Assessing the productivity of indigenous chickens in an extensive management system in southern Nyanza, Kenya

The present study was conducted to assess the performance of indigenous chickens under extensive system in southern Nyanza, Kenya. The study was carried out in two phases in Komolorume and Kawere villages in Rongo and Rachuonyo districts, respectively. The first phase was a cross-sectional study in 81 farms selected by cluster sampling to get the overview of the indigenous chicken production. A four-month prospective longitudinal study in 60 farms randomly selected from the previous 81 farms followed. Mean flock sizes per household were 20 and 18 birds in Komolorume and Kawere, respectively. Overall mean flock size was 19 birds ranging from 1to 64. The mean clutch size, egg weight and hatchability were 12 eggs, 48 g and 81% respectively in Komolorume and 10 eggs, 45 g and 70%, respectively, in Kawere. The chick survival rates to the age of eight weeks were 13% and 10% in Komolorume and Kawere, respectively. Mean live weights for cocks and hens were 2096 g and 1599 g in Komolorume and 2071 g and 1482 g in Kawere, respectively. The mean household cock to hen ratio was 2:5 and 2:4 for Komolorume and Kawere, respectively. The mean chick to grower to adult ratio per household was 8: 6:6 in Komolorume and 8:4:6 in Kawere. Clutch sizes and hatchability rates were significantly higher in Komolorume village (P?<?0.5). The productivity of the indigenous chickens was shown to be low compared to that of the improved chickens in other parts of the world.     

Egg production,fertility, hatchability and immune responses of some chicken strains under high ambient temperatures

This experiment was designed to investigate and compare the egg production, fertility, hatchability and immune responses of some local developed Egyptian chicken strains under high ambient temperatures. A total of 108 (26 weeks old) laying hens of Matrouh, Silver Montazah, Mandarah and Inshas (9 hens × 3 replicates × 4 strains) were used to evaluate the impact of thermal stress (24-34ºC) during summer season (June, July and August) on egg production, fertility, hatchability and immune responses. The obtained results revealed that final body weight (FBW/g) and body weight change (BWC/g) among different chicken strains were not affected. The daily feed consumption (FC/g) and feed conversion ratio (FCR) for Silver Montazah and Inshas strains were significantly (p ≤ .05) higher than those of Matrouh and Mandarah strains. The mean egg production (EP/%) and egg mass (EM) for Silver Montazah and Inshas strains were significantly (p ≤ .05) higher than those of Matrouh and Mandarah strains. The highest percentages of hatchability of total eggs (HTE) and fertile eggs (HFE) were recorded in Inshas chickens, while the lowest value was recorded in Mandarah chickens. Also, the highest embryonic mortalities (p ≤ .05) and lowest chick weight at hatch (CWH/g) were recorded in Mandarah chickens compared with the other strains. The highest values for antibody titres against phytohemagglutinin-P (PHA-P) were recorded in Mandarah chickens, while the least values were recorded in Inshas chickens.     

Variance components for live weight, body measurements and reproductive traits of pair-mated ostrich females

Estimates of genetic parameters for reproductive traits, live weight and body measurements were obtained using data from a pair-mated ostrich flock at Oudtshoorn in South Africa. Reproductive traits included total egg and chick production, along with hatchability percentage. Live weight, chest circumference and tail circumferences were recorded at the commencement and cessation of breeding. Heritability estimates (h(2)) were 0.23 for egg production, 0.20 for chick production, 0.10 for hatchability, 0.20 to 0.34 for live weight, 0.12 for chest circumference and 0.30 to 0.38 for tail circumference. Female permanent environmental effects (c(2)) amounted to 0.18 for egg production, 0.18 for chick production, 0.21 for hatchability, 0.32 to 0.36 for live weight and 0.23 to 0.32 for chest circumference. Service sire exerted significant effects only on hatchability (0.22) and subsequently chick production (0.09). Genetic correlations of reproductive traits with live weight were low to moderate, variable in sign, and did not differ significantly from zero. Correlations between live weight recorded at the beginning and end of the breeding season were unity for additive genetic and permanent environmental effects. Egg and chick production were highly correlated genetically and phenotypically, with the genetic correlation exceeding the theoretical limit. In unconstrained analyses, hatchability was positively related to chick production, including at the service sire level. Selection gains in the current flock and future generations are likely. No significant adverse relationships were found between live weight, body measurements and reproductive traits.     

