AFBI explores the impact of reducing human edible ingredients in the diet of early and late lactation dairy cows

A recent study at AFBI, Hillsborough has demonstrated that the milk yields of both early and late lactation cows can be maintained when offered rations containing reduced quantities of human-edible ingredients (cereals and soyabean meal), but while maintaining recommended energy and protein levels

However the milk fat and protein content of milk produced from cows offered the low human-edible ration in this trial was reduced. The following article describes the study in more detail.

Background

Dairy cows have the ability to digest feeds that are inedible to humans, such as grazed grass and grass silage, and utilise them to produce milk, that is then consumed by humans. However, higher yielding cows are normally fed large quantities of concentrates to support milk production and these concentrates often contain ingredients, such as wheat and maize, which could also be consumed by humans. The use of these “human-edible” ingredients in livestock diets is being increasingly challenged as we seek to feed a growing global population. Furthermore there are growing concerns about the sustainability of some feed ingredients used in dairy rations, for example, soyabean meal.

Given these challenges it makes sense to consider using ingredients in dairy rations which have a low human-edible content such as rapeseed meal and distillers grains and to reduce the use of soyabean meal. However the impact on dairy cow performance of adopting rations based on low human-edible ingredients needs to be assessed. Results from an earlier study indicated that reducing the inclusion of human-edible ingredients in dairy cow concentrates had little impact on the performance of mid-late lactation dairy cows. However it might be expected that there would be a negative impact associated with using more by-product ingredients in the diet of early lactation cows compared to later lactation cows. This was examined in a recent study within the DAERA funded SusMilk project which examined the effects of reducing human-edible feedstuffs (mainly cereals and soyabean meal) in the diets of early and late lactation dairy cows.

Research study

The experiment involved 40 dairy cows, 20 in early-lactation and 20 in late-lactation. All cows were offered one of two concentrate types in the form of a total mixed ration with concentrates containing either 51 % human edible ingredients (high human-edible concentrate) or 18 % human edible ingredients (low human-edible concentrate).  A list of the ingredients used in the rations (in decreasing order of inclusion) and nutrient composition is given in Table 1. Both concentrate types were formulated to have a similar crude protein (CP) and metabolizable energy (ME) concentration, while the high human-edible concentrate had a higher starch content than the low human-edible concentrate. Daily dry matter intake (DMI), milk yields, milk composition and edible feed conversion rate (eFCR) were measured during the experiment. eFCR was defined as the quantity of human-edible output in milk divided by the amount of human-edible feed used to generate it.

The key milk production results are presented in Table 2.  As expected, early lactation cows had a greater feed intake and milk yield and poorer milk composition than late lactation cows. However concentrate type had little impact on either feed intake or milk yield within early or late lactation groups. This disproved our hypothesis that early lactation cows would show a better response to the inclusion of human-edible ingredients in the diet. Nevertheless, irrespective of stage of lactation cows offered the high human-edible concentrate, in this study, produced milk with a higher milk fat and protein concentration. This in turn increased the value of each litre of milk produced and the “Margin-Over-Concentrate” for cows offered rations high in human-edible ingredients.

However cows offered the concentrate high in human-edible ingredients had a lower eFCR value than cows offered the ration low in human-edible ingredients.  Why is this important? While animals in all the treatment groups generated a greater human-edible output (milk) relative the quantity of human-edible inputs offered (concentrate), the response of cows offered the low human-edible concentrates was 2.5 times greater than that of cows offered the high human-edible concentrates. The improvements in eFCR observed with cows offered the concentrates low in human-edible feed ingredients demonstrates that we can make greater use of by-product ingredients in dairy cow diets and in doing so we can free up more human-edible ingredients to feed the growing global population.

Further studies are underway to assess the long term impacts of feeding these rations.

Summary

This experiment has demonstrated that feeding dairy cow rations based on low human-edible ingredients (no cereals or soyabean meal) had little impact on the milk yield of early or late lactation cows, although milk fat and protein concentration were reduced. As a result, in this study, Margin-Over-Concentrate decreased marginally. However cows offered concentrate with a reduced human-edible fraction produced milk with a higher human edible feed conversion rate.

Table 1. Ingredient composition and analysis of the rations used in the trial (listed in decreasing order of inclusion).

Table 1. Effect of reducing human-edible ingredients in the concentrate on the performance of early and late lactation dairy cows

¹Figures based on milk price of 37 ppl +/- changes in milk quality. Concentrates costed £293/t and £292/t for the low and high human-edible concentrates respectively (based on July 2024 costs).

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