Purdue Pork Page Archive
A.P. Schinckel, Department of Animal Sciences, Purdue University
To utilize the advantages of AI and genetic principles, there are four main concepts.
The rate of genetic improvement in a commercial pork producer's herd parallels the rate of genetic progress made by the seedstock suppliers. To make significant genetic progress for any economically important trait (growth rate, feed conversion, carcass merit, or liter size), performance records must be kept and superior animals selected to produce the next generation with the seedstock producers herd.
When selecting seedstock suppliers, review their genetic improvement program. A sound genetic improvement program should include four features: (1) accurate, complete performance records including animal identification, consistent measurement of all boars and gilts (not on-again, off-again or limited, partial performance testing), and ranking of animals within defined contemporary groups; (2) assessment of the genetic merit of economically important traits (growth rate, feed efficiency, carcass merit and reproductive performance) based on the individual's performance relative to its contemporary group and incorporating the performance of relatives; (3) indexes weighting traits relative to their economic importance in commercial pork production (the indexes should correctly rank the individuals relative to their intended use in crossbreeding systems); and (4) selection of the highest-ranking boars and gilts based on selection indexes. Seedstock producers should utilize selection indexes as their primary selection criteria. Some emphasis should also be given to physical characteristics such as reproductive and skeletal soundness.
A commercial pork producer cannot expect the genetic merit for economically important traits in his herd to consistently improve unless the seedstock producer uses superior performance tested boars. Therefore, commercial producers should purchase seedstock from suppliers who use exclusively superior performance tested sires and are selecting superior replacement gilts.
Terminal crossbreeding systems, specific crosses and rotaterminals offer substantial benefits in terms of profit per litter and consistency of the pigs and performance levels (PIH- 39). The key to the operation of terminal crossbreeding systems is the method of raising replacement gilts. Replacement gilts are produced in special matings. The high levels of productivity experienced with gilts and sows from these special gilt producing matings give the terminal crossbreeding systems their advantage. Operationally, the production of replacement gilts is the key to the terminal crosses.
Herds with weekly schedules should have lower replacement rates and in which case specific crossbreeding systems would be most profitable. The system returns for Hampshire- Duroc F1 boar Yorkshire-Landrace F1 female specific cross is presented in Table 1. The returns of a specific crossbreeding system is highly dependent on the replacement rate. Assumptions must be made as to the replacement rate and percent gilt selection. Assuming a 40% replacement rate per litter farrowed and a 50% gilt selection rate, i.e. 2.25 gilts selected per 4.5 gilts raised per litter, the percentages of matings needed of each cross are presented in table 1. The weighted average for all three tiers assuming no replacement cost is $9556 with 40% replacement rates and $9999 with 25% replacement rates.
The question for commercial producers is which method of gilt replacement is more economical and practical? The great-grandparent program involves operating all three tiers. The grandparent program involves purchase of the grandparent gilts to produce the parent gilt. The third option is to purchase the parent gilt. Using typical prices, 25 or 40% replacement rates and 50% selection rates, the returns for the three options are in Table 2.
Table 1. Percent Matings Needed and Average Systems Returns with 40% and 25% Replacement Rates.
| Tier | Cross | $ Net Return/litter | 40% Replacement rate* | 25% Replacement rate |
|---|---|---|---|---|
| Great grandparent | Y x Y | 23.97 | 3.3 | 1.4 |
| Grandparent | L x Y | 51.53 | 16.1 | 11.0 |
| Parent | HD x YL | 107.28 | 80.6 | 87.6 |
| System average | 9556 | 9999 | ||
* From Pork Industry Handbook, PIH-39
Table 2. Returns with Two Gilt Replacement Rates and Three Gilt Replacement Systems.
| 40% Replacement Rate | 25% Replacement Rate | ||||||
|---|---|---|---|---|---|---|---|
| Replacement Gilt System |
$ Cost above market price |
Gross $ return/litter |
Seedstock cost/litter |
Net return per litter |
Gross $ return/litter |
Seedstock cost/litter |
Net return per litter |
| Great grandparent | 1000 | 95.56 | 13.20 | 82.36 | 99.98 | 3.5 | 96.49 |
| Grandparent | 400 | 97.98 | 26.72 | 71.26 | 101.14 | 11.1 | 90.04 |
| Parent | 100 | 107.23 | 40.00 | 67.23 | 107.23 | 25.0 | 82.23 |
With specific crossbreeding systems, low gilt replacement rates are very important to reduce the number of replacement gilts needed in each tier. The economic impact of low replacement rates does not take into account the increased reproductive performance in conception rate, number weaned and unproductive sow days produced by having a higher percentage parity 3-4 females in your herd via the lower replacement rates with typical parity performance levels, number weaned increases 30 pigs per litter and conception rates increase 4% by decreasing replacement rates per litter from 40 to 25 percent. Thus, it is very important for any producer with high replacement rates to identify management, or genetic changes needed to increase sow productive lifetimes.
