Results
The addition of dietary lactose to the 30% level resulted in daily gains that numerically increased when lactose was fed during the 0 to 14-day postweaning period, but the response was not significant (P < 0.15). Daily gain increased linearly (P < 0.01) to the dietary lactose was demonstrated during the15 to 35-day postweaning period (Table 2). For the overall 35-day period there was a linear response (P < 0.01) to dietary lactose. Dietary soybean oil fed during the 0 to 14-day period resulted in an increased gain response (P < 0.05) but not during 15 to 35-day or for the overall 35-day postweaning period.
Daily feed intake increased during the 0 to 14-day and for the 15 to 35-day (P < 0.05) period when lactose was fed to weanling pigs. This subsequently resulted in a linear response to dietary lactose (P < 0.01) during the overall 35-day period. When dietary soybean oil was fed there was no effect of its dietary level on daily feed intake during the 0 to14-day period, but during the 15 to 35- day period the addition of this fat source reduced feed intake (P < 0.01).
Although the inclusion of lactose resulted in a numerically improved feed efficiency, the responses were not significant (P > 0.15). Dietary fat improved the gain to feed ratio during both the 0 to 14-day period (P < 0.01) and for the15 to 35-day period (P < 0.01). This resulted in an improvement in feed efficiency (P < 0.01) during the 35-day postweaning period.
As dietary lactose level increased pig serum triglyceride increased particularly at the 14-day period (Table 3). Dietary fat inclusion also resulted in increased serum triglyceride concentrations (P < 0.01) at both the 14 and 35-day period. There was a decline in serum triglyceride from the 14 to 35-day period suggesting better utilization of fat postweaning as pigs got older.
Dietary lactose had no effect on serum urea N concentration, but serum urea N concentrations declined (P < 0.01) at both the 14 and 35-day postweaning period when the dietary fat source was fed. As the dietary soybean oil and lactose levels increased, a decline in serum urea N occurred resulting in an interaction response (P < 0.05) at 35-day postweaning. This suggests that both energy sources were mutually beneficial in improving amino acid utilization when added in combination.
The effect of dietary lactose and soybean oil levels on body composition at 35-day postweaning is presented in Table 4. There was a trend toward a greater amount of body protein when pigs were fed both lactose and fat but the responses were not significant (P > 0.15). Dietary fat inclusion increaed body fat concentration (P < 0.01) at 35-day postweaning.