Growth, feed efficiency and carcass composition of finishing Friesian steers fed the beta-adrenergic agonist L-644,969

The beta-adrenergic agonist L-644,969 was evaluated to determine its effects on growth performance and carcass composition of Friesian steers. L-644,969 is the R,R isomer of 6-amino [[(1-methyl-3-phenylpropyl) amino] methyl]-3-pyridine methanol dihydrochloride. Four groups of 18 steers, averaging 380 kg body weight, were individually given ad libitum access to a pelleted concentrate diet that contained either 0, .25, 1.0 or 4.0 ppm L-644,969 for the final 12 wk of the finishing period. Live weight gain was not affected by L-644,969, but feed consumption was linearly reduced (5.5, 6.3 and 15.7%; P less than .01) and feed conversion efficiency was linearly increased (16, 25 and 31%; P less than .01) relative to unmedicated controls, respectively. In addition, L-644,969 quadratically increased carcass weight (3.7, 9.3 and 8.5%; P less than .01) and dressing percentage (2.7, 7.9 and 7.9%; P less than .001). The proportion of trimmed fat in the carcass was quadratically reduced (14.5, 29 and 36%; P less than .001) and yield of lean meat quadratically increased (6.7, 13 and 15.6%; P less than .001). beta-adrenergic agonist treatment altered the distribution of lean meat such that a greater (P less than .001) proportion of the total lean was in the hind portion of carcasses from treated animals. Based on these findings, we suggest that L-644,969 may have utility as an agent to improve efficiency of production of lean beef.     

Genetic parameters and genotype x environment interaction for feed efficiency traits in steers fed grower and finisher diets

The objective of this study was to examine the genetic parameters and genetic correlations of feed efficiency traits in steers (n = 490) fed grower or finisher diets in 2 feeding periods. A bivariate model was used to estimate phenotypic and genetic parameters using steers that received the grower and finisher diets in successive feeding periods, whereas a repeated animal model was used to estimate the permanent environmental effects. Genetic correlations between the grower-fed and finisher-fed regimens were 0.50 ± 0.48 and 0.78 ± 0.43 for residual feed intake (RFI) and G:F, respectively. The moderate genetic correlation between the 2 feeding regimens may indicate the presence of a genotype × environment interaction for RFI. Permanent environmental effects (expressed in percentage of phenotypic variance) were detected in the grower-fed steers for ADG (38%), DMI (30%), RFI (18%), and G:F (40%) and also in the finisher-fed steers for ADG (28%), DMI (35%), metabolic mid-weight (23%), and RFI (10%). Heritability estimates were 0.08 ± 0.10 and 0.14 ± 0.15 for the grower-fed steers and 0.42 ± 0.16 and 0.40 ± 17 for the finisher-fed steers for RFI and G:F, respectively. The dependency of the RFI on the feeding regimen may have serious implications when selecting animals in the beef industry. Because of the higher cost of grains, feed efficiency in the feedlot might be overemphasized, whereas efficiency in the cow herd and the backgrounding segments may have less emphasis. These results may also favor the retention (for subsequent breeding) of cows whose steers were efficient in the feedlot sector. Therefore, comprehensive feeding trials may be necessary to provide more insight into the mechanisms surrounding genotype × environment interaction in steers.     

Behaviour of early-weaned calves in indoor individual cubicles and group pens

Extract

Units have been designed to house calves for veal production, but only recently has a large intensive unit been designed to rear surplus dairy-bred calves for beef production in New Zealand. This was built by the Rangitaiki Plains Dairy Company, Edgecumbe, early in 1973 and consisted of two types of housing: a fully enclosed and insulated calf house with 500 individual cubicles in which to rear the animals till weaning at 5 weeks of age, and a “loafing barn” with slatted walls and sawdust floor to house calves for a further 5 weeks before sale as beef weaners.     

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.     

