Preparing for grazing - when’s best to buffer feed silage
With calving commencing and grazing just around the corner, it is essential to understand the effects of offering silage in the diet during early lactation.
The diet of dairy cows during early lactation can have a significant impact on animal performance. Increasing the proportion of grazed grass in the diet has a positive effect on milk production due to the high nutritive value of spring grass.
Closing farm cover in autumn has the biggest influence on spring grass availability. However, periods of low grass growth and adverse grazing conditions can lead to reduced grass availability in spring, resulting in the need for silage supplementation to meet herd demand.
The spring rotation planner (SRP) should be used to ensure grazed grass is in the diet throughout the first rotation, and concentrate and silage supplementation should be offered when necessary to avoid restricting cow’s intakes.
Restriction of intake during early lactation has a negative effect on animal performance. The timing and severity of grass deficits varies between years and is dependent on spring grass availability, growth rates, weather conditions and grassland management. Therefore, it is essential to understand the effects of offering silage in the diet during early lactation.
Spring grazing research at Teagasc Moorepark
A study was carried out at Teagasc Moorepark over a two-year period, investigating the impact of silage supplementation during the first 12 weeks of lactation on milk production. The objectives of the experiment were to investigate whether the rate and timing of silage supplementation had an effect on milk production.
A high and a low opening farm cover were established using two autumn closing strategies; the high opening farm cover began closing on 27th of September and the low opening farm cover began closing on the 11th of October.
Cows were randomly assigned to the high grass or low grass treatment as they calved during the subsequent spring. For the first six weeks, cows on the high grass treatment were offered a high daily herbage allowance with low silage supplementation and cows on the low grass treatment were offered a lower daily herbage allowance with high silage supplementation. From week 7 to 12 of the experiment, cows on the high grass treatment were offered a high daily herbage allowance with no silage supplementation and cows on the low grass treatment were offered a lower daily herbage allowance with 3kg DM silage/cow/day.
Results
During the first six weeks of lactation, there was a difference of 2kg DM/cow per day in silage DM intake (DMI) between the high grass and low grass treatments; however, this had no effect on milk production (Table 1). Cows on the high grass treatment for weeks 7-12 had significantly higher milk yields compared to cows on the low grass treatment. Total DMI were the same for both groups during this period, however, the inclusion of silage in the diet reduces feed quality, which had a negative impact on milk yield for the low grass treatment. The high grass treatment milk yields remained higher for a further 8 weeks once the experiment was finished and all cows had the same diet consisting of 17 kg DM/cow/day grazed grass plus 1 kg concentrate.
Table 1: The effect of high grass and low grass treatment on animal production during week 1-12 of lactation
| Week 1-6 | Week 7-12 | |||
|---|---|---|---|---|
| High grass | Low grass | High grass | Low grass | |
| Daily milk yield (kg/cow/day) | 20.5 | 20.5 | 24.5 | 23.6 |
| Milk fat content (%) | 5.59 | 5.60 | 5.12 | 5.13 |
| Milk protein content (%) | 3.64 | 3.67 | 3.51 | 3,40 |
| Milk solids yield (kg/cow/day) | 1.91 | 1.92 | 2.09 | 2.01 |
| Bodyweight (kg/cow) | 495 | 499 | 492 | 485 |
Protein content was significantly higher for the high treatment compared to the low grass treatment from week 7-12 of the current experiment due to the inclusion of silage in the diet of the low grass treatment (Figure 1). The high grass treatment also had significantly higher grass DMI (+ 3.4 kg) compared to the low grass treatment. The reduction in milk protein content is caused by the lower protein content and nitrogen retention of grass silage compared to grazed grass.
Figure 1: The effect of the high grass and low grass treatments on milk protein content (%) during the first 12 weeks of lactation
Conclusions
Increasing opening farm allows for higher daily herbage allowance which increases milk yield and milk protein content. Higher proportions of grazed grass in the diet improves the overall quality of the diet during early lactation and leads to improved animal performance.
Silage supplementation is often required in spring due to unfavourable grazing conditions or low grass availability. Silage supplementation can be used to avoid restricting intakes or grazing ahead of allocated areas in the spring rotation plan. However, it is best to offer silage supplementation during the first six weeks of lactation if grass supply is inadequate to meet herd demand throughout the first rotation.
This paper by Sarah Walsh, Michael Kennedy and Michael Egan first appeared in the Moorepark 2023 Open Day proceedings. For more on this publication, click here.