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SummaryFaecal output of 287 beef cows consisting of Hereford (H × H), Simmental × Hereford (S × H), Friesian × Hereford (F × H) and Brahman × Hereford (B × H) breeding was estimated using controlled release of chromic oxide (Cr2O3). All cows were from 6 to 10 years of age and had grazed on one of three pasture systems in the subtropics of New South Wales since they were 7–8 months of age. These pastures were designated as being of high, medium and low nutritive value. Faecal organic matter output (FOMO) was estimated in each of four periods (early lactation, mid lactation, late lactation, and non-lactating) during one annual production cycle.Herbage mass exceeded 2 t/ha on all pasture systems, but estimates of organic-matter digestibility, nitrogen content and pasture composition indicated large differences in pasture quality (high > medium > low). Live weight of cows averaged 604, 488 and 393 kg live weight on the high, medium and low pastures, respectively. There were significant differences in live weight between genotypes on the medium (B × H > F × H and H × H) and low (S × H ≡ F × H ≡ B × H > H × H) pastures but not on the high pasture).FOMO and dry-matter intake (DMI) differed significantly between genotypes among lactating cows on all pasture systems. Rankings on high pastures were reasonably consistent in all periods: S × H ≡ F × H ≥ B × H ≥ H × H, as were those on low pastures, B × H ≥ S × H ≡ F × H ≥ H × H. Differences on medium pastures were significant only during mid-lactation when B × H ≡ S × H ≡ F × H > H × H. Significant differences between genotypes were observed among non-lactating cows on high pastures only, where H × H ≡ S × H ≡ F × H > B × H. Lactating females had significantly higher FOMO and DMI than non-lactating females when compared across genotypes during early lactation on all pastures.

Milk yield was determined by the weigh-suckle-weigh method over 2 years (1983 and 1984 calvings), for a total of 305 purebred Hereford (HiH) and first-cross BrahmaniHereford (BiH), SimmentaliHereford (SiH) and FriesianiHereford (FiH) cows grazing three pasture systems at Grafton, New South Wales, Australia. The age of the cows ranged from 6 to 11 years. The data were used to evaluate different estimates of milk yield and to examine the effects of milk yield on growth of calves up to weaning.Of all the cow traits studied, average lactation milk yield (average of early, mid and late-lactation milk yields) had the highest correlation coefficient with calf 210-day weight (r l 0n73) and preweaning average daily gain (ADGtotal, r l 0n73), and explained 50 % of the variation in the calf traits. However, milk yield was also moderately correlated with other cow traits (liveweight and body condition score). Thus, to predict calf performance, milk yield data may not be required if detailed data on other cow traits are available. This is supported by the finding that differences in the coefficients of determination (R#) between models for calf 210-day weight and ADGtotal which included average lactation milk yield and other cow traits (highest R# l 69 %) and models which included other cow traits but no milk yield estimate (highest R# l 57 %) were 13 %.Cow breed rankings for average lactation milk yield were similar to those for calf 210-day weight and ADGtotal. On high quality pasture, SiH and FiH cows produced the most milk (SiH, 7n5 kg\day ; FiH, 8n3 kg\day ; BiH, 5n7 kg\day ; HiH, 5n5 kg\day) and weaned the heaviest calves (SiH, 255 kg ; FiH, 252 kg ; BiH, 215 kg ; HiH, 217 kg), while on low quality pasture, BiH and FiH cows produced the most milk (BiH, 4n2 kg\day ; FiH, 3n7 kg\day ; SiH, 2n9 kg\day ; HiH, 2n7 kg\day) but BiH cows weaned the heaviest calves (BiH, 180 kg ; FiH, 168 kg ; SiH, 159 kg ; HiH, 124 kg).

The characteristics and retail yield of carcases of 482 Angus, Charolais and Hereford sired progeny out of straightbred Hereford (HxH), and first-cross Brahman x Hereford (BxH), Simmental x Hereford (SxH) and Friesian x Hereford (FxH) dams were evaluated. The cattle had been raised and slaughtered for either the vealer (both sexes), yearling domestic (both sexes) or the heavy export steer market. The data were analysed within market type, and at a constant age at slaughter (281, 478 and 829 days for vealer, yearling domestic and heavy export carcases respectively) and also at a constant hot P8 fat depth (4.6, 7.8 and 14.9 mm for the three markets respectively) and constant hot carcase weight (160, 200 and 343 kg for the three markets respectively). At a constant age, carcases of Charolais sired progeny were significantly (P < 0.05) heavier (8-16%, depending on market type), leaner, had larger eye muscle area and higher dressing percentage than those of Angus and Hereford sired progeny. This resulted in 12 to 17% (P < 0.05) more kg of boneless saleable meat (retail yield) from carcasses of Charolais sired progeny. At a constant hot P8 fat depth, the magnitude of the sire breed differences increased, whereas at a constant hot carcase weight, the differences became non-significant or were reduced in magnitude. At a constant age, progeny of BxH dams had higher ( P < 0.05) dressing percentage than those of the other dam breeds for all market types except the vealer market. Progeny of FxH dams had more (P < 0.05) channel and kidney fat than those of the other dam breeds, even at a constant hot P8 fat depth. Retail yield, as a percentage of the boned side, was highest for carcases of progeny of BxH dams and lowest for those of progeny of FxH dams (70.2% and 70.3% v. 69.1% and 69.2%, for vealer and yearling domestic carcases respectively, at a constant age). Sire and dam breed effects for the individual primal cuts, as percentages of the boned side, were not significant for most of the primal cuts, and where significant, the differences were very small.

Pre-weaning growth of 482 Angus, Charolais and Hereford sired progeny out of straightbred Hereford (H x H) , and first-cross Brahman x Hereford (B x H) , Simmental x Hereford (S x H) and Friesian x Hereford (F x H) dams was evaluated. The dams grazed either high, medium or low quality pasture (pre-weaning pasture system) at Grafton, NSW. Progeny of dams from high quality pre-weaning pasture were slaughtered at 281 days of age for the vealer market. The progeny of dams from medium and low quality pre-weaning pastures were evaluated for post-weaning growth on pasture, on commercial properties in temperate NSW. They were slaughtered for either the yearling domestic (both sexes) or heavy export steer markets. Average daily gain (ADG) for the entire pre-weaning period was greater (P < 0.05) for Charolais (845 g/day) than Angus (790 g/day) and Hereford (783 g/day) sired progeny. This resulted in a higher ( P < 0.05) weaning weight of Charolais sired progeny of dams on high or medium quality pre-weaning pasture. On low quality pasture, however, sire breed differences in weaning weight were not significant (P > 0.05). This indicates that adequate nutrition should be provided for Charolais sired progeny to express their higher growth potential. Post-weaning ADG of Charolais sired progeny was higher (P < 0.05) than that of Angus or Hereford sired progeny, resulting in 14 months liveweight (for yearling domestic cattle) of 370, 345 and 345 kg and 27 months liveweight (for heavy export steers) of 635, 585 and 569 kg for Charolais, Angus and Hereford sired progeny respectively. Progeny of B x H dams on medium or low quality pre-weaning pastures had the highest pre-weaning ADG and weaning weight, but the lowest post-weaning ADG. This resulted in 27 months liveweight of 558, 582, 628 and 616 kg for steer progeny from H x H, B x H, S x H and F x H dams respectively.