Use of group records of feed intake to select for feed efficiency in rabbit

Models for genetic evaluation of feed efficiency ( FE ) for animals housed in groups when they are either fed ad libitum ( F ) or on restricted ( R ) feeding were implemented. Definitions of FE on F included group records of feed intake () and individual records of growth rate ( G_F ) and metabolic weight ( M_F ). Growth rate ( G_R ) as FE measurement on R was used. Data corresponded to 5,336 kits from a rabbit sire line, from 1,255 litters in 14 batches and 667 cages. A five‐trait mixed model (also with metabolic weight on R, M_R ) was implemented including, for each trait, the systematic effects of batch, body weight at weaning, parity order and litter size; and the random effects of litter, additive genetic and individual. A Bayesian analysis was performed. Conditional traits such as and were obtained from elements of additive genetics ( and ) or phenotypic ( and ) (co)variance matrices. In the first case, heritabilities were low (0.07 and 0.06 for and , respectively) but null genetic correlation between the conditional and conditioning traits is guaranteed. In the second case, heritabilities were higher (0.22 and 0.16 for and , respectively) but the genetic correlation between and was moderate (0.58). Heritability of G_R was low (0.08). This trait was negatively correlated with and of animals on F, which indicate a different genetic background. The correlation between G_R and G_F was also low to moderate (0.48) and the additive variance of G_F was almost four times that of G_R, suggesting the presence of a substantial genotype by feeding regimen interaction.     

群体饲喂条件下猪个体采食量的评估模型

在大多数生长试验中,试验动物往往成群地饲养在同一圈中。在试验过程中,有时有个别动物在生长速度上会表现出与其同伴较大的差异,或者死亡。出现此种情况时,如果不能为统计日平均采食量(average daily feed intake,ADFI)和饲料效率而对试验动物的圈采食量(penfeedintake,PFI)进行重新评估,那么试验数据集将丢弃该圈的观察值。因此,我们开发了一个模型,用来评估群体饲喂条件下猪的个体采食量(Individual feed intake,IFI),并通过群体饲喂模拟试验对该评估模型进行验证。在推荐模型中,将每个受影响圈的采食量(FeedIntake,FI)分为用于维持生存需要的采食量(FIm)和用于生长需要的采食量(FIg)两个部分。首先,试验期间个体猪的FIm按NRC(1998)所列出的维持生存所需代谢能的评估方法进行测算,然后将同圈内所有猪的FIm相加,即得到圈FIm。圈采食量(PFI)与圈FIm之差就是该圈动物用于生长所需的那部分采食量。接下来,把该差额部分的采食量平均分给圈内动物每单位增重上,即为FIg。最后,猪圈中被淘汰猪的IFI估测值即为所淘汰猪的FIm与FIg之和,原来的圈采食量(PFI)减去该FI估测值后即得剩余猪的新PFI。个体采食量评估的准确性取决于维持生存代谢能预测方程和饲料原料能量分析值的准确性。在模拟试验中,我们将推荐模型的精确度与2个其它模型的精确度作了比较。模拟试验1显示,在所有测试阶段中推荐模型的精确度至少高于其它2个模型中的任一种方法(P<0.001);模拟试验2也证明,推荐模型的精确度高于其他2种方法。由于IFI的人工计算相对麻烦,为此我们开发了饲料采食量校正电子数据表(feed intake correction spreadsheet,FICS),即一个利用宏指令可对FI进行校正的Excel电子数据表。FISC包括了推荐模型中的所有测算程序,用户可免费从指定的网页上下载Excel文件和使用说明书。     

The relationship of feeding behavior to residual feed intake in crossbred Angus steers fed traditional and no-roughage diets