Evaluation of breeding objectives for purebred and crossbred selection schemes for adoption in indigenous chicken breeding programmes

1. The aim of the study was to evaluate the genetic and economic breeding objectives for an indigenous chicken (IC) breeding programme in Kenya.

2. A closed three-tier nucleus breeding programme with three breeding objectives and two selection schemes was simulated. The breeding objectives included IC dual-purpose (ICD) for both eggs and meat, IC layer (ICL) for eggs and IC broiler (ICB) for meat production.

3. Pure line selection scheme (PLS) for development of IC pure breeds and crossbreeding scheme (CBS) for the production of hybrids were considered. Two-and three-way crossbreeding strategies were evaluated under CBS and the impact of nucleus size on genetic gains and profitability of the breeding programme were investigated.

4. Males were the main contributors to genetic gains. The highest genetic gains for egg number (2·71 eggs) and growth traits (1·74?g average daily gain and 57·96?g live weight at 16 weeks) were realised under PLS in ICL and ICB, respectively.

5. The genetic response for age at first egg was desirable in all the breeding objectives, while that for fertility and hatchability were only favourable under ICL and PLS in ICD. Faecal egg count and immune antibody response had low, but positive gains except under PLS where the later was unfavourable. ICB was the most profitable breeding objective, followed by ICD and ICL under all the selection schemes.

6. Although PLS was superior in genetic gains and profitability and recommended in breeding programmes targeting ICL and ICB, a three line CBS should be considered in development of a dual-purpose breed.

7. Increasing the nucleus size beyond 5% of the IC population was not attractive as it resulted in declining profitability of the breeding programme.     

Breeding goals for the Kenya Dual Purpose goat. II. Estimation of economic values for production and functional traits

Economic values for production traits (milk yield, MY, kg; 12-month sale weight, LW, kg; consumable meat percentage, CMP) and functional traits (doe live weight, DoWT, kg; number of kids weaned, NKW; kidding frequency, KF; kidding rate, KR, %; doe weaning rate, DoWR, %; doe survival rate, DoSR, %; post-weaning survival rate, PoSR, %; pre-weaning survival rate, PrSR, % and; residual feed intake of yearlings, RFIgamma, kg and does RFId, kg) were estimated for the Kenya Dual Purpose goat (KDPG) for systems under two bases of evaluation. The production systems included smallholder low-potential (SLP), smallholder medium-potential (SMP) and smallholder high-potential (SHP), while the bases of evaluation considered were fixed flock-size and fixed feed resource. Under both bases of evaluation, economic values were highest in SMP apart from the economic values for feed intake-related traits (RFIy and RFId). In SMP, the economic values under fixed flock-size scenario were KSh 71.61 (LW), 20.90 (MY), 45.20 (CMP), 13.68 (NKW), 3.61 (KF), 6.52 (KR), 12.39 (DoWR), 22.96 (DoSR), 22.87 (PoSR), 13.18 (PrSR), -2.76 (RFIy) and -3.00 (RFId). The corresponding economic values under fixed feed resources scenario were KSh 73.28, 29.39, 45.20, 16.91, 4.76, 9.45, 13.84, 25.67, 25.15, 16.19, -2.76 and -3.00. Generally in all production systems, economic values for most traits were higher under fixed feed resource than under fixed flock-size scenario. In all systems, the economic values for most of the traits were sensitive to changes in prices of feed, milk and meat. The positive economic values for most traits under fixed flock-size scenario and fixed feed resource indicates that a unit increase in genetic merit for the traits would have a positive effect on the profitability of the systems.     

