THE GENETIC EVALUATION OF BEEF SIRES USED FOR CROSSING WITH DAIRY-COWS IN THE UK - 1 - SIRE BREED AND NONGENETIC EFFECTS ON CALVING SURVEY TRAITS

An analysis has been carried out of over 88000 calving survey records for bulls of eight beef breeds tested in commercial dairy herds in Eng land and Wales. The data were collected from 1981 to 1993. The traits analysed were the degree of difficulty at calving, assessed from no di fficulty to serious difficulty, calf mortality to 48 h, gestation leng th, and subjective assessments of calf size and conformation. Major si re breeds in the survey were the Hereford (30070 records, 93 sires), C harolais (25816 records, 105 sires) and the Limousin (15420 records, 5 5 sires). Other sire breeds were Belgian Blue (5391 records, 24 sires) , Simmental (3864 records, 19 sires), Aberdeen Angus (2886 records, 12 sires), Piedmontese (2423 records, 7 sires) and the Blonde d'Aquitain e (2271 records, 8 sires). Information was routinely recorded on cow a ge (heifer or mature), sex of the calf, and the year and month of the calving, while cow size and the regional location of the herd were als o recorded in later years. Heifers had more difficult calvings, higher calf losses and shorter gestations than mature cows (all P < 0.05) Se riously difficult calvings and calf mortality were higher for male cal ves, which were also larger and had better conformation than heifer ca lves (P < 0.05). Sire breed effects were significant for all traits, a lthough sire breed ranking for calving ease was different for cow and heifer calvings and some interactions involving sire breed were also s ignificant. For cow calvings, the easiest calving breeds were the Here ford (1.1%) and the Aberdeen Angus (2.4%), while the Charolais (4.3%), Blonde d'Aquitaine (3.7%) and Simmental (3.1%) had most difficult cal vings. Gestation length differed between sire breeds, from Aberdeen An gus (281.0 days) and Hereford (282.7 days) up to the Limousin (288.1 d ays) and the Blonde d'Aquitaine (289.0 days). For calf size and confor mation, the Simmental, Charolais and Blonde d'Aquitaine were the best. In general, summer months were associated with lower incidences of di fficult calvings, lower losses and shorter gestations. Large cows had calves which were larger and of better conformation than small or medi um cows, but large cows also had longer gestations, more difficult cal vings and poorer calf survival (all P < 0.05). Statistical models are discussed that should be used for the genetic evaluation of calving su rvey traits, when beef bulls are to be used in dairy herds in the Unit ed Kingdom.