Impact of reducing human-edible ingredients in the diet of dairy cows offered silages harvested at different stages of maturity

In a recent study at AFBI Hillsborough the fat plus protein yield of mid lactation cows was maintained when they were offered rations containing reduced quantities of human-edible ingredients (cereals and soyabean meal).

Furthermore the same response was generally observed when these concentrates were offered with silages harvested at different growth stages. 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 to utilise them to produce milk for human consumption. 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 can also be consumed by humans. The use of these “human-edible” ingredients in livestock diets is increasingly being challenged as we seek to feed a growing global population. Furthermore there are concerns about the sustainability of some feed ingredients used in dairy rations, especially soyabean meal.

Given these challenges we should seek to make more use of by-product ingredients with a low human-edible content and to reduce the use of cereals and soyabean meal. However the impact on dairy cow performance of adopting rations containing more by-product ingredients needs to be assessed. Results from earlier AFBI studies indicate that reducing the inclusion of human-edible ingredients in dairy cow concentrates has little impact on the performance of early and late lactation dairy cows. Nevertheless it might be expected that utilising more by-product ingredients in diets based on silage with a lower nutritive value might have a negative effect on dairy cow performance. This was examined in a recent study within the DAERA funded SusMilk project. The experiment examined the effects of reducing the quantity of human-edible feedstuffs (mainly cereals and soyabean meal) in the diets of mid lactation dairy cows offered silages produced from grass ensiled at two stages of maturity.

Research study

The experiment involved 32 dairy cows. All cows were offered one of two concentrate types in the form of a partial mixed ration (45% concentrate and 55% silage on a dry matter (DM) basis). The concentrates contained either 52% 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 of the concentrates is given in Table 1. Both concentrate types were formulated to have a similar metabolisable energy (ME) concentration. The grass silages offered were harvested on 4 May and 17 May (Early cut silage (EC) and Late cut silage (LC)). EC and LC had a crude protein content of 14.5 and 12.5% DM and a D-value of 71 and 69% respectively. Half of the cows on each concentrate were offered EC, while the other cows were offered LC. All diets were formulated to ensure a similar metabolisable protein supply across all treatments. 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 outcomes are presented in Table 2.  Given the two week difference in cutting date and the very different characteristics of the swards at harvest, a much greater difference in D-value was expected. Nevertheless cows offered EC silage had a greater feed intake, tended to have a greater milk yield, produced milk with a greater milk fat content and had a higher fat plus protein yield than cows offered LC silage. Concentrate type had no impact on cow performance in this study. However the response to concentrate type did differ for each silage type (an interaction). For example, cows offered the low human-edible concentrate produced less milk when offered LC silage compared to cows offered EC silage. However the same response was not observed between silages with cows offered concentrates containing a high amount of human-edible ingredients. In addition increasing the human-edible content of the concentrate increased milk protein content with EC silage but this effect was not observed with LC silage. The reasons for this are not entirely clear although it should be noted that these differences were relatively small.

Cows offered the concentrates based on low human-edible ingredients had a higher eFCR than cows offered concentrates containing cereals and soyabean meal. This means that cows offered the low human-edible concentrate had a greater output of human-edible product than the human-edible input used to generate it. Margin-Over-Concentrate tended to be lower with cows offered LC silage and supplemented with the low human-edible concentrate, reflecting the lower milk yield and higher concentrate cost associated with this treatment.

A further study is underway to assess the long term impacts of feeding these rations and determine the carbon footprint associated with producing these concentrates.

Summary

An earlier harvest date improved both intake and fat plus protein yield even though the difference in D-value was relatively small. Decreasing the quantity of human-edible ingredients (no cereals or soyabean meal) in concentrates had little impact on cow performance but dramatically improved human-edible feed conversion rate. The results suggest that there is potential to make greater use of concentrate rations based on low human-edible or 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.

Table 1. Ingredient composition and analysis of the concentrates used in the experiment

Table 2.  Dairy cow response to concentrates differing in human-edible ingredients and silage cutting date

¹Figures based on milk price of 43 ppl +/- changes in milk quality. Concentrates costed at £316/t and £292/t for the low and high human-edible concentrates respectively (based on November 2024 costs)

²Edible feed conversion rate = human-edible milk energy output/ human-edible energy input

Notes to editors: 

AFBI is an arms-length body of DAERA delivering research and development, diagnostic and analytical testing, emergency response capability and expert scientific advice for DAERA and other government departments, public bodies and commercial companies in Northern Ireland, and further afield.

AFBI’s Vision is “Scientific excellence delivering impactful and sustainable outcomes for society, economy and the natural environment”.

AFBI’s Purpose is to deliver trusted, independent research, statutory & surveillance science, and expert advice that addresses local and global challenges, informs government policy and industry decision making, and underpins a sustainable agri-food industry and the natural and marine environments.

AFBI’s strategic priorities:

• Leading improvements in the agri-food industry to enhance its sustainability;
• Protecting animal, plant and human health;
• Enhancing the natural and marine environment;
• Delivering quality outcomes and impact;
• Enabling world class science through excellence in people, places & technology.

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