 ORIGINAL RESEARCH
Effect of dietary chromium tripicolinate on productivity of
sows under commercial conditions
Chad D. Hagen, PhD; Merlin D. Lindemann, PhD; Ken W. Purser,
MS, PhD
Hagen CD, Lindemann MD, Purser KW. Effect of dietary chromium
tripicolinate on productivity of sows under commercial conditions.
Swine Health Prod. 2000;8(2):59-63. This article is
also available in PDF format.
CDH: Iowa Select Farms; Reprint requests to MDL: University
of Kentucky; 611 W.P. Garrigus Building, Lexington, Kentucky 40546-0215;
email: mdlind1@pop.uky.edu; KWP: Prince Agri Products, Inc.
Summary
Objective: To further examine and clarify the effect
of supplemental chromium (Cr) from chromium tripicolinate on productivity
of sows (especially litter size) under commercial conditions.
Methods: Based on reproductive performance during a
3-month "pretest" period, 12 4000-sow units were assigned
to one of two dietary treatments: either to a "+Cr"
group that received 200 ppb supplemental Cr from chromium tripicolinate,
or to a "Control" group that received a standard commercial
ration without supplemental Cr. After a 6-month "loading"
period, reproductive performance was evaluated over a 12-month
"test" period.
Results: Dietary supplementation of 200 ppb Cr from
chromium tripicolinate had a positive impact on sows bred by 7
days postweaning, number of pigs born alive and weaned, and sow
mortality.
Implications: The use of a biologically available form
of Cr can positively affect total sow productivity and allow greater
animal output with no additional fixed capital inputs. This has
the potential to improve total enterprise profitability.
 Keywords: chromium,
sows, litter size, sow productivity
Received: February 26, 1999
Accepted: January 11, 2000
Sow productivity is a key factor in
modern pork production. Its direct effect on animal numbers and
ability to meet production volume objectives, combined with its
indirect effect on cost of production through overhead allocation,
make it a measure closely scrutinized at all levels of management.
The two principle components of sow productivity are litter size
and farrowing rate.
Recent research using supplemental chromium tripicolinate (CrP)
has demonstrated substantial improvements in sow productivity.
Studies1,2 have shown that CrP is associated with increased
litter size. Australian research3,4 in a series of
four experiments with > 4000 sows, demonstrated improved
farrowing rates and more sows bred within 7 days of weaning in
sows fed supplemental CrP. Based on these data, Campbell and Purser4
concluded that the use of CrP in breeding herd diets would improve
sow productivity by 0.4-1.0 pigs per sow per year.
The objective of the present study was to further examine and
clarify the effect of supplemental CrP on productivity of sows
in commercial conditions, particularly on litter size.
Materials and methods
Facilities and management
Twelve 4000-sow units under the same ownership and located
in the same state were selected for the study. All units were
under the same general management and were served by the same
feed mill. Breeding stock, facility design, equipment, and animal
management practices were uniform across all units. Any changes
that occurred during this study with respect to any of these factors
were kept uniform across all experimental units.
During gestation, sows were housed in individual crates. On
approximately day 112 of gestation, sows were moved to farrowing
rooms and housed in farrowing crates. Pigs were weaned at 16-17
days of age and sows were bred on the first heat after weaning.
At the beginning of the trial, the first service was a natural
service with second and third services by artificial insemination
(AI) in keeping with standard site practice. A transition to 100%
AI was made during the course of the trial at a similar time at
all sow units. Sows were predominantly PIC Camborough 15 at the
start of the study with a transition to PIC Camborough 22 by conclusion
of the study. Replacement gilts were moved to the gestation building
in the sow units at about 68 kg (150 lb) bodyweight (BW) and were
bred by standard practices at about 127 kg (280 lb).
