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1.
Evaluation of the efficiency of alternative two-tier nucleus breeding systems designed to improve meat sheep in Kenya 总被引：1，自引：0，他引：1
M.G. Gicheha I.S. Kosgey B.O. Bebe & A.K. Kahi 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2006,123(4):247-257
A deterministic approach was used to genetically and economically evaluate the efficiency of five two‐tier nucleus breeding systems for meat sheep in Kenya. The nucleus breeding systems differed in terms of whether the system was closed or open, in the type of animals that were involved in the movement of genetic superiority and in the number of selection pathways in each system. These systems were compared under four alternative breeding objectives based on monetary genetic gain and profit per ewe. The first objective simulated a situation where the flock size cannot be increased due to non‐feed related constraints (FLOCK). The second specifically assumed that the flock size is restricted due to limited amount of feed resources (FEED). The third and fourth objectives assumed that sheep performed only tangible roles (TR) and both tangible and intangible roles (IR) in the production system respectively. Monetary genetic gains were highest for all objectives in an open nucleus system with a certain proportion of commercial‐born ewes being introduced in the nucleus while at the same time utilizing young rams from the nucleus to breed sires and dams for the nucleus and commercial sector (ONyre). Utilizing young rams in a closed nucleus system for the dissemination of superior genes resulted in higher annual monetary genetic gain than utilization of old rams. Profit per ewe was significantly higher for FLOCK and IR in ONyre. In a closed system that allowed for downward movement of dams from the nucleus to the commercial sector to breed sires and dams, profit per ewe was highest for FEED and TR. The success of a nucleus breeding system should also focus on the profitability and logistics of establishing it. The implication of these results on the choice of two‐tier nucleus breeding systems for the improvement of meat sheep is discussed. 相似文献
2.
The importance of genotype x environment (region or management system) interactions for carcass traits in Japanese Black cattle was investigated using both univariate and multivariate animal models. The univariate approach was used mainly to test the significance of interaction effects. The multivariate approach was used to estimate genetic correlations, which indicated the magnitude of genotype x environment (GE) interactions. The more a genetic correlation deviates from 1, the larger the interaction. From the univariate approach, the addition of genotype x environment (region or management system) interaction (co)variance components resulted in an improved fit of the model for all traits in both cases (P < 0.001). However, estimates of genetic correlation between regions obtained from the multivariate approach for hot carcass weight, LM area, rib thickness, s.c. fat thickness, and marbling score were 0.97, 0.95, 0.93, 0.97, and 0.93, respectively. The corresponding estimates between management systems were 0.84, 0.92, 0.84, 0.90, and 0.97, respectively. These results indicate that GE interaction effects on carcass traits of Japanese Black cattle may be biologically unimportant. Therefore, breeding values obtained using the multivariate method would rank sires similarly in all environments. Consequently, carcass traits measured in these two different regions or management systems can be treated as the same traits. 相似文献
3.
Indigenous chicken (IC) and their production systems were characterized to understand how the whole system operates for purposes
of identifying threats and opportunities for holistic improvement. A survey involving 594 households was conducted in six
counties with the highest population of IC in Kenya using structured questionnaires. Data on IC farmers’ management practices
were collected and analysed and inbreeding levels calculated based on the effective population size. Indigenous chicken were
ranked highest as a source of livestock income by households in medium- to high-potential agricultural areas, but trailed
goats in arid and semi-arid areas. The production system practised was mainly low-input and small-scale free range, with mean
flock size of 22.40 chickens per household. The mean effective population size was 16.02, translating to high levels of inbreeding
(3.12%). Provision for food and cash income were the main reasons for raising IC, whilst high mortality due to diseases, poor
nutrition, housing and marketing channels were the major constraints faced by farmers. Management strategies targeting improved
healthcare, nutrition and housing require urgent mitigation measures, whilst rural access road network needs to be developed
for ease of market accessibility. Sustainable genetic improvement programmes that account for farmers’ multiple objectives,
market requirements and the production circumstances should be developed for a full realization of IC productivity. 相似文献
4.
Tobias O. Okeno Thomas M. Magothe Alexander K. Kahi Kurt J. Peters 《Tropical animal health and production》2012,45(1):193-203
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. 相似文献
5.