Two studies were conducted to determine the relationship of feeding behavior to a phenotypic expression of residual feed intake (RFI), a measure of efficiency. In Exp. 1, a feedlot diet containing roughage was fed (traditional). In Exp. 2, a no-roughage diet was fed. Residual feed intake, a measure of feed efficiency, was calculated for both studies. In Exp. 1, six feed-efficient (low RFI) steers and six feed-inefficient steers (high RFI) were selected from a contemporary group of 80 steers, and feeding behaviors were analyzed. In Exp. 2, nine feed-efficient and eight feed-inefficient steers were selected from a contemporary group of 40 steers. There were no differences (P > 0.13) in initial or final BW or ADG between efficient and inefficient groups in either Exp. 1 or 2. In Exp. 1, DMI and average eating bouts daily differed (P < 0.001), with efficient steers consuming less feed and eating fewer times per day. In Exp. 2, efficient steers consumed less (P < 0.001) feed, and average eating bouts daily tended (P = 0.07) to be fewer in efficient animals. Limited differences were noted in feeding behavior between groups, with inefficient steers from both studies having a more variable eating pattern throughout the day. The average daily eating rate did not differ (P > 0.20) between groups in either experiment. The average number of days comprising a feeding pattern for both efficiency groups in Exp. 1 and 2 was found to be 2 to 3 d and multiples of 2 to 3 d. In Exp. 1, the feed intake pattern of efficient and inefficient steers changed once they reached a BW of approximately 391 and 381 kg, respectively. This occurred near d 47 for the efficient steers and near d 32 for inefficient steers. In Exp. 2, the feed intake pattern of both efficient and inefficient steers changed once they reached a BW of approximately 399 kg, which occurred on d 31 for the efficient steers and on d 33 for the inefficient steers. From the measured variables, there were no differences in growth and limited differences noted in feeding behavior between efficient and inefficient groups. The results of the trials suggest increased variability of feed intake throughout the day for inefficient animals.     

Technical note: A model to estimate individual feed intake of swine in group feeding

In most animal growth experiments, groups of animals are housed within a pen. Occasionally, an individual animal shows a very different growth rate than its pen mates or dies during the experiment. When this happens, if pen feed intake (PFI) cannot be reestimated for the calculation of ADFI and feed efficiency, an observation will be lost from the data set. Therefore, we propose a model to estimate individual feed intake (IFI) of pigs in group feeding, with subsequent validation of the model using group feeding simulation studies. In the proposed model, the feed intake (FI) of each affected pen is partitioned into FI for maintenance (FI(m)) and FI for growth (FI(g)) for each animal within that pen. First, individual pig FI(m) for the period is calculated using the 1998 National Research Council estimation of ME for maintenance. Then, FI(m) for all pigs in the pen is summed. The difference between the summed FI(m) and the total PFI is that which supported growth in the pen. Next, FI(g) is calculated by apportioning the remaining feed equally to each unit of gain within the pen. Finally, the estimated IFI for the pig being removed from the pen is the sum of FI(m) and FI(g) for that pig; this FI estimate is subtracted from the original PFI to leave the new PFI for the remaining pigs. The validity of the estimated IFI is dependent on the accuracy of the maintenance energy equation and the energy analysis of the feedstuffs. In simulation studies, we compared the accuracy of the proposed method with 2 other methods. In simulation study 1, the proposed model showed better accuracy than at least one of the other methods during all tested periods (P < 0.001). In simulation study 2, the greater accuracy of the proposed method compared with 2 other methods was demonstrated again. Because calculation of IFI is relatively cumbersome, we developed a feed intake correction spreadsheet (FICS), an Excel spreadsheet containing macros for FI correction. All of the calculation procedures in the proposed model are included within the feed intake correction spreadsheet. The Excel file and instructions are being made available via a Web site.     

Association of serologic status for Neospora caninum and postweaning feed efficiency in beef steers.

OBJECTIVE: To determine the effects of serologic status for Neospora caninum on short-term weight gain, feed intake, and feed efficiency (feed intake/gain). DESIGN: Longitudinal observational study. ANIMALS: 34 weaned mixed-breed beef steers. PROCEDURE: Serologic status for N. caninum was determined for each steer on days 0 (weaning), 88, 116, 144, 172, and 200, using an agglutination test. Individual steer body weight was measured on days 0, 88, 116, 144, 172, 200, and 242 (slaughter). Daily feed intake was monitored from days 116 through 242. Serologic status was matched to animal performance for the period immediately following serum sample collection. A mixed mode, using repeated-measures with an unstructured covariance matrix, was used in the analysis. Breed, age, and pen effects were controlled for in the analysis. RESULTS: A reduction in average daily gain for the period following a positive serologic result was detected for the entire trial (6 measurements/steer). This may have been attributed to a significant impairment in feed efficiency rather than to an impairment in feed intake. Changes in serologic status in individual steers over time were common; additionally, the effects of serologic status on steer performance were also transitory. CONCLUSIONS AND CLINICAL RELEVANCE: Significant reductions in short-term weight gain and feed efficiency were associated with the presence of antibodies against N. caninum in postweaning beef steers.     

