Researchers: Mariola Grez and Thomas Crenshaw, University of Wisconsin-Madison
Hog producers strive to keep sows healthy and productive, ideally for multiple parities. In recent years, producers have seen an increase in uterine prolapses, and in most cases, these sows must be euthanized. University of Wisconsin-Madison researchers have recently looked at the risk factors for uterine prolapses to determine the causes.
The physiological mechanisms that allow the uterus eversion and protrusion are unknown. Hypocalcemia (low serum calcium concentration) is often implicated as a risk factor, which raises questions about dietary calcium supplementation. However, limited data are available to support that hypocalcemia occurs in sows at farrowing and the early phases of lactation.
In dairy cows, high-calcium diets fed during late-gestation suppress physiological mechanisms required for calcium intestinal absorption and calcium mobilization from bone. These processes are critical to maintain serum calcium levels during early lactation when the calcium demand increases for milk production. Thus dairy cows fed high-calcium diets have a greater prevalence of milk fever.
High-calcium diet studied
This experiment, conducted at the Swine Research and Teaching Center of the University of Wisconsin-Madison between December 2016 and January 2017, aimed to examine the relationship between a high calcium concentration in diets fed to multiparous sows and the development of hypocalcemia during the early lactation phase.
Twelve crossbred (Large White x Landrace) multiparous sows were fed with a control diet (0.65% calcium and 0.60% phosphorus) or with a high-calcium diet (1.75% calcium and 0.70% phosphorus). These diets were fed from gestation Day 90 until the end of lactation.
On Day 112 of gestation indwelling, venous catheters were placed in each sow. Blood samples were collected at 15-minute intervals within four designated times — 7 and 10 a.m., and 1 and 5 p.m. (0700, 1000, 1300 and 1700) — on gestation Day 113 and lactation Days 1, 3 and 5.
Venous blood gases, electrolytes and total serum calcium and phosphorus were analyzed. Unexpectedly, sows fed with the HCa diet presented a greater (P < 0.01) concentration of blood ionized Ca2+ and total serum calcium at each blood collection time. Ionized Ca2+ was 50% of the total serum Ca for both treatment groups.
Serum phosphorus concentrations were lower (P < 0.01) for sows fed with the HCa diet. Differences due to dietary treatments were not detected (P > 0.05) in blood gases (pH, O2, CO2 and HCO3-), electrolytes (K+, Na+, and Cl-) and blood metabolites (glucose and lactate).
Differences in reproductive parameters (litter size and pig weights) attributable to dietary treatments were not expected.
These parameters were recorded, but they were not statistically analyzed. The mean of pig weights at birth was 1.3 kilograms. The mean of litter size at birth (live born) and weaning were 14.7 and 11.4 pigs, respectively.
Unexpectedly, sows fed a high-calcium diet during the month before farrowing, displayed a consistent but slightly higher serum concentration of total calcium than sows fed a control diet (10.93 vs. 9.75 mg/dL).
No hypocalcemia after farrowing
Regardless of the dietary treatment, ionized Ca2+ represented 50% of the total calcium concentration in the serum. Therefore, the high-calcium diet provided during the prefarrowing period was not associated with hypocalcemia after farrowing. However, sows fed the high calcium diet had lower serum phosphorus concentrations compared with the control diet (3.5 vs. 6.0 mg/dL).
Clinical signs of hypophosphatemia (low serum phosphorus concentrations) were not observed. Differences in the blood gases and electrolyte measurements were not detected between sows fed the two dietary treatments. All of the blood gas and electrolyte levels were within the physiologically normal reference ranges. Hormones that regulated the physiological processes involved in maintaining the serum calcium and phosphorus concentrations are being analyzed.
In conclusion, hypocalcemia was not observed in periparturient sows fed with the HCa diets. Conversely, they presented hypophosphatemia. Future experiments should focus on factors other than hypocalcemia to identify causes of uterine prolapses in sows.