Reduced dietary crude protein in winter diets of dairy cows at CAFRE to reduce nitrogen excretion and ammonia emissions
Dairy cows are fed crude protein (CP) in order to meet their nutritional protein and amino acid requirements, to maintain bodily functions and to produce milk. However, dairy cows are not very efficient at utilising the nitrogen (N) supplied by CP. Indeed, some 75% of N is excreted in faeces and urine. There are significant environmental concerns as a result of this N excretion. For example, increases in nitrous oxide emissions from urine patches, leaching of nitrates from soil, leading to eutrophication of waterways and the topical issue at present in NI, ammonia emissions. Preliminary research has shown that by feeding lower CP diets, as well as reducing dietary cost, N efficiency can be improved, leading to reductions in urinary N excretion thereby reducing ammonia emissions from dairy cow housing and from slurry storage and spreading. Due to the above reasons, there is increasing interest in feeding lower protein diets, but doing so without compromising performance.
Application within the CAFRE Dairy Herd
For more than 15 years, the dietary crude protein content of the CAFRE dairy herd has reduced from the 18% CP traditionally recommended for peak lactation cows in the 1990’s to a target of 16.5% or less. The rationale for reducing the crude protein level in previous years has been based on cow health and fertility, to avoid the high yielding Holstein cow ‘milking off her back’. The focus on further reductions in dietary crude protein will be environmentally driven, with the objective of reducing N excretion and thus ammonia emissions.
During the winter feeding period, precision feeding of the CAFRE dairy herd allows key parameters to be monitored. Precision feeding of the herd encompasses use of the Keenan I-Pace, concentrate feeding data from the milking parlour software, weekly dry matter determination of forages, monthly forage quality analysis, and daily measurement of feed leftovers from each group of cows, thus allowing a weekly total dry matter intake for each group to be determined. This process allows key parameters to be measured and monitored on a weekly basis. One of these parameters is total protein levels being fed to different cow groups during winter. As shown in Table 1, CP% levels for last winter range from 15.9% for the fresh cow group to 16.7% for the high yielding group.
Table 1– Dietary crude protein levels fed to different cow groups during winter 2019
| Cow group | Crude protein content (as % of total dry matter fed) |
|---|---|
| Fresh cow group | 15.9 |
| High yielding group | 16.7 |
| Mid/late lactation group | 16.0 |
There are a number of methods to reduce CP in dairy cow diets, for example, increasing dietary starch concentration, accurate balancing of protein through the use of rumen un-degraded protein (RUP) and adding essential amino acids, i.e. methionine and/or lysine. CAFRE is currently considering the inclusion of rumen protected nutritional products for the 2020 winter feeding period as a means to reduce overall CP inclusion. Rumen protected products are digested in the small intestine, as opposed to being broken down in the rumen. For example, through the implementation of this nutritional strategy total CP% for the high yielders could potentially be reduced from 16.7 to 16.0%.
As further reductions in dietary crude protein are implemented within the CAFRE dairy herd, production, fertility and health parameters will be closely monitored. It is important to remember that when considering reducing CP levels in dairy cow diets, to seek professional nutritional advice and ensure all forages are analysed accurately and regularly to determine CP content. Research is ongoing in this field and CAFRE will closely follow research findings and adjust diet specifications to optimise performance while reducing emissions as new research findings become available.
