Since 1999 the biodiesel industry has increased exponentially. As a result, the production of crude glycerol, the co-product of biodiesel, has also increased. An experiment was conducted to evaluate the effects of crude glycerol in diets for lactating sows on sow and litter performance under heat stress conditions. Mixed parity (range = 0 to 13) sows (n = 345; 558 + 52 lb) were assigned randomly within gestation housing location and parity to 1 of 4 dietary treatments. Treatments consisted of: a corn-soybean meal based control diet; 3% glycerol; 6% glycerol; or 9% glycerol. Dietary treatments were imposed on d 109 of gestation when sows were moved into farrowing rooms. From day 109 of gestation until farrowing, sows received 5 lbs/d of their assigned diet. Beginning at farrowing, sows were allowed ad libitum access to feed throughout lactation. Sows and litters were weighed on day 0 of lactation, after litter size was standardized, and at weaning. Last rib backfat depth was recorded ultrasonically on day 0 and at weaning. Respiration rates and rectal body temperatures were recorded 3 days before weaning as an indicator of heat stress. Blood samples were collected 3 days before weaning from a randomly pre-selected group of sows (n = 84; 21 sows/treatment) to determine circulating glycerol and glucose concentrations. Dietary treatment tended (P = 0.08) to influence average daily feed intake of sows. Females fed 6% glycerol consumed less feed than sows fed 3% glycerol. Inclusion of up to 9% crude glycerol in the diet had no effect on sow weight and backfat losses, wean-to-estrus interval for sows that returned to estrus within 10 days post weaning, pre-weaning mortality, and average daily gain of piglets. Increasing dietary glycerol tended to linearly reduce (P = 0.10) litter size at weaning. Average daily gain of piglets was not influenced by the sow's diet.
Overall daily water consumption was not affected (P > 0.05) by dietary treatment. Adding glycerol to the diet did not affect respiration rates or rectal body temperatures indicating no efficacy in reducing heat stress of sows. Plasma glycerol levels increased linearly (P < 0.05) as crude glycerol increased in the diet. Glucose levels in blood plasma were not affected by dietary treatment. Increasing levels of crude glycerol in the diet had no effect (P > 0.05) on crude protein content of sow’s milk. Dry matter (P = 0.07), crude fat (P = 0.09), and ash (P = 0.09) content of milk tended to increase linearly with increasing dietary glycerol level. Increasing levels of dietary crude glycerol linearly increased (P < 0.05) lactose concentration in sow’s milk. Results from this study suggest that lactating sows fed diets containing up to 9% crude glycerol perform similar to sows fed a standard corn-soybean meal control diet.