A functional herd dynamics model was developed to estimate the effect of culling age on milk and meat production for Japanese-Saanen goats in relation to changes in prices of milk and meat. The model simulates life cycle production of bucks and does and their kids. Every production trait is first modelled as an individual trait and thereafter as a trait in the herd using a herd dynamics model. At the individual level, the survival curve function, the litter size function and the production traits function are combined. Data on growth and lactation were used to fit growth and lactation curves to estimated parameters using non-linear least squares regression technique and used in the production traits function. Using herd dynamics, the individual level functions are combined with the total number of animals function to estimate the total herd output and income efficiency at the herd level. Here, variables of culling days including the effect of difference in meat price value among goat categories (bucks, does, male kids and female kids) are used. Analysis of interrelations among the culling days of does, the price ratio and the income efficiency indicated that optimal culling days of does was shortened with an increase in the price ratio of meat to milk. However, when meat price value was different among goat categories according to actual situation of Japanese goat production, the optimal culling days of does could be fixed regardless of the change in price ratio and was calculated as 1730 days. This functional herd dynamics model can aid in decision-making regarding culling under several situations especially when there is a wide fluctuation in prices at local markets. 相似文献
6.
Genetic and phenotypic parameters and annual trends for milk production and fertility traits of the Sahiwal cattle in semi arid Kenya 总被引：1，自引：0，他引：1
Data comprising 7211 lactation records of 2894 cows were used to estimate genetic and phenotypic parameters for milk production
(lactation milk yield, LMY and lactation length, LL) and fertility (calving interval, CI; number of services per conception,
NSC and age at first calving, AFC) traits. Genetic, environmental and phenotypic trends were also estimated. Variance components
were estimated using univariate, bivariate and trivariate animal models on based restricted maximum likelihood procedures.
Univariate models were used for each trait, while bivariate models were used to estimate genetic and phenotypic correlations
between milk production and fertility traits and between LMY, LL, CI and NSC within each lactation. Trivariate models were
used in the analysis of LMY, LL, CI and NSC in the first three lactations. Heritability estimates from the univariate model
were 0.16, 0.07, 0.03, 0.04 and 0.01 for LMY, LL, CI, AFC and NSC, respectively. The heritability estimates from trivariate
analysis were higher for milk production traits than those from univariate analyses. Genetic correlations were high and undesirable
between milk production and fertility traits, while phenotypic correlations were correspondingly low. Genetic trends were
close to zero for all traits, while environmental and phenotypic trends fluctuated over the study period. 相似文献
7.
The objectives of this study were to estimate the environmental and additive and non-additive genetic effects on lactation curve and lactation parameters of crosses of Holstein (H), Brahman (B) and Brown Swiss (BS) in Olancho region in Honduras. The data consisted of 54,517 milk yield records from 192 dual-purpose crossbred cows lactating from 2000 to 2005 at the Universidad Nacional de Agricultura de Honduras (UNA). The lactation curve and lactation parameters of interest were the scaling factor to represent yield at the beginning of lactation (a), the factor associated with the inclining (b) and declining (c) slopes of the lactation curves, and the milk yield at initial day of lactation (MY20), peak milk yield (MYmax), day at peak milk yield (tmax), and the total milk yield (TM) per lactation, respectively. The incomplete gamma function (Wood function) was used to estimate lactation curve and lactation parameters from daily milk records of H × B, H × BS and BS × B crossbred cows. The environmental, additive and non-additive genetic effects on lactation curve and lactation parameters were estimated using Dickerson and Kinghorn models. The coefficients of determination of fitness of Wood's function (R2) ranged from 80% to 97% with an average of 93%. The lactation curve of the crossbred cows was similar to those reported for dairy cows grazing in the tropics. Lactation parameters such as MYmax, tmax and TM were significantly (P < 0.05) influenced by environmental sources of variation suggesting the necessity of differential management strategies. The moderate to large positive phenotypic correlation of MYmax and TM indicate that one of the milk yield parameters could be used as a selection criterion to improve either one or both traits. Despite the fact that both genetic models showed similar patterns, the absolute value of the parameters varied. For both models, individual additive genetic breed effect for H breed were significant (P < 0.05) and contributed more to TM than the BS breed. In the Dickerson model, highly positive significant (P < 0.01) effect on TM for H×BS and BS×B crosses was found. The Kinghorn model did not show significant effects of dominance on this parameter. The estimate of recombination effect for all crosses involving B breed were negative and significant (P < 0.05) for positive correlated lactation curve parameters. Although the inclusion of non-additive effects on crossbreeding genetic effects were not all significant for lactation curve and lactation parameters, non-additive effects should be taken into account to improve the Honduran dairy cattle production management. 相似文献
8.
This study estimated genetic and phenotypic parameters and annual trends for growth and fertility traits of Charolais and
Hereford cattle in Kenya. Traits considered were birth weight (BW, kg), pre-weaning average daily gain (ADG, kg/day) and weaning
weight (WW, kg); calving interval (CI, days) and age at first calving (AFC, days). Direct heritability estimates for growth
traits were 0.36 and 0.21; 0.25 and 0.10; 0.23 and 0.13 for BW, ADG and WW in Charolais and Hereford, respectively. Maternal
heritability estimates were 0.11 and 0.01; 0.18 and 0.00; 0.17 and 0.17 for BW, ADG and WW in Charolais and Hereford, respectively.
