Results and Discussion
The various sow and litter measurements for the various dietary lactation treatments are presented in Table 2. Lactation lysine level, lysine source, and dextrose did not affect sow body weights or backfat measurements (P > 0.15) during lactation. As expected, body weights of multiparous sows were greater (P < 0.01) than first parity sows (Table 3). The backfat thickness of multiparous sows was numerically lower at each interval, but only the measurements on day 110 of gestation and farrowing were significant (P < 0.01).
Feeding dietary lysine levels in excess of the NRC requirements had no effect on total and daily lactation feed intakes. Furthermore, the addition of synthetic lysine to the lactation diets failed to reduce feed intake as previously reported (Libal et al., 1997). Similar lactation feed intakes resulted in more total lysine consumed when sows were fed the higher lysine levels (Table 4). Despite the increased lysine intake, there were no beneficial effects on lactation performance (Table 2).
Although lysine levels failed to affect feed intake, the addition of dextrose did seem to have some effect on sow lactation feed intake. When 10 % dextrose was fed, lactation feed intake was numerically higher during each week post farrowing, with a trend for higher total lactation feed intake (P < 0.10). There was a parity x dextrose level interaction response for feed intake during the last week of lactation (Table 5). In this case, first-parity sows consuming the dextrose diets consumed more feed (P < 0.01) during the last 7 days of lactation, but this response was not demonstrated for older sows.
Fat and protein concentrations of colostrum and milk were not affected by dietary treatments imposed on the sows (Table 2). Multiparous sows, however, had lower (P < 0.01) milk protein concentrations than first-parity sows (Table 3). The return to estrus interval and subsequent litter size (total and live) were also not affected by the higher lysine or dextrose levels fed to the sows (Table 2).
Sow PUN concentrations at weaning were higher (P < 0.01) when the B+NL diets were fed. This suggests that the excess amino acids provided from the additional SBM were catabolized into urea and excreted. This resulted in the rise in PUN. Therefore, a low PUN indicates improved amino acid utilization (Coma et al., 1996). The decrease in PUN when synthetic lysine (B+SL) was fed suggested improved amino acid utilization. Feeding synthetic lysine therefore reduced the dietary crude protein content by approximately 2% compared to the diet using SBM. Consequently, the use of synthetic lysine reduced nitrogen excretion and resulted in improved amino acid utilization. Further improvements in amino acid utilization, as measured by PUN concentration, were not accomplished by feeding 10% dextrose.
The effects of dietary lactation lysine level and dextrose on litter and pig performance during lactation are presented in Table 6. Litter and pig weights and litter gains were not affected by either dietary treatment. There was a trend (P < 0.10) for pig gains between 3 days postpartum and weaning to increase when the B+SL diet was fed. The failure of litter growth rates to increase when sows consumed greater than 54 g lysine/day is in agreement with other researchers (Johnston et al., 1993; Touchette et al., 1998). Our study demonstrated no improvement in lactation performance when sows of this productivity level consumed lysine in excess of the NRC requirement.
Parity effects on litter performance are presented in Table 7. Multiparous sows nursed more pigs per litter. Individual pig weights were also greater for the older sows (P < 0.05). This resulted in heavier litter weights at 3 days postpartum and weaning (P < 0.05) for multiparous sows. Due to the shorter lactation length for the older sows (17 days), their litter and pig gains from 3 days postpartum to weaning were lower (P < 0.05) than for first-parity sows (21 days).
Although sow productivity in this study was satisfactory, it was somewhat below that of many high-producing sows. Increasing lysine level above the NRC recommendation did not improve lactation performance when our sows were supporting litter growth rates of approximately 5.1 lb/day (Table 7). However, sows supporting higher growth rates may benefit from increased lactation lysine levels.