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Use of chitosans to modulate ruminal fermentation of a 50:50 forage-to-concentrate diet in sheep

Neiker-Tecnalia - Granja Modelo de Arkaute, 46, 01080 Vitoria-Gasteiz, Spain

igoiri{at}neiker.net

Abstract

The objective of this study was to investigate the effects of chitosan on ruminal and cecal fermentation, and apparent digestibility in sheep. In a first trial, four ruminally fistulated sheep fed an alfalfa hay and concentrate diet formulated to meet 1.2 times their maintenance energy requirements were assigned to two treatments (no-additive control: CTR; 136 mg/kg BW of chitosan: CHI) in a 2 x 2 19-d crossover design. Samples of ruminal fluid and feces were taken for VFA and ammonia-N (NH₃-N) concentrations. At the end of each period of the crossover, ruminal fluid was used as inoculum for batch cultures (24 and 96 h), and the effects on rate and extent of gas production and fermentation parameters for starch, cellulose, and the same diet fed to the animals were calculated. In a second trial, four sheep fed the alfalfa hay and concentrate diet were assigned to two treatments (CTR and CHI) as for the first trial, this time in a 2 x 2 14-d crossover design. Apparent digestibility was studied. In the first trial, in terms of ruminal fermentation, CHI did not affect total VFA concentration or acetate proportion, but increased propionate proportion and propionate-to-acetate ratio (C3:C2), and decreased branch-chained VFA (BCVFA) proportion and NH₃-N concentration. In feces, CHI decreased total VFA concentration and acetate and butyrate proportions, and increased propionate, valerate, and BCVFA proportions and C3:C2 ratio. In batch cultures, when starch was used as substrate, CHI decreased acetate proportion and methane production, and increased propionate and valerate proportions and C3:C2 ratio. When cellulose was used as substrate, CHI decreased in vitro organic matter digestibility, total VFA concentration, propionate proportion, C3:C2 ratio, methane production, NH₃-N concentration, and gas production rate, and increased butyrate and BCVFA proportions and pH. When the alfalfa hay and concentrate diet was used as substrate, CHI decreased butyrate and BCVFA proportions, methane and asymptotic gas production, and gas production rate. In the second trial, CHI decreased NDF apparent digestibility. In conclusion, CHI shifted ruminal fermentation toward energetically more efficient routes, without reducing OM apparent digestibility.

Key Words: additive • antimicrobial • apparent digestibility • chitosan • ruminal fermentation • sheep