Monday, November 29, 2021
HomeFarmweek NewsDairyHigh concentrate levels don’t always pay with feed-to-yield

High concentrate levels don’t always pay with feed-to-yield

by Dr Aimee Craig and Dr Conrad Ferris,

Dairy Research Group, AFBI Hillsborough

FEED-TO-YIELD systems, in which concentrates are offered to individual cows according to their milk yield, are now common on local farms.

In these systems cows are often offered a ‘basal diet’ (normally silage plus concentrates) to support the energy requirements of the cow for maintenance, plus a given milk yield (M+). Additional concentrates are then offered to individual cows to support milk yields above those supported by the basal diet.

However, in recent AFBI studies examining feed-to-yield systems, milk fat percentage (and sometimes milk protein percentage) decreased at higher concentrate levels, and as a result, some of the potential economic benefits of these higher yielding cows were lost due to the lower milk composition payments.

Consequently, the current study was conducted to provide a better understanding of how feed-to-yield systems operate on local dairy farms, and to examine the physical and financial performance of individual cows within these systems.

The study, which was co-funded by DAERA (through the Research Challenge Fund) and by AgriSearch, was conducted by AFBI on 31 local dairy farms from August 2018 to May 2019. Participating herds were predominantly Holstein-Friesian (18 herds were pedigree registered), and had an average annual milk yield and concentrate input of 8,800kg and 2.9 tonnes per cow, respectively. On all farms concentrates were offered on a feed-to-yield basis.

Each farm was visited 4-5 times during the study period, silages and concentrates being offered were sampled, and detailed information on feeding practices collected. Information on milk production and milk composition was obtained from milk recording organisations. Individual cow dry matter intakes were estimated using equations developed by AFBI. While this article will focus on the physical and financial performance of cows, results for first lactation heifers were similar.

The feeding approaches adopted differed across the farms. On the majority of farms cows were offered a basal ration containing both forage and concentrate ingredients, prepared using a mixer wagon, with additional concentrates offered using in-parlour and out-of-parlour feeding systems.

However, on seven farms cows were offered a forage only basal ration, with additional concentrates normally offered using in-parlour and out-of-parlour feeding systems.

All farms adopted a concentrate ‘build-up’ period following calving, before moving onto a feed-to-yield approach. While most farms had started offering concentrates on a feed-to-yield basis by day-30 post-calving, on three farms this did not happen until at least day-60 post-calving.

In addition, the feed-rate settings for the concentrate feeders varied between farms.

While the majority of farms used a feed-rate of 0.45kg concentrate/kg milk, five farms used a feed-rate lower than 0.45, while two farms used a higher feed-rate.

Impact on intakes: The effect of concentrate intake on total dry matter intake and forage dry matter intake is shown in Figure 1.

As concentrate intakes increased, total dry matter intake also increased, as expected.

However, silage intakes stayed relatively constant across a wide range of concentrate levels, and did not fall off as might have been expected at higher concentrate levels. This is because higher yielding cows have a greater overall intake potential, and consequently, offering extra concentrates to these higher yielding cows does not appear to dramatically reduce silage intakes.

From a practical point of view, this outcome provides support for a key assumption which is made when cows are managed using a feed-to-yield approach, namely that the adoption of a single M+ value for all cows in a group is acceptable (i.e. the ‘basal diet’ can support a similar level of performance across a wide range of milk yields).

However, at a concentrate intake of 8kg per day the diet contained 37 per cent concentrate, while at a concentrate intake of 18kg per day, the diet contained 58 per cent concentrate (DM basis), while diet starch content increased from 12 to 16 per cent (DM basis) across this range of concentrate levels. So higher yielding cows offered high concentrate levels are more likely to experience digestive problems if the ration is not carefully formulated.

Impact on milk yield: In traditional ‘milk yield response’ studies the milk yield response to additional concentrates begins to decrease at higher concentrate levels.

However, within feed-to-yield systems milk yields show a linear increase with increasing concentrate levels (Figure 2).

This is as expected as additional concentrates are offered according to the milk yield of the cow, rather than the cow responding to the concentrates offered. While part of this increase in milk yield can be explained by cow genetics, other factors such as concentrate level during the build-up period, differences in forage quality, as well as general management, all affect the ‘response’.

