Animal performance
The intake potential of forage is a primary indicator of the production potential of that forage, therefore the effect of wilting on increasing the intake of silage is a key consideration. The main factors which influence the increase in dry matter intake of silage with wilting and consequently animal performance are:
- Drying rate in the field – high drying rate in the field gives greater increase in silage intake from wilting.
- Increase in dry matter content of the grass during wilting – greater lift in dry matter in the field gave greater increase in silage intake.
- Fermentation quality in unwilted silage – poor fermentation outcome in the unwilted silage gave higher intake response to wilting.
It is also considered that these three factors govern milk output in dairy cows and carcass weight gain in beef cattle.
The results shown in Table 3 illustrate the effects on the intake and milk production responses of wilting two contrasting crops of leafy, high digestibility grass. The crops differ in their fermentation characteristics when made as unwilted silage, producing either a good or a poor fermentation, but both crops gave good fermentations when made as wilted silage. The results of the effects of fast wilting are also contrasted with slow wilting.
Table 3. Increase in silage intake and milk yield resulting from wilting to increase the dry matter content of the grass by 10 percent
| Leafy crop with good unwilted fermentation potential1 | Leafy crop with poor unwilted fermentation potential2 | |||
|---|---|---|---|---|
| Wilting time to achieve dry matter target | 24 hours | 72 hours | 24 hours | 72 hours |
| Increase in silage dry matter intake (%) | 10 | 7 | 20 | 16 |
| Increase in milk yield (%)3 | 3 | -1 | 10 | 5 |
Interpretation of Results
Leafy grass with good unwilted fermentation potential - dairy cows
With leafy grass of good unwilted silage fermentation potential it is clear that achieving the target wilted dry matter content in the grass in 24 hours as opposed to 72 hours increased the lift in silage dry matter intake with wilting from 7 to 10 percent over the unwilted silage, with parallel changes in milk output of - 1 and plus 3 percent. The absence of increase in milk yield with the 72 hours wilt derives largely from the reduction in digestibility of this silage due to the prolonged wilt.
- Very leafy first cut, clean standing grass crop with little dead material in base of sward. Adequate sugars i.e. around 3 percent water soluble carbohydrate in grass.
Dry matter of grass 18 percent, D-value of grass 73 percent, crude protein in DM 16 percent. Ammonia N as percent of total N in silage 8 percent,
D-value of silage 73 percent, ME 11.9 MJ/KG DM
- Very leafy first cut grass crop, low in sugars, low in dry matter and high protein content. Water soluble carbohydrate around 1.5 percent. Dry matter of grass 15 percent, D-value of grass 73 percent, crude protein 19 percent. Ammonia N/total N in silage 20 percent, D-value of silage 67 percent, ME 10.7 MJ/KG DM.
- The cows in first half of lactation and of good yield potential.
Leafy grass of poor unwilted fermentation potential - dairy cows
When a leafy crop of grass has poor unwilted fermentation potential, the benefits from wilting are much greater in terms of increase in silage intake and milk yield with wilted versus unwilted silage. The greater responses to wilting in this situation derive from the depressed performance of animals with the poorly fermented unwilted silage. With this type of crop wilting to the target dry matter content in 24 hours produces major increases in silage dry matter intake and milk yield of 20 and 10 percent respectively (Table 3). The longer wilting period, namely 72 hours gives lower increases namely 16 and 5 percent respectively; the smaller benefit deriving mainly from the prolonged wilting period producing a lowered digestibility in the silage.
It is therefore clear that wilting has greater potential to give improvements in animal performance where the grass is young and leafy, with high applications of nitrogen.
Milk Composition
Wilted silage does improve milk composition. A recent rapid wilting study at Hillsborough, demonstrated an average increase in butterfat content of 0.15 percent and an increase in protein content of 0.11 percent. The increase in butterfat derives from the increase in forage intake, while the increase in protein content is considered to come from the higher total nutrient intake with wilted silage.
Body Condition
Wilted silage will improve the body condition of cows, provided intake is not restricted. A higher total nutrient intake when compared with unwilted silage results. The higher nutrient intake reduces the degree of underfeeding in early lactation and increases the nutrients available for replenishment of body reserves after the lactation peak. Wilted silage is therefore particularly useful in the diets of high yielding dairy cows to maintain body condition.
Beef cattle and wilted silage
Beef cattle respond to wilted silage in the same manner as dairy cattle, with increases in intake and in rates of gain, in comparison with unwilted silage. However, the responses by growing and finishing beef cattle are greatly influenced by the level of meal feeding. The benefits from wilting are greater where low levels of meal are being fed, and are considerably reduced at high levels of meal feeding. It is suggested that when meal feeding accounts for around 30 percent of total dry matter intake, the expected responses in carcass gain would be similar in percentage terms to the responses in milk yield of the dairy cows described in Table 3.