Another group of similar cows was milked TAD for the whole season as a control. All the cows were three years old or older and all groups were fed similarly on pasture and supplements.
Milk production effect
The OAD cows produced 20% less milksolids (MS) on a daily basis over the OAD milking period than cows milked TAD.
But importantly production remained 8% down for the rest of the season once they went to TAD meaning that daily production did not recover.
Across the whole season cows milked OAD for three weeks produced 7% less milk than cows milked TAD and cows milked OAD for six weeks at the outset of the lactation produced 12% less than TAD milked cows.
BCS, energy status and reproduction effect
Blood metabolites and hormone results showed cows milked OAD postcalving had better energy status over the OAD milking period than cows milked TAD.
The effect lasted for two to three weeks after switching to TAD. BCS loss was similar in the first four weeks post-calving but, by five to six weeks in-milk, cows milked OAD were about 0.2 BCS units higher than TADmilked cows.
By late lactation and with the return to TAD milking at either three or six weeks post-calving, there was no real difference between OAD and TAD-milked cows in terms of BCS.
However, indications from other studies show the longer the OAD period the greater the effect on BCS.
The early-season OAD milking tactic didn’t improve reproductive performance, with anoestrous intervals, submission rates, conception rates and pregnancy rates all similar to those milked TAD.
Workload
There are workload benefits to OAD milking during the early part of the season, and tactics such as limiting OAD to the first three weeks after planned start of calving will reduce total production losses.
Only cows that calve in the first week after the planned start of calving will experience the full production effect, while those calving in later weeks will only be milked OAD for a shorter time (less than three weeks) or won’t be milked OAD at all.
The decision to use the tactic will depend on an individual farm’s situation – staffing numbers, supplementary feed policy, seasonal challenges and infrastructure issues.
Modelling the whole-herd effect of milking OAD for the first three or six weeks after the planned start of calving shows a whole-farm annual milksolids reduction of 1-2%, or 3-5% respectively.
Milking OAD through the colostrum period only will reduce milksolids production by about 2%. At a $6/kg MS milk revenue the production loss equates to about $12,600 in lost revenue per 300 cows.
At a lower milk revenue that loss would be reduced, so farmers have to carefully weigh up the benefits in terms of stress, labour and ability to perform other tasks better against the milk revenue loss.
BCS BOOST
Milking OAD after Christmas can be used as a tactic to improve body condition score (BCS), but the reduction in feed intake will be minor.
DairyNZ studies have shown an 8% decrease in milk production if cows are put on OAD after Christmas, but if 60% of milk production is achieved by that period the loss in milk will only be about 3%.
Providing cows are still well-fed, studies have shown the move to OAD should result in cows being a quarter of a BCS unit higher at dry-off.
But it’s not a quick fix, with detectable changes in BCS not obvious until cows have been on OAD for six weeks.
Managing somatic cell counts (SCC) during a switch to OAD needs to be considered too.
Cows with mastitis or high SCC aren’t good candidates for OAD so other tactics need to be employed if the aim is to improve BCS.
While milking cows OAD will reduce production within a season the effects don’t carry through to subsequent seasons with mammary gland cells reset with each pregnancy.
OAD FOR HEIFERS
Bianca and Murray Harbutt with daughter Alison and their OAD-milked R2 heifers.
For Canterbury dairy farmers Murray and Bianca Harbutt, milking their heifers OAD from just before mating through to the end of the season ensures the best start for these valuable new herd members.
It’s a tactic they began using several years ago when they were equity partners in a 3000-cow dairy farming operation.
Logistically it made sense and also reduced pressure on the first-calvers through their first season in the large herd situation.
But when they bought their own 350-cow farm Murray and Bianca found it also made sense at the smaller scale too.
They still milk the heifers twice-a-day through the early part of the season ensuring good udder development after calving, but four days before mating they separate out the first-calvers and start milking them OAD.
Murray says they might get a couple that don’t suit the system for a variety of reasons, but an empty rate of just 2% for these young animals’ second mating ensures survival rates into their second season overall are good.
“We really see the benefits going into that second season – they go into that firing.”
During mating there’s less stress on both cows and people and it stays that way for the rest of the season.
“You probably can’t say it’s just the OAD that helps with that in-calf rate because there are so many things that affect that, but I think it is a big help.
“We really see the benefits going into that second season – they go into that firing,” he says.
The heifers are milked in the morning and will get themselves to the farm dairy once the paddock gate is opened.
The system means Murray and Bianca can run the farm on their own and with only the older cows to milk in the afternoon they have a little more time for other farm jobs, children’s events at school or after school-activities.
Murray says they have to watch the heifers aren’t checked through autumn because production won’t bounce back up again if it drops because of a cold spell or feed pinch.
Because they’ve run the system since they bought the Lowcliffe farm they don’t have a different system to compare it with in terms of production.
“But I don’t think we lose that much,” Murray says.
The little they might lose in production is probably accounted for in the low labour cost, good in-calf rate in the second mating and ongoing benefits from well-grown heifers.
• Check out DairyNZ’s Technical Series issue from June 2013 for more information at www.dairynz.co.nz/media/424985/technical_series_june_2013.pdf
