Evaluation of carcass characteristics of Bos indicus and tropically adapted Bos taurus breeds selected for postweaning weight

Data from 9 studies were compiled to evaluate the effects of 20 yr of selection for postweaning weight (PWW) on carcass characteristics and meat quality in experimental herds of control Nellore (NeC) and selected Nellore (NeS), Caracu (CaS), Guzerah (GuS), and Gir (GiS) breeds. These studies were conducted with animals from a genetic selection program at the Experimental Station of Sert?ozinho, S?o Paulo State, Brazil. After the performance test (168 d postweaning), bulls (n = 490) from the calf crops born between 1992 and 2000 were finished and slaughtered to evaluate carcass traits and meat quality. Treatments were different across studies. A meta-analysis was conducted with a random coefficients model in which herd was considered a fixed effect and treatments within year and year were considered as random effects. Either calculated maturity degree or initial BW was used interchangeably as the covariate, and least squares means were used in the multiple-comparison analysis. The CaS and NeS had heavier (P = 0.002) carcasses than the NeC and GiS; GuS were intermediate. The CaS had the longest carcass (P < 0.001) and heaviest spare ribs (P < 0.001), striploin (P < 0.001), and beef plate (P = 0.013). Although the body, carcass, and quarter weights of NeS were similar to those of CaS, NeS had more edible meat in the leg region than did CaS bulls. Selection for PWW increased rib-eye area in Nellore bulls. Selected Caracu had the lowest (most favorable) shear force values compared with the NeS (P = 0.003), NeC (P = 0.005), GuS (P = 0.003), and GiS (P = 0.008). Selection for PWW increased body, carcass, and meat retail weights in the Nellore without altering dressing percentage and body fat percentage.     

A meta-analysis of energy and protein requirements for maintenance and growth of Nellore cattle

A meta-analysis was conducted to determine NE and net protein requirements of growing bulls, steers, and heifers of Nellore purebred and Nellore x Bos taurus crossbreds. A database of 16 comparative slaughter studies (n = 389 animals) was gathered to provide enough information to develop equations to predict the requirements of NE(m), NE(g), and net protein for maintenance (NP(m)) and growth (NP(g)). The data were analyzed using a random coefficients model, considering studies as random effects, and sex and castrate status (bulls, steers, and heifers; n = 262, 103, and 24, respectively) and breeds as fixed effects. There were no differences in NE(m) requirements among sex and castrate status (P = 0.73) and breeds (P = 0.82). The combined data indicated a NE(m) requirement of 75 kcal/ kg(0.75) of empty BW (EBW) with a partial efficiency of use of ME for NE(m) of 0.67. The NE(g) requirement was different (P = 0.009) among sex and castrate status and tended (P = 0.06) to be different among breeds. The equation for NE(g) requirement for bulls was 0.0514 x EBW(0.75) x EWG(1.070); for steers, it was 0.0700 x EBW(0.75) x EWG(1.070); and for heifers, it was 0.0771 x EBW(0.75) x EWG(1.070), where EWG = EBW gain (kg/d). The partial efficiency of use of ME for NE(g) was not different among sex and castrate status (P = 0.33) and breeds (P = 0.20) and averaged 0.44. There were no differences in NP(m) requirement among sex and castrate status (P = 0.59) and breeds (P = 0.92); the overall NP(m) requirement was 1.74 g of NP.kg(-0.75) of EBW.d(-1). The overall MP requirement for maintenance was 2.59 g of MP.kg(-0.75) EBW.d(-1). The NP(g) requirement (g/d) was not different among sex and castrate status (P = 0.59) and breeds (P = 0.14); the overall equation was EWG x [217 - (12.8 x RE/EWG)], where RE = retained energy (Mcal/d). The percentage of RE deposited as protein (%RE(p)) decreased exponentially as the content of RE in the gain (REc, Mcal/kg of EWG) increased. Because no study effect was observed, we pooled the data across studies and the overall equation to predict %RE(p) was 10.1 + 167e((-0.66 x REc)). Our results do not support the hypothesis that bulls have greater NE(m) requirements than steers and heifers. Likewise, no significant differences in the NP(m) requirements among bulls, steers, and heifers were detected. Nonetheless, the NE(g) requirement of steers was greater than bulls and less than heifers. Even though the %RE(p) was negatively correlated with the concentration of energy in the EWG, our findings indicated no differences in NP(g) requirement among bulls, steers, and heifers.     

