Mowing before grazing is a strategy sometimes used to achieve target pasture residuals with the belief that intake is increased and surplus pasture will be converted into milk.
However, neither past nor recent research supports this belief.
Earlier research compared cows grazing mown pastures versus standing pastures and reported little or no benefit to cow production, and reduced pasture growth rates. However, these studies didn't investigate the longer-term effect of mowing pastures with higher-than-recommended pre-graze pasture covers.
DairyNZ researchers joined up with farmers, rural professionals, and university professors, to compare the outcome from grazing mown versus standing pastures at two pre grazing covers: moderate (MOD) — 2900 kilograms of dry matter per hectare (kg DM/ha) and high (HIGH) — 3500kg DM/ha.
The experiment was carried out at Lincoln University Research Dairy Farm from October 2016 to February 2017. There were four treatments (see table above right) and eight farmlets (two farmlets for each treatment), each with a stocking rate of 3.5 cows/ha. To achieve different pre-graze covers, rotation length was eight days longer (29 versus 21 days) in the HIGH compared with the MOD farmlets.
Results: Cow performance
Pre-graze mowing had no effect on cow performance, with cows in both mown and grazed herds averaging 1.8kg milksolids per day (MS/d) and a 4.2 Body Condition Score (BCS) throughout the experiment.
Pasture disappearance (pre-graze less postgraze yield) was greater in mown versus grazing treatments (+2kg DM/cow/d) but substantial mown material (2kg DM/cow/d) was left behind in the paddocks.
Combined with the lack of response in cow performance, this indicates there was no increase in cow intake with pre-graze mowing.
There was an effect of pre-graze pasture covers, with cows in the MOD farmlets producing 6per cent more milksolids than those in the HIGH farmlets.
Pre-graze mowing had a negative effect on pasture performance, reducing tiller numbers and pasture density.
This means, for a given height, there was less pasture available in the mown farmlets. This resulted in less silage being made, and more silage fed out to cows in the mown farmlets to maintain intakes.* Dairy NZ
Jane Kay is a senior scientist for DairyNZ