Silage Insights - Bale Silage Production
Determining dairy cow herd performance and health with in calf feeding

By Dr. Katrin Mahlkow-Nerge

The change from lactation to pregnancy and then back to lactating constitutes the greatest health, infectious and metabolic, risk for dairy cows. Especially ketoses and fatty liver are intrinsically linked to the forage management during pregnancy. Husbandry and forage of gestating cows are cornerstones for the health and the performance of the subsequent lactation.

In calf cows are the most important animals of the herd and their feeding generally aims at two goals:

1. Providing the animals with the best possible conditions for great food intake during early lactation so that they leave the negative energy balance as soon as possible, thus avoiding the risk of ketoses;
2. Averting the milk fever risk.

The main demands throughout are made on the two-tier feeding of the pregnant cow and the separate husbandry and feeding of pregnant and lactating cows.

• 1st phase (early pregnancy phase, 6-8 weeks to 3 weeks before giving birth): energy- and nutrition-reduced forage rations (5.5-5.7 MJ NEL/kg TM, 120-130 g raw protein/kg TM), usually with chaff; an energetic over-supply strongly increases the ketose risk of those animals after giving birth.
• 2nd phase (transit period, preparatory feeding, "Close up", initial feeding phase, 2-3 weeks before giving birth until giving birth): energy-rich and nutritious forage rations (6.4-6.8 MJ NEL/kg TM, 140-150 g nXP/kg TM, 100-150 g strength/kg TM) with ca. 25 - 30 % concentrated feed, but sufficient fibre supply for reducing the risks of abomasums displacement and first stomach acidosis (as a consequence of ketose).

It is particularly the appropriate (low in energy!) feeding of cows in early pregnancy that poses a difficulty to farmers - mainly from smaller farms. Why? The lactating dairy cows require lots of energy in their food, just like calves and young cattle during their first year and the transit cows during the last 14 days before giving birth. Such rations are usually based on energy-rich grass silages of the 1st or 2nd cut in combination with corn silages. However, cows in early gestation and young cattle in the 2nd year must be fed with low-energy food. Giving the same grass silages that are given to the dairy cows would therefore raise the energy content too high. Consequently, low-energy grass silages from the 3rd or 4th cut should rather be used for rations of cows in early gestation and young cattle.

If a silo with the 3rd cut should be opened in addition to the grass silo with the 1st cut, then the extraction feeds in both silos - especially in smaller dairy cow herds - are so low that there is a danger of reheat. Those problems hardly exist at large farms with 200 or more cows that have consequently 25 to 40 gestating cows and the corresponding number of young cattle.

But how can a small farm face those problems? By producing especially small, narrow silos or bale silage from the 3rd or 4th cut. This takes care of two problems at once:

1. Gestating cows are provided with low-energy food that can be used in a targeted manner, and
2. bale silages will be used within a very short period so that there is no danger of reheating.

The second goal in feeding in calf cows consists in avoiding milk fever diseases as much as possible. Milk fever - also called parturient paresis - is probably the most common metabolic disease in high-performance herds. The milk fever prevalence increases with increasing milk output (greater calcium needs/losses) and increasing age (due to the reduced number of hormone receptors on the target cells, the mobilisation processes require more time in older cows) of the animal. Furthermore, the propensity to have this illness is greatly influenced by husbandry, and especially feeding mistakes during the last two weeks of the gestation period in particular. This implies that the milk fever risk can be reduced by a controlled ration composition. The alcalotic / acidotic state of the animal - i.e. the acid-base balance - is key in determining the milk fever risk a cow might be exposed to. The more the cow's metabolism before giving birth is alkaline, the greater the risk of milk fever.

Potassium is the element with the greatest influence on the acid-base balance (Horst and Goff, 1997). This influence is much more significant than the impact of calcium. Potassium contents of > 15 g/kg TM translate into very high milk fever risks. This also means that the potassium content of the ration - for our purposes, the potassium content of the grass silage - is most instrumental in determining the milk fever risk.

Grass silages are usually rich in potassium and much more so than corn silages. The lower the grass silage and the lower the corn silage content of the ration, the more one can reduce the potassium content of the entire ration. But not all farms can increase the corn content of the total ration as they see fit, especially if they are located in mainly grassland regions. If that is the case, then the potassium content in the grass silage must be reduced via an altered green-/grassland and, especially, dung management. Low-potassium grass silages can be generated by manuring the grassland only very little if it is to be later fed to the gestating cows. It is even possible to completely exclude certain grassland areas from manuring for the preparation of silages of gestating cows. The dandelion and cow parsley content should be kept as low as possible since those plants are literal potassium powerhouses and therefore increase the potassium content of the silage.

Furthermore, new grass species are usually more fertile, thus having a potassium dilution effect.
The particularities during the special grass silage preparation play a significant role in the context of a milk fever prophylaxis for gestating cows. Such silages can be produced in round and squared bales since smaller farms only require small amounts. They can hence be used in a targeted manner while the gestating animals are fed appropriately and silage reheats are mostly avoided.

Numerous agricultural studies show that producing silages in round or squared bales is usually slightly more expensive than the production of large horizontal silos. This latter aspect should however only ever be the least important decision criteria, since economic comparisons only apply as long as bale and horizontal silages allow for equal performance and health in the animals. The sustained health and productivity influence the costs of the entire operational branch much more significantly than the short-term costs of silage preparation.

Animal health determines the exploitation period - and therefore efficiency - of animal husbandry. The decisive costs here are not the costs per forage energy unit but the costs caused by animal losses or premature elimination.

Dr. Katrin Mahlkow-Nerge is a consultant for ruminant nutrition at the Schleswig-Holstein Chamber for Agriculture in Germany.

 

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