Determination of creatinine excretion and evaluation of spot urine sampling in Holstein cattle

Four experiments were carried out to determine urinary creatinine excretion in Holstein growing bulls, lactating cows, and replacement heifers. In addition, we evaluated the use of spot sampling technique to estimate purine derivatives (PD) excretion. In Experiment I, 15 lactating cows were used in a randomized block design to compare creatinine excretion obtained in different time-spans of urine collection (during 6, 9, 12, 15, 18, 21, and 24 h). In Experiment II, four bulls were allocated in a 4 × 4 Latin square to evaluate the effect of diet (levels of cottonseed hulls of 0, 10, 20, and 30% of the DM) on excretion of creatinine. In Experiment III, 15 lactating cows were used to evaluate the effect of milk production (ranging from 3.9 to 36.7 kg/d) on daily creatinine and PD excretions. In Experiment IV, 22 replacement heifers were utilized to evaluate the effect of body weight (BW, ranging from 107 to 545 kg) on daily creatinine and PD excretions. For all experiments, total urine collections were made over 24 h and daily creatinine and PD excretions were determined. Different time-spans for total urine collection had no effect (P = 0.70) on creatinine excretion compared to the 24-h collection period, indicating a constant excretion rate of creatinine. The roughage source did not influence (P = 0.64) creatinine excretion by bulls, averaging 0.248 ± 0.008 mmol/kg BW. Similarly, milk production did not affect (P = 0.82) creatinine excretion in cows, averaging 0.212 ± 0.004 mmol/kg BW. In contrast, the creatinine excretion (mmol/kg BW) decreased linearly (P < 0.001) as BW of heifers increased, suggesting that creatinine excretion might vary with the degree of maturity of growing animals. There were no differences (P > 0.14) between the 24-h total collection and spot sampling technique in estimating daily PD excretion. The spot sampling technique may be used to estimate the daily excretion of urinary PD in Holstein cattle under practical conditions.     

Predicting metabolizable energy from digestible energy for growing and finishing beef cattle and relationships to the prediction of methane

Reliable predictions of metabolizable energy (ME) from digestible energy (DE) are necessary to prescribe nutrient requirements of beef cattle accurately. A previously developed database that included 87 treatment means from 23 respiration calorimetry studies has been updated to evaluate the efficiency of converting DE to ME by adding 47 treatment means from 11 additional studies. Diets were fed to growing-finishing cattle under individual feeding conditions. A citation-adjusted linear regression equation was developed where dietary ME concentration (Mcal/kg of dry matter [DM]) was the dependent variable and dietary DE concentration (Mcal/kg) was the independent variable: ME = 1.0001 × DE – 0.3926; r² = 0.99, root mean square prediction error [RMSPE] = 0.04, and P < 0.01 for the intercept and slope. The slope did not differ from unity (95% CI = 0.936 to 1.065); therefore, the intercept (95% CI = −0.567 to −0.218) defines the value of ME predicted from DE. For practical use, we recommend ME = DE – 0.39. Based on the relationship between DE and ME, we calculated the citation-adjusted loss of methane, which yielded a value of 0.2433 Mcal/kg of dry matter intake (DMI; SE = 0.0134). This value was also adjusted for the effects of DMI above maintenance, yielding a citation-adjusted relationship: CH₄, Mcal/kg = 0.3344 – 0.05639 × multiple of maintenance; r² = 0.536, RMSPE = 0.0245, and P < 0.01 for the intercept and slope. Both the 0.2433 value and the result of the intake-adjusted equation can be multiplied by DMI to yield an estimate of methane production. These two approaches were evaluated using a second, independent database comprising 129 data points from 29 published studies. Four equations in the literature that used DMI or intake energy to predict methane production also were evaluated with the second database. The mean bias was substantially greater for the two new equations, but slope bias was substantially less than noted for the other DMI-based equations. Our results suggest that ME for growing and finishing cattle can be predicted from DE across a wide range of diets, cattle types, and intake levels by simply subtracting a constant from DE. Mean bias associated with our two new methane emission equations suggests that further research is needed to determine whether coefficients to predict methane from DMI could be developed for specific diet types, levels of DMI relative to body weight, or other variables that affect the emission of methane.     

