Each dietary treatment had sows of similar parities and lactation length was similar across dietary treatments (Table 4). Dietary treatments had no effect on sow weight at farrowing and weaning, sow weight change during lactation, sow backfat at farrowing and weaning, sow backfat change during lactation, and percentage of sows returning to estrus within 10 days post-weaning. Overall, there was a tendency (P = 0.08) for average daily feed intake (ADFI) to differ among dietary treatments. Sows fed 3% glycerol ate more feed (P < 0.05) than those assigned to 6% glycerol. Sows fed the control diet had similar ADFI compared with sows fed the 3%, 6%, and 9% glycerol diets. We have no explanation for the decrease in ADFI of sows fed the 6% glycerol diet relative to sows fed the other diets. In research with grow-finish pigs, feeding increasing levels of crude glycerol up to 15% did not influence ADFI of pigs (Kijora and Kupsch, 1996; Lammers et al., 2008b). The percent of sows returning to estrus within 10 d postweaning was similar for all dietary treatments.
At farrowing, litters were cross-fostered to equalize initial litter size across dietary treatments. Litter size at weaning tended to decrease linearly (P = 0.10) as level of dietary glycerol increased (Table 5). Level of glycerol in the diet did not affect piglet pre-weaning mortality, weight of litters at birth (after cross-fostering), weight of litters at weaning, or ADG of piglets. Litter’s of sows fed the 6% glycerol diet tended (P = 0.07) to gain less than litters of sows fed the control diet. This led to a negative linear response (P < 0.05) in litter gain as glycerol increased in the diet from 0 – 6%. Presumably, the depressed gain of litters nursing sows fed 6% glycerol could be partially attributed to the tendency for decreased ADFI of these sows.
There was no significant diet by gestation housing interaction. There was a treatment by parity interaction (P < 0.05) for backfat of sows at farrowing and at weaning, however, this interaction appears to be caused by the much greater backfat depth of gilts and parity 1 sows compared to sows of parity 2 or greater. Significant treatment by parity interactions were not evident for any other performance measure. It should be noted there was a significant (P < 0.05) parity by gestation location interaction for ADFI, which appeared because sows of parity 2 or greater, regardless of gestation location, consumed more feed on a daily basis compared to parity group 1 sows. There were no interactions between dietary treatment and parity for litter performance.