INCREASING BEEF-PRODUCTION FROM DAIRY-COWS BY IMPLANTING EMBRYOS FROMMOET NUCLEUS BREEDING SCHEMES FOR BEEF-CATTLE

A closed nucleus breeding program for beef cattle, to increase beef pr oduction from the dairy herd, was studied. The nucleus will produce pu rebred beef embryos for implantation into dairy cows. The breeding goa l was an acceptable level of dystocia and a good beef production abili ty of beef calves born out of dairy cows, that did not produce dairy r eplacements. The selection of the founder beef breed, from which the n ucleus is established, should be based on its genetic level of daily g ain minus that of birth weight, when both expressed in their genetic s tandard deviation units. If initial birth weight is too high, which is probably the case for the continental European beef breeds, restricte d selection is applied to decrease birth weight and maintain daily gai n until acceptable birth weights are attained. Then, selection is for daily gain while keeping birth weights constant. Effects of nucleus si ze, number of offspring per donor, number of nucleus sires, genetic co rrelation between birth weight and daily gain, and sex ratio on geneti c gain and its variance are studied. Increasing the nucleus size, with equal number of sires, had a larger effect on the selection response than on the variance of the response. An increasing number of offsprin g per donor increased genetic gain as well as its variance. Highest ex pected genetic gain was achieved for selecting 4 to 8 sires per year i n the nucleus sizes studied. The optimal sex ratio was close to 0.5 in optimal schemes. If the difference between initial and acceptable bir th weights was 3 or 8 kg, expected time till attaining acceptable weig hts of 1.9 or 5.1 years, respectively, were found.