Forage utilization efficiency: an Australian perspective

In recent times there has been a global shift back to pasture-based dairy farming led largely by the “clean green” push. Although philosophically this may be the correct move by the dairy industry, care must be exercised that it is achieved in a thoughtful, controlled way in order for the appropriate management to be employed and sensible decisions made. The danger is in embracing radical changes without thoughtful and balanced evaluation of the potential consequences. Many times we see well-meaning farmers get into trouble changing too quickly with too little homework.

The key to profitability in pasture-based dairy farming is in understanding that balanced rations are more difficult to achieve, and stockmanship reigns as the most important skill. One needs to be very cow-focused to assess the need for diet changes. Computers and consultants cannot substitute for stockmanship. This paper will provide some basic concepts that need to be considered if pasture-based dairy production is your quest.


THE MAJOR FACTORS AFFECTING MILK YIELD

Milk production is the result of the coordination of many, many complex metabolic and physiological events in the cow. Numerous factors affect the efficiency with which the multitudes of cascades of biochemical processes are carried out. Yet, only a handful of factors need be attended with reasonable diligence by the farmer to allow all of the necessary events to proceed successfully, such that good milk responses are achieved in response to improved feeding levels.

For all intents and purposes, there are only seven factors that require significant management attention to maximise farm productivity. These factors are presented in Figure 1. Of these seven management areas, only cow condition and the four factors associated with the feed require day-today attention. Unexpressed genetic potential lies latent in most herds, and its improvement and the changing of calving patterns both require strategic decision-making processes to be employed.






COW CONDITION: EVALUATING DIET BALANCE

If one adheres to the 80/20 principle in farm management, body condition management is the 20% which leads to 80% of the success on the animal side. Cow condition is, in fact, the most important criterion for assessing the success of dietary balance when used in conjunction with milk production. It is also the key factor contributing to milk components, health and fertility.Youmust become very astute at monitoring and measuring, i.e., managing, body condition when most of the diet is ‘unknown’.


FORAGE QUALITY AND PASTURE UTILIZATION

With cow condition as a benchmark, this leaves the feed side, i.e., the pasture (or any other forage for that matter) and supplements (concentrate or roughage). It is the daily interaction of these that primarily determines day-to-day milk yield and composition, body condition, animal health and fertility. There is no difference between a total mixed ration (TMR) and a pasture-based ration in this respect; it is just a little more challenging to get it all right when basing the diet on pasture. My own experience is that when the shift from TMR to pasture is executed properly, yield and profitability can both be preserved. Moreover, health and fertility will improve if we manage the transition to pasture well.


FORAGE GROWING COSTS

As an observer to Australian and New Zealand dairy industries, you could be easily convinced that pasture is very cheap – so cheap that we waste more than half of what we grow. Unfortunately this is not a rare mindset. Australian and New Zealand farmers are still trying to survive while working an out-dated paradigm – that pasture is cheap. Even now, many advisers are still fertilising this perception.

A recent conference paper (Tease, 1997) discussed several case studies in which pasture costs were apparently consistently low, arguing that supplementary feed costs were threatening our farmers’ prosperity. His own data do not even support this conclusion (Figure 2). It is evident from this figure that the cash outlay for home-grown feed is low, and that purchased feed is of similar magnitude. Neither feed category threatens farm prosperity. However, when analysing farm cash flows of pasture-based dairy farm businesses, with an ounce of commonsense one quickly realises that most farmexpenses relate, either directly or indirectly, to the cost of growing pasture. I suspect the same is true of other forage-based dairy farms, although it may be diluted a little as farms move from home-grown forage to higher inclusions of concentrates and purchased forage.

By including the labour, overhead and depreciation costs, a very different picture of pasture begins to emerge (Table 1). In the table we see that pasture is quite expensive to grow. Also illustrated is the effect of increased pasture yield on the unit cost of growth. Although it may cost more to increase pasture dry matter yields, the higher yields produce significantly cheaper feed.


PASTURE UTILIZATION EFFICIENCY: THE LARGEST IMPACT ON PROFITABILITY

It is not enough simply to grow more pasture. Tonnes of pasture consumed is the key to farm profitability. First we have to grow more pasture to reduce the unit growing cost, and then we have to harvest the pasture efficiently. To make total sense out of this picture, we need to provide a series of examples. Table 2 expands on the previous table illustrating the effects of land values and farming systems and the effects of pasture utilisation on the true cost of pasture as a feed. Once the real-cost adjustments are made and pasture utilisation is considered, the homegrown feeds take on a new aura – they are not automatically cheap feeds. Growing costs (in Table 2) range from 10-13.6 c/kg DM. However, it is not until you consider the utilised pasture dry matter (UDM) costs that the real picture emerges. As you can see, every effort must be made to maximise the yield (total tonnes) of harvested pasture dry matter.




