As production systems begin to implement parity-based segregation of the breeding herd, producers and nutritionists have been able to take advantage of greater specialization of feeding programs for gilts and sows.

It's not that we haven't been aware of the differences in nutrient requirements of gilts vs. sows. But in facilities where they are housed together, it becomes extremely difficult to implement two separate feeding programs.

Because gestating gilts are still growing and depositing greater amounts of protein during gestation than sows, and typically have lower lactation feed intake, our nutritional programs have focused on meeting the gilts' requirements, realizing that in many instances we are overfeeding sows.

Therefore, parity-based segregation should allow for more specialized nutritional programs to minimize the costs of overfeeding, and hopefully, enhance breeding herd performance.

Gilt Development

The most important thing to remember in designing and implementing a gilt development protocol is that the feeding program will be of secondary importance to items such as early boar exposure and estrous detection, genetics and selection criteria, and environmental and other management factors.

That's why it is possible for many different types of feeding programs to be successful, depending on how the other important management criteria are implemented.

For instance, if replacement gilts are farrowed on the farm, or delivered as early weaned pigs, they can be fed the same nursery diets as the commercial pigs. In some cases, it may be desirable to slightly increase the feed budget to allow more of the early starter diet to be fed. This provides added insurance against any potential replacement gilts falling behind or becoming stunted.

A good time to do a preliminary selection is when gilts leave the nursery, examining them for good structural correctness, having at least 12 teats and the absence of ruptures or hernias.

Research from the University of Alberta and the Prairie Swine Centre in Saskatchewan, Canada, suggests that growth rate of replacement gilts should be neither too slow, nor too fast. Those researchers suggest that the ideal weight at breeding should be approximately 300 lb. Gilts that grow too slowly wind up being held too long before they reach their ideal breeding weight, thus accumulating excessive non-productive days.

For example, if a gilt weighs 200 lb. at first estrus, she will be on her fourth or fifth estrus by the time she reaches the 300-lb. target weight. Gilts that grow too fast have a large mature size and run the risk of increased susceptibility for locomotion problems that may affect lifetime breeding performance.

Table 1. Diet Options for Developing Gilts from 50 lb. to 250 lb.
Three phase Three phase with Fat
50 90 150 50 90 150
Ingredient 90 150 250 90 150 250
Corn 68.80 74.35 87.15 68.80 74.35 79.75
Soybean meal, 46.5% 28.25 22.80 10.10 28.25 22.80 12.40
Choice white grease 5.00
Monocalcium P, 21% P1 1.20 1.13 1.05 1.20 1.13 1.15
Limestone 19 18 18 19 18 17
Salt .35 .35 .35 .35 .35 .35
Vitamin premix with phytase .15 .15 .15 .15 .15 .15
Trace mineral premix .15 .15 .15 .15 .15 .15
Lysine HCl .15 .15 .15 .15 .15 .15
TOTAL 100.00 100.00 100.00 100.00 100.00 100.00
Desired Lysine, % 1.15 1.00 0.65 1.15 1.00 0.70
ME2, kcal/lb 1,504 1,506 1,510 1,500 1,505 1,611
Protein, % 19.0 16.9 12.1 19.0 16.9 12.5
Calcium, % 0.70 0.65 0.60 0.70 0.65 0.60
Phosphorus, % 0.64 0.60 0.53 0.64 0.60 0.55
Available phosphorus, % 0.32 0.30 0.27 0.32 0.30 0.29
Available phosphorus equiv., % 0.40 0.38 0.35 0.40 0.38 0.37
Lysine:calorie ratio, g/mcal 3.47 3.01 1.95 3.48 3.01 1.97
Avail. P:calorie ratio g/mcal 1.21 1.14 1.05 1.22 1.15 1.04
Feed budget, lb./pig 90 165 350 90 165 315
1Phosphorus
2Metabolizable Energy


Therefore, from 50 lb. to breeding, replacement gilts should be fed diets that promote good growth rate and skeletal development. These diets can be very similar to rations fed market hogs, with the exception that they won't be formulated for maximum growth and leanness, and they will contain greater levels of calcium and available phosphorus for bone strength.

Genetic potential for lean growth may be a factor in selecting lysine and energy concentrations of these gilt developer diets. With extremely lean genotypes, it may be advisable to add fat to the last developer diet (combined with relatively low lysine) in order to increase second-parity (P2) backfat depth to about 16 mm (.63 in.) by the time of breeding.

