypic frequencies were compared using the Chi-squared test. Associations between the genotype of each polymorphism and the traits were analyzed using the General Linear Model (GLM) of statistical software SAS. The least squares means of genotypes of the polymorphisms were compared using Students t test. The E2FB polymorphism in the LEP gene was associated with CFT, showing the potential for use in national programs for genetic improvement of beef cattle, through the inclusion of SNP in genotyping commercial tests. The TG5 polymorphism in the TG gene was not associated with any of the evaluated traits and was considered ineffective for selection of beef cattle in Brazilian herds.

A methodological approach to estimate the lactation curve and net energy and protein requirements of beef cows using nonlinear mixed-effects modeling1

The objective of this study was to evaluate methods to predict the secretion of milk and net energy and protein requirements of beef cows (Bos indicus and B. taurus) after approximately 1 mo postpartum using nonlinear mixed-effect modeling (NLME). Twenty Caracu × Nellore (CN) and 10 Nellore (NL) cows were inseminated to Red Angus bulls, and 10 Angus × Nellore (AN) were bred to Canchim bulls. Cows were evaluated from just after calving (25 ± 11 d) to weaning (220 d). Milk yield was estimated by weighing calves before and after suckling (WSW) and by machine milking (MM) methods at 25, 52, 80, 109, 136, 164, 193, and 220 ± 11 d of lactation. Brody and simple linear equations were consecutively fitted to the data and compared using information criteria. For the Brody equation, a NLME model was used to estimate all lactation profiles incorporating different sources of variation (calf sex and breed of cow, cow as a nested random effect, and within-cow auto-correlation). The CV for the MM method (29%) was less than WSW (45%). Consequently, the WSW method was responsible for reducing the variance about 1.5 times among individuals, which minimized the ability to detect differences among cows. As a result, only milk yield MM data were used in the NLME models. The Brody equation provided the best fit to this dataset, and inclusion of a continuous autoregressive process improved fit (P < 0.01). Milk, energy and protein yield at the beginning of lactation were affected by cow genotype and calf sex (P < 0.001). The exponential decay of the lactation curves was affected only by genotype (P < 0.001). Angus × Nellore cows produced 15 and 48% more milk than CN and NL during the trial, respectively (P < 0.05). Caracu × Nellore cows produced 29% more milk than NL (P < 0.05). The net energy and net protein requirements for milk yield followed a similar ranking. Male calves stimulated their dams to produce 11.7, 11.4, and 11.9% more milk, energy and protein, respectively (P < 0.05). The MM method is better than the WSW technique to detect genetic or environmental differences in milk yield among beef cows. The data obtained by the MM method and analyzed by NLME models allows the inclusion of fixed effects, random effects and an auto-regressive process in lactation equations to describe lactation curves and net energy and protein requirements. The NLME is a powerful tool to describe differences in the secretion of milk due to heterosis and cell mammary external stimulus in beef cows.

Feed efficiency and meat quality of crossbred beef heifers classified according to residual feed intake

This study aimed to evaluate feed efficiency and meat quality of 31 three-crossbred beef heifers during 84 days in a feedlot system. A 60:40 concentrate and sorghum silage ration on DM basis (ME = 2.73Mcal/kg of DM, CP = 11.90% DM) was fed ad libitum. Based on residual feed intake (RFI) calculations, the heifers were ranked in three groups of feed efficiency: High RFI (average mean = 0.776; n = 9), medium RFI (average mean = -0.010; n = 11), and low RFI (average mean = - 0.624; n = 11). High RFI heifers consumed 4.56% more DM per day than low RFI heifers (P 0.05) among RFI groups (1.40kg/day). No differences (P>0.05) were detected for digestibility of the nutrients: DM (64.00%), CP (60.01%), crude fat (72.90%), NDF (54.80%) and non-fibrous carbohydrate (NFC) (78.91%). There were no differences between low and high RFI groups for slaughter weight (475.00 vs. 479.55kg), hot carcass weight (259.09 vs. 261.44kg), Longissimus dorsi (LD) area (69.02 vs. 68.11 cm2), back-fat thickness (5.74 vs. 6.26 cm), shear force (5.45 vs. 5.19kg), sensorial traits of LD muscle, LD color (intensities L=40.47 a*=24.74 and b*=16.13) or commercial cuts yield. Low RFI heifers presented similar meat quality and carcass traits as high RFI heifers, however low RFI heifers consumed less DM (kg/d).