Pork producers have been lowering weaning age for over two decades. But an extensive field study in a 7,300-sow commercial herd raises serious questions about the economic burden of early weaning.

The first article in this series presents the results of a Kansas State University (KSU) study that took a hard look at the effects of weaning age on pig performance, costs and revenue relationships and the implications on finishing pig throughput.

Researchers found that as age at weaning increased, growth rates improved (particularly in the nursery), and postweaning variability and mortality declined. Bottom line — weaning older pigs was more profitable.

The KSU study served as the impetus for several Kansas and Nebraska producers to pull back on weaning ages. Thus began a “quiet revolution.” Their experiences with slightly later weaning ages and the move to later weaning in Denmark are featured in articles that follow.

In the U.S., it is common to wean pigs at between 12 and 19 days of age. Generally speaking, pigs within this age range are considered to have equal value, providing they meet minimum criteria.

No doubt, segregated early weaning programs have fostered the development of better diets for early weaned pigs; farrowing intervals have been shortened and pigs/crate/year have edged upward.

But, a quintet of KSU researchers felt there was more to this early weaning story than simply pushing more and more pigs through a set of farrowing crates. The team of researchers included Rodger Main, DVM; Steve Dritz, DVM; Michael Tokach; Robert Goodband; and Jim Nelssen. The group took a hard look at the impact of weaning ages on biological traits and profit margins of early weaning (15 days of age) vs. later weaning (21 days of age) programs.

Two trials involving 5,728 pigs were conducted to determine the effects of weaning age on performance in a three-site production system. Pigs from the 7,300-sow farm flowed to single-source, all-in, all-out nursery and finishing sites. Each 8 × 12 ft. nursery pen had an equal number of barrows and gilts, allotted to replicate normal weight distribution within each age group. Feeders and waterers were standardized.

In the first trial, involving 2,272 pigs, the researchers' objective was to quantify the impact of weaning age on pig performance within the three-site system. Litters were weaned at 12, 15, 18 or 21 days of age. All pigs were fed a common, three-phase nursery diet regimen (Table 1 ).

The second trial, with 3,456 pigs, aimed to evaluate whether changes in nursery diets would significantly affect growth in pigs weaned at different ages. Pigs were weaned at 15, 16, 18, 19, 21 or 22 days of age (expressed in the adjoining tables as 15.5, 18.5 and 21.5 days of age).

Each age group was fed a nursery feed budget classified as either “more complex” or “less complex” (Table 2 ). The classifications were based on the complexity of the formulation and the quantity of the complex diets fed.

Pigs were weighed individually at 42 days postweaning, with pen totals calculated. Weight and gender information were used to re-allot pigs within treatment groups: 1,920 pigs in Trial 1, 3,000 pigs in Trial 2.

In Trial 1, 10 barrows and 10 gilts were placed per 7.5 × 22 ft. finishing pen, while 12 barrows and 13 gilts were placed per 9.5 × 22 finishing pen in Trial 2. Pens were one-third slotted, two-thirds solid concrete. Feeders and waterers were standardized. Barns were curtain-sided, naturally ventilated. All pigs received the same finishing diet, designed to ensure that all nutrient requirements were exceeded for all groups.

Pigs were weighed off test individually at 156 days postweaning in Trial 1 and 153 days in Trial 2, with pen totals calculated.

In Trial 1, each block was sent to slaughter over a 28-day period, after being weighed off test. These pigs represented the “non-limited” finishing capacity group where all age groups were grown to a common market weight regardless of their growth rate.

In Trial 2, all pens in each block were marketed the day after being weighed off test. These were designated the “limited” finishing capacity group, which assumes finishing space is limited and all pigs are sold after a fixed number of days after weaning, regardless of age or weight.

Older Pigs Perform Better

In both studies, as weaning age increased, postweaning average daily gain (ADG) and wean-to-finish ADG improved. Likewise, as weaning age increased, pounds sold/pig weaned climbed and mortality rates dropped (Tables 3, 4, 5 ).

“The improvements in growth rate and mortality largely occurred in the initial 42 days postweaning, with some ongoing growth improvement to slaughter,” KSU researchers reported. The studies show increasing weaning age up to 21.5 days predictably improves grow-finish throughput within the three-site production system.

More specifically, in Trial 1, researchers noted that not only did weaning weight increase with age at weaning, but the variation in weaning weights was less as pigs got older.

“Nursery ADG, average daily feed intake (ADFI), mortality rate and 42-day postweaning weight improved as weaning age increased from 12 to 21 days,” they added. Likewise, feed conversion improved and 42-day post-weaning weight variation decreased as weaning age increased (Table 3 ).

In the finishing barns, ADG, off-test weight, off-test weight variation and average weight per day of age improved as weaning ages increased (Table 4 ). No differences in finishing mortality or carcass yield were noted. “However, when adjusting carcass lean measures to a common carcass weight, improvements in 10th-rib fat depth and percentage lean were observed as weaning age increased. The largest improvements in fat depth and lean percentage were observed as weaning age increased from 18 to 21 days (of age),” the researchers said.

As one might expect, when the full wean-to-finish period was analyzed, ADG, average gain/day postweaning, pounds sold/pig weaned and mortality rate improved as weaning age increased (Table 5 ).

“Average daily gain was calculated to be a more holistic measure of throughput, as weight and days lost due to mortality were not accounted for in the ADG calculations,” they said. “Contrarily, average pig gain is simply a measure of growth rate that is not influenced by mortality. Similar to ADG, pounds sold/pigs weaned more holistically evaluated the effects of weaning age on production system throughput.”

Generally, results in Trial 2 mirrored those recorded in Trial 1, with the exception that feed conversion in the nursery was poorer as weaning age increased. The complexity of nursery feeds (Table 6 ) did not affect growth rate, feed efficiency or mortality. However, pigs fed the more complex nursery feed budgets tended to have less variation in weight at 42 days postweaning.

