Data on Brahman and Hereford cattle and their crosses were used to estimate direct additive, direct heterosis, maternal additive and maternal heterosis effects for pre-weaning and post-weaning liveweights, average daily gain (ADG) and height at various ages. The cattle were born at Grafton, N.S.W., and raised on high, medium and low quality pastures until weaning. During the post-weaning period, the steers were grown in three environments in New South Wales, while the heifers remained at Grafton. Genetic effects were estimated by regression and the additive components expressed as deviations from Hereford effect. Weaning weight and pre-weaning ADG of Hereford calves (both sexes) were 237.8 kg and 827 g/day on high, 210.5 kg and 704 g/day on medium, and 128.3 kg and 425 g/day on low quality pastures respectively. Post-weaning ADG of Hereford steers (weaning to 36 months) and heifers (weaning to 30 months) was 296 and 240 g/day respectively. Direct heterosis was significant (P<0.05) for most traits. Estimates of direct heterosis for weaning weight were 24.9 and 20.2 kg, and for pre-weaning ADG were 79 and 68 g/day, on high and medium quality pastures respectively. Direct heterosis for ADG of steers (weaning to 36 months) and heifers (weaning to 30 months) was 91 and 76 g/day respectively. Estimates of maternal heterosis for weaning weights were 14.9, 30.9 and 37.8 kg and for pre-weaning ADG were 31 (not significant), 105 and 153 g/day, for high, medium and low quality pastures respectively. Maternal heterosis for ADG of steers (weaning to 36 months) was -47 g/day. There was a negative direct additive effect on post-weaning ADG in environments where pasture quality was good, but the effect was not significant on poor quality pasture. Maternal additive effect was negative for birth weight for high and medium quality pastures and positive for weaning weight and pre-weaning ADG on low quality pasture. The performance of untested crosses can be predicted from the estimates and models provided.

Two studies were undertaken at Grafton, NSW, to determine the effects of supplementing a subtropical hay diet with a mixture of non-protein nitrogen (urea) and protein (protected casein), on the feed intake and growth of 20 steers of four genotypes (Study I), and on the digestive and metabolic functions of 16 of the steers that were fistulated in the rumen (Study 2). All steers were reared in the one subtropical environment. They consisted of backcross Hereford (H) (H x BH), backcross F1 (BH x BH) and backcross Brahman (B x BH), all of 50% heterosis, and a first-cross F1 of 100% heterosis (BxH). Steers in both studies were confined in pens and offered a basal diet of chaffed pasture hay (digestibility 52f 1.4% and nitrogen [N] content of 6.1 � 0.2 g/kg dry matter [DM]) supplemented with minerals only (low N diet; 8 steers) or with urea or formaldehyde-treated casein and cottonseed meal (high N diet; 12 steers) for 49 days. There were eight steers, for each of the two diets in Study 2, which were fed for 30 days. There was a diet x genotype interaction (P < 0-05) in the daily DM intake (DMI) of hay by steers in Study 1. The mixed N supplement increased ( P < 0.05) DM1 (per kg liveweight) by 14% in HxBH and by 13% in BxBH steers, but there was no significant effect of the supplement on the DM1 of BxH and BHxBH steers. Daily liveweight change was increased (P < 0.05) by the supplement from -30 to 250 (s.e.d � 40) g/steer and there was no significant difference between genotypes. N supplementation increased ( P < 0.05) rumen volume (63 to 87 � 7.6 L) and fluid residence time (491 to 822 � 76.9 min) (P < 0.05) in BHxBH steers, but the increases in other genotypes were not significant. Rumen ammonia concentration (30 to 61 � 3 7 mg N/L) and plasma urea concentration (56 to 94 � 6-0 g N/L) were increased (P < 0.05) by supplementation. Total protozoa density in rumen fluid was greater (P < 0.05) in BxBH than HxBH steers but did not differ significantly between supplemented and unsupplemented steers. The HxBH steers had the lowest density of small entodiniomorph protozoa when N-supplemented, which was less (P < 0.05) than that in BxBH steers which had the greatest density. Supplementation increased (P < 0.05) N retention but only B x BH steers had a positive N balance. These experiments indicated that there are some physiological differences between genotypes. The BxH genotype with the high hybrid vigour had a high DM1 on the low digestibility hay diet without the N supplements and it transferred more urea from the plasma pool to the gut. The backcross steers (HxBH and BxBH) had low DM1 which increased when supplemented. The high content B. indicus steers (BxBH) had positive net retentions of N, but the results indicated that rumen protected proteins may be more usefully fed to steers with a lower B. indicus content.

