Emission reduction in dairy cattle - Approches via feeding
Within the context of adapting fertiliser and fertilising laws and ordinances and the current discussions on climate-relevant impacts of agriculture, the focus keeps on shifting to emissions from dairy cattle husbandry. It should be taken into account here that modern dairy cattle husbandry is not an end in itself. Generally, the keeping of dairy cattle serves to produce milk for human consumption. The target should therefore be the most efficient possible milk production. In this connection efficiency does not only mean cost efficiency, but also optimising the utilisation of nutrients. It is possible to influence the nitrogen and phosphorus emissions substantially via the feeding. Emissions of climate-relevant gases (above all methane, ammonia) should be taken into account as well when optimising the rations.
During the period 2012 to 2014, agriculture was involved in 50 % of the phosphorus inputs in German surface waters (UBA, 2017). In the supply/feed recommendations for dairy cattle (GfE, 2001), a recommended content of 3.4 to 3.9 g/kg dry matter (DM) is stated for phosphorus (P). Arithmetically, taking into account the unavoidable losses and the demand for milk formation, at a feed intake of 21 kg DM and a milk yield of 35 kg/day, this leads to a P requirement of 80 g per animal and day. Under the conditions of typical rations (maize silage combined with grass silage, supplemented by cereals and oilseed meal), no additional mineral phosphorus is generally required.
In the course of the increasing discussion on feeding "without genetic engineering" Rapeseed meal (RSM) is now the dominating protein feedstuff in German dairy cattle rations. Quantities of up to 6 kg RSM per animal and per day are frequently practised. By comparison with soybean meal (SBM) with 7.3 g phosphorus /kg DM, RSM has a phosphorus content of 12.5 g/kg DM. The high amounts of RSM used regularly lead to phosphorus contents of 4.5 to 5.0 g/kg DM in rations for high-yielding dairy cows (even when P-free mineral feed is used). This clear over-supply leads to elevated P-emissions that are passed into the nutrient cycle with the slurry and put a strain on the phosphorus balance of the farms.
In order to avoid additional surplus phosphorus on the farm under GMO-free conditions, it is therefore necessary to switch to concentrate feedstuffs with low P contents. In its Agricultural Experimental & Training Centre, House Riswick, The Chamber of Agriculture of the State of North Rhine-Westphalia investigated the extent to which the goal of lowering the total P contents of the rations with GMO-free feedstuffs is possible in practice (Pries, 2019). Two milk yield feeds with P contents set by selecting the components to achieve 6.4 g/kg or 4.8 g/kg. The share of RES and wheat was lowered by comparison with the milk yield feed of the control and replaced by distillers' grain and dry molasses. The main protein supplier in the milk yield feed of the trial group was RES (protected). In addition, a supplement of 14 g urea per kg feed was added. The adjustments in the composition of the milk yield feed led to the planned differences in the P content of the ration (Table 1). The lower content was at the level of the supply recommendations (GfE, 2001).
Table 1: Milk performance, P intake and P excretion in the trial (Source: Pries, 2019)
Fewer phosphorus emissions
There was no significant difference between the animal yields in the two groups. The adjustment in the composition reduced the daily P intake very clearly. At the same time the level of P emissions was reduced by the same order of magnitude. Under P-adjusted feeding conditions the adjustment of the milk yield feed made it possible to reduce the P emissions by 38 % even when continuing with GMO-free feeding.
In this trial it was possible to reduce the level of P emissions clearly by using rumen-protected rapeseed meal, Dried Distillers Grains with Solubles (DDGS), beet pulp and urea. The goal of lower P emissions can be achieved even with GMO-free feeding. However, a modified raw material input can also involve higher costs for the feed. Farms that target a reduction of P emissions from dairy cattle husbandry will generally first reduce the protein carrier input (high P contents). Optimising the feeding to reduce P emissions and optimised utilisation of the protein carriers is frequently accompanied by a lower protein supply. As the milk yield increases, the demands made of ruminal protein stability also rise.
Rumen-protected protein feedstuffs are then also frequently used (see Pries, 2019). As dairy cattle too are ultimately dependent on the amino supply to the gut, the importance of the amino acid pattern of the feed increases with rising protein stability. Table 2 shows the amino acid profile for milk, microbial protein and various protein carriers (Schuba and Südekum, 2012). The clearly visible differences in content explain the positive effects of an addition of rumen-protected amino acids described by the above authors depending on the initial ration/supply situation.
