Chemical factors involved in ruminal fiber digestion.

Dietary Buffering Requirements of the Lactating Dairy Cow: A Review

Energy requirements of grazing livestock seem to be poorly defined. Requirements generated from measurements in pen-fed animals present both theoretical and practical concerns when they are applied to grazing situations. In mature ruminants a majority of energy used for maintenance seems to be consumed by visceral tissues. Moreover, factors that affect visceral energy use are poorly understood. Energy supplementation to meet requirements and production demands is often practiced during periods of summer dormancy and in winter months. Source of supplemental energy varies widely and includes grains, readily digestible fiber sources, and high-quality forages. Intake and digestibility can be reduced or unaffected by energy supplementation. In some cases, lower levels of energy supplementation have been shown to increase utilization of grazed forage. Reductions in ruminal pH, often cited as the major cause of reduced fiber digestion, may not always explain reductions in intake and digestibility associated with energy supplementation. Livestock production is usually either enhanced or unaffected by energy supplementation. Additional research regarding energy requirements of grazing ruminants, visceral energy use, and mechanisms associated with reductions in intake and digestibility of grazed forage resulting from energy supplementation is warranted.

Influence of energy supplementation on grazing ruminants: requirements and responses

This paper focuses on dairy herd performance in the United Kingdom and southern Australia, where feed costs have been estimated to comprise between 40 and 67% of the total costs of production. The efficiency of conversion of grazed pasture, home grown forages and purchased feeds into milk has a major bearing on farm profit. Feed conversion efficiency (FCE), defined as ‘kg milk of standardised composition with respect to protein and fat concentrations produced per kg feed dry matter consumed’, is a useful measure of the performance of a farm feeding system, but is seldom used by dairy farmers. It could also be defined as ‘g protein plus fat produced per kg feed dry matter consumed’, given that farmers are often paid for these components. The value of estimating FCE on an annual or shorter-term basis is discussed in relation to accepted principles of feed utilisation and dairy cow energy requirements. The implications of feed intake, conversion of ingested nutrients into absorbed nutrients and the subsequent utilisation of these nutrients for milk production or other purposes, as well as the effects of stage of lactation on FCE, are reviewed. Measuring FCE and identifying opportunities for improvement is relatively straightforward in housed feeding systems, but is more problematic under grazing. Hence, approaches and the key assumptions in estimating FCE in grazing situations, as well as possible limitations of these estimates, are discussed. Finally, a case study examining the potential impact of improved nutritional strategies on FCE and on margin over feed costs is presented. It is concluded that, to remain profitable, dairy farmers need to have a sound knowledge of cow nutrition, along with appropriate measures of FCE to monitor the performance of their milk production system. Such indicators of the biological performance of the farming system are most useful when used in conjunction with appropriate measures of economic performance.

Feed conversion efficiency as a key determinant of dairy herd performance: a review

Efficient conversion of grazed pasture and supplementary feeds into milk is essential to the profitability of dairy farming in southern Australia as costs of production continue to rise. The application of diet formulation approaches to the nutritional management of grazing dairy cows provides unique challenges in predicting the interactions that occur between grazed herbage and supplementary feeds. How feed intake and associative effects between feeds in lactating dairy cows grazing pasture might affect estimated metabolisable energy supplied by the diet are examined. The effects of increasing feed intake in high-producing dairy cows on decreasing the digestibility of energy, and the compensatory effects of reduced methane production, are reviewed. The factors affecting intake of grazing cows and possible effects on digestibility are considered, and include characteristics of the pasture/forage and amounts and forms of concentrates. Estimates of the potential magnitude of negative associative effects in dairy cows have been made using 2 datasets from recent experiments. Finally, the potential importance of understanding and predicting the magnitude of associative effects for efficient pasture-based dairy production is discussed. It is concluded that although associative effects between feeds in grazing dairy cows cannot be predicted with certainty, and although they involve complex interactions among a number of variables, ignoring their occurrence can lead to significant errors in both feed evaluation and ration formulation.

Associative effects between feeds when concentrate supplements are fed to grazing dairy cows: a review of likely impacts on metabolisable energy supply

Associative effects of mixed feeds. II. The effect of dietary addition of bicarbonate salts on the voluntary intake and digestibility of diets containing various proportions of hay and barley

Shirley A. Gauld

Papers

Associative effects of mixed feeds. II. The effect of dietary addition of bicarbonate salts on the voluntary intake and digestibility of diets containing various proportions of hay and barley