Dr Andrew Dale answers questions on concentrate supplement strategies for grazing cows part 2

Published 10 July 15

A recent webinar by grassland researcher, Dr Andrew Dale from AFBI on concentrate strategies for grazing cows, generated a wide range of questions from the audience. This set of questions looks at issues such as fertility at grass and what kind of concentrate substitutes grazed grass the least. The first part of the questions was published in the previous issue of Forage for Knowledge.

If there were no in-parlour feeders, what is the best strategy to supplement cows and how much can be offered in one feed?

With in-parlour feeders the general guidelines suggest a maximum allowance of 5-6kg/milking of concentrates. This would be applicable to high-yielding, mature cows with a high intake capacity. The main limitations are the time cows are in the parlour and the adverse effect eating a large volume of concentrates in a short time has on the rumen environment.

In-parlour feeders target the concentrate intake to the individual cow. In their absence, it needs to be considered how concentrates can be allocated evenly across the herd. It’s unlikely that when concentrates are offered along a feed passage, either immediately prior to or immediately after milking, all cows will have access to the concentrates. Meaning, all cows will not receive a consistent intake. Mixing the concentrates with forage (for example, grass silage or maize silage) reduces the risk for the last cows not to have any concentrates. However, if grazed grass is readily available, the inclusion of a forage supplement will have an adverse effect on grass intakes, increasing the costs of the diet and potentially reducing the overall quality of the diet.

The risks of over/under feeding are obviously higher when more cows are involved and more concentrates are offered per head. Thus, to mitigate these risks, the herd could be split into two groups. The first group will then receive the concentrates in the morning, offered along a feed passage exiting the parlour, and the second group receives them in the afternoon. To reduce the risks of some cows eating large amounts, you could restrict allowance to 2-3kg/head. The main thing is that all cows that are offered the supplement need to be able to access it at the same time.


Would soya and maize be a better supplement than a mix of wheat and rape?

The quality of the energy and protein sources is something that is always discussed and in many ways the quality is reflected in the price. When feeding high levels of concentrates (5-6kg or more) per day, the quality of the components within the concentrates will be more critical and indeed, higher quality ingredients should be considered. If you’re only feeding 2-3kg/day, it’s unlikely this has a big impact on the overall animal performance, given the relatively low intake compared to overall daily intake (16-18kg DM/day).


What was the type of concentrate fed in the experiments outlined in the webinar (CP, NDF, Starch, Sugar) and did it change throughout the experiment?

All concentrates offered in these experiments were purchased from a commercial feed company in Northern Ireland and was commercially available to other dairy farmers. Crude protein contents were 19.1, 19.0 and 20.4% on a dry matter basis, with NDF of 290g/kg DM. Concentrates were consistent throughout the year within each study but varied slightly between studies due to price and availability of specific ingredients.


What type of concentrate substitutes grazed grass the least?

Research conducted at AFBI Hillsborough examined the effect of either high-starch type (barely, wheat, maize) concentrates versus high-fibre type (soya-bean meal, sugar beet pulp, citrus pulp) concentrates. These were offered at both 5 and 10 kg/day to grazing cows. Even at these high levels, concentrate type was found to have no effect on herbage intake, with the animals on the study being high-yielding (35 litres/day +). Therefore, minimising substitution is more to do with the level of supplement than the type of supplement, and targeting the supplement at the higher yielding cows.


Do you think the results of the first study in the webinar would have been different if the cows were early to mid lactation?

If the cows were early to mid lactation, then their yields would also have been higher or at least the range in yields would have been greater. In turn, this would have resulted in a higher requirement for concentrate supplementation, which in turn increases the risks of over/under feeding. I feel that the biggest factor that could influence the results is the range in individual yields between the cows.

Every farm and paddock is different. So how do you make sure what the correct level of milk yield from grass is to avoid over and under feeding during the season?

Unlike establishing long-term feeding rates in a confinement system, whereby you have a large quantity of fairly consistent conserved forage, and an idea of intake from the diet feeder on an almost daily basis, management in a grazing system must be much more reactive. The potential production from grass can vary on a daily basis due to a number of factors and really, the best approach is to keep an eye on the factors you can measure.

Grass intake is very often an unknown value, yet this is a critical part of trying to feed the grazing cow correctly. To do this, the quantity of allocated grass on, daily basis should be monitored, and once this is understood, it is easy to see if the planned intake is achieved. In this instance, supplement levels can be adjusted. The aim is to optimise the intake of grass, but there will be periods of unsettled weather when it is not possible to achieve high levels of grass intake. Make short-term adjustments to feed in this instance. Most importantly, however, is to make the appropriate downward adjustments in supplement levels once grass intakes increase again.

Furthermore, as you are trying to optimise the intake of grass, knowing the quantity of grass that is on the farm is also critically important. Making short-term subtle changes to feeding levels can help overcome deficits and surpluses in grass supply, while ensuring grass quality remains high – but only if deficits and surpluses are identified and dealt with promptly.


Is 18kg DMI feasible from grazed grass?

There are research papers which have quantified grass intakes of up to 18kg DMI from cows that were being offered high quality grass and received minimal or no supplementation. There is something of a balance to be had here in terms of striving to achieve very high intakes, and also challenging the cow to produce a post-grazing residual sward that will provide that cow with a high-quality sward in the next grazing. Maximum intakes are achieved when grass allowance is very high, yet this is not best practise due to the poor utilisation of the grass that is grown. In reasonable grazing conditions, with minimal supplementation (2kg/day), 15-16kg DM of grazed grass is a good target. As discussed above, if measurements of grass allowance are being taken, it is relatively easy to check if the cows are achieving their intake targets.


If taking 25–28l from grass, is there any impact on fertility, especially with fresh calving cows?

There are many examples of research studies which clearly demonstrate that concentrate feeding is not a solution to the infertility problem that exists in many herds. That being said, adequate levels of nutrition are important at all stages of the lactation, most notably in early lactation and in the run up to the breeding period. There are many spring block calving herds operating successfully across the UK, Ireland and beyond, whereby the herds are managed on minimal inputs of concentrate supplementation.

In many ways the preparation of the cow for this crucial stage begins at the end of the previous lactation. If the cow is dried off in the correct condition, offered appropriate mineral and vitamin supplementation during the dry period, calved down in a safe and clean environment and managed appropriately as she transitions from the dry cow diet onto the lactating diet, then this is where the chances of achieving high levels of fertility are optimised.

The aim is to be encouraging the cow that is healthy and in good condition to achieve high intakes of quality grass in the early lactation period, thus optimising nutrient intake. Again it’s about obtaining some knowledge about the herd, are they eating enough grass, what is the quality of the grass, are some cows in poor condition/losing too much condition?