Complete diets for dairy cattle

by J.B. Owen

Feeding complete wet diet from a mixer trailer

A system of self-feeding complete diets simplifies the feeding procedure, maintains high production, and allows efficient feed use.

The complete diet system for feeding dairy cattle — a radical departure from conventional individual rationing methods — involves the selffeeding of mixed diets based on a variety of available ingredients. The objective of the system is to simplify the process of feeding dairy cows so as to save labour and reduce capital costs on buildings while providing each cow with a well-balanced feed intake on a least cost basis.

J.B. Owen is Professor of Animal Production and Health, University of Aberdeen, Scotland, and heads a group of animal scientists and veterinarians in the School of Agriculture in Aberdeen which is engaged in developing promising ideas into commercial farm practice.

In the developed countries the use of complete mixed diets is now almost universal for pigs and poultry, and the emphasis in feed formulation is on the provision of a restricted number of standard diets appropriate to the stage of production of large groups, on a least cost basis. Dairy cattle, however, have been treated on a much more individual basis, with feed ingredients fed separately at specific times of day. Attempts are made not only to feed concentrates to each cow individually, but to adjust allowances frequently according to the level of production (Ministry of Agriculture, Fisheries and Food, Department of Agriculture and Fisheries for Scotland and Department of Agriculture for Northern Ireland, 1975). Self-feeding of complete mixed diets to beef cattle in large feedlots has become a popular feeding system, particularly in the United States, but application to dairy cows is a more recent development. Enough experience has now been gained in this field to ensure safety and efficiency in feeding valuable high-yielding dairy cows.

Mixed or separate diets?

Ad libitum feeding has obvious advantages, and many farmers in the United Kingdom and elsewhere are already using systems based on selffeed silage. Unfortunately, the evidence available indicates that allowing dairy cows continuous and simultaneous access to roughage and concentrates, but in separate hoppers, leads to inefficient overconsumption of concentrates. An even more serious result is that the roughage content of the diet can fall below the minimum safety level for the highyielding cow so that rumen function is impaired, milk fat content is reduced, and lactation inefficiency and predisposition to digestive upsets may be experienced (Owen et al., 1968). A mixed diet containing an optimum proportion of roughage, according to the stage of lactation, is therefore assumed to be an essential basis for a sound self-feeding system.

Intake/production relationship

An efficient feeding system must allow some adjustment of feed input according to nutritional need or output. Even in conventional systems where concentrates are strictly rationed, there is still considerable scope for variation in the total intake because of the flexibility in ad libitum roughage intake and differences in body size, as some cows, through inclination or social pressures, consume relatively less roughage than others. Recently, the idea that “flat rate” group feeding of concentrates to dairy cows can be just as efficient as individual rationing in many circumstances (Broster, 1975) has been gaining increasing acceptance. Therefore, a self-feeding system based on a diet broadly adjusted to the stage of lactation should be acceptable, and has the advantage of eliminating differences in the roughage/concentrate ratio among cows. Furthermore, it has been demonstrated (Owen et al., 1968; Monteiro, 1972; Greenhalgh and Reid, 1975) that within the limits of the lag of response in early lactation, voluntary feed intake by the dairy cow is associated with milk output during lactation (Figure 1). Self-feeding on the basis of at least two diets according to lactation appears to be an economic means of meeting the needs of the cow. In the period shortly after calving, the system helps to avoid overfeeding of concentrates and the attendant danger of upsetting rumen function.

Figure 1. Pattern of dry matter intake during lactation

SOURCE: Owen, 1976.

Dry matter intake

There is evidence that cows allowed to self-feed in groups on an appropriate complete diet tend to achieve a higher daily dry matter intake than those on conventional feeding. This is partly brought about by the processing effect of the mixing equipment, and partly by other more complex and less well understood factors (Allen, 1976; Coppock et al., 1972). This increased intake may enable the energy needs of the dairy cow to be catered for with diets of lower energy content, i.e. higher roughage and lower concentrate content, leading to a reduction in feed costs. The system ensures that no individual cow may consume less than the desired ratio of roughage to concentrates, but allows each cow to maximize its intake within that limitation.