Technical Note: The comparison of pH and redox potential in different locations in the reticulo-rumen of growing beef steers supplemented with different levels of quebracho extract

Rumen acidosis is a common metabolic disorder occurring when organic acid production exceeds clearance capacity, reducing ruminal pH. The occurrence of acidosis has been directly correlated to the ratio of concentrate to forage in the diet. However, rates of substrate fermentation and acid absorption vary at different locations in the reticulo-rumen. The objective of this study was to determine the pH and redox potential (Eh) in different locations of the reticulo-rumen using 16 ruminally cannulated steers (309 ± 43 kg) receiving different supplementation levels of quebracho extract (QT; Schinopsis balansae) within a grower type diet (CP: 13.4%; total digestible nutrients [TDN]: 70.4%; and ME: 2.55 Mcal/kg, dry matter [DM] basis). Animals were randomly assigned to one of four dietary treatments: QT at 0%, 1%, 2%, and 3% of DM (QT0, QT1, QT2, and QT3, respectively), containing about 0%, 0.7%, 1.4%, and 2.1% of condensed tannins (CT), DM basis, respectively. Animals were adapted to the basal diet for 12 d before being introduced to predetermined treatments for 4 weeks (wk), with diets provided twice daily to allow ad libitum intake. Weekly measurements of ruminal fluid pH and Eh were taken 4 h post-feeding using a portable pH meter with two probes (pH and redox) in four locations of the reticulo-rumen (reticulum, cranial sac, dorsal sac, and ventral sac). Data were analyzed using a random coefficients model with the pen as a random effect and wk as repeated measures, with DM intake included as a covariate. There was no interaction among treatments, location, and wk (P ≥ 0.882) on reticulo-ruminal pH. Overall, ruminal pH was lower for QT0 and QT1 compared to QT3 (P < 0.001). The pH in the reticulum was greater than those of the ventral and dorsal sacs (6.05 vs. 5.94, 5.89, respectively; P ≤ 0.001) but similar to cranial sac (6.00). Reticular pH was positively correlated with the ruminal locations (≥0.78; P < 0.001). The linear equation to estimate ruminal mean pH using reticulum pH had an intercept and slope different from zero (P ≤ 0.04), but CT (% DM) was not different from zero (P = 0.15), root mean square error of 0.15, and R² of 0.778: 0.723 (±0.36) + 0.857 (±0.059) × reticulum pH + 0.033 (±0.023) × CT. The Eh was lower for QT0 in week 1 than all other treatments (P < 0.001). We concluded that reticulo-ruminal pH differs among locations in the rumen regardless of QT supplementation level and days on feed, with reticular pH being the highest.     

Composition of peptide mixtures derived from simulated gastrointestinal digestion of prolamins from different wheat varieties

Gliadin content of wheat is highly variable, both qualitatively and quantitatively, in function of the plant genetic and of the growing conditions. The gliadins are among the major triggers of celiac disease: peptides derived from the gastrointestinal digestion of these proteins and absorbed from the lamina propria cause the immunological reactions that damage the villous structure in affected subjects. In the present work, the peptide mixtures generated by simulated gastrointestinal digestion of the prolamin fraction extracted from different wheat varieties (Triticum turgidum subsp. durum and Triticum aestivum) were characterized by LC/MS and LC-MS/MS techniques. Peptides related to the amount of α-gliadin, as well as toxic and immunogenic peptides for celiac patients have been identified and quantified using an isotopically labeled internal standard. The quantification demonstrated strong differences among the varieties tested. Some samples, belonging to the same varieties and/or cultivation area, showed a lower α-gliadin content, and a smaller amount of toxic and immunogenic peptides.     

Composition,abundance and phytoplasma infection in the hawthorn psyllid fauna of northwestern Italy

Hawthorn (Crataegus monogyna) is one of the natural hosts of Cacopsylla melanoneura, the acknowledged vector of ‘Candidatus Phytoplasma mali’, the causal agent of Apple Proliferation disease, a serious and growing problem for apple production in Europe, particularly in northern Italy. Wild plants could be important sources of both insects and phytoplasmas, but their role in the epidemiology of phytoplasma diseases and their insect vectors has never been thoroughly examined. Cacopsylla melanoneura’s primary host is hawthorn, a plant closely related to apple which often grows wild near orchards. Other psyllid species feed on hawthorn, but no data are available on their possible role as phytoplasma vectors. We investigated the hawthorn’s psyllid fauna in northwestern Italy using yellow sticky traps, beat trays, and molecular analyses from 2003–2005, to study the relationship between hawthorn, the phytoplasma and the insect vector. Population dynamics were monitored, and insects and hawthorn samples were analysed by polymerase chain reaction (PCR), restriction fragment length polymorphism (RFLP), and DNA sequencing for the presence of phytoplasmas. Cacopsylla melanoneura was the dominant psyllid species, followed by C. peregrina, C. affinis and C. crataegi. PCR and RFLP analyses revealed the presence of different fruit tree phytoplasmas in hawthorn plants, and in all four psyllid species.     

