A simulation study Using Matrix formulation was used to asses the flow of genes from the nucleus to the commercial population for three nucleus dairy cattle crossbreeding schemes involving indigenous (Zebu or native ) and exotic (European) animals under Kenyan conditions: Artificial insemination (A.I.) or natural mating F{sub 1} production, continuous crossbred (F{sub 2} inter se) production and multiple ovulation and embryo transfer (MOET) F{sub 1} production. The latter two schemes used MOET in the nucleus. cumulative discounted expressions (CDES) and cumulative discounted Revenues (CDR) were calculated to rank these schemes. The Pathways considered were sires and dams to produce sires and dams. The evaluation Criterion was milk production measured in age class 3 through 10 in F{sub 1} and F{sub 2} cow populations. the schemes were evaluated over a 30-year projected period with assumed interest rates of 0% and 10%. Further, the genetic level between the indigenous nucleus animals, the F{sub 1} males and commercial female population was calculated by defining the incidence vector h as the difference between the three groups. The F{sub 1} A.I. or natural scheme had higher CDES of 0.978 and 0.161 at 0% and 10% interest rates respectively. The corresponding values for F{sub 1} MOET scheme were 0.735 and 0.070 and those of F{sub 2} inter se were 0.676 and 0.079 at 0% and 10% interest rates, respectively. For a nucleus with 64 dams, CDR (US$) were 95.50 and 15.80 at 0% and 10% interest rates, respectively for F{sub 1} A.I. or natural scheme. The F{sub 1} MOET scheme had corresponding values of 62.05 and 6.90 while F{sub 2} inter se had 66.10 and 7.75. Under both interest rates, the F{sub 1} A.I. or natural mating schemes had higher CDES and CDR than the other two schemes and is faster in dissemination of genes to the commercial population. F{sub 2} inter se was intermediate. The genetic level of nucleus animal is higher than of F{sub 1} male and females because indigenous nucleus females contribute 50% of the genes. F{sub 2} cows are expected to lag behind F{sub 1} males genetically because the latter are used as parents of F{sub 2} cows. In conclusion, although CDES and CDR are higher for the F{sub 1} A.I. or natural mating schemes using inter se mating are promising in terms of logistics and combination of breed effects as indicated in other studies.

The ranking of genotypes (i.e., breeds and breed crosses) for economic performance depends on the production circumstances of the herd and the criteria for economic evaluation. In this study, the effects of evaluation criteria and production circumstance are quantified using data from the literature on six genotypes. The economic evaluation criteria measured at herd level included lifetime profit and lifetime profit expressed per day of calving interval, per day of productive lifetime, per day of total herd life, per unit of milk, and per unit of feed energy. Four production circumstances were studied; these circumstances included constraints on the output of milk and on herd use of concentrates, roughages, and both concentrates and roughages. Profit was determined based on the sale of milk, calves, cull cows, and heifers and the expenses incurred for concentrates and roughages, animal deaths, milking time, interest, and other inputs.Results indicate that production circumstances and evaluation criteria largely influence the ranking of genotypes and, therefore, the outcome of economic comparisons. The genotype that ranks the best under a certain criteria and circumstance ranks differently when these situations are altered. In economic comparisons of genotypes aimed at offering recommendations for implementation in smallholder dairy production systems in the tropics, the choice of the evaluation criteria should be determined by the limitation or constraint that characterizes the area where the genotypes are to produce or are currently producing. For example, for situations in which feed availability is limiting, genotypes should be ranked on total profit per unit of feed energy.The ranking of genotypes (i.e., breeds and breed crosses) for economic performance depends on the production circumstances of the herd and the criteria for economic evaluation. In this study, the effects of evaluation criteria and production circumstance are quantified using data from the literature on six genotypes. The economic evaluation criteria measured at herd level included lifetime profit and lifetime profit expressed per day of calving interval, per day of productive lifetime, per day of total herd life, per unit of milk, and per unit of feed energy. Four production circumstances were studied; these circumstances included constraints on the output of milk and on herd use of concentrates, roughages, and both concentrates and roughages. Profit was determined based on the sale of milk, calves, cull cows, and heifers and the expenses incurred for concentrates and roughages, animal deaths, milking time, interest, and other inputs.Results indicate that production circumstances and evaluation criteria largely influence the ranking of genotypes and, therefore, the outcome of economic comparisons. The genotype that ranks the best under a certain criteria and circumstance ranks differently when these situations are altered. In economic comparisons of genotypes aimed at offering recommendations for implementation in smallholder dairy production systems in the tropics, the choice of the evaluation criteria should be determined by the limitation or constraint that characterizes the area where the genotypes are to produce or are currently producing. For example, for situations in which feed availability is limiting, genotypes should be ranked on total profit per unit of feed energy.