Post-weaning growth and body condition, puberty and pelvic size of 197 heifers comprising straightbred Hereford (HxH) and Brahman (BxB), first-cross (BxH) and back-cross (HxBH and BxBH) heifers were evaluated. The heifers were born over a 3 year period, and grazed improved and semi-improved pastures following weaning at Grafton, New South Wales. Prior to weaning, heifers had been reared by dams on three pasture systems (high, medium and low quality pastures). Heifers from low quality pre-weaning pasture had higher (P < 0.05) post-weaning liveweight gain than those from high and medium quality pastures. BxH heifers gained 71 g/day more (P < 0.05) than the mean gain of their contemporaries of the other genotypes, whose gains were similar, from weaning to either 26 or to 30 months of age. Liveweight at all ages was influenced by genotype x pre-weaning pasture system interaction. At 30 months of age, BxH heifers from high and medium pre-weaning pastures were the heaviest. At the same age, but from low quality pre-weaning pasture, heifers with crossbred dams (HxBH and BxBH) were the heaviest. Wither height depended significantly (P < 0.05) on the proportion of Bos indicus genes, increasing from 113.8 cm in the HxH heifers to 124.4 cm in the BxB heifers at 30 months of age. BxH heifers had a higher (P < 0.05) body condition score than their contemporaries of the other genotypes, which were in similar condition, at 26 and 30 months of age. On average (across pre-weaning pasture system), 9% of BxB heifers had reached puberty by 22 months of age compared to 62, 95, 82 and 64% (s.e.= 9) for HxH, HxBH, BxH and BxBH heifers respectively. No significant genotype differences were obtained in the height, width and size of the pelvic opening of the heifers, measured just prior to the beginning of the mating season at 26 months of age.

Post-weaning growth of 186 steers comprizing straightbred Hereford (H x H) and Brahman (B x B), first-cross (B x H) and back-cross (H x BH and B x BH) was evaluated. The steers had been raised to weaning (8 months of age) by dams which grazed either high, medium or low quality pasture (pre-weaning pasture system) at Grafton, N.S.W. The steers were grown on pasture from time of weaning in one of three locations in New South Wales representing subtropical, temperate-good, and temperate-good to poor environments, and slaughtered when the average fat cover of the back-cross steers in each environment was 4-10 mm at the 12113th rib. Pre-weaning pasture system had a significant effect on post-weaning growth, with mean post-weaning (8-48 months of age) average daily gain (ADG) of steers from low (327� 8 g/day) being higher than that of steers from medium (304�6 g/day), which in turn, was higher than that of steers from high (276�9 g/day) quality pre-weaning pasture, indicating that steers from low and medium quality pastures exhibited compensatory growth. From 8 to 24 months of age, first-cross BxH steers had the highest ADG in all environments. The ranking of the other genotypes differed across environments. In the environment where growth rate was lowest (178 g/day for B x H), B x B and B x BH steers grew faster than H x H and H x BH steers; where growth rate was highest (584 g/day for B x H), the order was reversed; and where growth rate was intermediate (323 g/day for B x H), there were no significant differences in ADG among H x H, H x BH, B x BH and B x B steers. Steers from only two environments were retained after 24 months of age. Mean ADG from 8 to 36 or 48 months of age was not significantly different among straightbred and back-cross steers, but was lower than that for the first-cross steers. Genotype x environment interaction for liveweight at slaughter was not significant. First-cross B x H steers were 56 kg (11%) heavier (P < 0.05) than back-cross steers, which in turn, were 37 kg (8%) heavier (P < 0.05) than straightbred steers at slaughter.

Background: Feeding sweet potato (Ipomoea batatas, L. (Lam)) roots and forage to pigs is characteristic of smallholder farming in tropical countries and particularly the use of indigenous breeds and their crossbred progeny (mixed genotype, MG) growing pigs.Presenting forage as ensiled, fermented feed, is a recent technology to smallholder pig feeding in the Pacific region, which until now was not tested for metabolic contribution to effective nutrition for MG pigs and towards reducing the feed costs of production.Objectives: To determine the nutritional utilization of sweet potato for mixed genotype local pig breeds.Methods: Two metabolic trials tested the total tract apparent digestibility (TTAD) of nutrients and N balance in MG growing pigs fed ensiled SP roots (ER) or roots and vines (ERV), blended with two protein concentrates at 380, 400, 430 and 500 g/kg DM into four treatment diets, ER380, ER430, ERV400 and ERV500, compared against a standard wheat-based commercial pellet diet (STD). The trials were conducted using a 4 × 4 Latin Square design with two sets of four MG pigs at 23 kg (Trial 1) and 27 kg (Trial 2) starting BW. The trial pigs were offered one of four diets interchanged during four 8 d periods, with a 5 d adaptation phase and 3 d for total collection of faeces and urine. Pigs were housed in all-steel metabolic cages (1.0 m × 1.0 m × 1.5 m) on stands 0.7 m above floor level.Results: DMI was higher (2,290-2,739 g/d) for pigs on the SP-based diets (p < 0.05), ADG in Trial 1 was lower (686-718 g/d) but in Trial 2 was similar (944-1072 g/d) to pigs fed STD (p > 0.05), while the FCR (2.72-3.70) was higher than STD (p < 0.05) in both trials. DM, OM, CF, fats (EE), carbohydrates (NFE) and energy coefficients of TTAD were superior on the SP-based diets, but Ash, Ca and Total P CTTAD were reduced compared to STD (p < 0.05). N retained (g N/d) differed between the diets; 27.1 (ERV400), 20.8-24.8 (ER430), 27.7-29.0 (ERV500), 30.8-31.2 (STD); and did not reflect dietary CP or amino acid levels, dietary fibre content, or energy digestibility.However, N retention (NR% intake) and utilization (NR% digested) was inferior to STD for all SP-based diets except ER380 (Trial 2). Higher faecal N (g/d) (P < 0.05) suggested increased hind gut fermentation in pigs fed on SP-based diets, whereas higher urine N (g/d) (p < 0.05) indicated a lower N requirement. Conclusion:Dietary fibre in SP vines reduced nutrient utilization for growth but MG pigs adapted over time. Reduced protein and amino acid supplementation were recommended for MG pigs.