EFFECTS OF MAIZE AND ALFALFA GENOTYPES ON DAIRY-COW PERFORMANCES

In this trial, we attempted to evaluate the effects of alfalfa and mai ze genotypes fed to dairy cows. These genotypes were chosen from recor ds of previous trials with sheep for either their high or low digestib ility. Thirty-two cows were fed a diet based on maize silage ad libitu m (M+ or M- genotype) and alfalfa (A+ or A-) pellets (4.35 kg/day) in a 2 x 2 factorial experiment. Silage intake, milk yield and compositio n, body weight and body condition scores were recorded during the 15-w eek experiment. The maize genotype of high digestibility (M+) tended t o be ingested in larger quantities (14.4 vs 14.0 kg/cow/d) than the ot her genotype (M-), although showing a lower dry matter content (29.5 v s 31.2%). With this improved genotype, the milk yield was significantl y higher (28.1 vs 26.9 kg/cow/day; P=0.01) without decreasing effects in the fat and protein content of the milk, but with the cows increasi ng their body reserves (28.1 kg, P< 0.01). No differences were observe d in the body condition scores. The alfalfa effects were not so acute, but the distribution of the improved genotype (A+) improved the daily milk yield (28.0 vs 27.0 kg/day, P = 0.03) and the body condition sco res (P = 0.04). These principal effects appeared to be additive. The d iet built with the best genotypes (M+ A+ diet) provided 2.2 kg milk/co w/day more than with the inferior ones (M- A- diet), displaying a high er body weight gain and better body conditions, without showing any ne gative effects on the fat and protein contents. Thus, the choice of a given genotype (maize or alfalfa in this case) may have strong effect on cow performances. In the European Union, where each farmer has a mi lk quota, the choice of an improved maize or alfalfa genotype could be essential in limiting production costs.