ALUMNI CORNER: NUTRITION: ONLY PART OF THE EQUATION
Dairy ration formulation and evaluation models that predict performance based on animal, environmental, and nutritional inputs are commonly used in the dairy industry. Use of sophisticated models can allow nutritionists to formulate rations to achieve higher levels of milk and milk component production while managing feed costs. However, no model is perfect, so updates and improvements are necessary to keep models current and relevant to modern cows and production systems. Updates to the CNCPS model have been recently released and a new dairy NRC committee is being formed to update the Dairy NRC model.
These advancements in modeling are exciting and necessary to advance the dairy industry, but all models have limitations. Why? Nutrition accounts for only part of the factors that explain milk and milk component yields. Several other factors including reproduction, genetics, environment, and management also have big impacts on milk and milk component production. The CNCPS modeling group has made improvements to the CNCPS model to account for some of the non-nutritional factors, but more work is needed.
So, how much of the variation in milk yield is attributed to nutrition and what portion is due to all of the other factors? According to a field study conducted in Spain, about 50% of the variation in milk yield can be explained by the following non-nutritional factors (Bach et al., 2008):
1. Amount of feed offered to the cows daily
2. Presence of feed refusals
3. Number of stalls per cow
4. Pushing up of feed
5. Age at first calving
A total of 47 commercial dairy herds (about 3,130 lactating cows) were used in this field trial. During this 8-month trial, one TMR was mixed using the same feeds in a central location and then transported and fed to the different herds in the area. All herds were milked twice daily and cows were housed mainly in free-stalls with a few on a bedded-pack. Milk yield varied among the herds by 30 lbs even though the same diet was fed to each herd. All herds were located within a 30 mile radius, so the environment was similar as well.
Of the 5 factors above, factors 1-4 will have a direct impact on total daily feed intake, which is an essential part of modeling any ration. However, there may be other impacts of these factors on milk production that are not as easily measured.
The impact of age at first calving on milk production is not easily changed, and as expected, a higher age at first calving was associated with lower milk production. Age at first calving will have an impact on herd performance regardless of the ration the cows are being fed today. However, nutritional models do not currently account for this.
The purpose of reviewing and summarizing the Bach et al. (2008) trial is to remind ourselves that nutrition is only part of the equation for the dairy herd. Nutritionists in the field are often challenged with increasing milk production and/or milk components by manipulating the nutrient and ingredient composition of the ration within a relatively “fixed” management system. Even with the use of more sophisticated ration balancing software, we do not always see the production and/or component responses that the model predicts.
Models continue to evolve to include more of the non-nutritional factors, but incorporating the impact of all possible factors that impact milk production is a daunting task. No matter how good the model is at predicting milk and milk component production, there is no better “model” than the cow.
— Sarah Schuling
Sarah was a post-doctoral research associate at Miner Institute from September 2008 to June 2010. She works as a Dairy R&D nutritionist with Hubbard Feeds, Inc. She works out of her home office in Des Moines, IA and travels through all of Hubbard territory.