Use of antibiotics at dry off is coming under increasing scrutiny and this could change how we dry cows off in future.
- Achieving the recommended body condition score (BCS) targets is important to optimise milk production, reproduction, health and welfare.
- Energy is only partitioned to BCS when maintenance, activity, pregnancy and milk production demands are already met.
- Cows in cold and wet conditions require additional energy for maintenance, and thin cows require more energy than fat cows.
- Cows need time to gain BCS. They gain almost no BCS in the month before calving and often lose BCS in the two weeks following drying off. Even well-fed cows will not gain more than 0.5 BCS unit in a month.
- Different feeds have different efficiencies for BCS gain in the dry cow.
- Lower BCS cows must be dried off earlier to reach target BCS at calving.
The main objective of management in the last third of lactation is to set the cow up for the following lactation. This requires a focus on body condition score (BCS).
BCS targets have been defined from decades of research in New Zealand and internationally.
To optimise farm management (i.e. milk production, reproduction, health), mature cows should be BCS 5.0 at calving, with first and second calvers at 5.5 BCS1.
To achieve these BCS targets, cows must:
- have sufficient feed to eat above the requirements for maintenance, milk production, pregnancy and activity, and
- have enough time to increase BCS.
The fact that cows require a certain amount of feed to gain one BCS unit is clearly understood, however the amount of time needed is often forgotten2. Modern dairy cows and, in particular, the thinnest cows, do not partition much energy to BCS while milking3.
These cows must be dried off early to have sufficient time dry to gain condition for optimal BCS at calving.
BCS and animal welfare
Recent research by DairyNZ and AgResearch has shown that animal welfare is more likely to be optimal when cows calve at the recommended targets4.
Cows fatter than recommended had a higher risk of metabolic diseases, such as ketosis, while thinner cows were at a greater risk of infectious or inflammatory diseases, such as uterine infections. Thinner cows were less able to compete for scarce feed resources, prolonging hunger and further increasing the risk of disease4.
Thin cows at calving become even thinner cows at peak milk production1. In the Dairy Cattle Code of Welfare, any animal below BCS 3.0 must be managed immediately to increase BCS.
Although well-managed farms will sometimes have a small proportion of thin cows because of health issues (e.g. mastitis, metritis or lameness cases), ensuring that young and mature cows calve at the correct BCS minimises the need for intervention.
BCS and cold stress
The importance of maintaining cows in good condition is greater in colder climates. In these situations, subcutaneous body fat (just beneath the skin) acts as an insulating layer between the animal’s core and the environment. Therefore, cows in good BCS are better able to withstand cold.
Even when cows have adequate condition reserves, there is a temperature below which the animal must increase its metabolic rate to supply more body heat and maintain a constant core body temperature (i.e. the lower critical temperature). This means that maintenance energy requirements increase.
In New Zealand, if a cow is clean and dry and there is little wind or rain, cold stress is rare until ambient temperatures fall below -10°C. However, rain, wind and mud will result in cold stress at higher temperatures and extra energy is required for heat production.
For example, if the ambient temperature is 2°C and a wet cow is exposed to wind and rain in a muddy environment, an additional 16 MJ ME (or approximately 1.5 kg DM/day) is required just to maintain body temperature. This is on top of the usual maintenance, pregnancy and BCS requirements, and needs to be taken into consideration when determining feed allocation in colder weather.
Strategies to achieve BCS gain
There are four main strategies to achieve BCS gain:
- increase feed allocation to lactating cows
- once-a-day (OAD) milking
- dry off at-risk cows early
- feed dry cows for BCS gain.
At this stage of the season, it is too late to rely on the first two options. Increasing feed allowance or supplementing lactating cows has only a small effect on BCS gain, because genetic selection over several decades has resulted in cows that partition energy to milk at the expense of BCS.
DairyNZ research found that feeding an extra 3 kg DM/day of a high energy concentrate to a lactating cow for 100 days in autumn only increased BCS gain by 0.12 BCS units3.
Additionally, OAD during late lactation only has a small impact on BCS gain. In a recent experiment, cows milked OAD for 84 days in late lactation were only 0.25 BCS units greater at dry-off than those milked twice-a-day5.
