The interaction between lactose level and crude protein concentration on piglet post-weaning performance, nitrogen metabolism, selected faecal microbial populations and faecal volatile fatty acid concentrations

A performance study and a nitrogen balance study (2x3 factorial) were conducted to investigate the interaction between lactose level (215 and 125 g/kg) (lactofeed 70; 860 g whey permeate/kg, 140g soya bean meal/kg, Volac International, UK) and crude protein (CP) concentration (160, 195 and 210g/kg) on post-weaning piglet performance, nitrogen metabolism, faecal microbiology and faecal volatile fatty acid concentrations. In the performance trial, 252 piglets (7.6 kg; 33 days of age) were assigned to one of six dietary treatments following a 12-day period on a commercial creep diet (17 MJ/kg DE, 16 g lysine/kg). The experimental diets were fed for 28 days (days 12-40) and were formulated to have identical digestible energy (15 MJ/kg) and total lysine (14.5 g/kg) contents. In the N balance experiment, 24 boars (20kg live weight) were offered the same diets as in the performance trial. Faecal samples were collected for selected microbial populations. There was an interaction (P < 0.05) between lactose and CP concentration in daily gain (ADG) and daily feed intake (ADFI) (P < 0.01) during the weaner period (days 12-40). At the high lactose level there was a linear increase in ADG and ADFI with increasing CP. However, at the low lactose level there was no increase in ADG or ADFI above the medium CP. Pigs offered 215 g lactose/kg had a higher dry matter (P < 0.001), organic matter (P < 0.001), energy (P < 0.001), nitrogen (P < 0.01) and neutral detergent fibre (P < 0.05) coefficient of total tract apparent digestibility compared to pigs offered 125 g lactose/kg. There was an interaction between lactose and CP concentration for nitrogen intake (NI) (P < 0.05), urine pH (P < 0.05) and selected faecal microbial populations. At the high CP level, pigs offered diets containing 215 g lactose/kg had a higher NI and a lower urine pH than pigs offered 125 g lactose/kg (P < 0.05). However, the inclusion of lactose had no significant effect on either NI or urine pH at the low or medium CP concentration. At the low lactose level there was a linear increase in faecal E. coli population and a linear decrease in faecal Lactobacilli population with increasing CP. However at high lactose levels CP concentration had no effect on either E. coli or Lactobacilli populations. Pigs offered 215 g lactose/kg had a significantly higher Bifidobacteria population compared to pigs offered 125 g lactose/kg. There was a linear decrease in Bifidobacteria population as CP increased. In conclusion, at the high lactose level there was a linear increase in ADG and ADFI with increasing CP concentrations. There was no increase in these parameters above 185 g CP/kg at the low lactose level. (c) 2006 Published by Elsevier B.V.