Breeding objectives for indigenous chicken: Model development and application to different production systems

A bio-economic model was developed to evaluate the utilisation of indigenous chickens (IC) under different production systems accounting for the risk attitude of the farmers. The model classified the production systems into three categories based on the level of management: free-range system (FRS), where chickens were left to scavenge for feed resources with no supplementation and healthcare; intensive system (IS), where the chickens were permanently confined and supplied with rationed feed and healthcare; and semi-intensive system (SIS), a hybrid of FRS and IS, where the chickens were partially confined, supplemented with rationed feeds, provided with healthcare and allowed to scavenge within the homestead or in runs. The model allows prediction of the live weights and feed intake at different stages in the life cycle of the IC and can compute the profitability of each production system using both traditional and risk-rated profit models. The input parameters used in the model represent a typical IC production system in developing countries but are flexible and therefore can be modified to suit specific situations and simulate profitability and costs of other poultry species production systems. The model has the capability to derive the economic values as changes in the genetic merit of the biological parameter results in marginal changes in profitability and costs of the production systems. The results suggested that utilisation of IC in their current genetic merit and production environment is more profitable under FRS and SIS but not economically viable under IS.     

Effects of thymol and isoeugenol feed supplementation on quail adult performance,egg characteristics and hatching success

1. A study was conducted to evaluate whether feed supplementation with thymol or isoeugenol can alter Japanese quail growth rate and final body weight, the female onset of puberty, hen-day egg production and the physical and chemical characteristics of the egg, as well as its potential to alter hatchability.

2. From 4 to 16 weeks of age, birds from each cage (1 male: 3 females) were assigned to 1 of 3 treatments that differed in the supplement added to the feed: control, thymol or isoeugenol (400?mg/kg). The average ages (d) at first egg lay (FIRST), at 25% egg production (A25% EP), at 50% egg production (A50% EP) and weekly and cumulative hen-day egg production (HDEP) were calculated. In addition, physical and chemical characteristics of the eggs, their fertility and hatchability were also evaluated for each group.

3. Feed supplementation did not significantly affect growth rate, final body weight, egg production parameters, fertility and physical characteristics of egg or most of the fatty acid components of the yolk.

4. The group treated with isoeugenol showed an increase in the percentage of palmitoleic fatty acid compared to the control, with thymol group showing intermediates values.

5. Both thymol and isoeugenol supplemented groups showed increased hatchabilities, by 18·8% and 11·8%, respectively, compared to their control counterparts.

6. The improvement in the hatching success of the eggs from the thymol and isoeugenol supplemented groups without a negative impact on their performance may have important economic implications for future breeding programmes, particularly if these effects generalise from quail to other more commercially important poultry species, such as chickens or turkeys.     

Effects of low dietary protein and different allocations of food during rearing and restricted feeding after peak rate of lay on egg production,fertility and hatchability in female broiler breeders