Evaluation of the feed intake models in the Nordic feed evaluation system NorFor

Abstract

The objective of this study was to evaluate the feed intake models in the Nordic feed evaluation system NorFor. Data from 196 feeding experiments with dairy cows, and 17 experiments of periodical data, and 135 experiments of complete data with growing cattle were used in the evaluation by mixed model regression. The feed intake by both dairy cows and growing cattle were overestimated by the models. A linear bias indicated that over prediction increased with level of intake both by dairy cows and growing cattle. Most animal and diet factors were significantly related to the residuals, which indicated that those factors did not act independently in the predictions of feed intake. This kind of errors can restrict future ration formulation and animal performance, since animal production parameters included in the prediction models will be a consequence of the diet fed at the time they were measured.     

Site of protein digestion in steers fed sorghum grain diets. I. Effect of level of feed intake

Two digestion trials were conducted with seven crossbred, abomasally cannulated yearling steers (400 kg) to study the effect of level of feed intake on the site and extent of feed and microbial protein digestion. Steers, in a crossover design experiment, were fed an 81.5% steam-processed flaked (SPF) sorghum grain diet at either 95% (four steers) or 75% (three steers) of their ad libitum intakes. At the end of the first trial, steers were switched to the opposite treatment. Dysprosium (31 to 32 micrograms/g) was used as an external marker. Feed, abomasal contents and fecal grab samples were taken at 12-h intervals advancing by 2 h each day over a 6-d total fecal collection period. Organic matter (OM) intakes were 6,102 and 4,570 g for the two treatments. Higher level of intake increased (P less than .05) quantities of OM, crude protein and trichloroacetic acid precipitable protein entering the small intestine, digested post-ruminally and digested in the total tract. The higher level of intake decreased (P less than .05) the percentage of bacterial protein (BP) present in the abomasum and percent post-ruminal BP digestion; however, the amounts of BP and non-BP entering the small intestine and digested post-ruminally were greater (P less than .05) in steers fed 95% ad libitum. Most of the feed protein was degraded in the rumen with both treatments. Predicted true feed protein digestibilities were 91.1 and 91.7% for 95 and 75% of ad libitum intakes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma pharmacokinetics of oral chlortetracycline in group fed, ruminating, Holstein steers in a feedlot setting

Reinbold, J. B., Coetzee, J. F., Gehring, R., Havel, J. A., Hollis, L. C., Olson, K. C., Apley, M. D. Plasma pharmacokinetics of oral chlortetracycline in group fed, ruminating, Holstein steers in a feedlot setting. J. vet. Pharmacol. Therap. 33 , 76–83. Chlortetracycline HCl (CTC) has impacted profitable livestock production since 1945. However, pharmacokinetic parameters for CTC in ruminating cattle are unavailable in peer‐reviewed literature. A total of 18 steers were randomized to 4.4, 11, or 22 mg/kg/day p.o. CTC treatment groups (n = 6). Chlortetracycline treatment was offered as one‐half of the daily dose b.i.d. (160 total doses/group) for 80 days. Blood samples were collected at selected time points throughout an 83‐day study and analyzed with a solid phase extraction technique and novel ultrahigh performance liquid chromatography‐mass spectroscopy/mass spectroscopy analytical method. Noncompartmental analysis (NCA) determined individual pharmacokinetic parameters by treatment group with coefficient of variation (CV %) estimates. A one‐compartment open model with first order absorption and elimination, where absorption rate constant was equal to elimination rate constant, was fitted using nonlinear mixed effects modeling (NLMEM). NLMEM determined the primary pharmacokinetic parameters: volume of distribution (V/F, 40.9 L/kg) and rate constant (k, 0.0478 h^?1), and the secondary parameters: dose‐normalized area under the curve (AUC/D, 0.29 h·μg/L), clearance (Cl/F, 1.8 L/kg/h), elimination half‐life (t_1/2, 16.2 h), C_max/Dose (4.5 ng/mL), and time of C_max (T_max, 23.3 h) with improved CV estimates over NCA. Dose linearity was confirmed by anova of parameters derived from NCA by treatment group. Further studies are necessary for determining absolute bioavailability and pharmacokinetic–pharmacodynamic relationships of CTC in group fed, ruminating cattle.     