Now is the last opportunity to implement a plan for BCS gain. This plan should include: when to dry cows off and how much to feed them when dry.
Feeding dry cows for BCS gain
Compared with a lactating cow, a dry cow gains BCS more efficiently because she does not have the energy demand of milk production and has lower activity and maintenance requirements.
Different feeds are used with differing efficiencies in the dry cow. The amount of different feeds required to gain one BCS unit is presented in Table 1.
A critical factor in managing BCS gain in dry cows is the time required for a cow to gain BCS. Two things are important:
- A dry cow will not gain BCS for one to two weeks after drying off, due to the active immune response involved in the drying off process. This is often exacerbated by underfeeding these cows unnecessarily.
- Dry cows gain very little BCS during the month before calving (less than 0.1 BCS units) because of the large energy demands of the growing calf1. Research results indicate that feeding more than maintenance during the month before calving to try and gain additional BCS can increase the risk of metabolic disorders post-calving6.
Therefore, there are approximately 40 days during the dry period that a cow does not gain BCS. This needs to be taken into consideration when developing the feeding strategies for BCS gain.
Feed requirements per day
Figures 1a and 1b show how the days available during the dryperiod to gain BCS can affect the cow’s ability to achieve BCS targets.
Figure 1a is an example of a 450 kg crossbred cow dried off at 120, 90 or 60 days pre-calving, at BCS 4.0. The vertical bars represent required feed eaten/day at eight weeks pre-calving to gain one BCS unit.
If dried off at 90 days pre-calving, she has approximately 50 effective days to gain one BCS unit. This means that at eight weeks pre-calving, if she was fed pasture and pasture silage, she will need to eat 9.3 kg DM/day in total.
In this example, this is made up of 6.4 kg DM pasture/day for maintenance and pregnancy (DairyNZ Facts and Figures) 8 plus 2.9 kg DM pasture silage/day for BCS gain.
In comparison, if this cow is milked for longer and dried off at 60 days pre-calving, at eight weeks she will need to eat 13.7 kg DM/day. This is made up of 6.4 kg DM pasture/day for maintenance and pregnancy, plus 7.3 kg DM pasture silage/day for BCS gain.
Based on these assumptions, cows cannot consume enough energy to gain one BCS if the dry period is not at least 90 days. This is indicated by the blue bar on the figure which represents the typical intake of a dry cow being offered pasture and pasture silage (Figure 1a).
Best feeds for weight gain
New Zealand research indicates there are different efficiencies for BCS gain with different feeds during the dry period (Table 12). The energy in autumn pasture is used less efficiently for BCS gain compared with pasture silage, maize silage or PKE.
Figure 1b is the same 450 kg crossbred cow fed pasture and PKE.
If dried off at 90 days pre-calving and needing to gain one BCS unit, at eight weeks pre-calving she will need to eat 8.6 kg DM/day in total. This is made up of 6.4 kg DM pasture/day for maintenance and pregnancy plus 2.2 kg DM PKE/day for BCS gain.
Once again, if she is milked for longer and dried off 60 days pre-calving, at eight weeks pre-calving she will need to eat 11.4 kg DM/day. This is made up of 6.4 kg DM pasture/day for maintenance and pregnancy plus 5.0 kg DM PKE/day for BCS gain.
Therefore even when using a feed such as PKE, that is more efficient for BCS gain in dry cows, cows cannot eat enough on a daily basis to gain one BCS unit with a 60-day dry period.
Although the days to gain one BCS unit are dependent on feed type and amount of feed consumed, the examples emphasise the importance of drying cows off with enough time to gain BCS to reach calving targets.
Ideally, strategies to reach BCS targets should be put in place in early autumn. However, now is the final chance to action a plan which may enable these targets to be met. This should involve assessing the herd’s BCS and making decisions on drying cows off, feed type and feeding level.
- There are approximately 40 days during the dry period that a cow does not gain BCS.
- Cows fatter than recommended have an increased risk of metabolic diseases, such as ketosis, while thinner cows have greater risk of infectious or inflammatory diseases, such as uterine infections.
- Lower BCS cows must be dried off earlier to reach target BCS at calving.
This article was originally published in Technical Series April 2014