Antibiotic use in dairy herds in the Netherlands from 2005 to 2012.

The aim of this study was to examine the variation in antibiotic use and the effects of external factors on trends in antibiotic use at the herd level by using the number of daily dosages as an indicator for antibiotic use. For this purpose, antibiotic use was analyzed in 94 dairy herds in the Netherlands from 2005 to 2012. The herds were divided into 3 groups of farmers: one group was guided in their antibiotic use from 2008 to 2010 as part of the project, whereas the other 2 groups were not actively guided. The farms were located in 10 of the 12 provinces and were clients of 32 of the 300 veterinary practices that treat cattle. Sales invoices from the veterinary practices provided the antibiotic and cost data for the participating farmers. The number of animal-defined daily dosages (ADDD) indicates the number of days per year that the average cow in a herd is given antibiotic treatment. The average ADDD for all farms from 2005 to 2012 was 5.86 (standard deviation=2.14); 68% of ADDD were used for udder health, 24% for clinical mastitis and 44% for dry-cow therapy. Variation in ADDD among herds decreased during the study period. The trend in ADDD can be described as having 3 phases: (1) a period of increasing use coinciding with little public concern about antibiotic use (2005-2007), (2) a period of growing awareness and stabilization of use (2007-2010), and (3) a period of decreasing use coinciding with increasing societal concerns (2010-2012). The greatest reduction in use was for drugs other than those used to treat the udder. Drug use for mastitis treatment fell considerably in the final year of the study period, whereas farmers were reluctant to reduce use for dry-cow therapy. Almost 40% of the herds were given less than 2.5 ADDD for dry-cow therapy, which is equivalent to 2.5 tubes per average cow in the herd, and 20% used more than 3 tubes per cow. Use of third- and fourth-generation cephalosporins and fluoroquinolones dropped from 18% of ADDD during 2005 to 2010 to 1% in 2012, with a shift toward penicillins and broad spectrum drugs. The ADDD was 22% lower in 2012 than 2007, the year of the highest usage. The decrease in ADDD over time varied between the 3 groups of farmers. During the second phase of the study, the guided group began to display a reduction in use, whereas the other groups only displayed a significant reduction in the third phase. The reduction in antibiotic use has resulted in lower veterinary costs per cow in recent years.

Technical note: A mathematical function to predict daily milk yield of dairy cows in relation to the interval between milkings.

The milk production of a dairy cow is characterized by lactation production, which is calculated from daily milk yields (DMY) during lactation. The DMY is calculated from one or more milkings a day collected at the farm. Various milking systems are in use today, resulting in one or many recorded milk yields a day, from which different calculations are used to determine DMY. The primary objective of this study was to develop a mathematical function that described milk production of a dairy cow in relation to the interval between 2 milkings. The function was partly based on the biology of the milk production process. This function, called the 3K-function, was able to predict milk production over an interval of 12h, so DMY was twice this estimate. No external information is needed to incorporate this function in methods to predict DMY. Application of the function on data from different milking systems showed a good fit. This function could be a universal tool to predict DMY for a variety of milking systems, and it seems especially useful for data from robotic milking systems. Further study is needed to evaluate the function under a wide range of circumstances, and to see how it can be incorporated in existing milk recording systems. A secondary objective of using the 3K-function was to compare how much DMY based on different milking systems differed from that based on a twice-a-day milking. Differences were consistent with findings in the literature.

Computer-supported collaborative learning in the medical workplace: Students' experiences on formative peer feedback of a critical appraisal of a topic paper.

BACKGROUND: Medical workplace learning consists largely of individual activities, since workplace settings do not lend themselves readily to group learning. An electronic Learning Management with System Computer-Supported Collaborative Learning (CSCL) could enable learners at different workplace locations to discuss personal clinical experiences at a distance to enhance learning. AIM: To explore whether CSCL-enabled structured asynchronous discussions on an authentic task has additional value for learning in the medical workplace. METHODS: Between January 2008 and June 2010, we conducted an exploratory evaluation study among senior medical students that were engaged in clinical electives. Students wrote a Critical Appraisal of a Topic paper about a clinical problem they had encountered and discussed it in discipline homogeneous subgroups on an asynchronous forum in a CSCL environment. A mixed method design was used to explore students' perceptions of the CSCL arrangement with respect to their preparation and participation, the design and knowledge gains. We analysed the messages recorded during the discussions to investigate which types of interactions occurred. RESULTS: Students perceived knowledge improvement of their papers. The discussions were mostly task-focused. The students considered an instruction session and a manual necessary to prepare for CSCL. A high amount of sent messages and a high activity in discussion seem to influence scores on perceptions: 'participation' and 'knowledge gain' positively. CONCLUSION: CSCL appears to offer a suitable environment for peers to provide formative feedback on a Critical Appraisal of a Topic paper during workplace learning. The CSCL environment enabled students to collaborate in asynchronous discussions, which positively influenced their learning.