Table 2: Profile of essential amino acids from milk, rumen microbes and selected vegetable protein carriers (Source: Schuba und Südekum, 2012)
Broderick et al. (2008) examined to what extent the addition of rumen-protected methionine affects milk production and nitrogen emissions in dairy cattle with a reduced protein supply. The analysis examined four rations in which soybean meal was replaced step by step with wet maize and at the same time 0 / 5 / 10 / 15 g rumen-protected methionine was added per cow and per day. This reduced the protein content of the rations from 186 g/kg DM to 148 g/kg DM. With an addition of 5 and 10 g rumenprotected methionine per day, it was possible to at least compensate the reduced protein content of the ration (Table 3). The daily milk yield was even higher than in the control. However, with 148 g protein per kg DM and 15 g protected methionine per cow and day the milk yield was reduced by comparison with the other two supplement groups. In this group the lysine supply was evidently the closest limiting factor as the calculations of the authors show.
Across all the groups a direct connection can be seen between the protein content in the feed and the daily nitrogen (N) emissions via faeces and urine. These were up to 25 % lower than in the control. At the same time the utilisation of the nitrogen for the milk protein production increased from 26 to 34 %.
Table 3: Effekt einer reduzierten Proteinversorgung mit Zulage von pansengeschütztem Methionin (Broderick et al., 2008)
Against the background of the amino acids lysine and histidine with their closest-limiting effects for dairy cattle, Hristov et al. (2012) examined a ration with a protein content reduced to 135 g/kg DM with and without the addition of lysine and methionine or lysine, methionine and histidine. Without the addition of amino acids, the milk yield dropped to 35.2 kg/day (Table 4). By adding the limiting amino acids lysine and methionine or lysine, methionine and histidine in rumen-protected form, it was possible to increase the milk yield again. By adding all three amino acids the control level was reached again. The addition of amino acids accompanied by a reduced protein content made it possible to increase the nitrogen utilisation from the feed from 29 to 34 %.
Table 4: Influence of the supplementtion of protected amino acids in protein-reduced feeding (Source: Hristov et al., 2012)
Climate-relevant gas emissions
In our own studies too (Hovenjürgen, 2019) it proved possible to increase the milk yield by 2.3 kg per cow and per day by adding rumen-protected lysine and methionine (BEWI-FATRIX® LM 101). At the same time the utilisation of the feed nitrogen for milk formation was increased from 31.7 to 33.9 %. The standard emissions stated by the German Agricultural Society (DLG) in the "Balancing of nutrient emissions of farm livestock" (DLG, 2014) result in an N efficiency or N-utilisation of the feed nitrogen for milk formation of 22 to 28 %. With an adjusted protein supply in connection with supplementing the first limiting amino acids in rumen-protected form, it proved possible in a number of trials to increase the protein utilisation using rations customary in practice to 34 %. This is accompanied by a clear reduction of the N-emissions via faeces and urine. At the same time this distinctly reduces the potential for ammonia emissions in gas form. Up to 90 % of ammonia emissions (NH 3 ) and about 15 % of methane formation (CH 4 ) are attributed to animal husbandry worldwide (Flachowsky und Lebzien, 2005). Both trace gasses have a clear climate relevance.
CH 4 is considered to have 23 times the Greenhouse gas potential effect compared with CO 2 . By contrast with NH 3 , the CH 4 from animal husbandry is allocated chiefly to ruminants. The share from the large intestine digestion of monogastric animals is distinctly lower. CH 4 is produced unavoidably in microbial carbohydrate degradation in the rumen of ruminants by methanogenic bacteria. The methane secretion from ruminants can vary between 2 % (concentrate-rich feeding) und 15 % (fibre-rich feeding) of the gross energy intake and represents an energy loss for the animal. Depending on feed uptake, yield level, ration and other factors, between 20 and 25 g CH 4 per kg dry feed matter are emitted. Given the high importance of the need to maintain dairy cattle, it soon becomes clear that the greatest reduction potential with regard to the methane emissions per kg milk is the yield level of the dairy cow (Brade, 2014).
Figure 1: Excretions of nitrogen, phosphorus and methane per kg milk with and without protein /energy optimisation and use of BEWI-FATRIX® and BEWI-SPRAY® products. (Brade, 2014; DLG, 2014; own calculations)
The methane formation in the rumen can be influenced by a lower cell wall ration design. In the case of acetic acid formation (cellulose degradation) more CH 4 is produced than in the case of propionic acid formation (degradation of non-structural carbohydrates). The targeted use of fats in ruminant rations can also inhibit methanogenic microbes. The use of additives that demonstrably inhibit
methanogenic microorganisms (for example ionophores) is not allowed in the EU (Flachowsky und Brade, 2007). Rumen-protected fats (BEWI-SPRAY®) allow an effective energy improvement of the ration without offering a substrate for methanogenic microorganisms. The methane emission is not increased despite a higher energy supply. By using rumen-protected amino acids (BEWI-FATRIX®) and rumen-stable fats (BEWI-SPRAY®) it is possible to optimise dairy cattle rations as regards the utilisation of protein and energy carriers. At the same time these products allow a targeted reduction of the nitrogen, phosphorus and methane emissions per kg milk (Figure 1).
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Article made possible through the contribution of Dr. Michael Hovenjürgen and BEWITAL agri GmbH & Co. KG