Energy components of growth in Holstein steers fed formaldehyde- and formic acid-treated alfalfa or orchardgrass silages at equalized intakes of dry matter

Energy retention was compared in Holstein steers fed either alfalfa or orchardgrass silages for 164 d at either 65 or 90 g DM/kg.75 BW daily in a 2 x 2 factorial. Energy retention was estimated by slaughter-balance using an initial kill of eight steers at 216 kg and a final kill of eight steers per treatment at 326 kg. The ADG was not affected (P greater than .05) by silage, but steers fed alfalfa gained less (P less than .001) gut fill (they lost gut fill) and gained more (P less than .001) of the following than steers fed orchardgrass: empty body, 23%; fat, 50%; fat-free matter, 18%; protein, 16%; water, 17%; ash, 43%; gross energy, 31%; and carbon, 38%. With retained energy at 1.15 Mcal/d, retained energy was equally distributed between fat and protein. Increments of daily retained energy greater than 1.15 Mcal were deposited as 76% to fat and 24% to protein; this distribution was not affected by silage. The energy requirement for maintenance, with BW adjusted to equal gut fill, was not different (P greater than .05) at 130 kcal ME/kg.75 BW for steers fed alfalfa vs 125 for steers fed orchardgrass. Although not significant (P greater than .05), retained energy/ME intake above maintenance was 13% greater for steers fed alfalfa (.261) than for steers fed orchardgrass (.230), which supports the difference observed by calorimetry. The difference in dietary protein (25.6 vs 20.5%) did not contribute to the difference in energy retention because the differences in fat and protein retention could be explained totally by differences in daily energy deposition. The higher NDF of orchardgrass, or other fiber components, seems to be the most probable cause of its somewhat lower partial energetic efficiency relative to alfalfa.     

Effect of dietary concentrate content on feed intake,feed efficiency,and meat quality of Holstein steers fattened in a hot environment

The objective of this study was to investigate the effect of feeding high and low concentrate diets on feed intake and feed efficiency, the morphological characteristics of the rumen papillae, and meat quality of Holstein steers fattened under hot climate conditions in Oman. Ten male Holstein calves, of 5 months of age, were selected for the experiment. The animals were fed concentrate and Rhodes grass hay and were divided into two groups of high concentrate (HC, n = 5) and low concentrate diets (LC, n = 5), in which their feed intake, weight gain, and feed efficiency were evaluated across three growing periods. Feed intake and efficiency and average daily gain (ADG) of the HC group were significantly greater than for the LC group and were affected by the diet (p < .01) and the period (p < .001). Across the fattening periods, ADG declined in both groups, with ADG improved by 35% for steers on the HC diet compared to steers on the LC diet. Carcass meat quality was not affected significantly by the dietary concentrate level. In conclusion, our results can be used to make improvements in feed efficiency of Holstein steers under hot climate conditions.     

Using simulation models to predict feed intake: phenotypic and genetic relationships between observed and predicted values in cattle