Preoperative computed tomography and selection of patients with colorectal peritoneal carcinomatosis for cytoreductive surgery and hyperthermic intraperitoneal chemotherapy.

AIM: A survival benefit has been observed for colorectal cancer patients with peritoneal carcinomatosis treated by cytoreductive surgery with intraoperative hyperthermic intraperitoneal chemotherapy (HIPEC). However, this treatment modality is associated with a considerable morbidity and mortality and in a significant number of patients survival is not improved. We studied whether poor survivors could be identified on preoperative computed tomography (CT), in order to avoid unnecessary surgery. PATIENTS AND METHODS: Films of abdominopelvic CT scans from 25 such patients treated by cytoreductive surgery and HIPEC were retrospectively analysed by two radiologists separately. A simplified peritoneal cancer index (SPCI) was used to determine the extent of peritoneal involvement. Correlation between the on preoperative CT based SPCI-scores as well as number of involved abdominopelvic areas (N) and survival was examined with the log-rank test. The relation between each affected region and survival was evaluated with Cox regression analysis. RESULTS: The preoperative SPCI- and N-scores of one of the radiologists had no statistically significant prognostic value, while for the second radiologist SPCI > or = 7 and N > or = 4 were associated with particularly poor outcome. Additionally, the presence of ileocaecal region involvement and, depending on the radiologist, the occurrence of tumour deposits in the left subdiaphragmatic area on CT appeared to be unfavourable prognostic signs. CONCLUSIONS: The prognostic value of preoperative conventional CT appeared to be radiologist dependent and may, therefore, be of limited value in selecting colorectal cancer patients with peritoneal carcinomatosis who will not benefit from extensive cytoreductive surgery followed by HIPEC.

The potential impact of CT-MRI matching on tumor volume delineation in advanced head and neck cancer.

PURPOSE: To study the potential impact of the combined use of CT and MRI scans on the Gross Tumor Volume (GTV) estimation and interobserver variation. METHODS AND MATERIALS: Four observers outlined the GTV in six patients with advanced head and neck cancer on CT, axial MRI, and coronal or sagittal MRI. The MRI scans were subsequently matched to the CT scan. The interobserver and interscan set variation were assessed in three dimensions. RESULTS: The mean CT derived volume was a factor of 1.3 larger than the mean axial MRI volume. The range in volumes was larger for the CT than for the axial MRI volumes in five of the six cases. The ratio of the scan set common (i.e., the volume common to all GTVs) and the scan set encompassing volume (i.e., the smallest volume encompassing all GTVs) was closer to one in MRI (0.3-0.6) than in CT (0.1-0.5). The rest volumes (i.e., the volume defined by one observer as GTV in one data set but not in the other data set) were never zero for CT vs. MRI nor for MRI vs. CT. In two cases the craniocaudal border was poorly recognized on the axial MRI but could be delineated with a good agreement between the observers in the coronal/sagittal MRI. CONCLUSIONS: MRI-derived GTVs are smaller and have less interobserver variation than CT-derived GTVs. CT and MRI are complementary in delineating the GTV. A coronal or sagittal MRI adds to a better GTV definition in the craniocaudal direction.

Correlative 201Tl SPECT, MRI and ex vivo 201Tl uptake in detecting and characterizing cervical lymphadenopathy in head and neck squamous cell carcinoma.