Development work

Following the work in the 1960s on the basic aspects of complete diet feeding, there has been much development work in the United Kingdom at Cambridge University, the Aberdeen School of Agriculture and a number of commercial units, employing a variety of basic feed ingredients. These fall into two main categories:

1. Dry straw/cereal mixtures. These diets are based on dry cereal straw (as the roughage basis) mixed with cereals and protein supplements. These can be stored for extended periods so that hoppers can be filled at intervals of several days. The main disadvantage is the cost of processing the straw (by close precision chopping, or by milling through screens with apertures of about 10 to 15 mm) and mixing with the other ingredients.

Table 1. Comparison of conventional and self-feeding practices

SOURCE: Based on a study undertaken on a commercial farm in Cambridge, United Kingdom, using a Friesian herd split into two groups for two years.
¹ Fresh weight basis.
² Concentrate allowance only.

Examples of diets that have been used on commercial farms in the United Kingdom are given in Table 1 (D. Wilkins, 1975 [personal communication]).

Because of the cost of processing straw, the tendency has been to reduce the straw content to a minimum level of about 30 percent for the loose mix after a period of adjustment using transition diets.

Experience with the system has demonstrated that substantial simplification of the feeding system is achieved in practice with the elimination of parlour feeding, the reduction of feeding space, the reduction of feeding chores through mechanized feed preparation, and the replenishment of feed hoppers at intervals of several days; this, incidentally, allows exclusion of week-end feeding chores.

Table 2. Comparison of winter feeding of conventionally fed and self-fed groups of dairy cows

Commercial farm experience has shown that yields, milk quality and breeding regularity tend to improve under the system (Table 1). Although these findings are not based on rigorously controlled experiments and may largely reflect certain inadequacies in the conventional feeding system, they seem to point to a real value of the system, i.e. that it ensures high performance under a variety of circumstances and managerial skills.

2. Wet mixtures of silage/concentrates. Many dairy farmers use silage and other wet materials in diets for their dairy cows. In northern Scotland, grass silage, wet distillers' grains and roots with a high water content (e.g. swedes and turnips) often form the basis of winter feeding. Common systems of silage making involve precision chopping so that there is little difficulty in incorporating such material into a complete mixed diet. Roots, however, need suitable processing prior to incorporation, and even then some degree of selectivity can be exercised by the cow. Experience at the Aberdeen School of Agriculture (Allen, 1976) has shown that satisfactory results can be obtained by mixing wet and dry ingredients either in a specialist mixer trailer or by using less sophisticated conventional forage boxes where the ingredients are loaded in even layers so that mixing is accomplished as the material is dispensed into the feeding trough.

One apparent advantage of the specialist machine is the increased density of the resulting mixture due to the squeezing action of the augers.

Figure 2 shows the composition of a mixture of silage, distillers' grains and barley after processing in alternative mixing systems. The increased density and lack of aeration of the mixture give the material better storage properties, so hoppers do not need filling at the week-end — a powerful attraction for many dairy units where long working hours are a pressing problem. Table 2 summarizes results obtained in a development trial at Aberdeen.

Conclusions

As a result of the above development work, several important conclusions may be drawn:

1. Self-feeding of complete diets is capable of maintaining milk yield and quality in dairy herds that were formerly well managed on a conventional system. In some cases it has been the means of correcting inadequacies in conventional feeding and thereby raising yield and milk quality. The maintenance or improvement of production has normally been accompanied by savings in concentrated feed and more intensive use of roughage components.

2. The results have been achieved with a marked simplification of feeding routines allowing complete or partial replacement of feeding in the milking parlour and the restriction of feeding chores to once a day or less frequently during the week, and the elimination of week-end feeding work. The management and labour force in the units associated with these developments have reacted favourably to the adoption of the system.

3. Continual access to feed has allowed feeding space at the trough to be reduced. Figure 3 shows the dimensions of a feed trough suitable for a silage-based mixture. The saving in feeding space on the design of dairy units is far-reaching; for example, covered concrete feeding areas can be substantially reduced as compared to a unit based on more orthodox feeding methods, and thus lead to a substantial saving in capital cost.

4. There are two important and related safety aspects to be emphasized in self-feed systems:

   1. During the period of adjustment to self-feeding, a regime of transition diets must be adopted to avoid the danger of digestive upsets and acidosis through overeating. This involves changing from pasture feeding or conventional feeding by initially allowing free access to a diet containing a high level of roughage only. A starting diet containing 70 percent roughage (silage, hay or straw) in the dry matter has been found suitable under a variety of circumstances. The diet is adjusted to the required level of roughage over a period of about two weeks. Dairy cows can be changed to the system at any period of the lactation, although there are advantages in achieving transition before calving where this is possible.

