Evaluation of nutritional strategies to slow growth rate then induce compensatory growth in 90-kg finishing pigs

Abstract

Two 44-d experiments were conducted to evaluate nutritional strategies with different concentrations of dietary lysine (and other amino acids) on growth rate and subsequent compensatory gain of 90-kg finishing pigs. Three diets were formulated to contain 0.70 (control), 0.50 and 0.18% standardized ileal digestible (SID) Lys. In Exp. 1, 356 pigs (Line 241 × 600, DNA; initially 89.0 ± 1.10 kg) were used with 4 treatments. From d 0 to 28, pigs received either the control or the 0.50%-Lys diet. On d 28, pigs either remained on these diets or were switched the 0.18%-Lys diet until d 44. There were 18 pens per treatment from d 0 to 28 and 9 pens per treatment from d 28 to 44. From d 0 to 28, pigs fed the 0.50%-Lys diet had decreased (P < 0.001) ADG and G:F compared to those fed the control diet. From d 28 to 44, pigs switched to the 0.18%-Lys diet had decreased (P < 0.05) ADG and G:F compared to pigs that remained on the control or 0.50%-Lys diets. From d 0 to 44, pigs fed 0.50%-Lys diet for 44-d had decreased (P < 0.05) ADG, G:F, and percentage carcass lean compared to pigs fed the control diet. Pigs fed the 0.50%-Lys diet then the 0.18%-Lys diet had decreased (P < 0.05) ADG and G:F compared to other treatments. Pigs fed the 0.50%-Lys diet for 44-d and pigs fed the control diet then 0.18%-Lys diet had decreased (P < 0.05) ADG, G:F, and percentage carcass lean compared to control pigs. In Exp. 2, 346 pigs (Line 241 × 600, DNA; initially 88.6 ± 1.05 kg) were used to evaluate compensatory growth after varying durations of dietary lysine restriction. A total of four treatments were used including pigs fed the control diet for 44-d or fed the 0.18%-Lys diet for 14, 21, or 28-d and then fed the control diet until the conclusion of the experiment on d 44. There were 9 pens per treatment. On average, pigs fed the 0.18%-Lys diet grew 49% slower than the control. Compared to the control, ADG of pigs previously fed the 0.18%-Lys diet increased (P < 0.05) 28% during the first week after switching to the control diet and 12% for the rest of the trial. Despite this improvement, overall ADG, G;F, final BW, and percentage carcass lean decreased (linear, P < 0.05) as the duration of Lys restriction increased. In summary, feeding Lys-restricted diets reduced the ADG and G:F of finishing pigs. Compensatory growth can be induced in Lys-restricted finishing pigs, but the duration of restriction and recovery influences the magnitude of compensatory growth.

Evaluation of increased fiber, decreased amino acids, or decreased electrolyte balance as dietary approaches to slow finishing pig growth rates

“…Previously, complete removal of soybean meal and synthetic amino acids has been shown to slow growth rates 44%–55% when fed for either 16 ( Rao et al, 2021 ) or 42 days ( Helm et al, 2021 ), while partial removal slowed growth 15% over 28 days ( Rao et al, 2021 ). Similarly, we observed ADG over the 28 d study period to be reduced with increased corn inclusion (linear P < 0.001).…”

“…As a result, 97% corn-fed pigs were 22.9 kg lighter than CON-fed pigs after 28 days ( P < 0.001; Figure 2 ), confirming that amino acid restriction successfully limits capacity for growth. However, amino acid restriction may or may not reduce feed intake compared with pigs fed diets of adequate amino acid concentrations ( Helm et al, 2021 ; Rao et al, 2021 ). In the current experiment, overall ADFI was reduced (linear P = 0.002), being 19% lesser in the 97% corn-fed pigs compared with CON-fed pigs and 87% corn-fed pigs (treatment P < 0.001).…”

“…As the reduction in feed intake was lesser than the observed reduction in growth, gain efficiency was reduced 16% in 89% corn-fed pigs compared with CON-fed pigs, and was reduced 50% in 97% corn-fed pigs compared with CON-fed pigs ( P < 0.001). Although the observed sub-optimal feed efficiency would not be economical during normal market conditions ( Rao et al, 2021 ), during abnormal market conditions the efficacy, simplicity, and low-cost of this approach likely far outweighs any concerns associated with poor feed efficiency ( Norton et al, 2020 ).…”

“…As amino acid restriction limits capacity for protein accretion, an increase in carcass backfat is often observed ( Kerr et al, 1995 ; Ruusunen et al, 2007 ; Helm et al, 2021 ; Rao et al, 2021 ). In the current experiment, day 28 ultrasound backfat depth was not impacted by decreased EAA levels (treatment P = 0.971; linear P = 0.831).…”

“…Unfortunately, as slowing growth rates is largely converse to typical aims of pork producers, very little data were available regarding which dietary strategies worked best to slow growth rates. Since then, several groups have provided research demonstrating these strategies to be successful at slowing growth rates ( Helm et al, 2021 ; Rao et al, 2021 ). Our group previously evaluated several experimental approaches including high NDF, amino acid restriction, and acidogenic salt inclusion at a single level and determined all three to be effective at slowing growth ( Helm et al, 2021 ).…”