Effects of dietary supplementation with increasing doses of lactose on faecal bacterial populations and metabolites and apparent total tract digestibility in adult dogs

The effect of increasing dietary doses of lactose on canine faecal microbiota and apparent digestibility was evaluated. Fourteen adult healthy dogs [1–5 years of age, mean body weight (BW) of 19.0 kg] were fed with an extruded diet containing silica (5 g/kg) as a digestion marker. After a 20 d adaptation period, increasing doses of lactose were added to the dogs’ diet (0.5, 1 and 2 g/kg BW0.75/d) during three consecutive 20-d supplementation periods. Faeces were collected at the end of each period for analyses. Four dogs refused the diet added with lactose at 0.5 g/kg BW0.75/d and were excluded from the trial, as well as two dogs, which developed acute diarrhoea when lactose was fed at 1 g/kg BW0.75/d. Conversely, eight dogs remained healthy throughout the study. Faecal moisture was influenced by lactose (quadratic, p = .001), while faecal pH and ammonia were not affected by treatments. Lactose supplementations tended to linearly decrease isovalerate (p = .051) and quadratically influence n-valerate (p = .056) in canine faeces. No changes in faecal microbial populations were observed. Apparent digestibility of dry matter, Ca, K, Mn and Fe was influenced by lactose supplementation (quadratic, p < .05). Increasing doses of lactose linearly decreased Mg digestibility (p < .05). Furthermore, coefficients of crude protein, crude ash, P, Mg and Zn digestibility were tendentially affected (quadratic, p = .055, .089, .091, .065 and .065, respectively). In conclusion, 8 of 14 dogs displayed a good tolerance (absence of gastrointestinal signs) up to the highest dose of lactose (2 g/kg BW0.75/d). An evident prebiotic effect was not observed.