A NZ study in the “Review’ examined the effects of different feeding levels over the dry period. Cows prior to drying off were managed to have a dry-off BCS of either approximately 4.3 or 5.0. For the following five weeks, the skinnier mob was fed to reach a BCS of 5.0 and the fatter mob fed maintenance and achieved a BCS of about 5.2.
How the cows were fed during this early part of the dry period had no effect on the amount of milk, milk protein, or milk fat produced in the first 7 weeks’ post calving.
The second part of the experiment examined the feeding levels in the last 4 weeks of the dry period. Cows were allocated to be fed at 65%, 90%, or 120% of their requirements.
Cows fed at 65% of requirements were 0.25 BCS units lighter than the other two groups by 1 week pre-calving but by 4 weeks post calving there was no difference between groups.
For the first two weeks of lactation, cows fed at 65% of requirements in the last 4 weeks of the dry period produced less milk, fat, and protein than the other 2 feeding groups.
Calcium and magnesium levels were not affected by the feeding regimen in the early dry period but the blood calcium levels at calving decreased as the feeding levels increased in the 4 weeks pre-calving.
So, in summary, how the cows are fed to reach a BCS of 5.0 in the first part of the dry period is not too important. Restricting cows to 65% of requirements in the late dry period will have negative effects on health and productivity.
Also, overfeeding cows in the late dry period increases the risk of hypomagnesaemia. It would appear the rapid weight gain we are getting used to seeing with fodder beet is not detrimental.
Angus Campbell