Accounting for the effects of a ruminal nitrogen deficiency within the structure of the Cornell Net Carbohydrate and Protein System

The Cornell Net Carbohydrate and Protein System (CNCPS) prediction of fiber digestion and microbial mass production from ruminally degraded carbohydrate has been adjusted to accommodate a ruminal N deficiency. The steps for the adjustment are as follows: 1) the ruminal available peptide and ammonia pools are used to determine the N allowable microbial growth; 2) this value is subtracted from the energy allowable microbial growth to obtain the reduction in microbial mass; 3) this mass reduction is allocated between pools of bacteria digesting fiber (FC) and nonfiber (NFC) carbohydrate according to their original proportions in the energy allowable microbial growth; 4) the reduction in fermented FC is computed as the FC bacterial mass reduction divided by its yield (g bacteria/g FC digested); and 5) this reduction is added to the FC fraction escaping the rumen. Five published studies included information that allowed us to evaluate the response of animals to added dietary N. These evaluations compared observed and CNCPS-predicted ADG with and without this adjustment. The adjustment decreased the CNCPS overprediction of ADG from 19.2 to 4.7%, mean bias declined from .16 to .04 kg/d, and the r2 of the regression between observed and metabolizable energy (ME) or metabolizable protein allowable ADG was increased from .83 to .88 with the adjustment. When the observed dry matter intake was regressed against CNCPS-predicted DMI with an adjustment for reduction in cell wall digestibility, the r2 was increased from .77 to .88. These results indicated the adjustment for ruminal nitrogen deficiency increased the accuracy of the CNCPS model in evaluating diets of growing animals when ruminally degraded N is deficient.     

Adenosine triphosphate synthesis coupled to K+ influx in mitochondria

The influx of K+ into swollen mitochondria in the presence of valinomycin results in the synthesis of adenosine triphosphate in which approximately one H+ disappears per adenosine triphosphate synthesized. The synthesis is blocked by atractyloside but is insensitive to oligomycin and relatively insensitive to uncouplers.     

Predicting individual feed requirements of cattle fed in groups

A published model designed to predict individual feed required for the observed shrunk BW and ADG of growing cattle when fed in groups was modified and evaluated to improve its accuracy. This model is needed to accurately bill feed and compute cost of gain in marketing programs based on individual animal management. Because of its importance in predicting energy required for growth, a database of 401 steers was used to develop an equation to predict percentage of empty-body fat (EBF) from carcass measurements (12th rib fat thickness, hot carcass weight, USDA quality grade, and longissimus muscle area), which accounted for 61% of the variation in EBF with no bias (P > 0.1). When tested with an independent data set of 951 steers, the equation accounted for 51% of the variation with 1% proportional bias. The large variation in the carcass measurements at a particular EBF observed in this study indicates further improvement is limited by the inability of carcass measurements to account for variation in fat distribution in the various carcass components. Because of its importance in setting the target end point, a database of 1,355 steers and heifers was used to determine the relationship between EBF and USDA quality grade. These data indicate growing and finishing cattle reach Select and low-Choice quality grades at an EBF of 26.15 +/- 0.19 and 28.61 +/- 0.20%, respectively (P < 0.05). A data set of 228 steers from different breeds from two serial slaughter studies indicated 14.26 +/- 1.52 kg of empty BW change are required to increase EBF one percentage unit for cattle fed high-energy diets; this adjustment is needed to adjust final shrunk BW to the target EBF end point. The model to predict DM required with modifications developed in this study was evaluated with data from 365 individually fed cattle and it accounted for 74% of the variation in observed DM consumed with no bias (P > 0.1). When the revised model was applied to a commercial feedlot data set containing 12,105 steers and heifers, the total observed DM consumed was predicted with a bias of less than 1%. The model presented in this study accounts for differences known to affect animal requirements (breed type, BW and ADG, and weight at the target EBF end point) and can be used to fairly allocate feed to individuals fed in a group under commercial feedlot conditions.