Figure 2.Relationship between farm production level and feed cost.










Pasture utilisation efficiency is the factor with greatest impact on farm profitability. Figure 3 illustrates the relationship between gross margin and pasture utilisation (UDM/ha). Clearly, as the UDM increases, gross margin also increases. The poorer the pasture utilisation, the more expensive the feed (Table 2). Once this is established, the relationship betweenUDM and farm profitability becomes very strong as can be seen from making these adjustments in the case study analysis (Figure 4). Real pasture costs were in the order 14-28 cents/kg DM ($140-280/t) which is precisely the same story illustrated in Table 2. Without focus and an understanding of the real costs of pasture production, it would be easy to romance the pasture-based farming system with disastrous consequences.




Figure 3.Relationship between pasture dry matter utilised and gross margin.



MAXIMISING PASTURE USE EFFICIENCY

Only two aspects of pasture management require discussion:

1. Increasing the harvest efficiency of pasture currently grown.
2. Improving pasture yields.

Management priorities must, very definitely, be in this order since there are few farms on which grazing is the dominant means of harvest where utilisation of pasture is optimal. Improving pasture yield is outside the scope of this presentation. Suffice to say that species selection, grazing, fertiliser and irrigation management are all vital components.


INCREASING PASTURE UTILISATION EFFICIENCY: FORAGE QUALITY IS THE KEY

Numerous management factors influence the efficiency with which pasture is harvested. The most obvious are presented in Figure 5 and three of these are closely related: grazing management, pasture species and fertiliser management. Each of these has a tremendous impact on forage quality.

The quickest and most significant means of increasing pasture use efficiency is to optimise rotation length (i.e., the period fromone grazing to the next).




Figure 4. Relationship between farm production level and component cost of production (with revised home-grown feed costs).





Figure 5. Major factors affecting pasture utilisation efficiency.



Rotations that are too short reduce dry matter yields, while rotations that are too long limit pasture consumption by the cow as forage quality declines.

Owing to the relationship between neutral detergent fibre (NDF) and intake, no amount of concentrates can compensate for a poor quality forage base (Van Soest, 1994; Mertens, 1983). In Figure 6, this is illustrated on three basal rations containing either A) good quality (lucerne), B) fair quality (corn silage), and S) poor quality (bermuda grass) forages, all optimised for fibre.Without going into mathematical detail, the relationship described below in Equation 1 can be used to describe the limitations to intake, and thus production level (Mertens, 1983):





The underlying mechanism for the relationship between intake and NDF in Equation 1 is obvious. As fibre quality improves, intake, digestibility and passage rate all increase. The line in Figure 6 is there as a reminder that as milk yield improves, the percentage of NDF in the ration can be reduced since the maintenance of the rumen mat requires kilograms of NDF, not percentages.

An understanding of the physical role of NDF leads us to the limitations of our pasture-based management system. Figure 7 clearly illustrates the intake boundaries for our pasture (or forage)–based dairy rations. Once we accept that intake is primarily determined by dietary NDF, we quickly recognise that there is a limited number of feasible ration solutions for cows at different production levels. More importantly, the number of feasible rations diminishes as production expectations rise and/or forage quality declines. It is rather simplistic, but it serves as a guideline to get diet components in the right ballpark and is an incredibly good tool when educating farmers on the importance of fibre quality. Simply put, as NDF increases, dry matter intake decreases.

Typically our pasture NDF values increase quickly after optimum grazing height (maturity).A rotation only seven days too long may result in a 7-10% unit increase in pasture NDF and cause intakes to fall by up to 0.7% of liveweight (Table 3) or 2 kg DM/day. Not only will dry matter intake decrease, but energy density of the pasture also falls (by ~1MJME/kg DM), ultimately sacrificing 7-8 liters of milk/day. Table 3 clarifies this point, and the important role concentrates play in increasing total dry matter intake.






From the perspective of Figure 7, we can assemble a second equation:





Thus, the limit to feasible intakes is determined with liveweight as the controller, and NDF as the key variable to be managed. In practical terms this means:


A 500 kg cow will have an intake limitation of approximately 6.0 kg NDF.




Figure 6.The relationship between milk yield and NDF.





Figure 7. Using the NDF-energy intake system to identify the range of feasible rations for cows of different production levels (Mertens, 1992).



A 600 kg cow will have an intake limitation of approximately 7.2 kg NDF.

