Using Supplements And Crops Profitably

Dairy industry surveys show that the average response to supplements on New Zealand dairy farms is well below the levels measured in research trials, suggesting wastage of both supplements and pasture is the norm. John Roche, DairyNZ Principal Scientist Animal Science and Julia Lee, DairyNZ Scientist Farm Systems look at how to use supplements profitably.
calendar icon 13 June 2011
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Nutrient requirements of grazing dairy cows

Cows require energy, protein, fibre, minerals, and vitamins. This, however, does not mean that they need to be supplemented with all of these. When cows have sufficient pasture, there is little benefit to supplementing with anything, other than magnesium and some trace elements during spring.

The decision to feed supplements should be based on an understanding of the likely responses to that supplement; responses to consider include dry matter (DM) intake, milk production, BCS, reproduction, and health. Even in very dry conditions when the diet may be short of protein, supplementation with protein is not always profitable ie the extra milk production is not sufficient to meet the cost of the additional protein to the diet.


Pasture-based systems are a compromise between performance per cow and per hectare; cows should, therefore, not be expected to be fully fed or to produce as much milk as they would in a confined system feeding a total mixed ration.

For example, 500 kg cows grazing high quality pasture from 3000 kgDM down to 1500 kgDM (7 to 8 clicks on the rising plate meter) can consume 16-17 kg DM/day and 400 kg cows can consume 13-14 kg DM/day. The same cows could consume an additional 1.0 kg DM if residuals were 2000 kg DM/ha. This is a five to six per cent increase in DM intake/cow for a 30% wastage of available pasture. Furthermore, both DM and energy intake will be less in the next rotation because pasture quality will be reduced by leaving the greater residual. In this situation, cows will substitute 0.4-0.6 kg DM pasture for every kgDM supplement eaten in spring1 at pasture residuals of 7 to 8 clicks.

Milk production

Modern cows grazing high quality pasture to an even, consistent residual (for ryegrass pastures this is 3.5 to 4 cm or 7 to 8 clicks if measured by the rising plate meter on even ground) can produce up to 2.3 kg milksolids (MS). Although cows being fed a total mixed ration in confinement can produce more than 3.0 kg MS/day, nutrition is not the primary reason that prevents the grazing cow from producing this much milk; genetic (a cows ability to eat enough) and farm system limitations (e.g. time spent walking, energy cost of grazing, etc.) prevent them from producing this much milk.

If cows do not have sufficient pasture (i.e. they are grazing to less than 3.5 to 4 cm), energy is the primary limiting nutrient in cows producing up to 2.3 kgMS/day2. If aiming for production targets greater than this, the diet requires balancing for other nutrients. Farmers should be aware, however, that there are very few places in the world where chasing such MS yields are profitable, and even the subsidised systems of Europe and North America are recognising that milk yield/cow has a poor relationship with profitability; in fact, in many cases as MS/cow goes up, profitability goes down.

Milk price, supplement or crop price, supplement or crop quality, the total cost of feeding the supplement or crop, and the MS response to the supplement will dictate whether feeding supplements will be profitable. The milk production response to supplements will depend on how hungry the cow is, and, therefore, how much pasture she refuses when offered a supplement (i.e. substitution rate). The amount of pasture left behind (i.e. the post-grazing pasture residual or height) is the best measure of how hungry a cow is, and therefore, the likely response to supplements can be estimated by measuring post-grazing residual.

Extreme situations:

(Average pasture cover (APC) of less than 1800 kgDM in winter/spring, grazing residuals less than 6 clicks on the plate meter for more than two weeks) responses will be 10 to 12g MS/MJ Metabolisable Energy (ME). Responses to supplements greater than this will rarely be achieved.

“Normal” feed deficit situations: (residuals of 6.0 to 7.0 clicks) responses will be 7 to 8g MS/MJ ME.

Cows eating 95 per cent of ability: (i.e. residuals of 7.0 to 8.0 clicks) responses will be 5 to 7g MS/MJ ME.

Cows fed to appetite: (i.e. residuals of 8.5 to 10.0 clicks) responses will be 3 to 5g MS/MJ ME.

These estimates are based on results from research trials in New Zealand and around the world.

In situations where cows would be underfed if not supplemented (i.e. residuals of 6 to 7 clicks), MS responses are consistently 6 to 8g MS/MJ ME fed. This is approximately half of the MS increase promised by many feed companies and consultants. However, MS responses to supplements on many New Zealand dairy farms (3.5 to 4.5g MS/MJ ME) average approximately half of what has been achieved in research trials. This implies supplements are being wasted and/or are poor quality, or that residuals are greater than 7 clicks, and, therefore, pasture is being wasted.

This is the MS increase that farmers should budget on for their own farm when working out the price where supplement is profitable to feed unless they pay close attention to both supplement and pasture management.

