Improving feed efficiency and net merit by including maintenance requirement in selection of dairy cattle M.H. Lidauer, E.A. Mäntysaari, I. Strandén, P. Mäntysaari, T. Mehtiö & E. Negussie Natural Resources Institute Finland (Luke), Green Technology, FI-31600 Jokioinen, Finland martin.lidauer@luke.fi (Corresponding Author) Maintenance requirement ratio (MRR), i.e. the expected energy need for maintenance per kg energy correct milk produced, may be of interest in improving feed efficiency in dairy cattle. However, implementing the ratio as such into a selection index has constrains. In this study we applied Taylor series expansion to approximate MRR by a linear index including MRR’s component traits metabolic body weight (MBW), and milk (M), protein (P) and fat (F) yields. The index was compared with four other indices to assess the potential of the index to improve feed efficiency and net merit. The required variance components for building selection indices were estimated from feed efficiency observation of 539 Nordic Red dairy cows including the traits M, P, F, MBW, metabolizable energy intake (MEI), energy conversion efficiency (ECE), residual energy intake (REI) and MRR. Compared to the reference index (including M, P and F), highest net merit (+28%) and progress in feed efficiency (+45%) were achieved with an index including M, P, F, MBW and REI, and almost as good was an index of the difference between the denominator (M, P, F) and nominator (MBW) traits of MRR. The transformed linear index for MRR increased net merit (+18%) and progress in feed efficiency (+23%), yielded highest progress in M, P, and F, and less negative trend in MBW compared to the best index. In conclusion, inclusion of MRR into a selection index would favour high yielding cows, penalize heavy cows but not intake, and by this increase feed efficiency and net merit. Keywords: Ratio traits, Taylor series expansion, selection index, net merit, feed efficiency

Martin H Lidauer, Esa A Mäntysaari, Ismo Strandén, Päivi Mäntysaari, Terhi Mehtiö, Enyew Negussie

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume Biology - Feed Intake and Efficiency 1, , 815, 2018
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