1. A 3x2x2 factorial experiment was conducted with boiler breeder females to determine the effects of body weight gain (three levels) and conventional or lower crude protein concentrations in the rations during rearing, and restricted or ad libitum feeding after the peak rate of lay on egg production, fertility, hatchability, mortality and food consumption. 2. Compared with ad libitum feeding, conventional food restriction resulted in a decrease in average daily food consumption of 0.6 during rearing, 0.2 during early lay and an increase of 0.4 after the peak rate of egg production. Mortality was decreased by more than half. 3. Restricted birds had higher total and settable egg production, fewer defective or damaged eggshells and higher fertility and hatchability than those fed ad libitum. The modified (more generous) rearing programme resulted in lower rates of egg production and higher rates of mortality compared with the conventional food restriction programme. 4. Low-protein rearing rations were associated with higher rates of food intake, higher mortalities and lower rates of egg production than the conventional protein rations. There were no differences in the fertility or hatchability of eggs between birds fed on the two concentrations of dietary crude protein. 5. Ad libitum feeding post-peak was associated with higher rates of mortality to 60 weeks of age. Post-peak feeding had little effect on the rate of lay or egg weight in conventionally restricted birds fed high protein rations or in birds fed ad libitum. Restricted feeding post-peak decreased the rate of lay and egg weight in birds on the modified restriction programme and in conventionally restricted birds fed on the low protein rations. There was no effect of post-peak feeding on fertility or hatchability of eggs. 6. The total numbers of saleable chicks per kg food consumed were 1.83, 1.72 and 0.52 for conventional, modified and ad libitum feeding during rearing; 1.56 and 1.15 for restricted and ad libitum feeding post-peak: there were no differences associated with protein concentrations of rations fed during rearing.     

Performance of indigenous, Khaki Campbell and their reciprocal crossbred layer ducks under different management systems

1. The performance of indigenous ducks (ID), Khaki Campbell (KC) and their reciprocal crossbred layers was studied from 19 to 58 weeks of age. For each genotype, 4 x 18 ducks (3 males + 15 females) were reared under a semi-intensive system (SIS) and an intensive system (IS) with standard management, and 4 x 50 ducks (8 males + 42 females) were reared in an extensive system (ES) with traditional management. 2. In comparison to KC, ID were superior in terms of age at first egg, age at 50% egg production, egg weight, hatchability, eggshell thickness with higher egg shape index. KC ducks were superior to ID in body weight, egg production and feed/kg eggs. Egg quality was similar among the genotypes. Crosses were superior to their parent breeds in age at first egg, egg production and feed/kg eggs. They were also superior to KC in egg weight and egg-shell thickness with a higher egg shape index. 3. The performance of genotypes in the SIS and the IS was similar and superior to the ES except for fertility and yolk colour. 4. Significant heterotic effects were recorded for age at first egg, age at 50% egg production, egg production per duck-day, feed efficiency and egg weight in crosses. Performance was similar in the reciprocal crosses, but superior to their parent breeds.     

Effect of production system and flock age on egg quality and total bacterial load in commercial laying hens

The shell of the egg is essential in providing shape to the egg and ensuring safe packaging of the internal contents; however, shell defects have been shown to increase the risk of microbial contamination of eggs. Eggs were collected from commercial cage and free-range flocks at the ages of 25, 35, 45, 55, 65, and 75 wk. From each collection per flock, 30 eggs were processed for the eggshell and egg internal quality determination, 30 eggs for cuticle estimation, 30 eggs for mammillary layer ultrastructural features scoring, and 60 eggs for egg microbial enumeration. Translucency score and shell reflectivity were significantly higher in free-range eggs and increased with flock age in both production systems. Egg weight, shell weight, percentage shell, shell thickness, albumen height, Haugh unit, and yolk color were higher for cage eggs. The amount of cuticle was higher in cage eggs and fluctuated with flock age in both production systems. For the mammillary layer ultrastructural variables, a significant effect of production system and flock age was observed for early fusion, Type A bodies, and Type B bodies, whereas aragonite, depression, erosion, and hole were rarely observed. Variability of mammillary cap size, the incidence of poor mammillary cap quality, incidence of late fusion, alignment, Type A bodies, Type B bodies, and cubic cone formation were greater in the free-range versus cage system and increased with flock age in both production systems. The incidence of confluence and early fusion were greater in cage eggs and decreased with age in both production systems. Significantly lower total microbial load was observed for cage compared with free-range eggs, but the overall bacterial load recorded in this study was low. It can be concluded that cage eggs were better in overall quality when directly compared with free-range eggs.     

