DairyNZ principal scientist John Roche says farmers need to be focused on “feeding the wedge”, not the cow when thinking about adding supplements in their systems.
Looking at your feed wedge and filling gaps with supplements will ensure efficient use of supplements.
Substitution
The key thing to remember is that what you offer a cow isn’t what they eat, Roche says.
“Even if they were to eat that 1kg DM of supplement, they refuse a certain amount of pasture, depending on how well they’re fed, so their net energy increase is always less than that.”
This reduction in pasture intake when supplements are fed is called substitution. The main factor in substitution is how hungry the cow is, which is reflected in grazing residuals.
The hungrier the cow, the lower the residuals, which means there will be a lower rate of substitution causing a greater milksolids response. Low substitution rates are typically seen in autumn.
“As the amount of supplement offered increases, the total response to supplement declines. This is because the cow becomes less hungry with every kilogram of supplement and there is more substitution.”
Substitution is very rarely 100%. If you feed 1kg of grain, cows won’t refuse 1kg of grass.
“If they’re really well-fed and leaving high residuals behind, particularly in spring when substitution is at its highest, they could very well leave behind 0.6-0.7kg of grass behind, which means you have a very small increase in energy intake and therefore a small increase in MS production. If they’re hungry and grazing to 1200kg DM/ha residuals, substitution might be 20% and so for every kilogram of supplement they’re only refusing 200g of pasture. Substitution is driven by how hungry the cow is.”
Substitution is about 10% greater with silages than concentrates. Response to supplements, however, is driven by energy intake and not the source of the energy (ie, feed type).
Type of feed
The belief that supplementary feeds are better than pasture, from a milk production point of view, has no basis, Roche says. The difference between fibre and starch was researched in the 1870s by Gustav Kuhn of Germany, who found that ruminant animals produce the same amount of meat from fibre as they do from starch. The same has been shown in a number of studies in New Zealand by Roche and his colleagues.
“That’s the beauty of the rumen, it’s mass balance – energy in, energy out.”
One thing that people need to understand is that ME is a level playing field, regardless of the feed type it comes from. The ME is the energy in a feed, having removed the energy lost in faeces, urine and methane, Roche says.
“Any rumen inefficiency associated with feeding a feed, as in energy lost in methane, is already accounted for.”
DairyNZ scientist Dr John Roche.
However, the type of supplement that’s fed does have an effect on the composition of the MS produced. Barley and maize for example, feeds high in starch and sugar, typically increase the production of milk protein more than milk fat. On the flip side, feeds like palm kernel and soya hulls, which are high in fibre, tend to increase the production of milk fat rather than milk protein. However, the affect on composition is small and only lasts during the time when animals are consuming that supplement.
Deferred milk response
Stage of lactation is an important factor in the response a cow has to supplements. When a cow eats feed some of the energy is partitioned to body condition score replacement, particularly in mid to late lactation, which will eventually give a milksolids response. However, Roche says this is a very inefficient process.
Quality of feed
Apart from systems that feed a large amount of supplement per cow per day and in dry summers, the first limiting nutrient in a grazing cow is ME, so choosing a supplement that provides the cheapest form of ME is vital, basing purchases on megajoules (MJ) of ME rather than per kilogram of drymatter, Roche says.
“For example, if barley was sitting at $600 per tonne, with 12MJ of ME, that’s 5 cents per MJ of ME. Compare that to palm kernel at for example $200, with 11 MJ of ME, that’s 1.8 cents per MJ of ME.”
Although higher quality feeds with a higher ME will give a better milk yield response, these feeds are more costly and Roche says it’s a matter of weighing up the economics and whether production increases are significant enough to cover the costs.
Wastage
Feed wastage is an important factor to account for when weighing up the economics of supplementary feed. Wastage is estimated as follows: 5% in-dairy feeding, 10% feedpad, 15% feed trailers in paddocks, 20% in paddocks in dry conditions, 40% in the paddock in wet conditions.
Failing to pack a silage stack properly, cover it quickly or put tyres on correctly can let the silage lose 10% or more DM because of fermentation. Managing stacks and feeding to cows that are not grazing below 1500kg/DM residuals result in wastage of either supplement or pasture.
“What we start to see is the average response to supplement on farms in practical situations is far less than the research response, and a lot of this is down to wastage.”
Roche’s research suggests the response to supplements onfarm is on average two-thirds of what has historically been reported from research studies.
“So when we say that farmers can get an 80g increase in MS from a kg of supplement, which is closer to the truth than the 100g some people tell them, the average farmer is probably getting a 55g increase, the top 10-20% of farmers achieve the 80g and the bottom 20% are probably only achieving 30g.”
Costs
The fixed and variable costs associated with feeding supplement also need to be taken into consideration, Roche says.
The cost of the feed itself is only one of the costs involved.
“Variable costs go up by somewhere between 10 and 20% more than the actual cost of the feed, and depending on the system changes, there can be quite significant changes in fixed costs as well. It’s not as simple as $3.80/kg MS, so 80g of MS is worth 30 cents and I can buy feed for 25 cents, therefore 25 cents gets me 30 cents. In fact, the additional variable costs are 5-10c, eroding that presumed margin, and that doesn’t include any overhead costs associated with a farm system change.”
Replacing pasture with supplements will not improve milk production, and to be profitable, supplements should be used in situations of pasture deficits, Roche says.
