Feeding preferences and voluntary feed intake of dairy cows: Effect of conservation and harvest time of birdsfoot trefoil and chicory

摘要

Bioactive forages contain compounds, such as tannins, that are active against pathogens. They have been successfully used in ruminants to control parasite infections. Because cattle may find bioactive forages unpalatable, it is of interest to know if an afternoon harvest time, which has been shown to increase the percentage of nonstructural carbohydrates (NSC), hence palatability, may mitigate this. The objectives of this study were to quantify voluntary intake and preference of dairy cows for 2 bioactive forages, harvested in the morning and evening, in addition to determining their time spent grazing on each forage species. The forage species evaluated were fresh chicory harvested at 0700 h (FCAM) and 1800 h (FCPM), fresh birdsfoot trefoil harvested at 0700 h (FBAM) and 1800 h (FBPM), birdsfoot trefoil baleage harvested the previous summer at 0700 h (BBAM) and at 1800 h (BBPM), and third-cut alfalfa baleage harvested the previous summer and used as control (CON). Single forages were offered ad libitum in 30-min tests to 14 dairy cows to determine intake in a 7 × 7 Latin square (experiment 1). Every possible pair of forages (21 pairs) was then presented for a 30-min test to 8 different dairy cows, and feed intake was measured (experiment 2). Finally, time spent grazing on chicory and birdsfoot trefoil was measured on 12 dairy cows (experiment 3). The tests consisted of 2 d of restriction on 1 of the 2 fields for 1 h, and 2 d of free-choice sessions (1 h) between the 2 fields adjacent to each other. Grazing time and location of the animals on the field was assessed through 2-min scan sampling. In experiment 1, the highest voluntary intakes were for CON, BBPM, and BBAM. In experiment 2, BBPM was preferentially consumed over all other forages followed by CON and BBAM. Multidimensional scaling showed that preference for BBPM, CON, and BBAM in dimension 1 was positively associated with dry matter and nitrogen content, and negatively associated with hemicellulose and soluble N/total N. No relationships between dimension coordinates and any of the measured chemical composition variables could be found for the other 2 dimensions. In experiment 3, cows spent 71% of their time grazing in the birdsfoot trefoil field and 23% in the chicory field during the free-choice sessions. In conclusion, cows in the present experiments showed an overall preference toward baled forages compared with fresh forages, most notably toward birdsfoot trefoil baleage. Cow preference did not appear to be linked to harvest time (a.m. vs. p.m.).