Navigating your way through late lactation
Sarah Maher, Regional Manager Southeast, Alltech Ireland, body condition scores some heifers
Irish dairy farmers have faced many challenges in recent months. Decreasing milk price, poor weather conditions and nitrates derogation implications have all been common topics of discussion during farm visits.
As cows move further into late lactation, ensuring sufficient dry matter intake (DMI), meeting milk quality standards and ensuring cows are achieving body condition score (BCS) targets will be crucial for milk production in the current lactation and for a successful dry cow period.
Arguably, the most immediate challenge for farmers has been the prolonged wet weather. The dry matter content of grazed grass has decreased significantly recently, and this has put pressure on farmers to maintain their herds’ total DMI and, subsequently, milk production. If left unaddressed, milk production will fall at a steeper rate than it should.
As a rule of thumb, milk production should fall no greater than 10% per month relative to the previous month’s milk yield. For example, if a cow averaged 20 litres on September 1, the average daily milk yield should be no less than 18 litres on October 1 (a 2L/month decrease). Anything less than this signifies a potential DMI deficit.
The amount of DMI that is offered to the herd can be estimated through a calculation, and from this, we can work out an individual cows offered DMI. For example, if one hectare of grazing area per day is being allocated to a 100-cow herd and if the pre-grazing cover is 1,200kg dry matter per ha, 1,200kg dry matter per ha divided by 100 cows will mean that 12kg dry matter per cow per day is being allocated.
Depending on cow size, this will equate to a deficit of 6–8kg DM for grazing cows.
It is worth emphasising that estimated DMI per cow will fluctuate based on weather, and care should be taken around estimating DMI from grass on wet days, as dry matter of grass will be reduced, and subsequently readjusting the amount of supplementary feed offered to cows.
Strategies around overcoming decreased cow DMI include:
- Offering increased levels of concentrate supplement in-parlour;
- Feeding out good-quality grass silage (70%+ dry matter digestibility) at milking;
- Offering a partial mixed ration (as a buffer mix between grazing bouts);
- Housing cows part/full time depending on paddock accessibility and/or grazed grass availability.
It is well known that milk quality can deteriorate in late lactation. This can be attributed to naturally decreasing milk production as the cow nears dry-off and the housing period.
Milk solids, such as fat and protein concentrations, will increase, and recent UCD research has shown the importance of offering cows concentrate supplement to further improve milk fat and protein concentrations. Therefore, offering 2-4kg supplement in-parlour will be beneficial.
Milk quality components like somatic cell count (SCC) and total bacterial count (TBC) will also increase, which is undesirable from a milk processing perspective.
Milk recording will keep a farmer well informed as regards SCC in individual cows. A cow that qualifies for selective dry cow therapy should have a consistently low SCC throughout the lactation cycle.
It is also advisable that where cows have had clinical mastitis and/or high SCC previously, these cows should be considered candidates for a longer dry period, upon veterinary consultation. This will give the cows’ mammary gland(s) a better chance of recovering from previous mastitis infections.
Milk quality components like SCC and TBC will not be as easily manipulated through nutritional strategies in late lactation as they will with good hygiene standards.
That said, vitamin E supplementation, for example, through Alltech’s Sel-Plex, has previously been shown to significantly reduce SCC in early lactation.
Bulk tank milk lactose concentration must be maintained at more than 4.2%. On the one hand, low milk lactose concentration is associated with inadequate feeding in early lactation.
On the other hand, lower values in late lactation indicate that a significant proportion of cows are yielding <10 litres per day, and these cows should be considered for dry-off.
Other tips for maintaining a high standard of milk quality include:
- Washing with a caustic detergent (24–25%) twice per day post milking;
- Changing milk liners twice per year or every 2,000 milkings;
- Regular pressure washing of the facility;
- Bulk tank milk should be cooled rapidly to <4 degrees Celsius (helps to reduce TBC).
Your milk quality advisor will be able to provide further information on the above.
BCS is a measure of body fat deposition and is measured on a 5-point scale with increments of 0.25 points, with a score of 1 being an extremely emaciated animal and a score of 5 being an obese animal.
From the standpoint of a ruminant nutritionist, it is undesirable to see these extremities within a herd, as it usually indicates serious metabolic issues like ketosis and fatty liver syndrome post-calving.
It is worth noting that from dry-off to the post-calving period, the target is that cows should not lose more than 0.5 BCS. Anything beyond this indicates nutritional imbalances within the cow. Table 1 indicates normal BCS ranges by stage of lactation.
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Correcting individual cow BCS in late lactation is crucial. The main reason for this is that lactating cows utilise energy 25% more efficiently for body weight gain than dry cows do.
In contrast, trying to increase BCS in the dry cow period will likely require expensive imported feed, and the cow will also partition more nutrients to foetal growth, which can create issues around calving difficulty.
It is advisable to have the herd condition scored by a trained operator, particularly in late lactation. Once BCS is determined, it is easy to decide on the next course of action.
While over-fat cows are less common than under-conditioned cows in the context of late lactation, it is important that BCS is corrected in these animals as well.
These cows should receive limited concentrate supplementation in late lactation. They should also be grouped separately whilst still milking if the facility is available, and their energy intake should be restricted.
For example, if a cow is 2.75 BCS, she is off the target of 3 BCS. Research shows that 0.25 BCS is worth 12.5 kg of body weight. Therefore, the cow will have to put this on her back before dry-off to hit the target BCS of 3.
For under-conditioned cows in late lactation, a couple of strategies can be implemented to improve BCS:
- Increase in-parlour concentrate supplement by 2-3 kg;
- Milk cows once a day to reduce energy demand (low-SCC cows only);
- Dose (if possible) where faecal egg counts show worm burdens.