UNLABELLED: The value of SPECT with 201Tl chloride, in combination with MRI (particularly short inversion-time inversion recovery [STIR] sequences that suppress fat signals) to detect and characterize cervical lymphadenopathies (nodes > or = 1 cm), and ex vivo lymph node 201Tl uptake were studied in patients with squamous cell carcinoma of the head and neck. METHODS: Preoperative SPECT and MRI, displayed in similar planes, were compared with the histologic findings in 15 neck dissection specimens from 12 patients with squamous cell carcinoma of the head and neck (9 with unilateral and 3 with bilateral neck dissection). Results were evaluated topographically with regard to the lymph node compartments (levels) of the neck. In addition, in 8 of these patients, the 201Tl activity of dissected lymph nodes of 10 neck sides was measured immediately after surgery in a gamma counter and expressed as percentage of the injected dose per gram tissue (%ID/g). RESULTS: Sixty-two lymph node levels were evaluated histologically. The high sensitivity of MRI (92% versus 71% for 201Tl SPECT), which correctly detected lymph node involvement in 22 of 24 levels, and the high specificity of 201Tl SPECT (92% versus 71% for MRI), which correctly characterized as negative 35 of 38 lymph node levels without metastasis on histology, led to a combined 201Tl SPECT/MRI accuracy of 92%. 201Tl SPECT was particularly effective in excluding involvement in 9 tumor-free neck levels with pathologically enlarged lymph nodes on MRI but failed to confirm involvement in 5 other tumor-positive levels. Mean 201Tl uptake in 53 lymph nodes with confirmed histologic involvement was significantly higher than uptake in 145 tumor-free lymph nodes (0.0043+/-0.0022 %ID/g versus 0.0023+/-0.0014 %ID/g, P = 0.0001), muscle and fat tissue but clearly lower than salivary gland uptake. CONCLUSION: Although 201Tl SPECT is not sensitive enough to be used as an independent imaging modality for staging of the neck, its correlative application with MRI appears to be an accurate method for the assessment of regional spread in head and neck squamous cell carcinoma. The ability of 201Tl SPECT to characterize neck lymphadenopathies detected by MRI appears to be based on the difference in 201Tl concentration found in lymph nodes with and without tumor involvement.

Thallium-201 SPECT in the diagnosis of head and neck cancer.

UNLABELLED: The accuracy of SPECT with 201Tl-chloride for the diagnosis of primary tumors, lymph node metastases and recurrences in head and neck cancer was evaluated for clinical applicability. METHODS: SPECT images, obtained 60 min after administration of 150 MBq 201Tl-chloride, were compared with clinical, CT and/or MRI and histology results. In addition, whole-body images were obtained to detect distant metastases. RESULTS: In 79 patients studied for primary tumors (principally larynix, hypopharynx, oropharynx, nasopharynx and oral cavity), 201Tl SPECT correctly identified 69 of 73 (95% versus 88% for CT/MRI) histologically confirmed malignancies including 63 squamous-cell carcinomas. The method localized four occult naso- and oropharynx carcinomas not seen on CT/MRI and was correctly negative in two patients without tumor and in three of four patients with no confirmed primary tumor in the head and neck. With respect to regional spread, only patients who had cervical lymph node dissection were evaluated, and the findings were recorded per side of the neck. Thallium-201 SPECT correctly identified metastases in 31 of 36 neck dissections with proven lymph node involvement (86%), was correctly negative in nine and false-positive in one. Although the sensitivity of CT/MRI was clearly higher (97%), considerably more false-positive cases affected its accuracy (81% versus 87% for SPECT). In 30 patients investigated for recurrences, 201Tl SPECT correctly identified 27 of 29 microscopically confirmed tumor sites (93%) and was correctly negative in seven. Sensitivity of CT/MRI was lower (76%), and a greater number of false-positives (seven versus three for SPECT) further decreased its accuracy (64% versus 87% for SPECT). Distant metastases were detected in five patients. CONCLUSION: Thallium-201 SPECT appears to be an accurate method for the diagnosis of head and neck cancer. The method is particularly useful for detection of occult head and neck tumors and for assessing recurrences. It also may be of complementary value in the staging of primary tumors, in the differentiation of metastatic from reactive lymph nodes in the neck and, on the basis of whole-body scanning, for screening of distant metastases.

Computed tomography for the detection of neck node metastases in melanoma patients.