Experimental design
For allotment to one of two dietary treatment groups in September
1996, the 12 4000-sow units were ranked from highest to lowest
based on pigs weaned per mated sow per year (PWMSY) as recorded
on the PigCHAMP(R) database during a 3-month "pretest"
period. Beginning with the highest-ranking pair, one unit was
then randomly allotted within that pair to one of the two dietary
treatments, either:
- a "+Cr" treatment, in which supplemental CrP was
added to provide 200 ppb Cr to the breeding, gestation, and lactation
diets. CrP-supplemented diets were obtained by replacing 0.05%
ground limestone in the control diets with an equal amount of
CHROMAX(TM) brand CrP premix (0.04% Cr, Prince Agri Products,
Inc.; Quincy, Illinois); or
- a "Control" treatment, which received no supplemental
CrP.
Experimental diets were corn-soybean meal based with added
wheat middlings in gestation and added fat in lactation. Actual
ingredient use varied with the economics of the ingredient market.
Lysine concentrations were 0.55% for gestation, 0.95% for lactation,
and 0.85% for breeding. In a procedure similar to that previously
described for wheat middlings and fat, the use of lysine HCl varied
depending on economics. In no case did the concentration of lysine
HCl exceed 0.10%. Chlortetracycline was added at 220 ppm (200
g per ton) to the breeding and lactation diets. The lactation
diet was fed in the farrowing room and the breeding diet was fed
after weaning through the end of the third service and to nongestating
gilts. The gestation diet was fed at all other times.
After allotment, there was a 1-month "startup" period
to allow each unit to begin use of the appropriate experimental
diets. The start-up period was followed by a 6-month "loading"
period to allow sows and replacement gilts adequate time to build
body chromium stores and to assure that reproductive data obtained
was only for sows that had received the dietary treatment for
the entire gestational period. Finally, sow performance was evaluated
over the 12-month "test" period by evaluating the PigCHAMP(R)
records of the twelve sow units.
Statistical analysis
Analysis of covariance5 was performed using the
GLM procedure of SAS (SAS; Cary, North Carolina) with the pre-assignment
PWMSY as the covariate in the analysis. The continuous function
variable of PWMSY ranged from 19.5-24.9. Values for each response
parameter tested were those that PigCHAMP(R) calculated
for the 1-year test period for each of the 12 units. These values
were further divided for each unit into four parity groupings
(parities one, two, three, and greater than three) to assess the
potential for a unique response at different parities. Because
there were no dietary treatmentxparity interactions, the final
model included only dietary treatment as the single factor along
with the covariate.
Problems with porcine reproductive and respiratory syndrome
virus (PRRSV) were experienced during the "test" period
in the sow units used in this study. We conducted an ANOVA on
abortion data to evaluate the possibility that PRRSV may
have contributed to a bias in the results. Although the number
of abortions did not differ statistically (P >.20) between
treatments, we conducted a test for potential outliers.6,7
The statistical examination of the data to assess the impact of
the PRRSV outbreak on abortions by unit by month revealed some
months in sow units on each treatment that had higher abortions
than normal. The data set was temporarily adjusted to account
for abortion occurrences in these months and the analyses for
farrowing rate conducted again using analysis of covariance.
Cost:benefit evaluation
To put the observed biological results into an economic perspective,
several cost:benefit scenarios were modeled using the total farm
economic model developed for a Lotus spreadsheet (Compass Record
Keeping System 1983, Hog Cashflow; Ralston Purina, Inc.; St. Louis,
Missouri) (Table 1). To project potential
income over feed cost using these cost and price assumptions,
three different scenarios beyond the base "Control"
scenario were calculated:
- a "No response" scenario modelling the effect of
adding supplemental CrP to all breeding herd diets in a hypothetical
1000-sow herd with no biological response;
- a "Breakeven" scenario in which litter size was
adjusted to the point closest to breakeven ($0 profit) with supplemental
CrP; and
- a "Projected" scenario modelling improvements in
performance similar to those we observed in the present study
in sows in the +Cr group.
Common assumptions used in this evaluation were of a 1000-sow
farm with 125 farrowing crates that was weaning pigs at 17 days
of age. Market hogs were sold at 118 kg (260 lb). Costs used for
corn and 44% protein soybean meal and prices received for market
hogs and cull sows were the 10-year historical averages.8
Nonfeed costs were set at zero based upon the assumption that
they would not be affected by the changes observed in these data.
