Because the nutrient requirements change quite rapidly in the grower stage, increasing dietary phases can reduce diet cost and nutrient excretion.
Grower pigs are capable of tremendous rates of protein deposition and growth while converting feed to gain at better than 2:1 efficiency.
They don't require complex diets or specialty ingredients like nursery pigs. But they do require high levels of amino acids, and often have large growth responses to increasing dietary energy because of their relatively low feed intake in relation to their high capacity for growth.
Because of the relatively low feed intake in grower pigs (or early finishing pigs), and their high capacity for protein deposition, diet formulation and management strategies should focus on increasing feed intake during this stage.
The number of dietary phases to use in the grower stage depends on several factors, including the number of pigs in the building, feed mixing and delivery capability, as well as the age spread of the pigs.
Because the nutrient requirements change quite rapidly in the grower stage, increasing dietary phases can reduce diet cost and nutrient excretion. Most production systems change diets with every 30 to 40 lb. increase in body weight during the grower stage.
The first diet fed in this stage often has the shortest feeding period because of the high amino acid requirements. This first diet often contains growth-promoting levels of copper and other antimicrobials that are removed from later stages of production.
Once the number of dietary phases is determined, diets must be formulated for each phase. Keys to diet formulation in the grower stage are to:
Determine the most economical energy level;
Establish the lysine:calorie ratio for the genetics and production situation;
Set the ratio for the other amino acids;
Determine the available phosphorus level; and
Set levels of vitamins, trace minerals, calcium, salt and other necessary ingredients.
Determining the optimal energy level will depend on many criteria, including the relative cost of grains, fat sources and byproducts.
Another criterion that must be considered is the relative value of average daily gain (ADG), and impact of energy level on growth rate in the production situation.
If growth rate is improved by increasing the dietary energy level, margin over feed cost should dictate the correct energy level in the diet instead of feed cost per unit of gain.
For example, in many situations, adding fat to the diet will increase diet cost and feed cost per pound of gain. Because the added fat also increases ADG under most commercial conditions, the value of the increased gain also must be considered in the economic calculation of the ideal energy level.
Furthermore, because margin over feed cost would include the value of the increased gain, it would be more appropriate than feed cost per pound of gain for economic evaluation of the energy level.
There are many other examples where increasing dietary energy will increase ADG, but will also increase feed cost per unit of gain.
If, for instance, ample facility space is such that pigs will reach optimal market weight before they must exit the building, then the extra weight from increased ADG is not as valuable, and thus, optimal feed cost per unit of gain should dictate the energy level.
However, if facility space does not allow pigs to reach the optimal market weight, then the increased ADG will increase market weight, and margin over feed cost should dictate the optimal energy level.
In most production systems, adequate facility space is not available during the hot summer months. Thus, dietary energy levels higher than those required to minimize feed cost are often economical.
The most common mistakes that we have witnessed in grower pig nutrition programs are as follows:
Not understanding the production or economic response to changing dietary energy levels in the production system;
Not matching the lysine levels to the energy levels;
Not providing more additives and micronutrients than required;
Not adjusting feeders aggressively;
Not feeding a small enough particle size; and
Not always having feed available in the feeders.
Because of a lack of understanding of the importance of feed intake and energy responses in the grower stage, a common mistake in grower diets is the use of feed ingredients that are of lower palatability, or lower energy levels than what is required for optimal economic response.
These lower-energy or lower-palatability ingredients often lower the cost of the diet; however, their impact on feed intake and average daily gain must be considered in determining whether their use is economically justified.
The most economical energy level in grower diets can vary greatly between production systems or even within the same system due to changes in ingredient cost, market hog price and seasonality of growth rate.
Lysine and other amino acids should be adjusted along with the energy level of the diet. If the amino acid levels aren't adjusted as the energy level is changed, the pigs will either be underfed, resulting in lower performance or overfed, resulting in increased diet cost and nitrogen excretion rates.
Although the grower pig requires higher amino acid, energy, vitamin and mineral levels than older finishing pigs, producers need to be careful not to provide more nutrients and additives than are required.
A common problem for many producers is that “add packs,” similar to those used in nursery diets, are finding their way into grower diets.
Because each diet is fed at a minimum of 40 to 50 lb./pig in the grower phase, any unnecessary increase in diet cost will rapidly increase feed cost per pig. Each nutrient and feed additive should be carefully considered before increasing addition rate in grower diets.
Feeder management is critical to minimizing feed wastage and optimizing feed efficiency. Finely grinding feed to produce a particle size of 700 microns or less improves feed efficiency with most grains.
Reducing variability in particle size is the key to maintaining diet flowability when feeding mash with particle size less than 700 microns. We have observed greater flowability of grain ground with a roller mill compared to a hammer mill.
When finely grinding meal diets with high levels of added fat, it may be essential to use a roller mill. Recent studies at Kansas State University have shown that roller mill-ground corn with 6% added fat would have similar flowability as that of hammer mill-ground corn with no added fat.
Recommendations for amino acids and phosphorus are provided in Table 1 on page 35. The amino acids are listed as true ileal digestible (TID) amino acid recommendations. If corn-soybean meal diets are used, total amino acids levels can be used without many problems; however, if other energy or protein sources are added to the diets, digestible values should be used to account for variation in digestibility between ingredients.
Lysine recommendations continue to increase in the grower stage, due to increased protein deposition capability of modern genetics and feed intake in the field. Appropriate minimum ratios of other amino acids relative to lysine are also provided in Table 1.
We also recommend adjusting the levels of available phosphorus as the dietary energy level is changed, in order to achieve similar levels of available phosphorus intake. Thus, available phosphorus to metabolizable energy ratios are provided in Table 1.
Vitamin and trace mineral recommendations for grower pigs are provided in Table 2 on page 36. There is considerable debate on the ideal inclusion rates for vitamins and minerals. Some research indicates that higher levels of vitamins, such as vitamin E, or trace minerals, such as growth-promoting levels of copper, can be quite beneficial in the grower stage.
Other research shows little or no benefit. The recommendations in Table 2 are met by most commercial vitamin and trace mineral premixes.
Example diets of simple corn-soybean meal with no added fat and 5% added fat are provided in Table 3. Because of the high lysine requirement during the early grower period, the diets require high levels of soybean meal.
With the use of L-lysine HCl at 3 lb./ton, other amino acids (methionine and threonine) will be slightly deficient if they are not also added to the diet.
By adding fat to the diet, the lysine and soybean meal levels also must be increased. This increases the requirement for other amino acid additions.
Also, if justified economically, higher levels of synthetic lysine, threonine and methionine could be used before another amino acid becomes limiting.
Certainly, other ingredients also could be used in the diets if determined to be economical.
For these example diets, the feed budget is lower for the 5% fat diets to account for the reduced feed needs with the higher energy diets.