Aim: To determine whether Megasphaera elsdenii YE34 (lactic acid degrader) and Butyrivibrio fibrisolvens YE44 (alternative starch utilizer to Streptococcus bovis) establish viable populations in the rumen of beef cattle rapidly changed from a forage-based to a grain-based diet. Methods and Results: Five steers were inoculated with the two bacterial strains (YE34 and YE44) and five served as uninoculated controls. With the exception of one animal in the control group, which developed acidosis, all steers rapidly adapted to the grain-based diet without signs of acidosis (pH decline and accumulation of lactic acid). Bacterial populations of S. bovis, B. fibrisolvens and M. elsdenii were enumerated using real-time Taq nuclease assays. Populations of S. bovis remained constant (except in the acidotic animal) at ca 10 7 cell equivalents (CE) ml )1 throughout the study. Megasphaera elsdenii YE34, was not detectable in animals without grain in the diet, but immediately established in inoculated animals, at 10 6 CE ml )1 , and increased 100-fold in the first 4 days following inoculation. Butyrivibrio fibrisolvens, initially present at 10 8 CE ml )1 , declined rapidly with the introduction of grain into the diet and was not detectable 8 days after grain introduction. Conclusion: Megasphaera elsdenii rapidly establishes a lactic acid-utilizing bacterial population in the rumen of grain-fed cattle 7-10 days earlier than in uninoculated cattle. Significance and Impact of the Study: The study has demonstrated that rumen bacterial populations, and in particular the establishment of bacteria inoculated into the rumen for probiotic use, can be monitored by real-time PCR.

Cattle sired by Piedmontese or Wagyu bulls were bred and grown within pasture-based nutritional systems followed by feedlot finishing. Effects of low (mean 28.6 kg, n = 120) and high (38.8 kg, n = 120) birth weight followed by slow (mean 554 g/day, n = 119) or rapid (875 g/day, n = 121) growth to weaning on carcass, yield and beef quality characteristics at about 30 months of age were examined. Low birth weight calves weighed 56 kg less at 30 months of age, had 32 kg lighter carcasses, and yielded 18 kg less retail beef compared with high birth weight calves. Composition of carcasses differed little due to birth weight when adjusted to an equivalent carcass weight (380 kg). Calves grown slowly to weaning were 40 kg lighter at 30 months of age compared with those grown rapidly to weaning. They had 25 kg smaller carcasses which yielded 12 kg less retail beef than their counterparts at 30 months of age, although at an equivalent carcass weight yielded 5 kg more retail beef and had 5 kg less fat trim. Neither low birth weight nor slow growth to weaning had adverse effects on beef quality measurements. No interactions between sire-genotype and birth weight, or growth to weaning, were evident for carcass, yield and beef quality traits. Although restricted growth during fetal life or from birth to weaning resulted in smaller animals that yield less meat at about 30 months of age, adverse effects on composition due to increased fatness, or on indices of beef quality, were not evident at this age or when data were adjusted to an equivalent carcass weight.

Summary. On the subtropical north coast of New South Wales, Australia, kikuyu grass (Pennisetum clandestinum), biennial ryegrass (Lolium multiflorum) and mixed perennial ryegrass (Lolium perenne)–white clover (Trifolium repens) pastures grazed by dairy cows were plucked pregrazing to simulated grazing height, every 2 weeks for 2 years to determine seasonal changes in various nutrients and in sacco organic matter and nitrogen (N) degradability. Changes in nutrients during regrowth were determined in the ryegrass component of a mixed perennial ryegrass–white clover pasture by sequentially cutting pasture at 3- or 4-day intervals to 5 cm stubble height and non-structural carbohydrates in kikuyu by cutting at 4-day intervals in February–March. There was a significant effect of season on water-soluble carbohydrate (WSC) and crude protein (CP) content of perennial ryegrass with regrowth time, resulting in an 8-fold fall in the CP : WSC ratio from the 1 to 3 leaves/tiller stage of regrowth in mid winter, a 2-fold difference in mid spring but with no discernible difference in late spring. The metabolisable energy (ME) values for biennial ryegrass exceeded 11.9 MJ/kg dry matter (DM) from July to September and then fell markedly to <10 MJ/kg DM in November, coinciding with reproductive development. In perennial ryegrass–white clover pastures, mean ME was above 11 MJ/kg DM from May to September, but fell to < 9 MJ/kg DM in December while in kikuyu, the mean ME, over the recognised growing season, was 8.5 MJ/kg DM but in winter it was 9.5 MJ/kg DM. Fibre content in all pasture types showed a significant seasonal trend with the content of acid detergent fibre (ADF) in biennial ryegrass at 17% from May to August while the mean neutral detergent fibre (NDF) content was 37%. In perennial ryegrass–white clover, the mean ADF was <21% from May to August. The NDF content of kikuyu grass was about 60% during the growing season but 40% in winter. The calcium (Ca) : phosphorus (P) ratio in perennial ryegrass rose from <1 : 1 at the 1 leaf/tiller stage to 2.2 : 1 at the 3 leaves/tiller stage of regrowth due to a simultaneous fall in P and a rise in Ca. A fall in potassium (K) and a rise in magnesium (Mg) and Ca content in perennial ryegrass gave a very significant linear fall in K/(Mg + Ca), on a percentage basis, from 8 at the 1 leaf/tiller stage of regrowth, to 2.5 at the 3 leaves/tiller stage of regrowth. In kikuyu, the level of P changed significantly with season falling as the species became dormant. A fall in P and a rise in Ca content resulted in a high Ca : P ratio (2.5 : 1) in spring. The findings of this study give some insight into the reason why the content of various nutrients change in pasture and the implication of this for providing a balanced diet to dairy cows. A knowledge of these changes should provide the opportunity to balance nutrients in pasture by adjusting time of grazing and/or providing supplements of appropriate quality.