Common industry values were used for other input parameters (Table 1) and were kept constant.
Results
The allotment procedure resulted in an equalization of pigs
born alive per litter (the primary response of interest) during
the pretest period (10.37 for Controls versus 10.37 for the +Cr
group). Additionally, the evaluation of other reproductive responses
demonstrated that there were no measured differences between treatments
(P >.10) during the pretest or the loading period.
Sows in the +Cr group had a numerically (although nonsignificant,
P =.23) lower farrowing rate than Control sows (Table
2).
After adjusting for the PRRSV-caused abortions, farrowing rate
was virtually identical in the two treatment groups (80.00% versus
79.89%). Additionally, the adjustment did not alter the difference
or statistical significance of any other response parameters,
such as litter size, during the test period. Therefore, the nonadjusted
values are shown in Table 2.
The use of supplemental CrP did improve aspects of reproductive
performance during the test period (Table
2). Percent sows bred within 7 days was numerically increased
2.7% in sows in the +Cr group (P =.09) over Control sows.
Further, pigs born alive was improved by 0.37 pigs per litter
(P =.02) in the +Cr group compared to Controls, and pigs
weaned per litter was increased by 0.33 (P >=.02) in
the +Cr group. Sows in the +Cr group had a 1.57% lower (P
=.11) mortality than Controls. While there were also numerical
improvements of varying magnitude in wean-to-first-service interval,
nonproductive sow days, and PWMSY for sows in the +Cr group compared
to Controls, none of these differences was statistically significant.
There was no interaction between treatment and parity (P
>.48) (Figure 1 and Figure
2).
Cost:benefit evaluation
In the "no response" scenario, the total cost of
supplementation was $8107 per year or $8.11 per sow per year (Table 3).
The "Breakeven" scenario demonstrates that an increase
of 0.06 pigs weaned per litter resulted in 123 more pigs marketed
per year and increased gross income by an amount approximately
equal to the cost of chromium supplementation; increasing the
response to 0.07 pigs weaned per litter resulted in an increase
in income > $0.50 per sow per year.
The "Projected" scenario--which used the performance
changes we observed for litter size, wean-to-first-service interval,
and sow mortality in the +Cr group--resulted in a mean of 748
more pigs marketed and $40.08 more gross income over feed cost
per sow per year for the units included in this study.
Discussion
In the present study, about 100,000 litters were born during
the test period. This massive number of litters was reduced to
12 observations in the data set (one observation per unit for
the entire year); each data point, then, represents over 8000
litters (100,000 litters on the study / 12 sow units). Averaging
so many data points to get one observation per unit tends to minimize
the effect of nontreatment factors that normally can have a large
impact on interpretation of results. For this reason, the limited
PRRSV problems during the test period failed to affect the analysis
and the mean response values reported in Table
2 were not adjusted.
The lack of dietary treatment effect during the 6-month loading
period was expected. Producers should not expect to see an earlier
response in performance records because the mechanism of action
that provides for an increase in prolificacy would logically affect
the time frame required to see a response. For example, mechanisms
of action that affect stillborn numbers might be reflected in
a rapid change in production records because it is a near-parturition
phenomenon, while mechanisms of action that affected ovulation
rate might take >=115 days (an entire gestation period) to
produce a change in production records.
The mechanism of action related to CrP is not clearly understood
at present (and in all likelihood is not a unidimensional mechanism).
Research with CrP conducted in Brazil9 demonstrated
a significant increase in viable embryos (litter size at a midgestational
slaughter) when the diet of sows was supplemented with CrP at
200 ppb. But this phenomenon seemed to be due to a combination
of improved ovulation rate coupled with improved embryo survival,
because neither of these parameters, although numerically increased
by Cr supplementation, was statistically significant in itself.
These findings are consistent with our observation that the significant
(P =.02) increase of 0.37 liveborn pigs/litter in the +Cr
sows was probably the cumulative result of an increase in total
born (0.22), and a decrease in stillborn (.05) and mummies (.10).
