Grass silage – why high feed value is essential
The production of high feed-value silage should always be the objective of producers who feed silage to lactating dairy cows, growing and finishing beef cattle, and pregnant ewes. For me, the target for high feed-value silage is a DMD of greater than 75% writes Dr. Tim Keady, Teagasc researcher
Herbage from 1.2 million hectares (3 millon acres) of pasture is ensiled annually in Ireland. The feed value of the silage produced will have major consequences for ruminant performance next winter with carry-over effects into the following grazing season.
With the dramatic increase in input costs due to the fallout from the pandemic and the ongoing war in the Ukraine it is predicted that concentrate will be expensive next winter. One benefit of increasing silage feed value is its ability to maintain animal performance at a reduced level of concentrate supplementation. This is known as the ‘potential concentrate sparing effect’.
My aim in this article is to present the effect of high feed-value silage on animal performance when offered to lactating dairy cows, finishing beef cattle and pregnant ewes. The potential concentrate sparing effect of high feed-value silage is discussed.
Effect of silage feed value on animal performance
The feed value of grass silage is a combination of its intake potential and nutritive value. Digestibility is the key factor influencing both the intake characteristics and nutritive value. Therefore, digestibility is the most important factor influencing the performance of animals offered silage-based diets. There is a substantial volume of data in the literature on the impact of DMD on the performance of beef cattle, pregnant ewes and lactating dairy cows offered silage-based diets. This may be summarised as follows:
Beef cattle: The mean response expected for each 5% unit increase in DMD of silage offered to beef cattle is an increase in silage intake of 0.35 kg DM/day leading to an increase of 0.15 kg/day in liveweight gain and 0.11 kg/day in carcass gain, respectively. However the response in animal performance to improved silage DMD depends on the quantity of concentrate offered, which impacts diet forage:concentrate (F:C) ratio. When silage is offered without concentrate supplementation (e.g., to store cattle that will be turned out to pasture next spring) each 5% unit increase in silage DMD increases daily liveweight gain by 0.24 kg, equivalent to 36 kg additional body weight following a 150-day housing period.
Finishing beef cattle are offered concentrate to achieve the optimum level of performance. For finishing beef cattle offered a silage-based diet consisting of 60% concentrate, each 5% unit increase in silage DMD increases carcass gain by 0.09 kg/day. An increase in daily carcass gain of 0.09 kg/day is equivalent to 13.5 kg carcass weight valued €70/head during a 150-day finishing period.
Dairy cows: The mean response expected for each 5% unit increase in the DMD of silage offered to lactating dairy cows is an increase in silage intake of 1.0 kg DM/day resulting in an increase of 1.65 kg/day in milk yield and 0.04 of a percentage point in protein concentration, respectively. The response in animal performance to improved silage DMD depends on the quantity of concentrate offered. When silage is supplemented with low levels of concentrate (diet F:C ratio 80:20) each 5% unit increase in silage DMD increases milk yield by 2.9 kg/day. For diets where the concentrate is 50% of total food intake, each 5% unit increase in silage DMD results in an increase in milk yield of 1.3 kg.
Pregnant ewes: In prime lamb production the objective is to produce lambs that have a high birth weight and are born alive will little assistance. Studies at Athenry have shown that each 1 kg increase in lamb birth weight results in lambs that are 3.3 kg heavier at weaning. The mean response for each 5% unit increase in the DMD of silage offered to ewes during mid and late pregnancy is an increase in lamb weight at birth of 0.25 kg and an increase of 6.5 kg in ewe body weight at lambing. Ewes offered high feed-value silage have a higher body condition score at lambing and thus can mobilise body reserves during lactation without the requirement for concentrate supplementation post lambing.
Effect of silage feed value on potential concentrate sparing effect
When concentrate price is high relative to product price (meat or milk) one of the potential benefits of increasing silage DMD is the opportunity to maintain animal performance whilst reducing concentrate input. The reduction in concentrate feed level required to maintain a given level of animal performance is referred to the ‘potential concentrate sparing effect’. The following outlines the potential concentrate sparing effect of increasing the feed value of silage offered to beef cattle, lactating dairy cows and pregnant ewes.
Beef cattle: The potential concentrate sparing effect of increasing the feed value of silage offered to beef cattle depends on silage feed value and concentrate feed level. For example, for finishing beef cattle offered either 71 or 75 DMD silage and supplemented with 4 kg concentrate daily, the concentrate feed level could be reduced by 1.8 and 2.3 kg/head per day, respectively, if silage DMD is increased by 5% units. Thus, for a 150-day feeding period, total concentrate input can be reduced by up to 3.5 tonnes for every 10 cattle housed.
Dairy cows: Increasing the DMD of silage offered to dairy cows increases milk yield and protein concentration. An increase in silage DMD of 5% units enables the yields of milk fat and protein to be maintained whilst daily concentrate feed level is reduced by 3.3 kg.
Pregnant ewes: When based on lamb birth weight, and changes in ewe body weight, increasing in silage digestibility by 5% units can result in a reduction in concentrate requirement of 12 kg concentrate per ewe during late pregnancy.
Conclusions
1. Produce high feed value silage - DMD greater than 75%
2. Increasing silage feed value either
- increases animal performance or
- maintains animal performance at a lower level of concentrate supplementation
3. A 5% unit increase in silage DMD increases
- carcass gain of beef cattle by 0.11 kg/day
- milk yield of dairy cows by 1.65 kg/day
- lamb birth weight by 0.25 kg
4. A 5% unit increase in silage DMD enables animal performance to be maintained while reducing concentrate input by up to:
- 2.4 kg /day for finishing beef cattle – the equivalent to 3.6 tonnes for every 10 cattle
- 3.3 kg for lactating dairy cows
- 12 kg per ewe during late pregnancy
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