NYCTEROHEMERAL EATING AND RUMINATING PATTERNS IN HEIFERS FED GRASS ORCORN-SILAGE - ANALYSIS BY FINITE FOURIER-TRANSFORM

Average daily and within-day nycterohemeral patterns of eating and rum inating behavior were determined in six Holstein-Friesian heifers (ave rage BW = 427 kg) given ad libitum access to either com or grass silag e in a two-period crossover design. Rhythm components (number of cycle s/24 h) were characterized by finite Fourier transform of the 24-h mas tication activities as measured during 4 d by continuous jaw movement recordings. Average daily voluntary intake of corn silage was 8.2% gre ater (P = .05) than that for grass silage and was associated (P < .05) with fewer meals and shorter daily, unitary eating and ruminating tim es, and smaller number of rumination boli. Analysis of variance of the daily mean of hourly activities and Rhythm Components 1 to 12 indicat ed effects of (P < .05) silage type (S), animal (A), period (P), and a significant interaction (S x A x P) for each mastication activity. Th e finite Fourier transform was reparameterized to express the amplitud e (as periodograms) and phase of each rhythm component. Rhythm Compone nts 1, 3, and 4 contributed primarily to explaining the total dispersi on of the 24-h series of time spent eating and ruminating, for both si lage types and individual heifers. Relative importance of Rhythm Compo nent 1 of time spent eating, indicative of a main circadian pattern, w as related positively to pedigree value for milk production (P = .01) and negatively to milk protein concentration (P = .09). More evenly di stributed patterns of nycterohemeral time spent eating and ruminating with corn vs grass silage and according to heifers pedigree value migh t influence ruminal VFA production and proportions and thereby affect animal performance.