Body condition score

Supplementing cows does not prevent BCS loss during the first four to five weeks of lactation3, 4, 5, 6. Starch (grain or maize silage) or sugar (molasses) supplements do reduce the length of time that cows lose BCS in early lactation; however, the effect is small3.

For example: feeding a kg of starch or sugar each day during early lactation will reduce the period of BCS loss by 5 days3. This means that to reduce the period of BCS loss from 70 days (average for grazing cows) to 65 days, cows would have to receive either:

  • 1.5 kg DM of maize or wheat grain (1.7 kg fresh weight) or
  • 1.7 kg DM of barley (1.9 kg fresh weight) or
  • 2.5 kg DM maize silage (7.5 kg fresh weight) or
  • 1.3 kg DM molasses (1.7 kg fresh weight)

each day for 65 days (i.e. approximately 100 kg DM maize grain or 160 kg DM maize silage/cow). This would reduce total BCS loss in early lactation by 0.05 BCS units3 (e.g. from 4.15 to 4.20).

In comparison, feeding starch- or sugar-based supplements in mid- and late lactation does increase BCS gain. However, once again the response is much less than most people believe. On average, cows being fed 3 kg of concentrates each day of lactation (the equivalent starch to 5 kg DM of maize silage each day for 200 days) were 0.5 BCS units fatter than cows not receiving supplement (i.e. one tonne of maize silage DM fed to cows in mid- and late lactation would likely result in a 0.5 unit greater BCS at dry off). In comparison, feeding 80- 100 kg DM maize silage to dry cows would result in the same increase in BCS3.


Many people believe that high empty rates are a result of underfeeding cows, or that empty rates will be miraculously lowered through the addition of supplements. Studies from New Zealand and overseas consistently show that cows well fed on pasture from balance date to end of mating do not have improved reproductive performance when offered additional supplements. While nutrition does have an important role in influencing cow reproduction, the main effect is through BCS at calving, which is influenced by feeding in autumn and winter, and not in spring. Feeding levels after calving have only a small effect on cow fertility.

Several farm systems studies by DairyNZ have found that the major effect of feeding level on reproductive performance has been reflected in BCS at calving and the level of CIDR treatment required for anoestrous cows. Lower feed allowance systems that result in lower calving BCS tend to have higher anoestrous rates. With anoestrus treatment and good pasture feeding after balance date, 6-week in-calf rates have not been affected by a wide range of stocking rates and feeding levels7. Consistent with this, other data from New Zealand, Australia, and Ireland indicate no effect of supplementing cows with high quality energy supplements in early lactation on reproductive success.

These studies generally examined the effect of feeding before mating, and in all situations, cows were well fed on pasture during the breeding period (grazing residuals of 7 to 8 clicks). A recent DairyNZ study in Taranaki involving more than 750 cows examined the effect of a severe feed restriction during the breeding period on pregnancy results8. One group of cows was allowed to graze normally and consumed more than 14 kg DM pasture/day. The other group of cows was restricted to 8 kg DM pasture/day during the first two weeks of breeding. Restricted cows had a seven per cent lower 6-week in-calf rate; there was no difference in final empty rate.

Although a seven per cent reduction in 6-week in-calf rate is not trivial, it is important to note that this is the result of a very severe feed restriction for two weeks at the start of mating (energy intake was reduced by 45 per cent/day in restricted cows).Therefore, although it is important to feed cows well during mating, supplements are only likely to improve reproduction when cows are grazing below 7 to 8 clicks, and, even then, the benefit may not be large and will depend on the severity and duration of the feed deficit.


Although sudden changes to feeding level can cause metabolic disorders during early lactation, DairyNZ research results9 indicate that cows can adapt to severe restrictions (eating 8 kg DM/day for the first 5+ weeks of lactation), if the restriction is introduced gradually. Effects on milk production, BCS and reproduction will depend on the timing and severity of the restriction, and are outlined above. Although not desirable in most circumstances, it is important to remember that cows are resilient and can withstand periods of underfeeding. Ensure adequate supplementation with magnesium and trace elements through spring, and calcium through the colostrum period to avoid the common metabolic disorders.


If profit is the primary focus, carefully consider supplementary feeding options. Cows should only be supplemented if grazing residuals are less than 3.5 to 4cm (7 to 8 clicks on the rising plate meter); in these situations, responses to supplements will be 6 to 8 g MS/MJ ME (assuming low wastage of supplement). Under these circumstances, price paid for supplements must be less than five per cent of milk price (i.e. at a milk price of $6.00, supplement price must be less than 30 c/kg DM or 2.8 c/MJ ME). However, average response to supplements on New Zealand dairy farms is 3.5 to 4.5g MS MJ ME. If this is the response to consider, price paid for supplements must be less than 18 c/kg DM or 1.7c/MJ ME.

June 2011
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