Six genetic types were used in the Quality Lean Growth Modeling project to represent a range in average daily gain, backfat deposition and loineye area. Genetic type classification was explained in the previous article by Goodwin and is abbreviated in the adjoining key.

The results presented here are based on the ultrasound scanning backfat and loin muscle measures taken every 2-3 weeks during the test period. Pig weights were taken at each scanning. The rate at which traits changed were measured for the total test period at the three respective off-test weights (90-250 lb., 90-290 lb., 90-330 lb.). The rates of growth, backfat and loineye area were estimated for each pig. Those rates were used for the QLGM analysis. Other authors will show rates of change for intervals during the growth period.

Table 1 presents rates of increase in body weight (average daily gain), backfat and loineye area for the six genetic types measured in the QLGM project.

Line A clearly deposited fat at a faster rate and had a slower rate of increase in loineye area (LEA) with an intermediate rate of body growth. In contrast, line D had the highest rate of body growth but was intermediate for backfat and loineye area increases. Lines B, E and F had the lowest average daily gains but had lower fat deposition and higher increases in loineye area. Line C had the second highest rate of body growth, the second lowest rate of fat deposition and ranked third for highest rate of increase in loineye area.

Table 1 clearly shows there were marked differences among genetic types for changes in body weight, backfat and loineye area.

Producers wishing to use this information need to know which of the genetic types represented here most closely matches the hogs in their operations.

In order to more accurately establish genetic type, randomly select 50 or more animals in your herd. Weigh them and measure their backfat and loineye area at least twice between 100 and 250 lb. More frequent measurements add to the accuracy.

Remember that you need at least two different genetic types, diets, environments, etc. to have a comparison. The most difficult part of setting up a comparison is trying to identify genetic type since most producers have only one type to test. One option to obtaining a second type for comparative purposes is to get boar semen from a defined genetic type, breed your sows, then include their progeny in your trial as a control. Examples of defined genetic types would include the lines tested in the NPPC Sire Line National Genetic Evaluation Program (NGEP). Berkshire, Duroc, Hampshire, Danbred and Newsham Hybrids pigs were defined in that test.

For example, if you want to conduct an on-farm test to compare growth rate, then Duroc semen would be useful to produce the test pigs needed. Likewise, if you wish to compare meat quality traits, then Berkshire semen would be a good choice for the test pig comparison. Work with your semen supplier to identify genetic lines that will provide pigs for a more accurate comparison.

Additionally, sex-specific tests and replication of your trial will add to the accuracy. The rate of change in these traits, not absolute values, will provide you with the information needed for genetic classification.

Remember also, to account for your nutritional program when assigning genetic type, as diet will affect the traits represented.

Protein's Impact Four nutritional programs were fed in which energy, minerals and vitamins were held constant within the weight ranges. However, lysine levels differed between the four diets. Diet 1 contained the highest lysine level (exceeding NRC standards), while diet 4 had the lowest lysine level (deficient by NRC standards). Lysine levels with each nutritional program were adjusted as pigs grew. (See Goodwin's Table 7, page 24). The protein (lysine) source in all diets was corn and soybean meal.

Table 2 gives the rates of change in body weight (average daily gain), backfat and loineye area as influenced by the four lysine levels fed. Only the lowest level of lysine (diet 4) influenced body weight gain. However, backfat tended to increase as lysine level decreased. Pork producers may wish to feed higher levels of protein (lysine) to get leaner hogs for packer buying programs. However, the economics of this decision must be scrutinized, as frequently changing costs will determine whether the change is a profitable one.

High and low levels of lysine created less muscle growth than intermediate levels of lysine.

In general, for the average pig in the trial, diet 2 provided the best combination of growth, backfat deposition and loineye area increase.

Market Weight Impact Pigs were assigned to one of three off-test market weights when they were delivered to test groups. Designated off-test weights were 250, 290 or 330 lb. Rates of change in body weight, backfat and loineye area for the total trial period are shown in Table 3.

The table shows there were no differences in average daily gain (ADG) for pigs marketed at the three weights. However, backfat deposition was higher for the two heavier weights. Rates of loineye area increase were similar for pigs marketed at 250 and 290 lb., but pigs marketed at 330 lb. had higher rates of increase in LEA. There were no interactions between market weight and either diet or genetic type. Thus, similar results for diet and genetic type were found regardless of market weight.

These results also show that rates of body growth, backfat deposition and LEA growth did not change markedly among the different genetic types and/or diets as market weights increased. If you know the rates of change in these traits, you can predict their values for each end weight of any genetic type. Other authors will address rates of change during specific intervals, which may help fine-tune feeding and/or marketing programs further.

