Profitable supplementation

Published 11 April 14

Cost of production is a key driver of profit in dairy systems around the world, and on average,  cost of production increases with the use of supplementary feeds, said Dr John Roche, at the final day of the DairyCo Pasture Management Courses, which concluded last week. 

Knowledge about the responses that can be expected from offering supplementary feeds is important to enable farmers to make economically sound decisions. Response to supplement depends on wastage, substitution rates and partition of energy into either milk or Body Condition Scoring (BCS).

Pasture is such a nutritionally well-balanced feed, that cows will only benefit from alternative feeds when there is insufficient pasture to meet their daily requirements, or when they are unable to consume sufficient pasture (eg prolonged heavy rain or other weather events).

Supplements should be used to manage pasture by helping to maintain post-grazing residual heights of 3.5 to 4cm, and a suitable rotation length for the stocking rate and time of year. But it’s knowing when, and if, to offer supplements which can be hard.

Excess nitrogen and potassium in spring pasture, coupled with stressful climatic conditions make it necessary to supplement with magnesium as a precaution against grass staggers. Many herds benefit from calcium supplementation during the colostrum period for the prevention of milk fever.

Industry surveys show that average response to supplement is well below the levels measured in research trials, suggesting that wastage of both supplements and pasture is the norm. As an optimum, you’d be looking at a response of 0.8 – 1.2L milk/kg DM of supplement. In reality, the average is probably somewhere around half of that.

There will be a degree of feed wastage when supplementing cows and rates are usually a function of feed type and feeding infrastructure, with more wastage occurring in silage at the clamp face than concentrate fed in a shed.  

Substitution is when cows refuse pasture after consuming a supplement. Substitution rate is regulated by the brain, such that when cows consume energy, circulating nutrients and hormones signal the satiety centres of the brain to stop eating earlier – ie graze for less time.

This isn’t a result of the fibre content of the supplement; in fact, substitution rate in cows fed silage is only about 10% greater than in cows fed grain.

Response to supplementation depends on how hungry a cow is. Hunger cannot be measured directly but post-grazing residuals are a reasonable proxy. As covers go below 1,500kg DM/ha it becomes harder for the cows to graze, and responses to supplements will be good, in the 1.1 – 1.3L range. Between 1,500 and 1,800kg DM/ha responses will be in the 0.5 – 1.0L range, and by the time residuals are above 1,800kg DM/ha responses will be negative.

Supplementing cows does not prevent BCS loss during the first four to five weeks of lactation. Starch (grain or maize silage) or sugar (molasses) supplements do reduce the length of time that a cow loses BCS in early lactation but the effect is small.

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

  • 1.5kg DM of maize or wheat grain
  • 1.7kg DM of barley
  • 2.5kg DM maize silage
  • 1.3kg DM molasses.

In comparison, feeding starch or sugar-based supplements in mid-lactation does increase BCS gain, however, once again, the response is much less than most people believe. On average, cows being fed 3kg of concentrate each day of lactation were 0.5 BCS units fatter than cows not receiving a supplement.

International studies consistently show that cows well fed on pasture, from balance date to the end of mating, do not have improved reproductive performance when offered additional supplement. While nutrition does play an important role in influencing cow reproduction, the main effect is through BCS at calving, which is influenced by feeding in the autumn and winter, not in the spring.

If profit is the primary focus, carefully consider supplementary feeding options. Supplements should be used to manage pasture, not ‘feed cow better’. Watch out for, and manage, feed wastage as far as possible. Cows should only be supplemented if grazing residuals are less than 3.5 to 4cm (covers below 1,500kg DM/ha). Providing supplements above this level will not be profitable if cows have sufficient pasture, even though milk production will likely be greater, due to substitution.