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The effect of fiber properties on intake in a sub-tropical partial mixed ration dairy system.

K. A. D. Ison



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The effect of fiber properties on intake in a sub-tropical partial mixed ration dairy system.
K. A. D. Ison*1,2, M. A. Benvenutti1, D. G. Mayer1, D. G. Barber1. 1Queensland Department of Agriculture and Fisheries Gatton, QLD, Australia, 2The University of Queensland Gatton, QLD, Australia.

Partial mixed ration (PMR) dairy systems incorporate both a mixed ration and pasture in the diet of milking cows. This system has recently increased in popularity throughout the sub-tropical regions of Australia due to more irregular seasons leading to reduced pasture growth. However, the ideal strategies to maximize total intake, and the interactions between the 2 distinct diet components are largely unknown within sub-tropical PMR systems. The aim of this experiment was to identify how variability in fiber properties; 24h neutral detergent fiber (NDF) digestibility (24h NDFD), indigestible NDF (iNDF) and mincing energy (ME; indicates the physical resistance to chewing and rumination) within the mixed ration (MR) effect intake. The study took place at the Gatton Research Dairy, Queensland, Australia, during spring 2019. The experiment treatments were 3 diets composed of either a maize, white sorghum or forage sorghum silage base, with varying concentrate quantities to achieve differences in fiber properties while balancing for NDF (Table 1). All cows were offered 12.5 and 10 kg dry matter (DM) of MR and lucerne pasture. Diet 3 had the lowest 24h NDFD and highest iNDF (Table 1), however tended to have higher pasture and total intakes, 1.0 (SEM = 0.62, P = 0.40) and 2.0 (SEM = 0.17, P = 0.17) kg DM respectively more than Diet 1 or 2. Diet 3 was lowest in ME, indicating less chewing and ruminating was required to allow particles through the rumen, likely leading to increased passage rate and consequently higher intakes. Although not significant, these results indicate that estimating accurate intakes within PMR systems from chemical fiber characteristics alone, is likely inadequate. Future work should investigate the physical attributes of fiber such as mincing energy, which coupled with chemically measured fiber properties may improve the accuracy of intake estimates.Table 1. Chemical and physical fiber characteristics of each treatment

ItemDiet 1Diet 2Diet 3
NDF (%DM)27.927.627.7
24h NDFD (%DM)40.937.433.2
iNDF (%DM)9.810.711.0
Mincing energy (J/g DM)35.426.423.8

Keywords: partial mixed ration, fiber digestibilty.