AIMS: To assess the value of CT scanning for detection of lymph node metastases in the neck. METHODS: The appearance and site of the metastases was studied, as well as the sensitivity and specificity of CT. RESULTS: Nodal metastases did not always show a high contrast uptake and nodal density therefore cannot be used as a criterion for metastasis. Irregular contrast enhancement was seen in seven of the 21 tumour-positive necks. Frequently, metastases in the parotids, superficial nodes in the neck and in the posterior triangle were seen. The sensitivity and specificity of palpation and CT scanning were 87 and 100%, respectively. CONCLUSIONS: However, because small, clinically occult, melanoma metastases were frequently overlooked on CT, the role of this imaging modality in assessing occult metastases remains limited. Based on recent data from literature it is reasonable to speculate that ultrasound guided fine needle aspiration cytology (FNAC) will prove to be more effective than a non-invasive staging procedure of the neck in melanoma patients.

Report of a symposium on diagnosis and treatment of adult soft tissue sarcomas in the head and neck.

A series of presentations and discussions was held during a symposium on the diagnosis and treatment of adult soft tissue sarcomas in the head and neck (HNSTS). The purpose of this meeting was to define guidelines on diagnosis and treatment of HNSTS. The results of this symposium are summarized and condensed in this report. Recommendations are made for diagnostic strategies and for treatment. Diagnostic efforts in PET scanning and dynamic MRI need to be expanded to detect early recurrences. Firm pathological diagnosis remains the basis for further treatment strategy. Wide surgical excision, if feasible, in combination with radiotherapy is the treatment of choice.

The value of computed tomography scan versus an explorative surgical approach for removal of squamous cell carcinoma of the posterior pharyngeal wall.

BACKGROUND: The prevertebral fascia plays a key role in surgery of posterior pharyngeal wall tumors. Invasion of the prevertebral muscles determines the irresectability of the tumor and accurate diagnosis of invasion posteriorly is a prerequisite for major ablative surgery. METHODS: A retrospective study was performed to define the value of CT scanning versus open neck exploration with regard to the resectability of posterior pharyngeal wall carcinoma. The predictive value of preoperative CT scans was assessed and compared with the outcome of open neck exploration and resectability of the primary tumor, using the final histopathology report as a gold standard. RESULTS: Nineteen patients with 20 tumors were included in this study. Overall the CT scan was correct concerning prevertebral muscle status in 4 out of 20 (20%), whereas open neck exploration was correct in 18 tumors (90%). CONCLUSION: The predictive value of a suspicious CT scan in determining prevertebral muscle invasion is extremely low in this study. Open neck exploration seems to be superior for determining resectability of posterior wall carcinoma.

Preliminary experience with thallous chloride T1 201-labeled single-photon emission computed tomography scanning in head and neck cancer.

OBJECTIVES: To test the feasibility of single-photon emission computed tomography (SPECT) scanning with the use of thallous chloride T1 201 in patients with head and neck cancer and to decide its possible applications to improve the diagnosis and staging of head and neck cancer. DESIGN: Findings from SPECT with the use of 4.32 mCi of thallous chloride T1 201 were compared with those from clinical examination, computed tomography (CT), magnetic resonance imaging, ultrasound-guided fine-needle aspiration, and histologic studies. Primary sites and neck nodes were separately studied. Accuracy, sensitivity, and specifically were calculated for 19 patients who were being assessed for initial treatment (primary sites) and for 12 neck node dissections in 10 patients. SETTING: The Netherlands Cancer Institute, Antoni van Leeuwenhoek Hospital, Amsterdam. PATIENTS: A consecutive sample of 25 patients with head and neck cancers of different sites. The average age of the patients was 60.2 years, and there were 19 men and six women. The sites of the primary lesions were as follows: oropharynx (n = 5), larynx (n = 9), oral cavity (n = 4), nasopharynx (n = 1), hypopharynx (n = 3), and unknown (n = 3). RESULTS: For the primary lesions, SPECT identified 94% of the lesions; SPECT was more accurate in delineating four oropharyngeal lesions and one nasopharyngeal lesion. In 12 neck node dissections, SPECT identified all of the positive lesions and two negative lesions, whereas CT detected two false-positive lesions. Single-photon emission computed tomography gave less information about the number of nodes and the anatomy than did CT or magnetic resonance imaging. CONCLUSIONS: Single-photon emission computed tomography with the use of thallous chloride T1 201 appears to be useful in helping to identify occult primary lesions, particularly in the oropharynx. It may assist CT or magnetic resonance imaging in identifying a recurrence of cancer in tissues or in lymph nodes, and in screening for distant metastases. Although no nodes were identified that were not already seen with the use of CT or magnetic resonance imaging, SPECT may help to eliminate the false-positive lesions, and SPECT with the use of thallous chloride T1 201 appears to be a valuable new tool in helping to diagnose and stage head and neck cancer.

