Predicting and improving dry matter intake of dairy cows

(c) Agefotostock

Feeding cows must consider two aspects: what feeds can be grown in the farm and what needs to be bought, and how the feeding should be optimized. Optimization is either searching for the minimum or the maximum. Optimization problems must consider the factor to be minimized or maximized, the factor to be optimized and its relation to the first factor and different constraints. Different optimization possibilities are for example lowest cost, highest milk yield / protein yield / milk fat yield or minimizing P / N emissions and excess nutrients.

Optimization should also be done for different time periods. Short-term optimization is usually just optimizing feeds based on their current costs and perhaps balancing the homegrown feeds with bought feedstuffs. Medium-term frame optimization is about planning how to use pastures, what crops to grow and how the crop rotation is implemented. Long-term optimization is about what type of feed to use (total mixed ratio, liquid / solid / semi-solid feeds) and what kind of machinery and knowledge is needed to produce and distribute the feed for the animals.

There are several different recommendations for cattle, many of which have been referenced to in this blog. However, every cow, heifer and calf is unique, and every cattle has its own specific needs. Feed optimization should consider the prices of the feeds, the professionally analysed qualities of the home-grown feed and the predicted eating capacity of the animals (TDMI, total dry matter intake). These provide data for calculating the estimated milk yield, which is the basis of calculating the nutritional needs of each animal group. For detailed information about the TDMI, please refer to Huhtanen et al. (2008).TDMI index is calculated for silage DM intake (SDMI) and concetrate DM intake (CDMI) separately. TDMI = SDMI + CDMI - 1000, and each TDMI point is approximately 90-100 g DM / d.

Online SDMI calculator by MTT

SDMI and TDMI are normalized so that an average silage gets 1000 points. The "average" in this system refers to a grass-based silage with 25 % DM, D-value of 680, 80 g/kg of acids and an NDF content of 550 g/kg DM. 1 If a feed gets 100 points, the cows will eat 10 kg DM of the said feed in a day, but only 8 kg DM of a feed with 80 points.  To get a better understanding of TDMI and its components, please refer to the online calculators provided by the Finnish research institute MTT: SDMI calculator and  CDMI / TDMI calculator.

CDMI differs from TDMI and SDMI. It describes how much less silage the animal eats when the amount of concentrate is increased. Generally, the more concentrate is offered, the less silage the animals eat. The replacement ratio is approximately 0.47: for each 1 kg of concentrate added, the cows decrease their consumption of silage by 0,47 kg. Protein in the concentrate impacts consumption to both directions: when the crude protein content of the concentrate incerases over 170 g/kg DM, consumption of feed increases; when the amount of rumen-digestable protein increases, consumption decreases. Cows are hence able to regulate their intake of nutrients by altering their consumption of concentrate and silage (Kuoppala et al 2008).


Several factors affect the eating potential of the cow. The factors can be classified into four main categories:

• Feed-based factors
• Animal-based factors
• Environmental and management factors
• Interactions.

Examples of changes in the body after feeding.

Feed factors are the amount and quality of feeds used, and their effects in the digestive tract (e.g. metabolites). For example, ammonia from formed from excess amino acids send inhibitory signals to the metabolism. Feed with low digestibility sends physical inhibitory signals as the rumen fills up. Animals factors are size of the cow, milk yield, genetic traits and the state of lactation and age of the animal. Environmental factors consider the management of the animals: how the feed is distributed, number of feeding places in the barn, length of day, climate and weather. Interactions are different interactions between the other factors. For example, some breeds react more strongly to hot weather, and thus eat and produce less.

So why is it important for a cow to eat as much as possible? Dairy cows have been bred to produce spectacular amounts of milk, which far exceeds the needs of the calf. The production of milk requires huge amounts of nutrients, but the cow can only eat a certain amount of feed a day. The nutritients it doesn't receive from feed are absorbed from the animal's own tissues, leading to weight-loss and possible metabolism-related illnesses. Feed optimization can ensure that the cow gets the right amount of right feeds with accetable costs. Increased eating also increases milk yield. Studies have shown that the regression between TDMI and milk yield is 0,9499.

The farmer has several possibilities to increase TDMI and thus increase the milk yield:

• Ensure a high D-value for the silage. 10g / kg DM increase in D-value increases cfeed consumption by 175 g DM/day.
• Ensure successful preservation (fermentation, baling, wilting). Oxygen-free preservation and low pH prevent molding and wrong types of fermentation. When the fermentation acids increase 10 g / kg DM, consumption decreases 128 g DM d.
• Include whole crop silage or forage and cereal silage into the basic grass-based silage. Inclusion of 30-70 % of red clover increases consumption by 1,3 kg and milk yield 1,3 kg / day.
• Include peas, oat or broad beans to the silage.
• Optimize the DM content of the silage. Consumption increases linearly until 42 % of DM, and then begins to decrease.