Results independent of increased sow feed intake during heat stress
By Jay S. Johnson, Allan P. Schinckel and Robert M. Stwalley
Elevated summer temperatures can reduce milk production in lactating sows in an attempt to decrease metabolic heat production. Unfortunately, this can result in poor litter growth performance. Reduced milk production and litter growth is often attributed to the reductive effects of heat stress on lactating sow feed intake. As such, management practices to improve sow milk production and litter performance during heat stress events are often focused on maximizing sow feed intake. This is achieved through nutritional additives, dietary manipulations and altering feeding schedules. However, recent research by our group suggests that reduced sow feed intake does not fully explain lost milk production and litter growth performance during heat stress events.
Sow cooling pads developed by our group are proven to be effective in allowing lactating sows to maintain a normal body temperature when managed under heat stress conditions (Fig. 1, 2). However, the effects on sow milk production and litter growth performance were previously unknown.
A total of 12 multiparous lactating Yorkshire x Landrace sows and their litters were provided either a sow cooling pad (six total) or a non-functional sow cooling pad (six total) and then managed under heat stress conditions (cycling 83 to 92°F) until weaning. Sows and litters were maintained within farrowing crates placed within custom designed indirect calorimeters (Fig. 3). This allowed for individual measurement of metabolic heat production on day 4, 8, 14 and 18 of lactation, which can be considered an indirect measure of milk production.
From farrowing to weaning, sow body temperature was measured hourly, respiration rate was monitored four times daily and feed intake was measured daily. Litter weights were recorded at birth, days 4, 8, 14 and 18 post-farrowing, and at weaning.
Study results demonstrated that the cooling pads were effective in reducing sow respiration rate and maximum body temperature throughout the course of lactation (Fig. 4). However, no improvements in sow feed intake were detected when comparing sows with and without functional cooling pads (Fig. 4).
Despite the lack of feed intake improvements, metabolic heat production was increased overall for sows provided a cooling pad (Fig. 4). This result may indicate that cooling alone can allow sows to maintain higher milk production under heat stress conditions independent of greater feed intake.
As a likely result of improved milk production, litter average daily body weight gain and weaning weights were greater for litters of sows provided cooling pads (Fig. 5). This is further confirmation that the cooling pads improved sow milk production independent of increased feed intake under heat stress conditions.
Taken together, this study provides evidence that sow cooling pads can be an effective strategy to improve lactating sow welfare and performance under heat stress conditions and increase litter growth rate independent of increased sow feed intake. Research to more fully understand the mechanisms by which heat stress directly affects sow milk production is currently being undertaken.
This work was supported in part by the Pork Checkoff (Grant 200225168), National Pork Board, Des Moines. We would also like to acknowledge other co-authors of this research including Taylor Jansen, Michaiah Galvin, Jason Graham and Tyler Field.
Johnson is a USDA research animal scientist, Schnickel is a professor of animal science and Stwalley is an assistant clinical professor of agricultural and biological engineering, all based at Purdue University.
