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The drive to increase the output of animal product in some sectors of ruminant livestock production has led to greater use of feeds such as cereal grains and soyabean meal that are potentially human-edible. This trend has caused concern since, by so doing, ruminants compete not only with monogastric livestock but also with the human population for a limited global area of cultivatable land on which to produce grain crops. Reasons for using potentially human-edible feeds in ruminant diets include increased total daily energy intake, greater supply of essential amino acids and improved ruminal balance between fermentable energy and degradable protein. Soyabean meal, produced on land that has been in arable cultivation for many years can fulfil a useful role as a supplier of undegraded dietary protein in diets for high-yielding dairy cows. However, in the context of sustaining the production of high-quality foods from livestock to meet the demands of a growing human population, the use of potentially human-edible feed resources by livestock should be restricted to livestock with the highest daily nutrient requirements; that is, potentially human-edible feed inputs should be constrained to meeting requirements for energy and protein and to rectifying imbalances in nutrient supply from pastures and forage crops such as high concentrations of nitrogen (N). There is therefore a role for human-edible feeds in milk production because forage-only systems are associated with relatively low output per head and also low N use efficiency compared with systems with greater reliance on human-edible feeds. Profitability on farm is driven by control of input costs as well as product value and examples are given of low-cost bovine milk and meat production with little or no reliance on potentially human-edible feeds. In beef production, the forage-only systems currently under detailed real-time life-cycle analysis at the North Wyke Farm Platform, can sustain high levels of animal growth at low feed cost. The potential of all-forage diets should be demonstrated for a wide range of ruminant milk and meat production systems. The challenge for the future development of ruminant systems is to ensure that potentially human-edible feeds, or preferably human-inedible by-products if available locally, are used to complement pastures and forage crops strategically rather than replace them. [ABSTRACT FROM AUTHOR]

Abstract: Highlights of progress in the production of silage over the past 50 years include the introduction of improved hybrids of maize (Zea mays L.), the forage harvester, the big baler, polyethylene covering for horizontal silos, stretch‐wrap film for bales and novel additives designed to improve the fermentation and aerobic stability of silage. The key biochemical pathways in the silage fermentation have been described together with the effects of microbial and chemical additives on fermentation and aerobic stability during the feed‐out phase. The significance of oxygen and water in silage fermentation has been quantified and efficacy of covering silos has been established, with recent progress in the development of oxygen barrier film. Future perspectives include improving food safety and animal health by increasing the hygienic quality of silage, reducing the environmental impact of silage by decreasing loss of nitrogen to soil and atmosphere, reducing methanogenesis in the rumen and increasing methane yield from silage as biofuel, and the use of silages as feedstocks for multiple end uses in biorefineries. [ABSTRACT FROM AUTHOR]

Implications of silage hygienic quality for animal production were investigated on forty-five dairy farms in South West England. Samples of grass and maize silages and of total mixed rations ( TMR) were obtained together with information on silage technology, herd size and animal production. Samples were analysed for mycotoxins, bacteria, yeasts, moulds and chemical composition. Thirteen mycotoxins were assayed, but none were detected in the samples of grass silage. However, mycotoxins were found in 0·9 of all maize and other silage samples, with deoxynivalenol and zearalenone predominating. There was no relationship between total mycotoxin concentration and mean lactation milk yield per cow. Enterobacteria counts tended to be higher in maize silage than in grass silage and higher still in TMR - a cause for concern. There were no relationships between mould counts and mycotoxin concentrations in silages, implying that mycotoxins may have been produced in the field pre-ensiling. [ABSTRACT FROM AUTHOR]

Nutrition affects the environmental impact of milk production through its direct influence on enteric fermentation and excretion of undigested and excess nutrients, especially nitrogenous compounds, in manure and its indirect influence on daily level of milk output per cow and fertility. The higher the level of milk production and fertility, the lower the emissions intensity, or carbon footprint, of a dairy herd. Increasing feed efficiency reduces greenhouse gas emissions per litre of milk because emissions are spread over higher product output per cow. Nitrogen use efficiency and cow fertility can be increased and diet carbon footprint reduced by altering diet formulation to utilise by-product raw material feeds of low carbon footprint. [ABSTRACT FROM AUTHOR]

A range of options was explored to test the hypothesis that diets for dairy cows could be formulated to reduce the carbon footprint (CFP) of feed, increase efficiency of conversion of potentially human-edible feed into milk, increase nitrogen use efficiency (NUE) and reduce methane (CH4) emissions per kg milk. Diets based on grazed grass, grass silage, maize silage or straw, supplemented with raw material feeds, were formulated to meet requirements for metabolizable energy and metabolizable protein for a range of daily milk yields. At similar levels of milk yield, NUE, predicted CH4 emissions and diet CFP were generally higher for diets based on maize silage than for those based on grazed grass, grass silage or straw. Predicted CH4 emissions and human-edible proportion decreased, while NUE increased with the increasing level of milk yield. It is concluded that there is potential to reduce the environmental impact of milk production by altering diet formulation, but the extent to which this might occur is likely to depend on availability of raw material feeds with low CFPs. [ABSTRACT FROM PUBLISHER]

The concentration of crude protein in grazed New Zealand pasture is typically in excess of 200 g/kg DM, which exceeds the requirement of the dairy cow and is reflected in elevated levels of daily urinary nitrogen (N) excretion, estimated to average 262 g N/head or 751 kg N/ha. This has adverse environmental consequences, including leaching of nitrate from soil into water courses and atmospheric emissions of nitrous oxide. Problems associated with pasture as the sole feed for dairy cows include weight loss in early lactation, poor fertility and reduced lactation length. Low-protein supplements can reduce N excretion rates and increase N use efficiency. A simple feeding strategy is proposed in which pasture is supplemented with maize or whole-crop wheat silage at 5 kg DM/cow per day from the start of the pre-calving dry period on winter run-off pasture to 100 days post-calving, and from 250 days post-calving to the end of lactation. The expected response, at an assumed substitution rate of 0.7 kg decrease in pasture intake per kg silage DM, is an increase in metabolisable energy of 10 to 15 MJ/cow/day, equivalent to 33 to 48 g milk solids (MS)/kg DM of supplement. This strategy is expected to result in significantly lower urinary N excretion by the cow. Actual responses in daily milk output, from published experiments where grazing stocking rates were increased to take account of reduced herbage intake, ranged from 50 to 100 g MS/kg DM of supplement. Other benefits include early lactation bodyweight maintenance, higher percentage of cows calved which are pregnant at 150 days in milk and increased lactation period. Constraints for farmers to implement such changes include cost of silage, value of milk sold, failure to integrate forage maize or wheat in rotational cropping with pasture, and the relatively poor aerobic stability of maize and whole-crop wheat silages. [ABSTRACT FROM AUTHOR]