Accuracy and homogeneity of total mixed rations processed through trailer mixer or self-propelled mixer, and effects on the yields of high-yielding dairy cows

Abstract

Total mixed ration (TMR) quality depends on feed levels and values, and appropriate diet formulation, but also on diet preparation practice. We examined the accuracy and homogeneity of rations, as affected by the machinery used for TMR preparation, and their effects on dairy cow performance. Multiparous Israeli-Holstein cows (n = 216) were stratified into 2 groups, according to milk yields, days in milk, parity, and body weight; they were fed the same formulated TMR, prepared by either a trailer mixer (TM) or an self-propelled loading mixer (SPLM). To examine the accuracy of diet preparation we have recorded and analyzed 10 times the difference between the programmed and the actual loaded content (as fed matter) of each feed ingredient. For evaluation of the accuracy and homogeneity of the ration contents, the TMRs from 6 spots along the feeding trough were sampled at 10 time-points, and the samples were analyzed for DM, protein, ADF, aNDF and ash contents; the results were compared with the programmed values. On another 7 occasions, samples of the TMRs were taken from 3spots along the feeding trough for evaluation of the particle sizes distribution using the Penn State Particle Separator. The mean difference – in percentage units – between the programmed and actual, loaded concentrate feeds was similar (∼5.7 %) for both TMRs (SEM = 1.5; P = 0.98), but for forage feeds it was +17.6 and - 0.6 % (SEM = 3.7; P = 0.001), for TM and SPLM TMR, respectively. The mean differences of contents (in percentage units; DM basis) between the programmed and prepared diets, were: for protein – 1.1 and 0.9 % (SEM = 0.2, P = 0.25), for ADF – 2.7 and 1.3 % (SEM = 0.2, P < 0.001), and for aNDF – 6.9 and 5.7 % (SEM = 0.2; P < 0.002), in TM and SPLM TMRs, respectively. Except for ash content, the chemical-composition homogeneity was greater in the SPLM TMR than in the TM TMR. The fraction of particles>19 mm was 2.9 percentage units greater (P = 0.04), and that of particles ≤8 mm was 3.3 percentage units less (P = 0.04) in the TM than in the SPLM ration. The milk yield was 1.2 kg/d greater (2.7 %) in cows fed the SPLM than in those fed the TM TMR (P < 0.001), and the milk-fat content was 0.8 g/kg greater in cows fed the TM TMR (P = 0.03). In conclusion, the accuracy and homogeneity of the SPLM-prepared TMR were greater than those of the TM-prepared TMR, which influenced the cows’ performance. This study demonstrates the importance of the preparation machinery for TMR quality, indicating that more attention should be dedicated in practice and research to the methods used for TMR preparation.