Direct-maternal genetic correlations ranged between −0.46 and 1.00; −0.51 and −1.00; −0.47 and −0.39 for BW, ADG and WW in
Charolais and Hereford, respectively. Genetic correlations ranged from −0.99 to unity and −1.00 to unity for growth and fertility
traits respectively. Prospects for improvement of growth and fertility traits exist. 相似文献
9.
Economic values for production and functional traits and assessment of their influence on genetic improvement in the Boran cattle in Kenya 总被引：1，自引：0，他引：1
T.O. Rewe D. Indetie J.M.K. Ojango & A.K. Kahi 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2006,123(1):23-36
Economic values for production (sale weight in steers, SWs, kg and heifers, SWh, kg; dressing percentage, DP; consumable meat percentage, CMP and milk yield, MY, kg) and functional (cow weight, CoWT, kg; cow survival rate, CoSR, %; postweaning survival rate, PSR, %; feed intake of cows, FIc, heifers, FIh and steers, FIs, kg DM) traits were estimated for six production systems utilizing the Boran breed in Kenya. The influence of the estimated economic values on genetic improvement was also assessed using different selection indices. The six production systems were described according to their sale age, levels of input and final goal, namely, short‐fed medium input beef (SMB); long‐fed medium input beef (LMB); short‐fed high input beef (SHB); long‐fed high input beef (LHB); long‐fed low input dual purpose (LLD); and long‐fed medium input dual purpose (LMD). Two evaluation bases were considered: fixed herd size and fixed pasture input. In the fixed herd‐size situation, the economic values for production (except MY in beef systems) and functional traits (except FI in all systems) were positive meaning a unit increase in genetic merit of these traits had greater influence on revenues than costs. As expected, the economic value for MY was negative in the pure beef systems (SMB, LMB, SHB and LHB) and positive in the dual‐purpose systems (LLD and LMD). When compared with the economic values estimated in the fixed herd‐size situation, in the fixed pasture input situation they were lower for feed intake in the three classes of livestock and other traits related to it in all systems. These traits were CoSR, CoWR, PSR, CoWT, SWh and MY. The economic values for CoWT in LLD and LMD were negative (KSh ?11.14 and ?15.33 respectively). The economic values did not influence much the direction of the genetic response in each trait in the different production systems. However, the magnitude of the actual gain was dependent on the index applied. The magnitude of the economic values for production and functional traits estimated in this study suggest that genetic improvement of these traits will have a positive effect on profitability of Boran cows kept in dual‐purpose systems and when herd size is restricted. In beef systems, genetic improvement of MY will have a negative effect on profitability, especially when restrictions on herd size and feed exists. 相似文献
10.
Direct and maternal (co)variance components,genetic parameters and annual trends for growth traits of Dorper sheep in semi-arid Kenya 总被引：2，自引：2，他引：0
Kariuki C. M. Ilatsia Evans D. Kosgey Isaac S. Kahi Alexander K. 《Tropical animal health and production》2010,42(3):473-481
Genetic and phenotypic parameters were estimated for lamb growth traits for the Dorper sheep in semi-arid Kenya using an animal
model. Data on lamb growth performance were extracted from available performance records at the Sheep and Goats Station in
Naivasha, Kenya. Growth traits considered were body weights at birth (BW0, kg), at 1 month (BW1, kg), at 2 months (BW2, kg),
at weaning (WW, kg), at 6 months (BW6, kg), at 9 months (BW9, kg) and at yearling (YW, kg), average daily gain from birth
to 6 months (ADG0–6, gm) and from 6 months to 1 year (ADG6–12, gm). Direct heritability estimates were, correspondingly, 0.18, 0.36, 0.32, 0.28, 0.21, 0.14, 0.29, 0.12 and 0.30 for BW0,
BW1, BW2, WW, BW6, BW9, YW, ADG0–6 and ADG6–12. The corresponding maternal genetic heritability estimates for body weights up to 9 months were 0.16, 0.10, 0.10, 0.19, 0.21
and 0.18. Direct-maternal genetic correlations were negative and high ranging between −0.47 to −0.94. Negative genetic correlations
were observed for ADG0–6–ADG6–12, BW2–ADG6–12, WW–ADG6–12 and BW6–ADG6–12. Phenotypic correlations ranged from 0.15 to 0.96. Maternal effects are important in the growth performance of the Dorper
sheep though a negative correlation exists between direct and maternal genetic effects. The current study has provided important
information on the extent of additive genetic variation in the existing flocks that could now be used in determining the merit
of breeding rams and ewes for sale to the commercial flocks. The estimates provided would form the basis of designing breeding
schemes for the Dorper sheep in Kenya. Implications of the study to future Dorper sheep breeding programmes are also discussed. 相似文献