Abstract Gilt development is essential for optimizing sow productivity and longevity, while reducing culling rate. It was hypothesized that lowering SID Lysine content in the diet during the rearing would reduce lean growth, promote fat deposition, and therefore improve gilt body condition at farrowing. The aim of this study was to evaluate how this nutritional strategy affected growth, body composition, and reproductive performance at first farrowing. The study was conducted with 72 gilts (age: 79 ± 4 d) with an initial body weight (BW) of 24.95 ± 3.48 kg at arrival. Until approximately 50.5 ± 5.29 kg BW, gilts were fed a common diet (10.4 MJ/kg NE, 9.8 g SID Lys/kg). Thereafter, animals were weighed, distributed into two groups according to BW, and assigned to one of two dietary treatments until detection of the third estrus. A 4-phase feeding strategy was used and gilts were fed ad libitum. Treatments consisted of a control diet formulated according to standard recommendations for growing gilts (50–65 kg: 9.83 MJ/kg NE, 8.80 g SID Lys/kg; 65–85 kg: 9.75 MJ/kg NE, 8.20 g SID Lys/kg; 85–105 kg: 9.91 MJ/kg NE, 7.60 g SID Lys/kg; 105-120 kg: 9.92 MJ/kg NE, 7.00 g SID Lys/kg) and an experimental slow-growth diet applying a 30% reduction in SID Lysine and amino acids (50–65 kg: 9.91 MJ/kg NE, 6.16 g SID Lys/kg; 65–85 kg: 9.88 MJ/kg NE, 5.74 g SID Lys/kg; 85–105 kg: 9.85 MJ/kg NE, 5.32 g SID Lys/kg; 105-120 kg: 9.86 MJ/kg NE, 5.00 g SID Lys/kg). Gilts were individually monitored (days 1, 24, 38, 66, 79, 94, and 123) for BW, backfat thickness, and loin muscle depth. After detection of the third estrus, gilts were inseminated and subsequently fed approximately 2.6 kg/day of a common gestation diet until farrowing. During the rearing period, gilts fed diets with reduced SID Lysine exhibited lower growth rate, gaining 70 g/day less than controls (ADG: 0.95 vs. 0.88 kg/day; P 0.01). Although average daily feed intake did not differ overall, gilts in the reduced SID Lys treatment showed a higher feed conversion ratio (2.81 vs. 3.03; P 0.01). No significant differences between treatments were observed in backfat thickness or loin muscle depth. At farrowing, the number of total born, liveborn, and piglets weaned per litter did not differ between treatments. In conclusion, feeding diets with a 30% reduction in SID Lysine compared with standard recommendation during the rearing period decreased growth rate but did not affect body composition (backfat thickness, loin depth) or reproductive performance at first parity.
Márquez et al. (Wed,) studied this question.
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