Effects of different physical forms of starter on digestibility, growth, health, selected rumen parameters and blood metabolites in Holstein calves

•Texturized starter digestibility was reduced due to its hard corn.•Soybean and distillers dried grain reduced pelleted starter intake and ADG of calves.•Texturized starter fed calves tended to have rumination behaviour earlier. This study was designed to determine whether physical forms of starter feed could influence digestion, growth, rumen fermentation parameters, and blood metabolites in Holstein dairy calves. Sixty-three female calves (averaging 41 kg body weight (BW)) were randomly assigned to 1 of the following 3 starter diets differing in physical form or formulation: texturized starter (TS; n = 21), pelleted starter with the same formula as TS (PSA; n = 21), and a commercial pelleted starter (PSB; n = 21) with a different formulation. Twelve male calves were selected and randomly assigned to each treatment group to determine feed digestibility using indigestible neutral detergent fiber (iNDF) and acid insoluble ash (AIA) as the internal markers. The dry matter intake (DMI) of calves in three treatments was not different within the first 6 wk (P = 0.19), and there were also similar gain-to-feed ratios (P = 0.91) and Average daily gain (ADG) (P = 0.26). During wk 7, starter DMI of the calves in TS and PSA groups was greater than PSB animals (P < 0.01). The ADG of TS and PSA-fed groups were greater than the animals fed with PSB during wk 7. Offering TS resulted in tendentionally greater starter DMI and ADG than PSA during the following 2 wk after weaning (P = 0.08, P = 0.09). During the 9-wk study, calves receiving PSB had lower ADG than the other two treatments (P = 0.04), but there were no differences in gain-to-feed ratio (P = 0.86). Serum biochemical parameters were not different among the 3 treatments. Calves began exhibiting ruminating behavior for TS about 2 d numerically earlier than that for PSA and PSB (P = 0.54). Butyrate in the rumen of PSB-fed animals was greater than in PSA and TS calves (P < 0.01) on day 63. Also, PSB-fed calves had a greater ruminal acetate: propionate ratio than calves receiving PSA and TS (P < 0.01) on day 49. The TS starter had the lowest digestibility of CP, DM, and ADF (P < 0.01) by both digestibility methods. Overall, the pelleted starter with soybeans and distillers dried grains had lower DMI and ADG than the other pelleted starter and texturized starter which had the same formulation.