Oestrus control and early pregnancy diagnosis in the swamp buffalo: comparison of enzymeimmunoassay and radioummunoassay for plasma progesterone.

A preliminary study has been undertaken, in order to investigate the suitability of a progesterone assay in blood plasma for oestrus control and pregnancy diagnosis in the swamp buffalo (Bubalus bubalis ). Progesterone was determined both by radioimmunoassay (RIA) and by enzymeimmunoassay (EIA). Values obtained by EIA were considerably lower than values obtained by RIA. This may be partly due to the fact that only RIA values were corrected for procedural losses. Blood samples were taken on day 1 (= day of insemination) and on days 24, 27 and 30 after insemination (p.i.). Additional samples from pregnant animals were taken around day 170 p.i.. Normal progesterone values during oestrus were lower than 0.5 ng/ml, and generally the same low values were found in case of non-pregnancy at days 24, 27 and 30 p.i.. Pregnant animals showed in all cases progesterone concentrations higher than 0.5 ng/ml at days 24, 27 and 30, as well as around day 170 p.i.. These preliminary results indicate that the analysis of progesterone in plasma may be suitable for fertility control in the swamp buffalo. Furthermore we suggest that a modified EIA method can be used as a simple and rapid oestrus detection test under field conditions.

A simple enzymeimmunoassay of milk progesterone for monitoring fertility in dairy buffaloes.

A simple, sensitive, direct (without extraction) enzymeimmunoassay (EIA) was usec to determine progesterone levels in whole milk samples of 400 Nili-Ravi dairy buffaloes. The mean progesterone values 22 d after A.I. were significantly higher in pregnant (16.6 +/- 9.2 ng/ml) than nonpregnant (below 5 ng/ml) animals. The mean progesterone values were below 0.34 +/- 0.12 (the detection limit) both at estrus and in cases of clinically diagnosed inactive ovaries, 3.18 +/- 1.9 at proestrus, 2.25 +/- 1.2 postestrus and 13.22 +/- 6.74 at Day 10 of the estrous cycle. Twenty buffaloes confirmed pregnant for 2 to 3 mo, had a mean value of 20.3 +/- 4.5 ng/ml. The EIA test is very reliable in the selection of nonpregnant buffaloes (100 %) and the confirmation of inactive ovaries and of estrus. Differential diagnosis of inactive or active ovaries can be made by analyzing two milk samples at a 7-d interval.

Applications of a multiphasic growth function to body composition in pigs.

A multiphasic growth function was used to relate growth of body components to phases of total growth for pigs. Each phase of growth was characterized by asymptotic weight, age at maximum gain, and duration. Age at maximum gain and duration were expressed as a ratio and assumed constant for all phases. One application involved weights of total DM predicted directly with a diphasic function and indirectly with monophasic functions of fat-free DM and fat. Another involved weights of carcass side predicted directly with a diphasic function and indirectly with monophasic functions of offal + muscle + bone and fat + skin. Components were grouped on age at maximum gain. There was good agreement for asymptotic weight between body components and phases, and general agreement for age at maximum gain and for duration, except for carcass weights. A multiphasic growth function may provide a way to examine fat-adjusted weight in living animals because growth of fat appears as a late phase in a multiphasic description of total body growth.

Effect of duration of feed quality restriction on body dimensions in lambs.

We measured the effect of duration of feed quality restriction and the consequent compensatory growth on body dimensions in 18 crossbred Swifter (Texel sire x Flemish dam) male lambs born in March 1994 and weaned at approximately 2 mo of age. The lambs were fed grass straw (46 g CP/kg DM) for ad libitum consumption and 35 g CP x kg(-75) x d(-1) mixed concentrates (173 g/kg DM). At approximately 3.5 mo of age and average live weight of approximately 34 kg, the lambs were allotted to six blocks, each block with three lambs of approximately the same live weight. Within each block, the three lambs were then randomly assigned to two restricted treatments (R1 and R2) and a control (C) treatment. In treatments R1 and R2, feed quality was restricted by withholding concentrates for 3 and 4.5 mo, respectively. A growth model was developed to study the effects of restriction and subsequent compensation after realimentation (6.5 and 8 mo for R1 and R2 groups, respectively). During restriction, live weight and growth in body dimensions were suppressed. Bone length measures such as body length and ulna length were less affected than live weight. The response in testes girth to restriction was almost immediate. At the end of the experiment (age of about 14 mo), R1 animals fully compensated. However, the R1 animals had higher testes girth (P < .001), chest girth (P < .01), and chest depth (P < .05). Extending the duration of feed restriction did not have a significant effect on the rate of losses in live weight and body dimensions during restriction. At the end of the experiment, except for withers height and trunk length, the R2 animals did not compensate fully in live weight and other dimensions. However, the parameter estimates suggested that the R2 animals may need a relatively longer period of realimentation to reach to the same size as R1 and C animals.