The objectives of this study were to evaluate the accuracy of the Decision Evaluator for the Cattle Industry (DECI) and the Cornell Value Discovery System (CVDS) in predicting individual DMI and to assess the feasibility of using predicted DMI data in genetic evaluations of cattle. Observed individual animal data on the average daily DMI (OFI), ADG, and carcass measurements were obtained from postweaning records of 504 steers from 52 sires (502 with complete data). The experimental data and daily temperature and wind speed data were used as inputs to predict average daily feed DMI (kg) required (feed required; FR) for maintenance, cold stress, and ADG; maintenance and cold stress; ADG; maintenance and ADG; and maintenance alone, with CVDS (CFRmcg, CFRmc, CFRg, CFRmg, and CFRm, respectively) and DECI (DFRmcg, DFRmc, DFRg, DFRmg, and DFRm, respectively). Genetic parameters were estimated by REML using an animal model with age on test as a covariate and with genotype, age of dam, and year as fixed effects. Regression equations for observed on predicted DMI were OFI = 1.27 (SE = 0.27) + 0.83 (SE = 0.04) x CFRmcg [R2 = 0.44, residual SD (s(y.x)) = 0.669 kg/d] and OFI = 1.32 (SE = 0.22) + 0.8 (SE = 0.03) x DFRmcg (R2 = 0.53, s(y.x) = 0.612 kg/d). Heritability of OFI was 0.27 +/- 0.12, and heritabilities ranged from 0.33 +/- 0.12 to 0.41 +/- 0.13 for predicted measures of DMI. Phenotypic and genetic correlations between OFI and CFRmcg, CFRmc, CFRg, CFRmg, CFRm, DFRmcg, DFRmc, DFRg, DFRmg, and DFRm were 0.67, 0.73, 0.41, 0.63, 0.78, 0.73, 0.82, 0.45, 0.77, and 0.86 (P < 0.001 for all phenotypic correlations); and 0.95 +/- 0.07, 0.82 +/- 0.13, 0.89 +/- 0.09, 0.95 +/- 0.07, 0.91 +/- 0.09, 0.96 +/- 0.07, 0.89 +/- 0.09, 0.88 +/- 0.09, 0.96 +/- 0.06, and 0.96 +/- 0.07, respectively. Phenotypic and genetic correlations between CFRmcg and DFRmcg, CFRmc and DFRmc, CFRg and DFRg, CFRmg and DFRmg, and CFRm and DFRm were 0.98, 0.94, 0.99, 0.98, and 0.95 (P < 0.001 for all phenotypic correlations), and 0.99 +/- 0.004, 0.98 +/- 0.017, 0.99 +/- 0.004, 0.99 +/- 0.005, and 0.97 +/- 0.021, respectively. The strong genetic relationships between OFI and CFRmcg, CFRmg, DFRmcg, and DFRmg indicate that these predicted measures of DMI may be used in genetic evaluations and that DM requirements for cold stress may not be needed, thus reducing model complexity. However, high genetic correlations for final weight with OFI, CFRmcg, and DFRmcg suggest that the technology needs to be further evaluated in populations with genetic variance in feed efficiency.     

Adaptation of wheat and protein-mineral concentrate intakes by individual hens fed ad libitum in sequential or in loose-mix systems

1. Feed intake and performance of birds given sequential or loose-mix feeding was investigated from 19 to 42 weeks of age. A complete diet was fed as control (C). A balancer diet (50) was fed either sequentially (S50) or in a loose-mix (L50) with wheat. This diet was formulated to provide a similar nutritive value as C assuming a 50 : 50 diet and wheat intake. Another balancer diet (25) was fed sequentially (S25) or in a loose-mix (L25) with wheat. The diet was to provide a similar nutritive value as C assuming 75 : 25 diet and wheat intakes. In sequential feeding, only wheat was fed in the morning (4 h after lights-on) and the balancer diet in the late afternoon (4 h before lights-off). In the loose-mix treatment, a mixture of the two diets was fed throughout the 16-h daily light. Each treatment was given ad libitum to 25 birds in individual cages. 2. Birds fed on L25 had lower total feed intakes than those receiving C, S50 or S25. Protein intake was reduced with L25 compared to C, S50, S25 and L50. Metabolisable energy (ME) intake was, however, similar among all treatments. Egg production and weight were reduced with L25 compared to S50 and S25. Body weight (BW) was lowered with L25. However, there was high individual variation in all variables. 3. Feeding system (sequential vs loose-mix) had no effect on ME intake. However, the loose-mix treatment reduced feed and protein intake due to lower balancer diet intake. It also resulted in low egg production, egg and BWs compared to sequential feeding. The weights of pancreas and gizzard were heavier with sequential and loose-mix compared to the control. 4. The loose-mix treatment reduced egg-laying performance. Sequential feeding resulted in similar egg-laying performance to conventional feeding and thus could be used to advantage in situations where it is applicable.     

Adipose tissue lipogenesis in growing steers adapted to different levels of feed intake

