In the January 99 Dairy Newsletter I made the point that there is a linear relationship between the level of peak milk production and how much milk a cow will produce during that lactation. Less than this and production is compromised, but greater than this isn t necessarily bad because, as some producers with high herd averages have noticed, their DIM at peak are actually much higher, probably because the cows are fed and managed better. The second part of the dairyman s question from last month was whether higher producing herds peak later in their lactation.
Solid line is a regression of the data.
This relationship is not as clear as the plot of peak milk against average production per cow, but it is still positive. What I think is happening is that you are seeing the effect, rather than the cause. Cows in higher producing herds keep going up in production longer before they peak and therefore reach peak production at a higher level, further out in lactation. Some of my rationale is shown in Table 2. LTD is a measure of how many pounds of milk a cow has produced up to a certain point in her lactation.