Effects of forage type and age at which forage provision is started on growth performance, rumen fermentation, blood metabolites and intestinal enzymes in Holstein calves

The aim of this study was to determine the effects of two forage sources supplemented either from Day 3 or Day 15 of age on growth performance, rumen fermentation, blood metabolites, intestinal enzymes and incidence of diarrhoea in Holstein bull calves. Forty neonatal male Holstein calves (40.6 +/- 5.8 kg BW) were randomly assigned to five treatments, with eight replicates each, including calves fed starter feed without any forage provision (Control; CON), and the same starter plus either chopped alfalfa hay started fed from Day 3 (AE) or Day 15 of age (AL) or chopped oat hay fed from Day 3 (OE) or Day 15 of age (OL). The study finished when all calves were weaned at 56 days of age. During the experimental period average daily gain, starter intake and total dry matter intake were similar among calves fed either of five dietary treatments (P > 0.05). Empty rumen weight (proportional to bodyweight) was greater in CON calves than in OL calves (P < 0.05). The AL calves had a lighter small intestine compared with CON, OL and AE calves, but similar to OE. Frequency of diarrhoea was not affected by dietary treatment (P > 0.05). Rumen concentration of total volatile fatty acids and pH were similar among dietary treatments (P > 0.05). Control calves had a lower molar proportion of acetate compared with OL calves, but similar to the other calves (P < 0.05). Forage-fed calves had similar molar proportion of butyrate to CON calves. Acetate to propionate ratio was higher in OL-fed calves than in those fed CON and AE diets (P < 0.05). Rumen concentration of NH3-N tended to be higher (P = 0.059) in CON calves than in forage-fed calves. During experimental period, serum concentrations of globulin, total protein, glucose and total cholesterol were similar among dietary treatments. Calves fed OE had lower serum concentration of albumin than those fed other diets (P < 0.01). Serum concentration of triglycerides (P < 0.05) was greater in calves fed AE followed by those fed AL and then those fed CON, OL and OE. The AL-fed calves had a higher serum lactate dehydrogenase compared with AE and OE fed calves, but similar to calves fed OL and CON. Duodenum amylase concentration was greater (P < 0.05) in AE-fed calves compared with CON-fed calves, but similar to calves fed AL, OL and OE. Calves fed OL had greater (P < 0.05) ileum lipase concentration than those fed OE, but similar to calves fed AL, AE and CON. In conclusion, provision of chopped alfalfa or oat hay to calves either from Day 3 or Day 15 of age resulted in similar starter intake and total dry matter intake and feed efficiency and physical development of the reticulorumen compared with calves fed the CON diet, which justifies the supply of forage to young calves, even at an early age, as forages are generally cheaper than starter concentrates.