Replacing concentrates with a high-quality hay in the starter feed of dairy calves: II. Effects on the development of chewing and gut fermentation, and selected systemic health variables

Early development of the rumen, rumination and fermentation is highly important in dairy calves. Yet, common rearing practices with feeding of concentrate-rich starters may jeopardize them because of lacking physically effective fiber (peNDF). The main objective of this study was to establish the influence of the composition of the calf starter feed (only forage with two different qualities or concentrate-rich starter diet) on chewing behaviour, rumen development, rumen and hindgut fermentation, and selected systemic health and stress variables of dairy calves. The experiment was carried out with 40 newborn Holstein-Friesian calves, randomly assigned to four different solid feed treatments: MQH = 100% medium-quality hay (9.4 MJ ME, 149 g CP, 522 g NDF/kg DM), HQH = 100% high-quality hay (11.2 MJ ME, 210 g CP, 455 g NDF/kg DM), MQH+C = 30% MQH + 70% starter concentrate, HQH+C = 30% HQH + 70% starter concentrate). All calves were up to 14 wk in the trial and received acidified whole milk ad libitum in the first 4 wk of life, thereafter in reduced quantity until weaning on 12 wk of age. Water and the solid feed treatments were available ad libitum throughout the trial. Chewing activity was measured in wk 4, 6, 10, and 12 using Rumiwatch halters. Until wk 3, rumen fluid, feces and blood were sampled weekly, thereafter every 2 wk. Rumen mucosal thickness (RMT) was measured on the same days with rumen fluid samples. Data show daily variation in eating and ruminating activity and proportion of certain SCFA in total SCFA in rumen fluid and feces of calves offered different feed treatments.