Nutrient flows in agriculture in The Netherlands with special emphasis on pig production.

Annual nitrogen (N), phosphorus (P), and potassium (K) flows in agriculture in The Netherlands were identified and quantified in 1990, with special emphasis on pig production. Also, the effects that various management strategies in pig production have on NPK emission in 1990 were compared using a static deterministic simulation model. Ammonia emission from pig production in 1990 (60.9 Gg N) exceeded the defined target for the year 2000 (12.7 Gg N). Measures that affect volatilization of ammonia directly (i.e., introduction of low-emission stables, manure storage facilities, or manure application techniques) reduced ammonia emission most effectively. These measures, however, should be combined with a reduction in application of artificial N fertilizer to avoid an increase in N losses through leaching, run-off, or denitrification. Targets for ammonia emission in the year 2010 require a reduction in the pig population of 24 to 62%, in addition to implications of measures described in this article. National NPK losses in 1990 through leaching, run-off, or denitrification, predicted at 223.5 kg/ha for N, 32.7 kg/ha for P, and 67 kg/ha for K, exceeded government targets for the year 2010 (185 kg N/ha; 8.7 kg P/ha; norm not set for K). Reducing application of artificial NPK fertilizer reduced national NPK losses most effectively. For P, use of phytase and feeding pigs in accordance with their P requirements is required, in addition to limited use of artificial P fertilizer to meet targets for the year 2010. Hence, from an environmental point of view, pig production in The Netherlands is limited primarily by ammonia emission targets for the year 2010.

A model for individual egg production in chickens.

Our primary objective was to improve on an existing model for the individual weekly egg production curve by modeling the curve as a sum of logistic functions: one for the increasing phase of production and a sum for the decreasing phases. To illustrate the model, we used four data sets from two pairs of individuals. For these data, the model consisted of an increasing phase and a single decreasing phase of production: y(t) = m k1((1 - e(-t))/(1 + e(-t))) - m(k1 - k2)((1 - e(-t))/(1 + e(-(t-c2)))) where y(t) is egg production at week t, m is maximum production during a specific time interval, k1 is proportion of maximum production for the increasing phase, k2 is proportion of maximum production for the decreasing phase, and c2 is point of inflection from the upper level of the increasing phase to the lower level of the decreasing phase; thus, c2 is a measure of persistency of egg production. For one pair of individuals, production was about 88% of maximum (k1) for the increasing phase and about 76% of maximum (k2) for the decreasing phase. For the other pair, production was about 91% of maximum (k1) for the increasing phase and about 75% of maximum (k2) for the decreasing phase. Persistency (c2) was about 25 wk for one pair and about 28 wk for the other. Predicted total 52-wk production was within one or two eggs of actual production. The secondary objective was to improve estimation of model parameters by summarizing egg production data by 1-wk, 2-wk, or 4-wk intervals and by using cumulative egg production instead of weekly production. For weekly production, estimates of parameters changed only slightly, as intervals increased from 1 wk to 2 wk or to 4 wk. Predicted total 52-wk production, however, decreased up to five eggs as interval increased from 1 wk to 4 wk. For cumulative egg production by time t, Yt, the model was Yt = 7 k1[2 Ln((1 + e(t))/2) - t] - 7(k1 - k2)[(1 + e(-2)2) Ln((e(c2) + e(t))/(1 + e2c)) - te(-c2)]. For cumulative production, estimates of parameters changed only slightly, if at all, as intervals increased from 1 wk to 4 wk. Predicted 52-wk production, however, approached the actual number as interval increased from 1 wk to 4 wk. Prediction of annual (52-wk) egg production based on part-record production for only the first 22 wk might lead to over-prediction because persistency of production lasted longer than the part record. Genetic gain from selection to improve annual production, therefore, might be increased if selection accounted for persistency of production and for the multiphasic shape of the individual egg production curve, and if data were summarized by 4-wk intervals and cumulated.