丝羽乌鸡蛋品质对种蛋受精率和受精蛋孵化率的影响

试验就丝羽乌鸡蛋品质因素对种蛋受精率和受精蛋孵化率的影响进行了研究.结果显示,哈氏单位和蛋白高度越大,受精率和受精蛋孵化率越高(P＜0.01);蛋重对受精率有一定的影响,蛋重与受精率呈一定正相关关系(r=0.0619,P＜0.1),随着蛋重增加,受精率也会增大;蛋壳强度与受精蛋孵化率呈一定负相关关系(r=-0.1808,P＜0.1),蛋壳强度太大的鸡蛋其受精蛋孵化率反而下降;蛋壳颜色与受精率呈强的负相关关系(r=-0.2848,P＜0.01),即蛋壳颜色越深的鸡蛋其受精率越高;而蛋黄颜色与受精蛋孵化率呈强的负相关关系(r=-0.2328,P＜0.05),即蛋黄颜色越浅的鸡蛋受精蛋孵化率越高;蛋形指数、蛋壳厚度、蛋比重等指标对受精率及受精蛋孵化率未有显著影响.     

Comparison of performance and mortality in the Hybro Normal and Hybro Giant meat poultry breeders and their offspring

The performance and mortality of similarly managed parent flocks of Hybro Normal and Hybro Giant meat poultry was compared. The overall daily egg production at 6–9 months of age was insignificantly greater in the Hybro Normal compared to the Hybro Giant parents (p>0.05). The Hybro Normal parents had a significantly higher average daily egg production (56.08%) compared to that of the Hybro Giant parents (52.03%) during their sixth month of age, one month before the production peak (p<0.05). The Hybro Giant parent-males had a significantly higher average daily mortality during the sixth and seventh months of age compared to the parent males of the Hybro Normal breed (p<0.05); however, the females of the Hybro Normal parents had a significantly higher daily mortality during the sixth month of age compared to the Hybro Giant parent females (p<0.05). The percentage hatchability was significantly lower in eggs collected from the Hybro Giant birds compared to those collected from the Hybro Normal birds during the sixth and ninth months of age.The mean live weights at 45-days old of five flocks of Hybro Normal offspring was 1535 g compared to a mean live weight of 1870 g of five similarly managed flocks of the offspring of the Hybro Giant birds (p<0.05). The feed conversion by the offspring of both breeds was not significantly different (p>0.05). The mean percentage lameness in the five flocks of the offspring was 2.34% for Hybro Normal and 9.26% for Hybro Giant (p<0.05).In summary, the overall performance of the Hybro Normal parent stock was superior to the Hybro Giant breeders regarding egg production and hatchability of their eggs; however, the weight gain of the Hybro Giant broiler flocks was superior to that of the Hybro Normal, but this was associated with a higher incidence of lameness.     

仙湖肉鸭配套系的选育进展

为了进一步稳定和提高仙湖肉鸭配套系的质量和生产性能水平,利用佛山科学技术学院科研禽场仙湖肉鸭核心群第6世代的种鸭,采用家系选育和个体选育相结合的品系选育方法,经过4个世代的系统选育,获得了较大的遗传进展。第10世代A系肉鸭49日龄平均活重达3.89千克,饲料转化率为2.69,胸腿肌率达24.3%;B系第9世代种鸭64周龄平均产蛋量达210个,种蛋受精率和入孵蛋孵化率分别为88.4%、83.5%。     

Genetic-economic evaluation of traits in a broiler enterprise: the relative genetic-economic values

Selection for growth rate and food utilisation (assuming annual genetic gains of 3 and 1.5% respectively) have about the same economic value and account for 94.3% of the annual potential economic savings in the production costs of an integrated broiler enterprise. Selection for more hatching eggs (annual genetic gain of 1.7 eggs) accounts for only 4.2% and selection for fertility, hatchability and reduced mortality have a value of less than 1% each. The introduction of the dwarf gene (dw) has a questionable economic value. Even if growth rate and fertility are not reduced by using dwarf females, the economic importance will equal no more than two generations of selection for growth rate. As egg production increases, the relative economic value of growth rate and food utilisation will increase, while the advantage of using dwarf females will decrease. Both body weight and body fat content (which are correlated with food utilisation) are moderately heritable and if body fat can be measured reliably in live birds, this may aid breeding for economic advantage.     

