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Energy partition in Holstein × Gyr lactating cows raised under tropical conditions.

J. P. Sacramento



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Energy partition in Holstein � Gyr lactating cows raised under tropical conditions.
R. R. Silvi1, M. R. Santos1, J. P. Sacramento*2, L. G. R. Pereira3, A. L. Ferreira3, F. S. Machado3, T. R. Tomich3, M. M. Campos3. 1State University of Santa Cruz Ilheus, Bahia, Brazil, 2Federal University of S�o Jo�o del Rei S�o Jo�o del Rei, MG, Brazil, 3Brazilian Agricultural Research Corporation EMBRAPA Dairy Cattle Juiz de Fora, MG, Brazil.

It is believed that in tropical conditions crossbred Holstein � zebu cows has a difference in the energy partition of the diet when fed restricted or ad libitum. Therefore, the objective of the study was to evaluate the effects of nutrition plans and parity on the energy partition. Twenty-eight late lactation crossbred (3/4 Holstein � 1/4 Gyr) cows (BW = 552 � 88.13 kg and MY = 15.12 � 4.16 kg/d), were evaluated using a respiromimetric chamber under tropical climate conditions. Two nutrition plans (ad libitum and restriction) and 2 parities (primiparous and multiparous), were used in a 2 � 2 factorial arrangement of treatments in a completely randomized design. The cows were fed a diet consisting of 74% corn silage and 26% concentrate and restricted cows were fed 80% of the required net energies for multiparous cows and 85% for primiparous cows. There were no effects of parities in energy partition. Cows fed ad libitum had higher intakes of gross energy (306 vs. 179 MJ/d), digestible energy (212 vs. 121 MJ/d), metabolizable energy (185 vs. 104 MJ/d) and net energy for lactation (65 vs. 33 MJ/d); showed highest heat production (102 vs. 75 MJ/d), energy loss as feces (94 vs. 57 MJ/d), urine (12 vs. 8.5 MJ/d) and methane (14. vs. 9.0 MJ/d), compared with restricted cows (P < 0.001). There was interaction for heat production between feeding levels and parities (P = 0.002), with higher values for primiparous cows fed ad libitum. The metabolizable energy efficiency used for maintenance was 0.61 and 0.58 MJ (P = 0.016) for ad libitum and restricted treatments. The energy partitioning for body tissues was higher for ad libitum cows (0.34 vs. 0.32 MJ/MJ, P < 0.001). However, cows fed restriction diet had lower metabolizable fraction use for heat production (0.54 vs. 0.73 MJ/MJ, P < 0.001). The energy balance (Mcal/d) was 5.7 for ad libitum cows and −0.1 for restricted cows (P < 0.001) owing to restriction level imposed to multiparous cows. Ad libitum cows had higher energy balance, in response to higher levels metabolizable energy, above maintenance exigencies.

Keywords: calorimetry, Girolando, metabolism.