Impact on milk composition: As concentrate intakes increased, milk fat per cent decreased on the majority of farms, while milk protein per cent was relatively unaffected by concentrate intake (Figure 3).

A further examination of the data indicated that 56 per cent of the reduction in milk fat content could be explained by cow genetics, while the remaining 44 per cent of the reduction was likely explained by the effects of diet. This suggests that with higher yielding herds, farmers have placed a greater focus on milk yield than on milk composition when selecting sires.

On closer examination of the results, there were a small number of farms that experienced either no, or only a small decrease in milk fat per cent at higher concentrate levels. The reasons for this were unclear, and it is likely that no single factor was responsible.

Nevertheless, contributing factors appear to have included: similar genetic potential for milk fat per cent across all cows in the herd, the inclusion of alternative forages in the diet, lower than average concentrate intakes, and diets with slightly lower starch contents.

Economic performance: The impact of this reduction in milk fat content on the value of each kg of milk produced is shown in Figure 4 (based on typical composition payments in Northern Ireland). For cows with a concentrate intake of between 6-8kg/day, there was a bonus of 2.3 pence per kg of milk produced, while at a concentrate intake of 16-18kg/day, there was a deduction of 0.1 pence per kg milk.

It is important to remember that these are average values: the impact of increasing concentrate levels on the milk composition of some individual cows can be much greater. Farmers should use their milk recording data to examine the milk composition of the highest yielding cows in the herd as some individual high yielding cows may be producing milk with very poor composition.

To examine the economic impact further, margin-over-feed costs (£/cow/day) were calculated at a range of milk prices (18, 26 and 34 pence per kg milk), using a concentrate price of £260/tonne and a grass silage cost of £123/tonne dry matter (Figure 5).

At all milk prices examined, the marginal economic benefits decreased at higher concentrate levels.

This was a result of:

1) The decreasing value of each kg milk produced due to the reduction in compositional bonuses, and, 2) The increasing cost of each kg of diet consumed due to the increasing contribution of concentrates to the diet.

Nevertheless, at a milk price of 34 pence/kg, margins per cow continued to increase even when the highest yielding cows were fed up to 17-18kg concentrate/day. The same pattern was observed when remodelled at a concentrate cost of £300/t, albeit margins were lower.

Thus, from an economic perspective, when milk price is high, high concentrate feed levels can make economic sense for the highest yielding cows in the herd. However, at these and higher concentrate levels, cows move close to a ‘metabolic tipping point’, with a very real risk of rumen problems unless rations are very carefully balanced and managed.

In addition, when operating at these high concentrate levels, it becomes increasingly difficult for farms to meet current environmental legislation in relation to phosphorus balances, with this legislation likely to become stricter in the future.

The sustainability of milk production systems in which large amounts of ‘human edible’ cereals are fed to cows is also likely to be challenged long term.

At a moderate milk price (26 pence/kg milk), the benefit of increasing concentrate levels beyond 14kg/cow/day was much reduced, even for high yielding cows. This benefit was reduced even further when remodelled at a concentrate cost at £300/t.

At an exceptionally low milk price (18 pence/kg milk) the benefits of feeding more than 12-14kg concentrates to the highest yielding cows were minimal, and actually became negative at a concentrate cost of £300/t.

The latter indicates that farmers should carefully consider the effects of ‘chasing extra litres’ when milk price is moderate/poor, as for many cows there will be little financial benefit from doing this.

Although feeding additional concentrates at a moderate milk price may increase margins, this may not be the most profitable option by which to produce milk.

While it cannot be examined within the current dataset, there is evidence from other research that when silage quality is good, improved margins may be achieved by adopting lower feed rates post peak lactation. This is something that future research should examine.

Take home message for feed-to-yield systems

n Forage intakes remained relatively unchanged across a wide range of concentrate levels

n Milk fat content was reduced at higher concentrate levels, reducing the value of each litre of milk produced.

n When milk price is good, margins with the highest yielding cows in the herd continued to increase at higher concentrate levels.

n At a moderate milk price the economic benefits of feeding individual cows more than 14 kg concentrate per day were small

Acknowledgements: This study would not have been possible without the cooperation of the 31 farmer co-researchers who took part. Funding from DAERA and AgriSearch is also gratefully acknowledged.

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