The swine industry is currently facing an enormous amount of public pressure to eliminate the use of individual gestation stalls in favor of group housing for gestating sows. Since over consumption of feed is a common problem in gestating sows, there is a need for development of an inexpensive, low-maintenance feeding system that can limit feed intake of the sow while still providing all essential nutrients. Most aggressive behavior of group-housed sows occurs during feeding. Allowing sows ad libitum access to feed may decrease aggression and improve sow welfare. The use of self-feeders could be an ideal option for producers utilizing group-housed gestation systems; however, over-consumption of feed may be a problem. Decreasing dietary cation-anion difference (DCAD) by the addition of ammonium chloride or calcium chloride has been shown to decrease feed intake in pigs and may be useful in the development of a simple feeding strategy that reduces excessive feed intake of ad libitum fed gestating sows housed in groups. The objective of this pilot study was to determine the most efficacious dietary cation-anion level that will allow mature gilts to self-regulate their feed intake when fed ad libitum in group housing.
Ninety, six to nine month-old crossbred gilts (Duroc x Chester White x Yorkshire) were used in this study. The gilts weighed approximately 284 pounds, were housed in groups of five per pen and were offered one of three dietary treatments ad libitum for 45 days. Gilts were blocked by weight and randomly assigned within block to treatment pens. Treatment pens were equipped with one self feeder located over slotted floors. After a preliminary week of feeding a standard finisher diet, diets were randomly assigned to treatment pens (two pens/diet). This procedure was repeated in each of three trials (30 gilts/trial). The treatment diets consisted of one of the following levels of DCAD: 50 (control), -225, or -450 mEq/kg diet, and the gilts were fed their respective diet ad libitum for 45 days. All diets met or exceeded the nutritional requirements indicated by the NRC (1998). Water intake was not restricted. All diets were corn- and soybean meal-based, and DCAD levels
were lowered by the addition of ammonium chloride. Calcium content was kept constant across treatments by the addition of calcium sulfate. Gilt weights and ultrasound backfat measurements were taken every week. Feed disappearance was recorded at these times by weighing pen feeders. Room temperatures were maintained between 22 and 29 ºC and gilts were monitored daily for feed intake, as well as general well-being. Any wet feed was removed daily from the feeder, weighed, and a sample was kept for dry matter analysis. Dietary cation-anion difference had a direct linear relationship with average daily feed intake (as DCAD became more negative feed intake decreased). The -225 treatment did not affect BW, ADG, gain/feed, backfat, or blood pH when compared to control gilts. However a significant reduction in urine pH was observed for this treatment. While -225 DCAD resulted in reduced feed intake during the first two weeks, gilts became accustomed to the diet and increased feed intake over the remaining four weeks. The -450 treatment resulted in significantly reduced BW, ADG, gain/feed, and urine pH when compared to control gilts for the entire 45 day period. There were trends for blood pH and backfat gains to decrease with decreasing DCAD. The results of this study suggest that decreased DCAD may be a useful tool in regulating feed intake of group-housed gilts, effectively suppressing feed intake with no apparent negative effects on body condition or general well-being.
The -225 DCAD treatment did not have the desired effect on reducing feed intake and weight gain in group-housed gilts over a sustained period of time. The -450 treatment did effectively suppress feed intake and weight gain with no observable negative side effects. However, by the end of week 6 average daily feed intakes of the -450 treatment were approaching the control diet intakes. Results from this study indicate that the addition of chloride to swine diets may be an effective strategy to decrease feed intake, while maintaining body condition and nutrient digestibility. This is of particular use in gestating sow diets, where producers have modified gestation housing to group housing and need an economic method for feeding the sows. This study observed the effects of added dietary chloride on gilts only, and although no negative side effects on body condition, nutrient digestibility, or skeletal integrity were noted over the course of the trial, prolonged induced metabolic acidosis may eventually lead to clinically detrimental side effects. This study fed altered DCAD for 45 days. If gestating sows are housed in stalls until pregnancy is verified at 35 days, then group housed until day 110 of gestation when sows are moved into farrowing stalls, DCAD must be maintained for 75 days or 11 weeks. Longer trials are needed in order to determine the extent of acclimation of DCAD treatment. Further research is needed in order to determine whether or not similar effects would be observed in gestating sows if fed similar diets over the course of gestation.
