Many dairy farms have long, protracted calving and mating periods but not by choice. A recent Dairy Australia study of the reproductive performance of Victorian dairy herds found the average six week in-calf rate was fifty per cent.
One of the key influences of reproductive performance is calving well before the mating start date. So having a tight calving pattern is a big part of good reproductive performance. The challenge is getting cows calving early in the first place.
From the Dairy Australia study, we know the bulk of the cows contributing to the six week in-calf rate calved in the first six to nine weeks. Only 20 per cent of the cows that calved in the three weeks before mating started contributed to the six week in-calf rate (ICR). Almost none of those cows that calved on or after mating started contributed to the six week ICR.
Basically, cows not calving in the first six to nine weeks have a pretty low chance of getting back in calf in time to maintain a tight seasonal calving pattern.
Given the current spread of calving on most farms, there is a need to intervene in order to achieve a significant improvement in calving spread and reproductive performance.
One strategy to improve reproductive performance is to consider a shortened mating period. All the cows that get incalf will be early-calvers next season, but something needs to be done with those cows not in calf at the end of the shortened joining period.
For some farms, those cows that do not get in-calf could comprise a significant proportion of the herd. So cows not incalf need to be managed profitably.
The strategy is to retain these cows in the herd as long as they are considered valuable to the business.
Three options come to mind.
One is to delay the mating for a year with the view to join them to calve in a seasonal pattern in the following year. Research into longer lactation suggests that the top half of the herd on two year lactations will produce almost as much milk solids as their herd mates that have had two 10 month lactations.
We also know that many cows on two year inter-calving intervals will have lower milk production and dry off earlier than the desired two months before calving.
A second option is to mate the empty cows about six months later and have a split calving pattern. This suits some farmers but not others. If split calving doesn't suit, these cows could be sold to farmers who have a need for cows calving at this time.The price of a sound milker is much higher than a cull cow,plus you have six months extra milk income compared to culling at the end of twelve months.
A third option is to keep milking the carry over cows until they are no longer required and sell them as cull cows. Of course early selling of some, or all of the long lactation cows can also be applied to the other options if the season is not favourable for keeping them.
Incorporating longer lactations into your system will impact on the feed plan due to more cows milking through, often in winter when paddocks can be wet or summer/ autumn when pasture might be limiting. Cash flow will change and annual milk income could drop slightly in the transition phase, increasing once the calving pattern is tightened.
How short a mating?
A seasonal calving herd will have about 15 weeks from start of calving to start of mating. Given the dismal reproductive performance of cows calving within three weeks prior to mating, shortening the mating period to 12 weeks would seem desirable if rapid progress is to be made.
How many cows to extend?
Shortening the mating period to 12 weeks could initially result in 30 per cent of cows being candidates for a longer lactation. So it might be a two or three year plan for some farms.
Given that most herds have a 20-25 per cent heifer replacement rate each year, it is not necessary to keep many of the carryover cows. The number could be adjusted at any time as seasonal conditions and economics dictate.
The number of carry over cows will reduce significantly in subsequent years as there will no longer be late-calvers once you use a short mating period.
Using a 12 week mating, the number of cows considered for longer lactations next year will drop from ~30 per cent to around 10-15 per cent (given average reproduction performance). This is without improving other factors that are associated with in calf rate. This number is much more manageable.
Just how much to shorten the calving-mating interval is an individual choice, but it is clear that many farms will remain in a poor reproduction cycle unless they do something to avoid late calving.
No single solution
There is a concerted industry effort to improve reproductive performance. With no silver bullet in sight, improved reproductive performance will require a multi-facetted approach. It is important to consider all aspects associated with good reproductive performance.
For more information please contact Greg O'Brien DEPI Ellinbank, on (03) 5624 2288.
This work is supported by DEPI, Dairy Australia and the dairy service levy.