MODE OF MANAGEMENT FOR 30-MONTH-OLD STEERS IN DAIRY BREEDS [French]

摘要

The effects of several modes of cattle management were tested on the increase of production characteristics in 30-month-old steers from Normandy, fattened on grass, using dairy breed steers (Friesian and Normand). The first trial evaluated the effects of pasture grazing on steers before they reached I year of age, and the type of feed (maize or grass silage) consumed during the winter, when the animals were brought indoors, between 9 and 14 months of age. In the 2nd trial, the 2 growth rates between 4 and 14 months were compared. Here, the effect of succeeding periods of nutrition restriction during winter and high feed supply in pasture were studied. In trial 3, the restriction period occurred between 21 and 26 months. In the 4th trial, there were 2 periods of restriction, between 9 and 14 months and between 21 and 26 months. The measurements of the live weights and growth rates were recorded (table III). The body and carcass composition at slaughter were also measured (tables IV and V). A total of 275 steers were slaughtered at 707 kg live weight They had a mean carcass weight of 375 kg. Their carcasses were analysed to be 65.7% lean and 17.7% fat. Steers that experienced pasture grazing before I year of age had an advantage over the steers at the transition at the 2nd grazing at 14 months (fig 1). On d 15, these steers were 25 kg (live weight) heavier and this advantage was conserved until slaughter, where they had the same carcass composition after a 38 d shorter fattening period. Thus, steers that had grazed before attaining I year of age had a better adaptability at the next grazing period at 14 months. The nature of the silage used during the winter between 9 and 14 months had no effect on the subsequent growth and eventual carcass composition. In the 2nd trial, steers that had a high level of growth before reaching 9 months of age had a subsequent advantage which was conserved and permitted a shorter fattening period. A good growth compensation was observed during the following pasture period for the effects of the restriction period occurring between 9 and 14 months. After the restriction between 21 and 26 months, the duration of fattening increased (22 d in the 3rd trial) (fig 2). In all of the trials, the carcasses of the restricted steers were less fat. After a period of restriction, all the animals showed an increased growth rate. This increase varied with the age of the steers during the restriction period. If it occurred before the animals had obtained 9 months of age, there was poor growth compensation. After this age, however, the growth compensation was complete, and there was even an increase in fattening for the period of restriction between 21 and 26 months. A restriction period that occurs in winter after the animals have reached 9 months of age or a small level of growth before 9 months permits economizing on expensive forage and allows for a better use of pasture. However, high forage diets permit easier slaughtering of the beef. The level of growth in winter is chosen in relation to the duration of the pasture period of fattening.