Discussion
During the initial weeks postweaning the pig is in an energy deficient state. This is largely due to an inadequate feed intake immediately upon weaning where it often leads to a loss of body weight. It is not uncommon for pigs during the first few days postweaning to refuse their diets and therefore to metabolize much of their body fat as a needed energy source. The acceptability of the initial diet postweaning is therefore of extreme importance to the young pig, and the incorporation of specialized feeds into starter diets is essential in stimulating feed intake. The diets fed during the nursery period should be comprised of feeds that are palatable and highly digestible so that maximum growth rate can be achieved as soon as possible postweaning.
There are also many enzymatic and physiological changes that are occurring in the intestinal tract of the weaned pig. The digestion and absorption systems change dramatically upon weaning. Carbohydrates are hydrolyzed to simple sugars, absorbed and used for both energy and protein synthesis, whereas fat is metabolized and used as energy or deposited as fat. This experiment evaluated these two different energy sources (lactose and soybean oil) and evaluated their effectiveness on postweaning performance in the diets of young pigs.
Our results demonstrated improvements in daily gains, feed intakes and protein deposition when lactose or soybean oil was fed to weanling pigs. The effects of high levels of lactose were beneficial throughout the nursery period, but in our experiment the responses were perhaps greater during the latter part of the nursery period. Lactose was also effective in increasing feed intake during the initial weeks postweaning, responses that were more pronounced during 15 to 35-day postweaning period. The higher feed intake thus contributed to the increased daily gain and body protein that was demonstrated when lactose was included in the diet.
Daily gain also improved when dietary fat was fed during 0 to 14-day postweaning period. In this experiment we did not achieve improved weight gains during the later 15 to 35-day period, but other experiments have shown the growth response during the latter period. Dietary fat levels did, however, reduce the daily feed intake during the 15 to 35-day postweaning period.
The combination of dietary lactose and fat thus resulted in the highest daily gains and feed efficiencies. The results indicate that an additive effect exists between dietary lactose and fat on postweaning pig especially on feed efficiency.
Serum triglyceride concentrations tended to increase as the dietary lactose level increased at 14 and 35-day postweaning. This suggests that this energy source was in excess and body fat was synthesized. When soybean oil was added, serum triglyceride concentrations also increased at each measurement period postweaning suggesting that the soybean oil was effectively absorbed. Serum urea nitrogen concentration decreased as the dietary fat levels increased at both 14 and 35-days postweaning. This suggests that the amino acid utilization was improved when fat was incorporated into the diets of weanling pigs.