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Maintenance energy requirements of two Holstein genotypes managed under pasture-based system.

D. Talmón



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Maintenance energy requirements of two Holstein genotypes managed under pasture-based system.
D. Talmón*1, M. Garcia-Roche1, A. Mendoza2, M. Carriquiry1. 1Departamento de Producción Animal y Pasturas, Facultad de Agronomía, Universidad de la República Montevideo, Uruguay, 2Instituto Nacional de Investigación Agropecuaria Colonia, Uruguay.

Milk production from grazing cows is often lower than that observed in different feeding systems due to their greater maintenance energy requirements (MEm). Twenty-eight multiparous fall calving Holstein dairy cows of New Zealand (NZH; 547 ± 67 kg BW and 3.27 ± 0.20 BCS at calving; n = 14) and North American (NAH; 589 ± 43 kg BW and 2.95 ± 0.23 BCS at calving; n = 14) origin were used to estimate MEm in each genotype. Cows grazed a Dactylis glomerata and Medicago sativa mixed pasture with 15.1 ± 5.8 kg DM/cow/day of herbage allowance, above 5 cm of ground level, and were supplemented individually to supply 33% of the estimated daily dry matter intake as concentrate. Heat production (HP) was measured, at 115 and 192 ± 19 DIM, using the heart rate-O2 pulse technique and retained energy (RE) in milk and tissue were estimated according to NRC using milk yield and composition and changes in BW and BCS, respectively. Metabolizable energy intake (MEI) was calculated as HP + RE. Data were expressed as kJ/kgBW0.75/d. Linear regressions of dependency of HP on MEI (HP = b ± MEI + a) and fasting HP (FHP; regression intercept, a), heat increment (regression slope, b), energy efficiency (k; 1 − regression slope, 1 − b) and MEm (FHP/k) were calculated for each Holstein genotype. Considering the complete data set (n = 1), total RE, HP and MEI ranged from 664 to 966 kJ/kgBW0.75/d, 885 to 1167kJ/kgBW0.75/d, and 1549 to 2133 kJ/kgBW0.75/d, respectively. Regressions of HP on MEI were significant (P < 0.05) for both genotypes (Table 1). The MEm was 17% greater for NAH than NZH cows which may partially explain the lack of difference in milk-solid yield observed frequently between genotypes when both are managed under a pasture-based system. Moreover, average MEm of both genotypes was 46% above the proposed by the NRC model (540 kJ/kgBW0.75/d) probably associated with grazing activity and the high proportion of herbage in the diet.Table 1. Relationship of heat production (HP; kJ/kg of BW0.75/d) to ME intake (MEI; kJ/kg of BW0.75/d) and calculated maintenance energy (MEm)

Geneticsr2FHP(a)Slope(b)km(1 − b)MEm(FHP/km)North American0.415690.330.67853New Zealand0.574630.370.63729Keywords: indirect calorimetry, grazing.