The association between feed intake and lipogenic activity in adipose tissue was investigated in growing cattle. Twenty-five 300-kg steers were allotted by BW to one of five levels of intake of a single high-energy corn-corn silage-based diet. Steers were adapted to diets over 4 wk and intakes were adjusted weekly to achieve steady but varying rates of growth. Daily intakes (% of BW) averaged .92, 1.15, 1.64, 2.28 and 2.69 and resulted in growth rates over the final 3 wk of -.28, .07, .71, 1.67 and 1.69 kg/d, respectively. Lipogenic activities in biopsied tissue and circulating concentrations of glucose and insulin were lowest at maintenance feeding and below but increased linearly (P less than .01 for lipogenesis; P less than .1 for glucose and insulin) as intake increased above maintenance. Mean minimal and maximal rates (mumoles.-min(-1).10(6) cells(-1)) or concentrations were fatty acids synthesis ([14C]acetate---fatty acid)), .065 and .723; fatty acid synthetase (NADPH oxidized), .266 and 2.97; lipoprotein lipase (fatty acid released), .048 and .359; glucose (mg/dl), 60.4 and 70.7 and insulin (ng/ml), .70 and 1.66. In a preliminary study with the same 25 steers fed ad libitum, nearly 25% of the variability in adipose tissue lipogenesis was accounted for by variation in feed intake. Results indicate that activities of lipogenic enzymes and lipogenic capacity in growing steers coordinately adapt to the level of feed consumed and that nutrient availability and(or) insulin concentrations may participate in this adaptation.     

Comparative evaluation of mathematical functions to describe growth and efficiency of phosphorus utilization in growing pigs

Success of pig production depends on maximizing return over feed costs and addressing potential nutrient pollution to the environment. Mathematical modeling has been used to describe many important aspects of inputs and outputs of pork production. This study was undertaken to compare 4 mathematical functions for the best fit in terms of describing specific data sets on pig growth and, in a separate experiment, to compare these 4 functions for describing of P utilization for growth. Two data sets with growth data were used to conduct growth analysis and another data set was used for P efficiency analysis. All data sets were constructed from independent trials that measured BW, age, and intake. Four growth functions representing diminishing returns (monomolecular), sigmoidal with a fixed point of inflection (Gompertz), and sigmoidal with a variable point of inflection (Richards and von Bertalanffy) were used. Meta-analysis of the data was conducted to identify the most appropriate functions for growth and P utilization. Based on Bayesian information criteria, the Richards equation described the BW vs. age data best. The additional parameter of the Richards equation was necessary because the data required a lower point of inflection (138 d) than the Gompertz, with a fixed point of inflexion at 1/e times the final BW (189 d), could accommodate. Lack of flexibility in the Gompertz equation was a limitation to accurate prediction. The monomolecular equation was best at determining efficiencies of P utilization for BW gain compared with the sigmoidal functions. The parameter estimate for the rate constant in all functions decreased as available P intake increased. Average efficiencies during different stages of growth were calculated and offer insight into targeting stages where high feed (nutrient) input is required and when adjustments are needed to accommodate the loss of efficiency and the reduction of potential pollution problems. It is recommended that the Richards and monomolecular equations be included in future growth and nutrient efficiency analyses.     

Technical note: Use of near-infrared reflectance spectroscopy to predict intake and digestibility in bulls and steers

Multiple fecal samples were collected from growing Angus bulls (264 to 419 kg of BW, 3.0 to 11.4 kg/d of DMI) to predict DMI of a corn-silage-based diet. Contemporaneous digestion trials were conducted with the same diet in 12 steers in yr 1 to 3 and bulls in yr 4. Near-infrared spectra from fecal samples (n = 730 from 282 growing bulls, n = 240 from 36 steers and 12 bulls for digestion trials) were obtained from dried and ground fecal samples, and modified partial least squares regression was used to develop equations to predict DMI and DM digestibility (DMD). Although mean predicted DMI of the growing bulls (7.52 ± 0.04 kg/d or 22.4 ± 0.1 g/kg of BW) was within 2% of mean measured DMI (7.63 ± 0.06 kg/d or 22.7 ± 0.1 g/kg of BW), the mean of paired differences within samples (0.11 ± 0.04 kg/d or 0.3 ± 0.1 g/kg of BW) was greater (P < 0.01) than zero. Measured DMD (72.3 ± 0.5%) was identical (P < 0.97) to predicted DMD (72.3 ± 0.5%), and DMD for bulls in the digestion trial did not differ (P < 0.27) from DMD for steers. Prediction of intake requires incorporation of some measured values from the set of fecal samples to be predicted. Lack of similarity between spectra of fecal grab samples from the growing bulls and daily fecal collection of steers and bulls in the digestion trials in this study indicates the need for further verification before prediction of DMD with fecal grab samples.