Clarence Froese, M.Sc., P.Ag., Director of Nutrition, Genesus Inc.
Proteins consist of a number of structural components including amino acids. During digestion the bonds holding these components together are broken, hence freeing the individual amino acids to be absorbed into the bloodstream. Here they are transported throughout the pig’s body and used to rebuild new proteins required for maintenance, growth, reproduction, and lactation. When discussing pigs’ protein requirements, nutritionists are most often referring to their amino acid requirements.
There are a total of 20 amino acids present in pig body protein and of these, 10 must be supplied through the diet. These are termed essential amino acids as they cannot be synthesized by pigs in large enough quantities to meet their daily needs without dietary supplementation. The essential amino acid that is in shortest supply in typical feed ingredients relative to the pig’s daily requirements is lysine. For this reason, lysine is termed the first limiting amino acid in pig diets. When determining dietary ingredient addition rates, nutritionists must firstly ensure that the lysine level of the final mixture is adequate to meet the pigs’ daily requirements.
Only a certain proportion of the amino acids in feed ingredients is available to the pig, with the remainder being excreted. Numerous digestibility trials on different feedstuffs have been performed to determine their available amino acid levels. A commonly used measure to express availability is Standardized Ileal Digestibility (SID) which reflects the net disappearance of ingested amino acids at a certain point in the small intestine, corrected for endogenous losses. The pig’s true requirements for amino acids are most accurately expressed in terms of SID levels as opposed to total levels.
Genesus recently completed a number of controlled research trials to determine the response of their full program barrows and gilts (offspring from Genesus F1 female and Genesus Duroc male) to varying levels of daily SID lysine intake.
Each trial consisted of 5 treatments, with treatment diets formulated to contain 80, 90,100,110, and 120% of a base diet lysine level. The base-level diet (determined from previous trials) contained 1.15, 0.98, 0.86, 0.75, and 0.67% SID lysine, fed over 5 respective feeding phases.
Each phase was 3 weeks in duration, with pig weights averaging 65 lbs. (30 kg) at the start of the trial and 290 lbs. (130 kg) at the end of the trial. Diets were based on corn, soybean meal, corn DDGS, fat, and soy hulls and were formulated to contain the same energy level across treatments
Data collected were body weights (every 3 weeks), daily feed disappearance (pen basis), mortality, and real-time ultrasound measurement of backfat and loin muscle area (every 3 weeks). The performance and carcass results from these trials are summarized in Figures 1, 2, and 3 below.
The following conclusions can be made from these data:
- Average daily SID lysine intakes ranged from 17.4 grams/day for pigs on treatment 1 (80% of base diet lysine level) to 26 grams/day for pigs on treatment 5 (120% of base diet lysine level). Pigs fed the base diet achieved a daily SID lysine intake of 21.76 grams/day. (Figure 1)
- Average daily gain and feed:gain ratio showed continual improvement up to a daily SID lysine intake of 21.76 grams/day. Beyond this daily intake, no further improvements were obtained. (Figure 1)
- Cost of gain remained relatively unchanged up to a daily SID lysine intake of 20-21 grams/day, beyond which it began to rise significantly. (Figure 1)
- Backfat thickness remained unchanged across all 5 treatments at lighter or heavier liveweights. (Figure 2)
- Loin muscle area improved up to a daily SID lysine intake of 19.62 grams/day, beyond which no further improvement was obtained. (Figure 3)
Based on these trials, it was concluded that Genesus pigs will exhibit a performance response to increasing SID lysine intakes up to a level of 21-22 grams/day, and a carcass muscle area response up to a level of 19-20 grams/day. These daily intakes should be readily achieved by full feeding corn-based diets with the following dietary lysine specifications:
Table 1. Recommended Dietary SID Lysine Levels
(Genesus Mixed Sex, Corn Based Diets)
|DIETARY SID LYSINE LEVEL, %|
For more information on specifications for feeding Genesus pigs, please contact your nutritionist or consult the Genesus website for a complete copy of the Genesus Feeding Guidelines.
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