Post - Peak decline in milk production

12% per month drop off peak for October and November would not be uncommon. Cows on controlled diets internationally would only drop 5% or less per month post peak.

Every year dairy farmers are faced with a large drop in cow milk production after peak milk is achieved. The extent varies but 12% per month drop off peak for October and November would not be uncommon. This is not “normal” for dairy cows, as cows on controlled diets internationally would only drop 5% or less per month post peak.

There appear to be regional differences in the extent of this post-peak decline (ppd), with southern areas having less trouble.

If cows are dropping in production at this early stage in lactation then we can expect our high BW dairy cows to be losing weight at the same time in an attempt to maintain milk production. And all this is occurring in October/November when we are trying to mate cows for next season as well in our seasonal dairy system.

Attempts by Intelact Nutrition to solve this problem area for our clients and identify the key nutritional factors involved have only been partially successful. There does not appear to be any one factor in pasture involved. We can expect pasture grazed to drop in ME concentration by 1mJ of ME/kgDM at this time of year as ryegrass enters it’s reproductive phase and more stalk is present. Since we know that 1 litre of 4% fat milk requires 5mJ of ME (1 litre of 6% fat milk near 6.2mJ of ME), then it is not difficult to see why cows consuming 15-18kgDM produce 2-3 litres less milk with the lower quality grass. Intake is driven mainly by cow size, stage of lactation and quality of feed offered.

The nutrients within grass change in Oct/Nov as well as ME. Protein can become marginal for high milk production, soluble carbohydrates (sugars) start to reduce, fibre components (ADF or acid detergent fibre, and NDF or neutral detergent fibre) increase.

Sol CHO = Soluble carbohydrate
NDF = Neutral detergent fibre
CP = Crude protein
DOMD = digestibility

Methods of maintaining pasture quality would normally include “topping”, closure of area for silage or hay, perhaps moderate use of N to maintain leafiness. More long term solutions might include use of late heading ryegrasses like Impact or Quartet, use of tetraploid ryegrasses like Quartet or Nevis, “stitching” ryegrass pastures with higher quality Italians or hybrids like Flanker or Maverick Gold, use of species other than ryegrass like Fescue that encourage higher clover %.

An alternate strategy might be to supplement with higher quality nutrients (higher ME value than grass at this time) to attempt to maintain diet quality while the pasture quality is sorted out by the above methods. It is important when doing this to avoid wasting pasture – a trap that many have fallen into in the past. Higher stocking rates make it easier to justify supplement at a time when peak pasture growth is occurring, or alternately good decisions on closure for silage are needed. The following experiment helps illustrate what can happen:

1200 cows in 6 (average to above average productivity/ha) herds in the Te Awamutu region were split into half on tag numbers in each herd, were fed either molasses in the exit area in troughs (750mls consumed daily) or 1.5kg high energy meal in the paddock straight after morning milking from 1st September to 1st December. Half of each herd remained as a control (no supplement) and cows in each group were fed equal allocations of pasture each day (often grazing the same paddock split by a fence). Results varied from farm to farm, but on average productivity increased slightly in supplemented groups by approx 0.07kg MS/kgDM supplement fed (similar to many supplement trial results in NZ), supplemented cows gained more (or held more) condition than control cows, and empty cows at the end of the season were half the level in the supplemented groups (3.5% vs 7% MT). There was no difference in anoestrous level at mating in the groups, suggesting the gain in MT cows was due to better conception. Whilst it would be unwise to assume all herds would respond in a similar manner, these results do suggest that there are advantages in maintaining a higher quality (and offering greater quantity) diet through Sept/Oct/Nov. Any surplus pasture created by “substitution” (cows eat less grass when presented with most supplements as above) would need to be managed carefully to make such a supplement policy successful. It should be no surprise that anoestrous level was not altered by the supplement as most anoestrous is determined by calving condition and feeding levels just before and after calving, not feeding at mating time in Oct/Nov. At current milk prices and supplement prices the supplementation practiced above would have been break even or slightly profitable on most of these farms studied.

These results suggest it is important to consider diet “quality” as well as “quantity” fed at this time of year.