Systematic review: efficacy of exogenous enzymes for dairy calves

The aim of this review is to quantify the strength of evidence for the efficacy of exogenous enzymes (EE) in dairy calf rearing, by systematically identifying, consolidating and discussing existing research on the subject. This review identified 17 articles that measured the effect of EE alone or in combination with another treatment on indicator variables for calf performance, behaviour, health or environmental output; 15 studies realised a positive effect of enzyme supplementation on at least one variable, and one study realised a negative effect of treatment on body parameters. Inconsistent results were noted for effects of EE on growth and feed efficiency. Studies that combined EE with another treatment, did not tend to find performance improvements compared to stand-alone treatments. However, several studies were underpowered which could have limited their ability to detect effects on primary response variables. All papers that measured digestibility found an increase in fibre digestibility from enzyme treatment; however, this did not always result in improved feed efficiency or growth. Reductions in non-nutritive oral behaviour, increased resting time and rumination, were observed in studies measuring calf behaviour, as were enhanced rumen development and reduced cost of calf rearing; suggesting that EE could enhance calf health and welfare, whilst having additional advantages for rearing economics. Future research into the efficacy of EE in dairy calves is worth pursuing. However, a targeted and evidence-based approach to experimental design is required, with due consideration given to enzyme actions and interactions, as well as robust power analysis for sample size.