The numerical decrease in stillborn and mummified pigs is presumably
related to late-term uterine conditions that affect fetal survival
while the increase in total born pigs is probably also a function
of ovulation rate. As with the Brazilian research,9
the P values we calculated for all of the components were
not all of the same magnitude. Other studies have demonstrated
clear time course effects on the magnitude of response, with greater
responses being observed after greater periods of supplementation.2
The improvement in rebreeding values (percent sows bred within
7 days) we observed is consistent with studies from Australia,3,4
and the improvement in litter size (born alive and weaned per
litter) is consistent with other studies performed in the United
States.1,2 In herds practicing early weaning, in which
the average number of litters per sow per year can be expected
to be 2.0-2.4, these improvements should increase sow productivity
by 0.7-0.9 pigs per sow per year.
The numerical (though not statistical) increase in PWMSY observed
was due to the effects on litter size. Pigs weaned per mated sow
per year can also be affected by farrowing rate changes, although
we did not observe any effect of CrP supplementation on farrowing
rate in this study. The lack of a significant difference in farrowing
rate between treatments may seem inconsistent with our observation
that the number of sows bred by 7 days postweaning was significantly
improved in the +Cr group (P =.09). The sows-bred-by-7-days
parameter does not evaluate total percentage of sows rebred. The
failure to alter farrowing rate in this study accounts for the
lack of an observed effect of CrP on nonproductive days.
Other researchers3 have reported that supplementation
with CrP reduced death loss from 5% in unsupplemented sows to
1.3% in supplemented sows, while our observations noted a trend
toward lower mortality in the +Cr sows. This work in swine is
consistent with work in the poultry industry that observed improvements
in broiler mortality with supplementation of CrP.10,11
While the mechanism of this action is not totally understood,
it may be mediated via the effects of Cr on cholesterol and steroidogenesis.
The interrelationship of Cr with cholesterol (from which steroid
hormones such as cortisol are built) should not be overlooked.
Demonstrations of the effect of Cr on cholesterol and steroids
have been observed in multiple species.12-17
The normal effects of parity on litter size are evident in
our study. The benefits of the supplementation are demonstrated
to be very uniform across the parities for the litter size responses.
Although we observed no parity x treatment interactions (P
>.33), the effects we found of CrP supplementation on sow measures
seem to be dependent on the base performance (Figure
2), with greater responses in situations of lower performance.
If this is in fact true biologically, it simply suggests that
Cr status is not the sole factor affecting these responses but
that it is a contributing factor. It should also be remembered
that females at all parities had been supplemented with CrP for
a period of time prior to the collection of this data. For parity-one
females, supplementation was begun at about 68 kg (150 lb), and
for advanced-parity females it was initiated at least 6 months
prior to the observations we made in this study.
The mechanism of action of Cr to elicit these metabolic responses
has been clarified during the past decade. Evans and Bowman18
have demonstrated an increase in amino acid and glucose
uptake by rat skeletal muscle cells due to preculturing of the
cells with Cr from CrP, which facilitates more efficient utilization
of these nutrients. More recent work19,20 suggests
that Cr is involved with insulin via a mechanism that activates
a membrane enzyme by a Crbinding protein of low molecular weight
that is released concomitant with the insulin response to a meal
and also by stimulating insulin-receptor enzyme activity specifically
in the presence of released insulin. Garcia, et al.,17
recently observed Cr dose-related effects on tissue sensitivity
to insulin in pregnant gilts and found that oxytocin, as well
as progesterone (a steroid), were affected by CrP.
Implications
- This study, performed under commercial conditions, demonstrated
that supplementing feed with CrP improves litter size and rebreeding
efficiency.
- These improvements are observed after continuous feeding
during a "loading" period, which was 6 months in reproducing
females and from at least 68 kg [150 lb] in replacement gilts
in this study.
Acknowledgments
Appreciation is expressed to Steve Abrams for production record
compilation and interpretation.
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