Calculating dairy cow intakes can be tricky
Published 16/08/2011 | 05:00
Milk production has been sliding steadily over the last month and figures of 1.3-1.6kg of milk solids per cow per day have been common for groups over recent weeks. I find it interesting how comparable members of a discussion group can be, with often only 0.2kgMS/cow between farmers. Low figures of 1.0-1.2 have been presented on occasion, especially where once-a-day milking (OAD) is in play or herd health issues, eg IBR, high SCC, have been a problem.
However, benchmarking at one particular discussion group in the first week of August revealed a large divergence in milk solids per cow varying from 1.9kg to 1.4kgMS/cow/day, with meal being fed at 0-2kg/ cow/day.
Within this group there were a range of cow breeds and type, varying from large Holstein Friesian cows to small Jersey cross cows with liveweights varying from around 600kg to 450kg respectively.
Calving date was comparable, though calving rate did vary between herds. Interesting as this may be, its relevance actually lies with the impact this was having on cow appetite, feed requirement, and the average pasture cover.
As the group walked around the farm in question it became apparent, on scoring the paddocks in terms of pasture mass, that the lads that had cows producing the high levels of 1.8-1.9kgMS/cow were underscoring pasture mass compared to the others.
Obviously the conversation moved towards the method of assessment, and most actually suggested that they used the cows to re-assess their measurements through back calculation, and then the penny dropped!
As target pasture cover is calculated using the formula below, the assumed intake per cow was obviously having an impact on the perception of available grass cover in the paddock, as shown in the example.
Target pre-grazing cover = (stocking rate x intake of pasture x rotation length) + residual cover eg 3.5cows/ha x 15kg DM grass/cow x 22days + 50kgDM/ha = 1205kgDM/ha versus 3.5cows/ha x 18kg DM grass/cow x 22days + 50kgDM/ha = 1436kgDM/ha.