Other, less-extreme genotypes may achieve this 300-lb. target weight and 16 mm, second-parity backfat depth at breeding on regular grain and soybean meal-based diets formulated to lysine levels slightly below standards for maximum growth rate and leanness.

The justification for the weight and P2 backfat depth targets of 300 lb. and 16 mm at breeding are based on the premise that gilts need to have enough total body protein reserves to buffer against excessive weight (protein) loss during lactation, when feed intake is generally low.

Recent data from the University of Alberta indicates that milk production (litter weaning weights) and subsequent reproductive performance were greater in high-lean body mass sows that lost less protein in lactation. They speculate that a larger lean mass may buffer against the decreases in performance associated with severe protein loss during lactation. There is probably less conclusive evidence to support the recommendation of 16 mm of P2 backfat depth at breeding, other than this amount will allow for easily reaching the targeted fat depth of 19 mm (.74 in.) at farrowing, based on expected gestation feed intake and weight gain.

The diets listed in Table 1 are possible options for moderate growth during the development period. Care should be taken to closely gauge gilt weight gain, so if the targeted weight is not reached or exceeded, diets can be modified based on specific rearing conditions.

In most cases, at around 250 lb., gilts will be moved to the breeding barn, where feed intake should be limited to approximately 4.5 lb./day, again adjusted based on the goal of a 300-lb. gilt at 210 days of age.

Then around Day 190 — or two weeks before breeding — feed intake should be increased to 6 lb./day to flush gilts and increase ovulation.

Immediately after breeding, feed intake should be cut back to 4 lb./day for five to seven days postbreeding.

Then, once sows have been bred, feed intake can be adjusted based on size and desired weight and backfat gain during gestation.

The data in Table 2 shows the calculated amount of extra feed above maintenance (approximately 4 lb./ day) provided over the first 100 days of gestation to achieve the desired weight gain.

Table 2. Feed Intake Above Maintenance Requirements to Achieve a Certain Weight Gain*
Desired weight gain Total feed, lb. Extra feed required from Day 0 to 100, lb.
30 45 0.2
40 60 0.3
50 75 0.4
60 90 0.5
70 105 0.7
80 121 0.8
90 136 0.9
100 151 1.1
*Maintenance requirements for a 300-lb., 350-lb. and 400-lb. gilt will be met with 3.25, 3.50, and 3.75 lb./day of a corn-soybean meal diet, respectively. These intake amounts assume all sows will be fed 6 lb./day from Day 100 to 114.


Conclusion

Management of the replacement gilt has become a critical issue in determining the overall reproductive efficiency of the breeding herd. A management and nutrition program that allows for moderate levels of growth performance from birth to selection will positively affect reproductive performance and longevity.

It is apparent that gilts should enter the breeding herd with greater tissue reserves (protein), and should be fed without significantly reducing these reserves, to ensure a long breeding life.

Parity Effects on Lactation Feed Intake

Parity 1 (P1) and P2 females consume less feed than older parities (Table 3).

If only one diet is practical on the farm, parity distribution should be evaluated to determine the most economical approach. This will typically mean formulating diets to meet the gilts' requirements, realizing we will be overfeeding the rest of the herd.

However, if production systems have the opportunity to separate gilts and Parity 1 sows from older sows, consider using the following approach:

Formulate the first diet for P1 and P2 females (this diet should be formulated to minimize protein tissue loss), and formulate the second diet for the other parities (this diet should be formulated to maximize litter weight gain in the older parities).

Table 3. Lactation Feed Intake and Lysine Intake as Influenced by Parity and Dietary Lysine Level
Parity
Item 1 2 3 4 5 6 7
Lactation feed intake, lb. 10.1 11.5 13.5 13.1 14.0 13.7 14.3
Lysine intake with one diet (.95% lysine), g./day 43.7 49.6 58.1 56.4 60.3 59.0 61.8
Lysine intake with two diets (.9% and 1.2% lysine), g./day 55.2 62.6 55.1 53.5 57.2 55.9 58.5
Adapted from Dritz et al., 1994.


This approach will allow similar total amino acid intakes for all parities as demonstrated in Table 3. Thus, formulating their diet to a higher amino acid level allows similar grams per day of consumption.

