Replacing human-edible feed ingredients with by-products increases net food production efficiency in dairy cows.

Discipline: nutrition/feeding; Key words: forage, distillers grain, rapeseed meal, sugar beet pulp.

Reducing on-farm storage and retail waste should increase agricultural resource efficiency and, thus, food availability. One way of reducing waste and increase efficiency could be to reduce inclusion of human-edible products such as cereal grain (e.g. maize, wheat, oats etc) and soybean meal in the diets fed to dairy cows in intensive production systems. With more than 70% of global agricultural land already being used to produce feed for livestock, using human-inedible products as animal feed is becoming important, one option being to increase the use of by-products from the human food, fibre and bio-fuel industries in the diet of dairy cows at the expense of human edibles. This was the topic investigated by Dr J. Karlsson and colleagues, the results of which they published in the Journal of Dairy Science, Volume 101 of 2018, page 7146 to 7155. The title of their paper is:Replacing human-edible feed ingredients with by-products increases net food production efficiency in dairy cows.

The authors examined whether feeding a by-product-based concentrate combined with high-quality grass silage to high-producing dairy cows will affect feed intake and milk production differently, when compared with a conventional diet. They also studied the effect thereof on the efficiency of human food production. In a changeover experiment with four 21-day periods, 24 dairy cows in mid-lactation were offered 9.6 kg of dry matter per day with one of four concentrates and high quality grass silage ad libitum. The control concentrate was based on cereal grain (wheat, oats and barley) and soybean meal (CG-SBM), whereas the three by-product-based concentrates contained sugar beet pulp (SBP) in combination with mainly heat-treated rapeseed meal (RSM), distillers grain (DDG), or a mixture of both. All diets were formulated to be iso-energetic and iso-nitrogenous.

The contents of starch were lower and the contents of NDF higher in the by-product-based concentrates compared with the control CG-SBM. The content of CP was 5 g per kg of DM higher in the concentrate SBP-DDG compared with the other concentrates. All cows, regardless of treatment, consumed their concentrate ration. Silage intake did not differ between treatments; however, starch intake was about 10-fold higher for the

CG-SBM concentrate than the by-product-based concentrates, whereas NDF intake was lower for the CG-SBM concentrate than for the by-product-based concentrates. The RSM-containing diets had lower OM digestibility and the by-product-based diets had higher

NDF and lower CP digestibility compared with the control diet. Milk from cows fed the control diet (CG-SBM) had the lowest fat and highest lactose content, whereas cows fed SBP-DDG produced lower yields of protein. In general though, no differences in yield of milk and yield of energy corrected milk (ECM) were observed among the different treatments.

There were also no differences in the effect of the different diets on cow BW or BCS. The control CG-SBM diet was less efficient in terms of HeFCE (human edible feed conversion efficiency) and net food production compared with the by-product-based diets. The net production of human-edible CP and gross energy was negative in the control diet. The SBP-DDG diet showed the highest efficiency of net production of HDEAA (human digestible essential amino acids). 

In conclusion, the results showed that by- products can be fed to cows without compromising milk yield and composition to the benefit of agricultural resource efficiency and competition with man for human-edible products.