   2. Care must be taken to ensure a continuous round-the-clock supply of feed, although prudent stockmen adjust daily allowances to minimize, but not eliminate, carry-over of surplus from one day to the next. If for some reason the feed does run out for a period of four hours or more, it is advisable to adopt the transition procedure (i.e. using the higher roughage level for the first feed following a period of feed deprivation), although transition to the normal level can be relatively rapid, depending on the length of the period of accidental deprivation.

5. Development work has not identified a need for filling the feed hoppers more often than once a day, whatever the type of diet used. In many large beef feedlots it is still customary to feed twice a day; this may be because adjustment of feed allowance to reduce surplus can be achieved with less danger of the animals being without feed for any length of time. Another factor is that in large units, feeding twice a day may have no significant effect on either the labour requirement load or the transport cost.

   Avoiding week-end feeding is a possibility with many mixed diets, provided they are suitably processed and the feed container is suitably designed to allow for a sufficient capacity of feed to be continually within the cow's reach.

6. The system ensures that the feeder can dictate the roughage content of the diet of each cow. This is an important advantage for safeguarding health and milk quality and ensuring a high level of roughage intake. Traditional thinking about individual rationing of dairy cows implies that the choice of a single optimum roughage/concentrate ratio for group feeding would be difficult and ultimately wasteful; in practice, however, the decisions on diet formulation resolve themselves rather simply. With good dairy breeds in early lactation, most situations favour a high proportion of concentrates giving a total dietary ME concentration of 10–12 MJ/kg DM, provided the roughage is in a “coarse” form (either chopped or very coarsely ground). The extent to which this level is reduced in later lactation to a minimum of about 8 MJ/kg DM and the manner of reduction depend on the type of cow, the relative costs of roughage and concentrates, and the particular circumstances of the unit.

   In some commercial units the herd is divided into two groups according to calving, and the composition of the diet offered to any group is adjusted one to three times during the production cycle so as to give two to four diets over the year. With the knowledge that two diets provide a safe norm, the producer will be able to adapt his own procedure with experience to suit his own local circumstances.

Figure 2. Effect of processing on diet

7. A specialized application of the use of self-fed complete diets is as an adjunct to heavily stocked pasture. This ensures full utilization of pasture production without subjecting the cow to a fluctuating energy intake. In this case, complete diets are offered ad libitum and are so formulated that the cow exerts the right grazing pressure before any substantial change to a higher intake of feed supplement is made. Experience at the Aberdeen School of Agriculture (Allen, 1976) has shown that cereal/straw mixtures of the kind suitable for mid-lactation feeding can be successfully used for this purpose, and can lead to substantial savings in the area of grass used by the dairy herd. This system would be particularly applicable in areas where grass growth is uneven and unpredictable.

Figure 3. Feed trough giving easy access and storage space

SOURCE: E.R. Harrison, 1976 [personal communication].

References

Allen, P.N. 1976. Complete diets in practice. Dairy Farmer, 23(3): 19–21.

Broster, W.H. 1975. Some considerations in simplified feeding systems for dairy cows. In U.S. Feed Grains Council and University of Aberdeen Department of Animal Production. Simplified feeding for milk and beef, p. 113–125.

Coppock, C.E., Noller, C.H., Crowl, B.W., McLellon, C.D. & Rhykerd, C.L., 1972. Effect of group versus individual feeding of complete rations on feed intake of lactating cows. J. Dairy Sci., 55: 325–327.

Greenhalgh, J.F.D. & Reid, G.W. 1975. Feeding dairy cows to appetite. Proceedings of the British Society of Animal Production (new series), 4: 111–112.

Monteiro, L.S. 1972. The control of appetite of lactating cows. Anim. Prod., 14: 263–282.

Owen, J.B., Miller, E.L. & Bridge, P.S. 1968. A study of the voluntary intake of food and water and the lactation performance of cows given diets of varying roughage content ad libitum. J. agric. Sci., 70: 223–225.

Owen, J.B. 1975. Complete diets for dairy cows. In U.S. Feed Grains Council and University of Aberdeen Department of Animal Production. Simplified feeding for milk and beef, p. 85–93.

United Kingdom. Ministry of Agriculture, Fisheries and Food, Department of Agriculture and Fisheries for Scoltland, Department of Agriculture for Northern Ireland. 1975. Energy allowances and feeding systems for ruminants. London, hmso. Technical Bulletin 33.