In many situations a yearling mating strategy for beef heifers may be only moderately successful because genetic and nutritional factors prevent a proportion of them from reaching puberty before the end of mating. For example, Morgan (1981) reported that 40% of Hereford heifers grazing pasture at Hamilton failed to reach puberty by 17 months of age. Age and weight at puberty can be modified by both preand post-weaning nutrition (Menge et al. 1966; Wiltbank et al. 1966; Arije and Wiltbank 1974). The desirability of such manipulation of the growth of heifers must be considered both in terms of the extra costs and also the biological implications of rapid early growth (Johnsson and Obst 1980; Robinson 1981).

Researchers world-wide have studied feed conversion efficiency (FCE) in a range of species. The pig and poultry industry, partly through selection for FCE, have improved their competitive position against the red meat industries who have placed little direct selection pressure on their species for FCE. In pigs, selecting for increased FCE based on an ad lib. feeding system (AFCE) improves FCE, but can result in some unacceptably fat animals (Luxford, pers. comm.). Selecting for increased FCE using diets comprising only 85% of required daily intake, a scale feeding system (SFCE), produced pigs with faster genetic gain, improved FCE and leaner carcasses, compared with an AFCE feeding system (McPhee et al. 1988). Our experiment was conducted to compare the two systems as a test for FCE in cattle. Twenty-eight Hereford Angus cross steers, liveweight 349 ± 16 kg, P8 fat 4.5 ± 1.2 mm (mean ±s.d.) were randomly allocated to two treatments: ad lib. feeding (AFCE), or scale feeding (SFCE). The diet comprised a pelleted lucerne and grain based ration (15% CP, 10.7 MJ ME/kg) with 0.5 kg of straw fed daily. Each group of steers was fed one of these diets for 50 days, weighed after a 12 hour fast, then fed the other diet for 50 days. This process was repeated, so that each steer was fed each ration twice, for a total of 100 days on each treatment. This cross over design was partly to negate the effect of body composition change on FCE. The SFCE ration was calculated on 1.75% of the starting liveweight for each animal at each feeding period. The mean gross FCE of the steers was 10.1 and 11.2 kg DM/kg liveweight gain for the AFCE and SFCE diets respectively (l.s.d. 0.91kg). The P8 fat gain, measured ultrasonically, was 3.0 mm and 0.4 mm on the AFCE and the SFCE diets respectively (l.s.d. 0.8mm). Total feed intake (s.d. 60.3 kg DM) and total weight gain (s.d. 8.1kg DM) for a 50 day AFCE feeding period showed considerable variation with a significant positive correlation between these traits (r = 0.7). With SCFE the variation in intake is restricted (s.d. 23.8), but the variation in liveweight gain was still quite large (s.d. 6.2 kg) and the correlation with intake was non significant (r = 0.1) (Figure 1.)

Pregnant Hereford cows were fed one of four drought rations commencing 3-6 months pre calving, and then one of two drought rations during the first 13 weeks of lactation. Cows fed 4.0 kg cracked wheat (CW) +0.5 kg pasture hay lost less weight pre-calving than those fed a similar amount of whole wheat (WW) (+0.6 vs -27.0 kg, respectively; P

Pregnant Hereford cows of live weight 462+:5 kg (meaS -104 and 1.0; -137 and -1.3; -87 and -1.1; -106 and -1.6, respectively. Pregnant cows can be fed rations consisting solely of whole wheat; however 3.5 kg was inadequate for a satisfactory liveweight change. No advantage was found by adding straw to the wheat ration, but wheat at pasture gave the best performance. All rations appeared inadequate for optimum performance from lactating cows under the conditions of this experiment.