The economic impact of grandparent and great grandparent programs is also important. The very largest producers have within house great grandparent programs. Small herds, less than 300 sows, will find it more difficult to manage grandparent or great grandparent program. Their best long term alternative may be to form a cooperative gilt multiplication system. For example six 300 sow herds might construct a 300 sow multiplier herd with grandparent gilts bred to a second maternal line of boars to produce replacement parent gilts.
Commercial producers with 7X farrowings per year have high replacement rates due to sow culling and potentially larger gilt pools. The most economical crossbreeding system for these producers is a rotaterminal including 2 maternal lines of boars mating in a rotation to produce replacement gilts and the terminal cross with rotaterminal crossbreeding systems. The genetic merit of the maternal line boars and the correct matings for replacements i.e. York sired females mated to Landrace boars and Landrace sired females mated to Yorkshire boars are very important.
Maternal Example. Let's take a specific case. Assume through AI, that boars are available that are in the upper 1 percentile of the breed for MLI (Table 3). Let's further assume that you produce 4 litters per month from this semen over a 15 month period, a time that corresponds to the useful breeding life of a boar we might buy. MLI index units are worth $1 per unit per daughter. You keep 2 gilts from each litter and they average 3 litters each over their productive life. Hence, a total of 360 daughters are expected to be produced from these superior maternal boars.
For comparison, let's assume the boar chosen for natural service was from the upper 20% of the breed for MLI and he costs us $1000. You quarantine him for 30 days and house him for the 15 month breeding period at a cost of $2 per day. Let's assume an 80% farrowing rate for both systems.
The expected return over costs for this scenario is presented in Table 5. Note that a semen cost of $15 per dose and 2 services per mating the expected return over costs for AI to the better boars is in excess of $3800. Even at a higher semen cost the AI route would still be a bargain.
Terminal Example. Now lets take a terminal example. In this case let's again take boars from the upper 10% of the breed for use in AI. These (Table 5) would be 18.0 index units better than that of a boar in the 20 percentile that we might purchase. The value of a MLI index unit is $1.0 per pig and let's assume you plan to produce over a 15 month period 6 litters per month of 9 pigs each for a total of 810 pigs by whichever method we choose. Table 6 shows the calculations for this situation. If one assumes that the natural service boar costs us $1000 and that we handle him as we did the maternal example boar mentioned above, his total cost would be $1960. If semen costs were $10 per dose and you mate each sow twice, with an 80% farrowing rate the net return over costs for the AI system would be $1168.
Table 3. Upper 1 and 20% Percentile Index EPDs for Young Yorkshire Sires
| MLI | SPI | TSI | |
|---|---|---|---|
| 1% | 129.85 | 115.6 | 147.3 |
| 20% | 118.23 | 107.3 | 129.3 |
| diff | 11.62 | 8.3 | 18.0 |
Table 4. Maternal Sire Example
| Sire difference | = | 11.62 index units |
| Value per index unit/day | = | $1.00 |
| 15 mos x 4 litters/mo | = | 60 litters |
| 2 daughter saved per litter | = | 120 daughters |
| 3 litters per daughter | = | 360 daughter litters |
Table 5. Expected Return for Maternal Example
| Differences in net income 11.62 x 360 | = | $4,183.20 |
| Boar & maintenance costs @ $2/day | = | $1,960.00 |
| $6,143.20 | ||
| Semen costs @ $15 | = | $2,250.00 |
| Return over costs | = | $3,393.20 |
Table 6. Terminal Sire Example
| Sire difference | 18.0 | index units |
| Unit value | .10 | per pig |
| Total value | 1.80 | per pig |
| 15 mos x 6 litter/mo x 9 pigs/litter | 810 | pigs |
Table 7. Expected Return for Terminal Example
| Differences in net income 810 x 1.80 | = | $1,458.00 |
| Boar & maintenance costs @ $2/day | = | $1,960.00 |
| $3,418.00 | ||
| Semen costs @ $10 | = | $2,250.00 |
| Return over costs | = | $1,168.00 |
In summary there are for items that commercial producers must consider when applying genetic principles in conjunction with critical insemination; (1) identify seedstock producers, (2) implementation of terminal crossbreeding systems with low replacement rates and gilt replacement costs, (3) the use of superior sires via A.I. and (4) identification and use of the superior maternal A.I. sires.
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