Effect of exposure to individual ration components on feed sorting of dairy heifers

Abstract Text: This study investigated the effect of exposing heifers to individual feed components on extent and pattern of feed sorting upon transition to a novel ration. Twelve Holstein heifers (403.3±17.3 d old, weighing 409.8±11.3 kg), consuming a familiar mixed silage-based ration (FMR; 41% corn silage and 59% haylage) ad libitum, were transitioned to a novel total mixed ration (NTMR; 41.6 % haylage, 36.5% corn silage, 14.6% high moisture corn, and 7.3% protein supplement, DM basis) according to 1 of 2 treatments: direct transition to NTMR (DIR) or exposure to NTMR components individually prior to receiving NTMR (COM). Heifers were tested in replicates of 6 and fed individually with automated feed bins. During adaptation (d 1 – 4), all heifers were offered FMR. During transition (d 5 – 12), DIR heifers received NTMR, whereas COM heifers received NTMR components offered separately, in amounts according to NTMR composition (target 15% orts). After transition, all heifers received NTMR (d 13 – 20). Feed intake and feeding time were determined daily. Fresh feed and individual orts were sampled every 2 d for particle size analysis and NDF content. The particle size separator consisted of 3 screens (18, 9, and 1.18 mm) and a bottom pan resulting in 4 fractions (long, medium, short, and fine). Sorting activity for each fraction was calculated as actual intake as a percentage of predicted intake. Data were summarized by period and treatment and analyzed in a general linear mixed model. There was no effect of treatment on intake (10.6 kg DM/d, SE = 0.58, P = 0.46) or feeding time (172.3 min/d, SE = 4.2, P = 0.75) across the study. After transition to NTMR, COM heifers sorted to a greater extent than DIR, sorting against long particles (95.4 vs. 98.9%, SE = 0.5, P < 0.001) and for short particles (101.7 vs. 100.6%, SE = 0.4, P = 0.04). Heifers fed COM also tended to sort for fine particles more (102.4 vs. 100.7%, SE = 1.0, P = 0.09). Differences in sorting resulted in COM heifers tending to have lower NDF intake, as a % of predicted intake (98.9 vs. 100.5%, SE = 0.6, P= 0.07). These results suggest that degree of feed sorting in heifers may be influenced by method of transition to a novel ration. 

Keywords: dairy heifer, feed sorting, feed presentation