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) 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 because 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 several 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% 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 system, concentrate feeding data from the milking parlour software, weekly dry matter determination of forages fed, monthly forage quality analysis and measurement of feed leftovers from each group of cows (twice/week), 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 an ongoing basis. One of these parameters is total diet protein levels being fed to cow groups during winter. These are generally in the range 15.5-16% crude protein on a total diet basis across each group of animals.
