What quality of silage is needed for milking cows?
With the beginning of the second rotation just around the corner, lower grass availability on some farms means that silage may have to be re-introduced to the diet.
As part of the ‘Nutrition of the spring-calving dairy cow in the early lactation period’ Q&A document published in early March, Dr. Joe Patton and Dr. Aisling Claffey took a closer look at optimum silage quality and meal feeding rates.
What quality silage is needed for milking cows?
Silage for milking cows should be at least 74 % DMD, well preserved with good energy and intake characteristics. Cows will voluntarily eat > 13 kg dry matter of this type of silage, making early lactation feeding and supplementation very straightforward.
On the other hand, cows will struggle to eat 10-11 kg DM of poor quality silage (< 68 % DMD or less). This intake effect, combined with lower UFL value per kg of feed, significantly limits the cows’ energy and protein intake and milk solids yield supported by the diet (Table 1).
Table 1: Early lactation milk yield supported at different concentrate feeding rates and silage quality
| Concentrate kg as per fed | |||
|---|---|---|---|
| Silage DMD | 4 | 6 | 8 |
| 66 | 13.8 | 16.4 | 19.1 |
| 74 | 18.4 | 20.9 | 23.5 |
In early lactation, cows will exceed these levels of milk production supported by the diet due to mobilisation of body reserves, as there is a metabolic imperative to produce milk in the weeks immediately after calving. For this reason, there is a particular risk of excess body condition score (BCS) loss in early lactation where diet are inadequate over a prolonged period.
Extra meal feeding will not fully solve the nutritional problem of low DMD silage. This is because the realised feed value of the extra concentrate declines as the proportion of concentrate in the diet rises, due to a reduction in whole diet digestibility. In other words, the cow utilises her whole diet less efficiently when concentrate feeding rates are high relative to forage intake. There is also the risk of clinical digestive upsets and acidosis to consider with very high concentrate proportions, in addition to the extra feed costs incurred.
In farm situations where the only silage available in low DMD and access to grass is limited:
- Put grass in the diet at least once per day, even if ground conditions are less than ideal. Cows will eat 5-6 kg DM grass in 3-4 hours which adds energy and protein to the diet
- Feed 2kg of a high fibre straights like hulls or beet pulp where grazing is impossible
- Review your silage plan for 2025. A typical spring calving dairy herd needs >50 % of its silage at 74 % DMD plus. National average in 2024 was 69 % - there is much scope to change.
What level of meal feeding is optimum? What is the expected response?
When we compare the cow’s energy requirement for milk (0.43 to 0.45 UFL per kg) to the energy content per kg concentrate as fed (typically 0.92 to 0.95 UFL), there is, theoretically, sufficient energy in 1 kg concentrate to produce more than 2 kg milk. However, in a grazing scenario with adequate pasture allowance and quality, a 2:1 milk yield response to additional concentrate supplementation is impossible. A more standard range of expected response is 0.5 kg to 1.3 kg milk per kg concentrate fed, around a mean of 0.8 to 0.9 kg milk per kg concentrate fed depending on a whole range of considerations.
A key underlying factor determining milk responses is substitution rate, or the proportion of forage displaced by increasing concentrate supplementation. Factors that affect substitution rate and the milk yield response to concentrate include the proportion of concentrate in the diet, pasture and silage quality, quantity of forage offered, type and quality of supplement offered (alternative forage/ concentrate).
In early lactation, there is typically minimal substitution observed for the first 3 kg concentration offered. Increasing concentrate allocation beyond this will result in reduced grass DMI and reduced total diet digestibility. However, an increase in total DMI and milk yield are observed. This increased milk production is not linear, and thus the marginal milk response for each additional kg of concentrate is typically lower than at the previous rate of supplementation. Table 2 illustrates this pattern of response to increasing concentrate across two different levels of pasture quality. There is a diminishing financial return to the farm as the supplement rates increase and the response rate declines. This also means that, by definition, feeding extra concentrate to maximise milk yield will not result in maximum profitability of the farm. In fact the expectation would be that as concentrate feed levels are increased that the profitability would be reduced.
Table 2: Impact of pre-grazing cover and concentrate allocation on grass DMI, total DMI, milk yield and response to concentrate in mid-season
| High quality pasture | Meal kg as fed (0.88 DM) | Grass intake* | DMI | Milk kg | Response per kg as fed |
|---|---|---|---|---|---|
| Leafy, low NDF content 1,400kg DM/ha pre-grazing cover | 0 | 16.8 | 16.8 | 23.9 | - |
| 2 | 16.2 | 17.9 | 26.2 | 1.15 | |
| 4 | 15.6 | 19.1 | 27.8 | 0.8 | |
| 6 | 14.9 | 20.2 | 29.0 | 0.60 | |
| Low quality pasture | Meal kg as fed (0.88 DM) | Grass intake* | DMI | Milk kg | Response per kg as fed |
| Stemmy, high NDF content >2,000kg DM/ha pre-grazing cover | 0 | 14.8 | 14.8 | 17.1 | - |
| 2 | 14.5 | 16.3 | 19.7 | 1.32 | |
| 4 | 14.0 | 17.5 | 21.8 | 1.03 | |
| 6 | 13.4 | 18.7 | 23.7 | 0.93 |
Note also that the marginal response to concentrate is best where pasture quality is poorest, i.e. where the diet and cow performance is least favourable. For this reason, it is not valid to evaluate the overall economics of pasture and supplement strategies on a response-to-concentrate basis. It is much more important to focus on increases in pasture utilisation, proportion of grazed grass in the diet, and milk solids efficiency per kg of pasture consumed.