Although some studies have reported genetic variability in feed efficiency between Holstein andJersey cows, results are inconsistent. It has been suggested that average feed efficiency in dairy herds should range from 1.4 to 1.6 pounds of 3.5 percent fat-corrected milk per pound of dry matter intake (DMI).
When feed efficiency is calculated this way, it does not differentiate between the energy used for separate bodily functions, such as maintenance, lactation and body tissue accretion. Therefore, it is not possible to distinguish if the energy used for milk production is originating from the diet or from the mobilization of body reserves. As a result, cows that mobilize more body tissue might appear more efficient.
Jerseys better balance
Early in lactation, cows mobilize body fat to support their energy requirements for milk production. Tissue reserves are replenished during late lactation or the dry period. Energy balance reflects the difference between dietary energy uptake and its use by the body to support maintenance, growth, production and reproduction. Maintenance requirements consist of the energy needed to maintain the basal metabolism, conduct voluntary body activities and maintain body temperature.
Therefore, when the animal is in negative energy balance, stored body fat and tissues are mobilized to meet additional needs. There is a large amount of literature available describing the energy status of Holsteins during lactation. However, information regarding energy metabolism of Jersey cows is lacking. In a review of 26 experiments using Holstein cows, the period of negative energy balance lasted approximately 50 days with the maximum negative energy balance observed at 11 days postcalving.
Continue reading this article published in Hoard’s Dairyman.