加丽素红对海兰蛋鸡生长及产蛋性能的影响

试验探讨加丽素红对海兰蛋鸡生长及产蛋性能的影响,为加丽素红在畜牧养殖业中的合理使用提供依据。试验采用随机分组的方法,设立一个对照组、两个剂量组(分别添加80和8 000 mg/kg加丽素红)。每组海兰蛋鸡36只,分别饲喂基础饲料和添加不同剂量加丽素红的饲料。结果表明,通过对鸡的体重、平均日增重、平均日采食量、料重比等生长性能指标的统计分析,加丽素红对上述指标无显著影响;通过对开产蛋重、产蛋率、平均蛋重等产蛋性能的统计分析,加丽素红对上述指标无显著影响;但加丽素红可以使蛋鸡的开产日龄提前。     

复合益生菌发酵饲料对纳雍土鸡生长性能、屠宰性能和肉品质的影响

文章旨在研究复合益生菌发酵饲料对纳雍土鸡生长性能、屠宰性能和肉品质的影响,试验采用单因素试验设计,将120只40日龄的健康纳雍土鸡随机分成2组(对照组和试验组),对照组饲喂基础日粮,试验组饲喂复合益生菌发酵饲料,检测平均日增重、平均日采食量、料重比、屠宰率、半净膛率、全净膛率、胸肌率、腿肌率、a*值、b*值、L*值、p...     

Dynamic Modelling of a Traditional African Chicken Production System

A dynamic stochastic model, SimFlock, was developed with the purpose of simulating the dynamics of a traditional African chicken flock at smallholder level. The model simulates outputs, e.g. total number of chickens produced, egg production and net return after entering flock, or area-specific biological parameters. Biological parameters include hatchability, egg production, growth and survival of various age groups, full-grown weights as well as some decision parameters like farmers' need for meat consumption, and slaughtering and selling age of chickens. A simulation job is defined by 'states of nature' (biological parameters specified directly or drawn at random from the hyperparameters), number of replications and number of days to be simulated. Three simulation jobs were selected to demonstrate the use of the model: one with the default settings; one with collection of eggs for 20 days; and one in which growth rate was increased to double. After simulation, the results of each job were compared in relation to total number and weight of chickens produced, egg production and net return. SimFlock could be used as a management or extension tool to identify the biological parameters of major influence on production. Improvement of these parameters will have the largest impact on output.     

Farmers’ breeding practices and traits of economic importance for indigenous chicken in RWANDA

Data on breeding practices and traits of economic importance for the indigenous chicken (IC) were collected through personal interviews using structured questionnaires and direct observations of chicken management practices. The study was conducted from November 2015 to January 2016 in Rwamagana, Rulindo, Ruhango, Kicukiro and Muhanga districts of Rwanda. Data were collected and analysed through computation of indices, which represented a weighted average of all rankings of a specific trait. Spearman’s non-parametric rank correlation was calculated for ranking of traits of economic importance to indicate the directional effects. The results on chicken ecotypes and their attributes showed that prolificacy, mature weight, disease tolerance, egg number and heat tolerance were highly preferred. The dwarf ecotype was most abundantly reared (38.84%) and considered to be significantly smaller and to have poorer growth rate, but to have better prolificacy than other indigenous chicken ecotypes. Selection of breeding cock and hen was based on disease tolerance, body weight at sexual maturity, body size and growth rate. In addition, for hen, mothering ability and egg fertility (Fer) were considered. Indices for the traits perceived by farmers as of primary economic importance were egg yield (0.093), disease tolerance (0.091), high growth rate (0.089), prolificacy (0.088), high body weight (0.087) and egg fertility (0.083). The most important traits considered by the marketers were body weight (BW), disease tolerance (Dtol), plumage colour (Pcol), egg yolk colour (EYC), meat quality (MQ), growth rate (GR) and egg yield (EY) whereas for consumers, meat quality, egg yolk colour, egg yield, body weight and growth rate were considered. Among traits perceived as important by farmers, a positive and significant correlation was found between BW and GR and Fer. Correlation was moderate for BW and prolificacy, drought tolerance (Drtol), Dtol and EYC. BW was negatively correlated with temperament (Temp), heat tolerance, Pcol and egg shell colour (ESC). Regarding marketers and consumers’ preference rank correlation, positive and significant correlation was between BW and GR and MQ. As such, appropriate ecotypes (indigenous chicken) which have these characteristics need to be identified and utilised more based on their performance and adaption to the environment conditions to ensure efficient IC production.     