But use caution. The data in Table 3 was collected from a farm with excellent lactation feed intake with about 140 lb., 21-day adjusted litter weaning weights. On many farms, lactation feed intake may be lower; therefore, the dietary lysine percentages may need to be adjusted accordingly.

Farm Diet Options

The diets listed in Table 4 are possible options for producers with parity-segregated breeding farms.

Gestation and lactation diets are formulated to offer gilts slightly higher lysine and other amino acid concentrations compared with sows. Some producers may choose to add soy hulls or another source of fiber to their lactation diets.

In these cases, the dietary lysine percentage has been changed to correspond with the decreased energy content of the diet, and the anticipated increase in feed intake to provide similar caloric intakes.

Table 4. Gilt and Sow Gestation and Lactation Diet Options
Gestation diets Lactation diets
Ingredient,% Gilt Sow Gilt Sow Gilts Sows
Corn 81.70 83.50 78.35 80.01 58.60 65.80
Soybean meal, 46.5% CP2 14.50 12.70 12.95 11.25 34.70 27.45
Choice white grease 3.00 3.00
Monocalcium P, 21% P1 1.65 1.65 1.55 1.55 1.55 1.55
Limestone 1.00 1.00 1.00 1.00 1.00 1.01
Salt .50 .50 .50 .50 .50 .50
Vitamin premix with phytase .25 .25 .25 .25 .25 .25
Trace mineral premix .15 .15 .15 .15 .15 .15
Sow add pack .25 .25 .25 .25 .25 .25
Soy hulls 5.00 5.00
TOTAL 100.00 100.00 100.00 100.00 100.00 100.00
Total lysine, % 0.65 0.60 0.63 0.58 1.20 1.00
ME, kcal/lb 1,490 1,490 1,441 1,442 1,550 1,550
Protein, % 13.7 13.0 13.2 12.6 21.1 18.4
Calcium, % 0.76 0.75 0.76 0.76 0.80 0.80
Phosphorus, % 0.68 0.67 0.64 0.64 0.73 0.70
Available phosphorus equiv., % 0.48 0.48 0.46 0.46 0.48 0.48
Lysine:calorie ratio, g./mcal 1.98 1.83 1.98 1.83 3.51 2.93
Avail P:calorie ratio g./mcal 1.47 1.46 1.45 1.44 1.42 1.39
1Phosphorus
2Crude Protein


Estimating Gestation and Lactation Feed Intake

With the help of closeout spreadsheets, there is so much more accurate information today on nursery and growing-finishing pig feed intake than in the past.

Yet in the sow herd, we seldom evaluate herd gestation feed intake, and in lactation, many still rely on inaccurate and outdated feed intake cards.

Better estimates of gestation and lactation feed intake can be estimated based on monthly feed delivery.

To calculate average herd gestation feed intake, simply divide the tons of gestation feed delivered over a set time period by the number of gestation crates, times the number of days in the period.

In situations where sows are group housed or combinations of gestation crates and pens are used, divide feed delivery by gestating sow inventory, times the number of days in the period.

Total Feed = 625 tons × 2,000 lb. = 5.27 lb./day


Crates × Days 650 crates × 365 days


Using this method of calculation, we target a gestation feed intake of between 5.0 and 5.4 lb. as ideal. When feed intake amounts are higher than this, a representative sample of the herd should be scanned for backfat, because average backfat will very likely exceed the desired 19 mm (.74 in.) at farrowing.

In lactation, we take the average of two calculations. The first divides the total feed delivered in a set time period by the number of farrowing crates, times the number of days in the period.

Total Feed = 419 tons × 2,000 lb. = 10.2 lb./day


Crates × Days 450 crates × 182 days


The second method is based on the number of lactating days. From computerized sow records, we determine the number of litters weaned in a period, times the average lactation length; then the total feed delivered is divided by this number.

Total Feed = 419 tons × 2,000 lb. = 12.2 lb./day


Litters × Lactation Length 3,615 × 19 days


The first method should underestimate average lactation feed intake, because it counts the days that crates are either empty or containing sows before they farrow as consuming lactation feed. The second number overestimates lactation feed intake, because the feed given to sows before they farrow is counted as lactation feed.

However, the true daily lactation feed intake has to be somewhere between 10.2 lb. and 12.2 lb., or an average of about 11.2 lb.

If there is greater than a 3-lb. difference in the estimated feed intake among the two equations, this usually indicates that sows are gestated for several days in the farrowing crates and further analysis is needed.