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The effect of changing the carbohydrate composition of the concentrate component of the diet of grass silage fed cows on milk yield and composition
Abstract
With the current production targets and pricing structures prevailing within the UK dairy industry, the incentives for the dairy farmer are to maximise milk protein content whilst controlling the yield of milk and milk fat widiin individual farm quotas. Manipulation of milk fat content by nutritional means is relatively easy, but increasing die protein content of milk by similar means is more difficult and certainly less predictable. Increasing the crude protein content of the diet will invariably stimulate the synthesis of milk protein, but tiiese changes are often associated with a parallel increase in milk volume, such mat milk protein content shows little change. In contrast, several studies have shown mat changing the nature and amount of carbohydrate in the diet can substantially improve milk protein content; Krohn et al., (1985), Roberts & Martindale, (1990), Yan & Roberts (1992, 1993) and Phipps et al (1993). At the same time, the increased use of caustic treated wheat (soda grain) on U.K dairy farms has in part been associated with consistent improvements which have been observed in milk protein content. The primary aim of this study was to consider the effect of replacing part or all of the concentrate portion of grass silage fed cows with alternative carbohydrate rich feeds on me yield of milk and milk constituents. The second objective was to compare the use of soda grain with a 50:50 mixture of rolled wheat and sugarbeet feed on dairy cow performance.
Dietary manipulation of milk fat content and/or fatty acid composition is becoming a feasible, and for certain niche–markets, attractive means of boosting the nutritive value and acceptability of milk and its secondary products. However it is not yet possible to indicate equivalent ways of manipulating milk protein content and/or composition. This paper will consider current knowledge on milk protein biosynthesis and the opportunities for nutritional manipulation. Recent infusion studies which have linked changes in mammary amino acid metabolism with changes in milk protein content will be examined in an attempt to elucidate key features of the metabolic regulation of the dairy cow which need to be addressed if the British consumer is to have the choice of higher protein (possibly designer protein) milk products. This review will (in part) utilise data from a joint project at the Rowett Institute and Reading University funded by a consortium comprising government (MAFF, BBSRC and SOAEFD) and agribusiness (MDC, Purina Mills and Hendrix).
Molasses has been fed to dairy cows for about a century. Extensive studies have shown that its energy value is worth from 75 to 100% that of maize when up to 10% of molasses is fed in a complete diet and high molasses inclusion in the diet can be detrimental to the responses of the animals. Nevertheless, the maximum inclusion rate of molasses in a diet that cows can tolerate has still been unclear. Few publications are available to describle the responses of cows to very high molasses feeding. This is a question, however, that both farmers and advisers are concious of. The present experiment was designed to evaluate the effects on milk yield and composition, feed intake, liveweight gain and health of lactating cows fed on very high levels of molasses, in comparision with those fed a relatively low level.
Fifteen British Friesian late lactation cows (168 ± 6 days calved) all in second lactation or more were randomly allocated to a 3 x 3 changeover experiment with 21 day periods. The cattle were fed individually through Broadbent Calan Gates ad libitum on a complete diet of silage plus a liquid supplement including molaferm 20 (a mixture of 80% cane molasses with 20% condensed molasses solubles supplied by United Molasses Ltd.), soyabean meal and fish meal.
Cane molasses is extensively used as an energy source for cattle because of its high content of water soluble carbohydrates. However, its very low crude protein content and its ability to reduce non-protein-nitrogen (NPN) utilisation in ruminants in comparison with cereal grains may restrict its inclusion in dairy cow rations. Adding vegetable protein or urea to a cow ration containing high levels of molasses may therefore result in a better match between the nitrogen and energy requirements of rumen microorganisms. A previous experiment showed that lactating dairy cows could be fed molasses in a grass silage-based complete diet up to 312 g/kg DM without adverse effects (Yan and Roberts, 1992). The present experiment was subsequently undertaken to evaluate the responses of lactating dairy cows to protein levels in complete diets containing this high level of molasses
Stigende maengder roemelasse i fuldfoder til malkekoer
- C C Krohn
- P E Andersen
- T Hvelplund
Study of mixed forage diets for dairy cows for Milk Marketing Board of England and Wales
- R H Phipps
- J D Sutton
- B A Jones
Fodder Beet: A review of research findings in relation to animal production
- D J Roberts
- J F Martindale