Lactation diets are composed mostly of carbohydrates that are not fully fermented by rumen microbes. The aim of this study was to evaluate exogenous fibrolytic (Fibrozyme, Alltech Inc., Nicholasville, KY) and amylolytic (Amaize, Alltech Inc.) enzymes on nutrient intake, sorting index, total-tract apparent digestibility, ruminal fermentation, nitrogen utilization, milk yield, and composition of dairy cows in mid-lactation. Thirty-two multiparous Holstein cows (181 ± 35 d in milk, 571 ± 72.7 kg of body weight, and 29.6 ± 5.24 kg/d of milk yield at the start of experiment) were blocked according to milk yield and randomly allocated to treatments in a 4 × 4 Latin square design. Treatments were (1) control, basal diet without exogenous enzymes; (2) fibrolytic enzyme (FIB), dietary supplementation of Fibrozyme at 12 g/d (51 IU of xylanase activity/kg of diet dry matter); (3) amylolytic enzyme (AMY), dietary supplementation of Amaize at 8 g/d (203 fungal amylase units/kg of diet dry matter); and (4) both fibrolytic and amylolytic enzymes (FIB+AMY) added at the same dose of the individual treatments. Enzyme products were added to the concentrate during its preparation (once a week). The supply of FIB and AMY had no effect on nutrient intake and digestibility. However, an interaction effect was observed on sorting index of feed particle size between 8 and 19 mm. Amylolytic enzyme increased the sorting for feed particles between 8 and 19 mm, only when fed without FIB. In addition, AMY decreased the sorting for feed with particle size greater than 19 mm. An interaction effect was observed between FIB and AMY for ruminal butyrate concentration and N excretion. Amylolytic enzyme increased ruminal butyrate concentration in cows treated with FIB. Further, FIB decreased milk protein production and feed efficiency only in cows not fed AMY. Amylolytic enzyme reduced urinary N excretion. Exogenous enzymes had no effect on milk production and composition of dairy cows. This study lacks evidence that fibrolytic and amylolytic enzymes can affect nutrient digestibility, ruminal fermentation, and performance of mid-lactation cows.

Our objective was to evaluate the effects of providing increasing levels of chitosan on nutrient digestibility, ruminal fermentation, blood parameters, nitrogen utilisation, microbial protein synthesis, and milk yield and composition of lactating dairy cows. Eight rumen-fistulated Holstein cows [average days in lactation = 215 ± 60.9; and average bodyweight (BW) = 641 ± 41.1 kg] were assigned into a replicated 4 × 4 Latin square design, with 21-day evaluation periods. Cows were assigned to be provided with four levels of chitosan, placed into the rumen through the fistula, as follows: (1) Control: with no provision of chitosan; (2) 75 mg/kg BW; (3) 150 mg/kg BW; and (4) 225 mg/kg BW. Chitosan had no effect on dry matter intake (P > 0.73); however, chitosan increased (P = 0.05) crude protein digestibility. Propionate concentration was increased (P = 0.02), and butyrate, isobutyrate, isovalerate and acetate : propionate ratio were decreased (P = 0.04) by chitosan. Chitosan had no effect (P > 0.25) on acetate, pH and NH3 ruminal concentration. Glucose, urea, and hepatic enzyme concentrations in the blood were similar (P > 0.30) among treatments. Nitrogen balance was not affected, but chitosan increased milk nitrogen (P = 0.02). Microbial protein synthesis was not affected by chitosan (P > 0.44). Chitosan increased (P = 0.02) milk yield, fat-corrected milk, protein and lactose production. Chitosan changes ruminal fermentation and improves milk yield of lactating dairy cows; therefore, we conclude that chitosan can be used as a rumen modulator instead of ionophores in diets for dairy cows.