Multiphasic analysis of growth curves in chickens.

A multiphasic function that considers body weight to result from an accumulation from more than one phase of growth was used to describe growth curves for Rhode Island Red (RIR) and White Leghorn (WL) males and females, from hatching to 45 wk of age. Mean body weight gains were fitted by iteratively reweighted nonlinear regression using the multiphasic function: (formula; see text) where yt is mean gain (grams) at age t; n is number of phases; tanh is hyperbolic tangent; for each phase i, ai is half asymptotic weight; bi is growth rate relative to ai (weeks-1) and ci is age at maximum gain (weeks). For each phase, maximum gain is aibi and duration (days required to attain about 75% of asymptotic yield during that phase) is 2bi-1. Estimates of parameters clearly point to the diphasic nature of growth and to differences between phases of sexes. First and second phases accounted for 97% of total asymptotic weight. For the first phase, males attained 70% of their asymptotic weight, whereas females attained 85%. Duration of the first phase was 15 wk. For the second phase, it was 12.5 wk for RIR and 10 for WL males, whereas it was 5 wk for RIR and 6 for WL females. Maximum gain during the first phase averaged 144.4 g for males, 108.8 g for females, 156.2 g for RIR, and 97.0 g for WL. During the second phase, it was 68.0 g for RIR males and females but 71.5 and 55.9 g for WL males and females, respectively. Age at maximum gain during the first phase was 12.0 wk. During the second phase, it was 24.2 wk for RIR females, 2.6 wk later than for males, whereas it was 27.3 wk for WL females, 8.3 wk later than for males. For a fixed total asymptotic weight, partitioned between two phases of growth, a higher, longer, and later first phase was associated with a lower, shorter, and later second phase; the association was greater for males than for females.

Characterization of poultry egg production using a multiphasic approach.

Egg production for an individual hen is described by a multiphasic model in which each phase is determined by number of eggs within a clutch, including internally laid eggs, and pause between clutches. Number of eggs in a clutch is determined by circadian rhythm, which consists of a daily rhythm and lag. Internal laying is a result of asynchrony in the development of the oviduct and the ovary. Pause consists of a circadian rhythm and a period called delay. It is expected that lag and internal laying are determined genetically, whereas delay is determined by the environment, especially by photoperiod. A multiphasic model was developed to characterize egg production by lag and delay, expressing cumulative egg number in terms of time. Data need to be adjusted for internal laying prior to the analysis. The inverse function, expressing time in terms of cumulative egg number, was used to estimate average lag and delay for individual hens. Hourly data from four hens over a 16-day period were analyzed to estimate parameters for lag and delay. Data were preadjusted for internal laying and for pause. Lag ranged from -.08 to 2.11 h, and was related positively to number of clutches and, consequently, related negatively to average length of clutch and total number of eggs over the period. Average delay was about 16 h, which may be determined by the light:dark ratio.

A model for persistency of egg production.

The objectives of our study were to propose a new definition for persistency of egg production and to develop a mathematical model to describe the egg production curve, one that includes a new measure for persistency, based on the proposed definition, for use as a selection criterion to improve total egg production. Persistency of egg production is an important determining factor for total egg production. Hens with the same total production, however, can exhibit different egg production curves because of differences in persistency. We propose a new definition for persistency of egg production: the number of weeks during which a level of constant production is maintained. No egg production model exists that includes a measure of persistency in terms of duration of time or that allows this measure of persistency to be derived from model parameters. It was necessary, therefore, to develop a new model to describe an egg production curve for a flock: equation [see text] and for an individual: equation [see text] where y(t) = egg production at time t, t1 and t2 = times at transition, r = duration of transition, y(p) = level of constant production, b4 = rate of decline in production, and P = persistency of constant production. These parameters measure directly the important biological characteristics of an egg production curve. To illustrate the model, six data sets were used: two from flocks (one pullet flock and one hen flock) and four from two pairs of individuals. The proposed definition of persistency should be important for genetic selection because it might be desirable to select for increased persistency. The novel approach to the definition and measure of persistency presented here should provide a better understanding of the relationship between the new measure of persistency and other characteristics of egg production.