Embryo transfer for dissemination of κ-casein bb genotype and improvement of milk clotting properties

Background and Objective: Milk production and cheese industries need to balance the genetic progress in milk yield and protein content with the need for improving milk coagulation properties and workability. Our objective was to determine how rapidly and to what extent Milk Clotting Properties (MCP) could be improved by using Embryo Transfer (ET) to increase the frequency of the κ-casein BB genotype and reducing A and E variants in an Italian Holstein herd with a low prevalence of the favorable genotype. Materials and Methods: In a herd of 352 cows, with a relatively low distribution of the favorable κ-casein BB genotype (11.0%) and poor milk clotting properties, κ-casein BB animals were superovulated (36 out of 39) and bred with SexedULTRA™ sex-sorted semen of κ-casein BB bulls in order to improve milk workability and cheese yield. Forty-five embryo transfer sessions yielded 203 embryos, 108 pregnancies and 98 females, of which 89 calved and entered the first lactation. Results: Milk composition and coagulation properties differed significantly among the groups considered (p<0.05) and were more favourable for cheese-making in the groups with a higher percentage of κ-casein BB animals whose tank and pool milk samples consistently showed greater (p<0.05) fat, protein, casein and κ-casein B content and improved clotting properties with lower (p<0.05) r and k20 and higher (p<0.05) a30. Conclusion: In the relatively short period of the project, the embryo transfer program allowed the establishment of a herd whose milk has considerably improved composition and clotting properties