Performance in the finishing stage of the second trial reflected that seen in Trial 1. Weaning age did not affect off-test weights, mortality rate or carcass yield. However, when measures of leanness were adjusted to a common carcass weight, wean age by nursery feed budget interactions were seen for 10th-rib fat depth, loin depth and lean percentage (Table 7 ). The more complex feeds improved carcass yield and, as a result, increased average carcass weights.

“These results indicate that weaning age has a significant and repeatable effect on growing pig performance within a given set of health and management conditions. These linear improvements in growth and livability largely occur in the 42-day postweaning period, with some ongoing growth improvements in the finishing phase. Altering nursery feed budgets according to weaning age did not affect wean-to-finish growth performance,” they concluded (Table 8 ).

Impact on Costs, Revenue

KSU researchers also studied the effects of weaning age on growing pig costs and revenues within the three-site production system, assuming “limited” or “non-limited” finishing capacities as described above.

“In both trials and finishing capacity scenarios, income over costs and cost/cwt. improved linearly as weaning age increased,” they reported. “Increasing weaning age up to 21.5 days resulted in linear increases in weaned pig value within a three-site production system.”

The tendency to assign a common value to pigs regardless of weaning age or weight, so long as they meet a minimum standard, may be a mistake because it could lead to false conclusions about the financial performance of the breeding herd.

Sow farms can be viewed as either a cost center or a profit center. Regard-less, pig value or cost of production is calculated on a per-pig-weaned basis. “Weaned pig production is the only segment of the production chain that does not have weight as the common denominator for cost information or in the matrix for revenue generation,” the researchers noted.

“These accepted standards for measuring cost and generating revenue operate under the premise that all weaned pigs meeting a minimum standard are of equal value,” they added. Consequently, weaning age is reduced in an effort to wean more pigs from the farrowing crates available.

To test the philosophy, researchers applied cost and revenue information to growth performance data to model the economic implications of the various weaning ages on a per finishing pen basis from results of Trials 1 and 2. Trial 1 had 96 pens with 20 pigs/pen; Trial 2 featured 120 pens with 25 pigs/pen.

A standardized cost/year of $30/pig space in the nursery and $38/pig space in finishing, using the assumptions in Table 9 , were used. Actual nursery feed costs were used. However, since feed consumption was not measured in finishing, researchers applied a common finishing feed cost/lb. of gain. Results are presented on a per-pig-weaned and a per-head-sold basis.

“Expressing performance and financial information on a per-pig-weaned basis enables all wean-to-finish throughput, cost and revenue information to be brought back to a common denominator,” they explained. “This enables treatment differences in throughput and financial performance to be quantified in a manner that directly relates to value of the weaned pig and removes mortality-induced bias in traditional wean-to-finish closeout data analysis.”

Because the complexity of the feed budget had no effect on wean-to-finish growth performance in Trial 2, cost and revenue data were analyzed on a per-finishing-pen basis.

In Trial 1, feeder pig cost increased as weaning age increased because older pigs ate more. Quantitatively speaking, however, feeder pig costs were moderately flat as weaning age increased from 12 to 21 days, partially because mortalities declined as weaning age increased.

“In both the limited and non-limited finishing capacity scenarios, revenue and income over costs/pig weaned increased and cost/cwt. decreased as weaning age increased from 12-21 days,” the researchers stated (Table 10, 11 ). “Cost/head sold decreased with weaning age, when all age groups can be marketed at an equal pig weight,” they added. Trial 2 results reinforced those found in Trial 1.

“Increasing pounds sold/pig weaned improved margins and production cost/cwt. These studies indicate that weaning age substantially affects the value of weaned pigs within a given three-site production system,” the researchers observed.

Rates of Improvement

Carrying their analysis one step further, data from the trials were modeled to determine the linear rates of improvement observed as weaning age increased from 15 to 21.5 days.

“Each day increase in weaning age increased initial weight (taken prior to weaning) by 0.57 lb. and weight sold to slaughter by 3.71 lb./pig weaned,” the researchers explained. “In the financial analysis, income over cost increased 94¢/wean age day in the limited finishing space scenario and 53¢/wean age day in the non-limited finishing scenario.

“Therefore, if finishing space is limited, increasing weaning age from 16 to 19 days is predicted to improve income over cost by $2.82/pig,” they said.

In this final analysis, KSU researchers drew data from 192 finishing pens (4,518 pigs) and presented the results as the “rate of change/day increase in weaning age.” These rates of change were also translated to a “per pound of weaning weight” basis (Table 12 ). These data need to be interpreted with the understanding that the incremental pound increase in weaning weight is due to increased lactation length, they reminded.

“The primary difference in the limited vs. non-limited finishing capacity is that the value of growth rate is more fully recognized when finishing spaces are limited,” they said.

“The linear improvements observed with the increasing weaning age illustrate the magnitude of the measured response to increasing weaning age from 15 to 21.5 days in these studies. Understanding the effect of weaning age on weaned pig value demonstrates the need to identify lactation crate utilization inefficiencies or facility restrictions that may be constraining whole-system throughput.

“There was a $3.18 (non-limited grow-finish space) to $5.64 (limited grow-finish space) per weaned pig difference in realized margin observed as weaning age increased from 15 to 21.5 days.

“These data indicate that simply assessing a common value to weaned pigs, regardless of age or weight, may lead to incorrect conclusions concerning sow herd productivity. Improving lactation crate utilization, altering weekly farrowing targets, decreasing week-to-week variability in the number of sows farrowed or increasing lactation capacity are the primary means of increasing and maintaining consistency in weaning age,” researchers concluded.