Variation in Milk Yield Within Dairy Herds

摘要

Variation in milk yield within a given farm can be rather large, and variation differs among groups within a farm. Formulation of diets for dairy cows necessitates the adjustment of the milk yield above the average for a herd/group so that the higherproducing cows are less compromised. One approach is to formulate diets based on the mean + 1 standard deviation (SD), and these statistics are readily available, or easily computed, from on-farm computer records programs. Using three herds, the mean, median, and SD were calculated for the herds and groups within the herds. The SD for the herds differed and the SD differed within herds, but some groups had higher SD based on it being a very heterogeneous group (e.g. hospital pen). The distribution of data with such heterogeneous groups may not be normally distributed around the mean. Variation within farms may be higher than one expects, resulting in excessive underfeeding of the higher producing animals in the group. Making use of such data on variation in milk yield in formulating diets can improve nutrient availability to animals, improve income over feed costs (lOFC), and provide information to the consultant that they can discuss with the farmer which may result in a new grouping strategy for improved herd performance.