Guinea fowl (<Emphasis Type="Italic">Numidia meleagris</Emphasis>) production by small-holder farmers in Zimbabwe

Guinea fowls are a source of high-value meat and eggs, and the birds are more disease resistant than other types of birds. A survey was conducted in ward 23, Chipinge district, Zimbabwe, to characterise guinea fowl management practices and to identify constraints and potential opportunities for increased guinea fowl productivity. Purposive sampling was used to select 84 out of possible 252 guinea fowl owners. Data were collected by direct observation on guinea fowl varieties, feeding strategies and housing facilities. A semi-structured questionnaire was used to collect data on farmer experiences, perceptions and common challenges encountered. A chi-squared test was conducted using the IBM SPSS Statistical Package for Social Sciences (SPSS) version 21. The study revealed that famers keep guinea fowls under free-range management. The average production indices were flock size 18 ± 12, egg production 89 ± 50, hatchability 63.8% and keet survival rate of 75%. Approximately 42.9% of the farmers provide supplementary feed albeit not systematically. There was a significant association between provision of supplementary feed and keet survival rate (χ ² = 21.600, df = 2, P < 0.016) as well as provision of housing and flock size (χ ² = 38.508, df = 3, P < 0.018). The housing provided was substandard. Major challenges faced by farmers were predation, low hatchability and lack of access to profitable markets. The provision of supplements and better housing for birds could improve guinea fowl productivity.     

Associations between genotypes at codon 171 and 136 of the prion protein gene and production traits in market lambs

OBJECTIVE: To determine whether selection for the homozygous A136 R171 genotype that confers resistance to classic scrapie infection negatively affects production traits in sheep. ANIMALS: 996 commercial lambs obtained from 2 flocks at separate locations across 3 consecutive years. Procedures-Genotyping at codon 136 and 171 was performed by use of commercially available testing or a single-nucleotide polymorphism assay. Carcass data were collected without knowledge of genotype approximately 24 hours after slaughter by an experienced grader. The model to analyze associations between prion protein (PRNP) genotype and production traits was based on genotype, breed, or both as fixed effects and days on feed as a covariate. RESULTS: Average daily gain was significantly associated with only combined codons 136 and 171. In flock 1, weaning average daily gain was significantly greater in AA136 sheep than heterozygotes; the difference between QR171 and RR171 sheep, compared with QQ171 sheep, were not significant although QR171 and RR171 sheep had higher values. However, in flock 2, average daily gain was significantly greater in AV136 sheep than AA136 sheep and in QR171 sheep than QQ171 sheep. CONCLUSIONS AND CLINICAL RELEVANCE: Findings suggest there is an advantage for average daily gain in lambs with an arginine allele at codon 171, but there were no other genotype effects on production traits. Thus, selection for the resistant arginine allele at codon 171 to comply with USDA scrapie eradication guidelines should not be detrimental to lamb production in commercial flocks. Effects of codon 136 on average daily gain were ambiguous.