This is incredibly important to understand when managing a pasturebased dairy ration. A cow can only fit somuch in! Pasture quality management is the most challenging aspect of low-cost dairying systems. Even relatively small changes in pasture quality have an enormous impact on dry matter intake as noted in Table 3. The other challenges such as dealing with differences in genetic potential, nutrient balance, etc., pale by comparison.


USING SUPPLEMENTS TO MAXIMISE PROFITS FROM PASTURE

It is the number of tonnes of pasture dry matter harvested that primarily determines whether profits are made or lost. The most profitable means of achieving high levels of pasture utilisation is to take advantage of the complementary properties concentrates offer.


THE ROLE OF SUPPLEMENTS IN THE PASTURE-BASED FARMING SYSTEM

Supplements provide the vital links between pasture management and animal management. More aggressive grazing reduces the pasture allocation per cow, often reducing the consumption of pasture per cow. This in turn compromises the efficiency of feed conversion. More importantly, the risk of running out of feed increases as grazing management is intensified through higher stocking rates, restricted use of fibrous supplements and improved genetic potential of the herd. Supplements, therefore, play the critical role of insurance against running out of feed, and help maintain high feed conversion efficiencies. If used as an integral part of themanagement system, supplements result in significant profits. However, this is rarely seen in practice.


ECONOMICS OF CONCENTRATES IN PASTURE-BASED DAIRY RATIONS

Dairy farmers in southeastern Australia and New Zealand rely heavily on pastures to provide the nutrients required for milk production. Typically, lactating dairy cows receive rations similar to those presented in Table 4. The most common ‘reason’ for concentrates to be used on farm is the recognition that they contain the potential to realise high production levels per cow and simultaneously per hectare by intensifying grazing management. In practice, this rarely happens without external guidance due to a fall in pasture utilisation when supplements are fed. The net result is usually a marginal cost/benefit scenario from supplement use (Table 5). Even if production per cow and per hectare are improved, responses such as this fail to capture our audience, but rather leave them a little frustrated.


SUBSTITUTION

In understanding Equation 2, it becomes obvious that as NDF intake approaches maximum, the use of supplements will force some forage out of the diet. The frustration of substitution is that the theoretical responses to supplements are rarely met.

The energy in cereal grain (12.2-12.7 MJ ME/kg DM) is sufficient for about 2.3 litres of milk. At 23.1 cents/kg for concentrate and 25 cents/liter for milk, this represents an enormous opportunity for profit. Even if you only get half of this, it still represents pretty good value for money! Yet typical responses to concentrate supplements are sufficiently poor that their value is still subject to a good deal of debate.





Cereal grain, specifically wheat with an energy density of 12.7 MJ/kg DM, contains sufficient energy for about 2.6 liters of milk, yet such responses are never recorded. The extent to which the response falls short of the 2.6 liters/kg DM wheat is the extent to which one or other of the following have occurred:

• substitution
• the imbalance of nutrients in the rumen, or
• the partitioning of nutrients between milk production and body tissue

Since substitution refers to the drop in pasture intake caused by the intake of supplements, the production response is usually less than the potential intake. In turn, the marginal rate of response often becomes just that – marginal.


MANAGING SUBSTITUTION

Management of fibre quality alone is insufficient to extract the best from pasture-based dairy systems. The seeking of feasible dietary solutions also entails a quest for matching supplements to pasture (forage) to ensure maximum use and control of quality pasture.

Substitution will be minimised by dietary balance, body condition management and grazing management; however, an element will remain.

This can be eliminated by additional cows to maintain or increase the effective grazing pressure. When the system is managed well the profitability cannot be disputed. Table 6 shows the progress made by BESTfed Nutrition clients as our working relationship develops.






Unless moderate increases in stocking rate occur in conjunction with significant increases in milk yield, supplements will provide little economic benefit to the farm business.When used as an integral part of the management of the dairy feedbase, supplements have a large positive cost/benefit ratio (Table 6). It is also evident that as production per cow rises, margin over feed cost also rises. When the effects of increased concentrate use combine with increased stocking rates and higher production per cow, the effects on margin over feed costs per hectare are huge.



REFERENCES

Mertens,D.R. 1983. Using neutral detergent fibre to formulate dairy rations and estimate the net energy content of forages. Proc. Cornell Nutrit. Conf. Ithaca, NY pp 60-68.

Mertens,D.R. 1992. Nonstructural and structural carbohydrates. In: Large Dairy Herd Management, American Dairy Sci. Assoc. (Ed: HH Van Hern and C.J. Hilcox) p 219.

Tease, I. 1997. The economics of increasing milk production. Gipps Dairy Conference. Dept Natural Resources and Environment. pp 12-26.

Van Soest, P.J. 1994. Nutritional ecology of the ruminant. Cornell University Press, Ithaca, NY.