Feeding Cows In Late Lactation
Updated: Mar 9
Providing enough dietary nutrients to keep your cows milking through to 300 days should be a core goal of NZ dairy farms. LIC statistics for the 2019/20 season showed the average lactation for NZ dairy cows at 268 days, which represents future opportunity.
To achieve this, we need to implement pasture management principles and complementary feeding practices that provide improved nutrient levels to our cows. This is to not only improve peak milk production, but to reduce post peak decline and increase days in milk without excessive body condition loss.
Late lactation signals that we are entering into something of a 'wrapping up' phase, however we still need to remain focused on some vital objectives. The levels of milk yield achieved during this stage depends very much on how good the diet was during mid lactation, the flatness of the milk curve and pasture availability and quality. If milk production has been allowed to free-fall during mid lactation, your cows will be unlikely to have any significant up regulation of milk yield now. Cows struggling for body condition should not be pushed hard into late lactation to make up for poor early lactation management. Consider drying off poor body condition score or high somatic cell cows earlier.
Currently many cows will be at least 22 weeks pregnant, or a little over halfway. Hormonal adaptations taking place within her body will start having a greater impact on the way she partitions energy before giving us milk production. Our pregnant dairy cows will start prioritising glucose for the growing foetus instead of the mammary gland and milk production. Glucose requirements for pregnancy have a steady increase, at the same time glucose requirement for pregnancy is decreasing due to decreasing milk yield. As a result, our cows are quite efficient at building body condition, provided we are meeting the energy requirements for maintenance, walking, pregnancy, milk production and body condition gain.
We can further influence where cows are partitioning energy by feeding diets high in carbohydrate and energy, but low in protein. This is where feeds such as Maize Silage or cereal grains can be a great fit for boosting cow condition in late lactation.
Cows are much more efficient at increasing body condition score (BCS) while they are lactating than during the dry period. During lactation, every kg of live weight gain (LWG) will cost around 42MJ ME/kg LWG. During the dry period that same kg of weight gain will cost around 55MJ ME/kg LWG. Ideally the desired BCS at calving should be achieved by the time cows are dried off. Our current understanding points us towards a target BCS at calving of 5-5.5. For some farms that may be challenging and at a bare minimum aim for a BCS of 4.5 at dry off and aiming to put on 0.5 BCS during the dry period.
For those weighing their cows daily ensure that weight gain is greater than foetal growth accumulation. Foetal growth will contribute to the weight gain of cows in late lactation, so ensure cows are actually gaining body condition and not just progressing in pregnancy.
As we can see from Table 2, we do need to feed more during late lactation if we are wanting to extend milk production and build body condition. It is achievable but we need to ensure we are getting enough kilograms of dry matter intake to do so.
How we meet this energy requirement will depend on what supplements and diet ingredients we are able to utilise on farm but remember that higher levels of NDF such as from silage and maize silage may limit dry matter intake. Any time we are feeding starch in the diet, always include a rumen buffer such as Acid Buf.
Milk is rich in minerals that can only come from within your cows. We really need to replenish what has been given over the course of the year for the continued health and productivity of the cow and her developing unborn calf. Failure to replenish these minerals can mean greater incidence of metabolic disease, poor animal health, poor milk production and poor reproductive performance. We will run through the cow’s annual calcium and phosphorous mineral requirements in another article.
The absorbed Calcium per kilogram of Milk produced varies slightly with the protein content of milk. There is also a breed effect, with Friesian cows requiring 1.22g Ca/kg of milk and Jersey or Kiwi X type cows requiring 1.45g Calcium/kg of milk.
If the cow has insufficient bio-available calcium from the diet, then Calcium is mobilised into the blood from recently remodelled bone (last 90 days) to make up the difference. Up to 800-1300g of Calcium can be mobilised from bone to support milk production during early lactation and is only restored to bone during the last 20 to 30 weeks of lactation and the dry period (Ellenberger et al. 1931). Failure to do so can result in osteoporosis and/or greater incidence of milk fever at calving time!
Fast growing pastures in autumn can run Calcium levels as low as 0.4%/kg DM. If such pasture is fed with other low calcium feed supplements such as Maize silage, PKE, or cereal grains, then it is not uncommon to see cows going down with Milk fever (Hypocalcaemia). This should sound alarm bells as it is a sign that we have insufficient remodelled bone for the cows to mobilise calcium from.
Phosphorous is another macro-mineral contained in Milk (0.7-1.2g P/kg milk/day). If there is insufficient dietary Phosphorous, then cows will mobilise this from their bones. Phosphorous deficiency can show up as reduced appetite or voluntary dry matter intake, poor milk production, poor reproductive performance, or pica (eating strange objects e.g., rocks).
Late lactation is a great time to refill the bone deposits as the process takes time.
Fodder beet, Maize Silage and Forage brassicas can all be low in Phosphorous. Levels can vary significantly so it is important to have an extended feed test to ensure you are feeding the optimum level for the animals’ requirements.
Don't rely on book values as this could mean under or over supplementing your animals with minerals. The easiest way to find the calcium or phosphorous content of your forages is by taking an extended feed test and sending through to your feed laboratory. . Thankfully, we can fix this by providing the correct amount of Limestone, Di-Calcium Phosphorous (DCP) or other calcium/phosphorous supplements to your cows.
For advice and strategies on getting the right nutrition balance and minerals for your herd in late lactation contact us on 0274273081 or email: Steve@cowcentric.co.nz
Article written by:
Steve McGill BAppsc, AARNe
Farm Consultant/Ruminant Nutritionist