Growth Rate Differences If you have identified your pigs' genetic type, taking into consideration the diets fed to those pigs when classifying them, you may use Tables 4 through 7 to help guide you toward matching diets to your goals for growth rate, backfat and loineye size. Table 4 presents the genetic type by diet effects for average daily gain. Remember, references to a diet, by number, covers the four nutritional phase-feeding programs fed from 90 lb. to the designated off-test weight. (250, 290, 330 lb., respectively. (Review QLGM Nutritional Programs, Table 7, page 24).

Except for line A, diet 1 produced the highest ADG. Line C had a marginally higher gain with diet 2. All other lines had reduced ADG as protein in the diet decreased.

If your lines resemble line A, you could use diets 2, 3 or 4 to achieve the fastest growth rates, if that is your goal. For the other genetic types, differences among diets 1, 2 and 3 are small and of little importance.

Thus, only the fattest line responded favorably to low lysine levels while only the lowest lysine level had an important impact on the faster-growing and/or leaner pigs. Therefore, producers have a relatively wide range of diet choices to maximize profits.

Backfat Variables Rates of change in backfat deposition by genetic type and diet are shown in Table 5.

All genetic types tended to have faster rates of backfat deposition as protein level in the diet decreased. Lines with high rates of fat deposition and low rates of muscle increases (lines A and D) deposited fat faster. Similarly, lines with low rates of fat deposition and high rates of muscle increase (lines B and E) also responded to lower protein levels by depositing fat quicker. The effect of protein level on backfat deposition in lines C and F were small, however.

It is most interesting to note that lower protein in the diet had essentially the same effect on the fatter lines as it did on the leaner lines. Only line C, a faster growing line with intermediate fat deposition, and line F, a slower growing line with intermediate fat deposition, were unaffected by changes in protein in the diet.

Based on rate of fat deposition, you would choose diet 1 for lines A and B. Diets 1 and 2 are of equal value for lines D and E, while lines C and F did best on diet 2. Again, the adjoining key can help you classify your market hog type if you have not conducted on-farm tests to help classify your genetic type.

Loineye Dilemma Rates of change in LEA were perplexing because intermediate levels of protein (diets 2 and 3) resulted in faster increases in LEA for all genetic types. Diet 4 was inferior for all genetic lines except line E, which had the lowest rate of LEA increase on diet 1. The relatively slow-growing, high-muscle line, line B showed little change in muscle growth as protein level changed. In contrast, line E, which was also slow growing with good muscle development, had a very low rate of muscle growth on high protein but did well on the other diets.

All lines tended to have similar loineye muscle growth at the two intermediate levels of protein. A general recommendation would be to feed diets 2 or 3 for best LEA growth.

Sex Differences Sex significantly influenced ADG, backfat and LEA (Table 8).

Gilts grew slower, had lower rates of fat deposition and slightly higher increments of loineye area. The effects on backfat for each sex were essentially the same as changing diets.

However, changes in the diet did affect the two sexes differently. Only very small changes in ADG were evident for barrows on the different diets. However, ADG for gilts tended to decrease as protein levels decreased (Table 9). This might suggest the need for higher protein levels for gilts.

Sex effects on backfat were somewhat different for the different genetic groups (Table 10). Sex differences were quite similar for lines B, C, D and E.

On the other hand, two lines (A and F), which tended to be relatively slow growing with moderate to high fat deposition, had large differences between the sexes for rate of fat deposition.

This observation reinforces the need to consider sex differences when on-farm trials are conducted, particularly when genetic types have a large difference between barrowsand gilts.

Conclusions In summary, marketing pigs at 250, 290 or 330 lb. had little effect on rates of change in body weight or loineye area during the total growth period. Marketing at these weights did not interact with genetic type or diet. In other words, lean pigs stayed leaner and fat pigs were fatter at all weights.

Both genetic type and diet influenced the rates of change in body weight, backfat and LEA. The rate of backfat deposition was higher at heavier weights. Further, significant interactions existed between genetic type and diet, such as the fattest type (line A) growing fastest on lower protein diets.

The choices of which diet to use for a genetic type depend on which trait you want to emphasize - body weight (ADG), backfat or LEA.

Table 7 presents a summary of diet(s) recommended for each genetic type for each of the respective traits. Again, the nutritional program differences are presented in Goodwin's article.

Diets 3 and 4 would probably never be recommended. Diet 2 appears to be the best general recommendation, but one may choose a diet depending on genetic type and the importance placed on a trait.

Further, these recommendations are based solely on performance; economics have not been considered.

Packer buying systems and the value of feed efficiency and growth rate (addressed by other authors) will help determine the nutritional programs offering the most profitable returns.