Nutritional approaches to slow late finishing pig growth: implications on carcass composition and pork quality

Abstract

Although pork producers typically aim to optimize growth rates, occasionally it is necessary to slow growth, such as when harvest facility capacity is limited. In finishing pigs, numerous dietary strategies can be used to slow growth so pigs are at optimal slaughter body weights when harvest facility capacity and/or access is restored. However, the impact of these diets on pork carcass quality is largely unknown. Thus, this study aimed to evaluate the efficacy of dietary strategies to slow growth in late finishing pigs and evaluate their effects on carcass composition and pork quality. Mixed-sex pigs (n = 897; 125 ± 2 kg BW) were randomly allotted across 48 pens and assigned to 1 of 6 dietary treatments (n = 8 pens/treatment): (1) Control diet representative of a typical finisher diet (CON); (2) diet containing 3% calcium chloride (CaCl2); (3) diet containing 97% corn and no soybean meal (Corn); (4) diet deficient in isoleucine (LowIle); (5) diet containing 15% neutral detergent fiber (NDF) from soybean hulls (15% NDF); and (6) diet containing 20% NDF from soybean hulls (20% NDF). Over 42 d, pen body weights and feed disappearance were collected. Pigs were harvested in 3 groups (14, 28, and 42 d on feed) and carcass data collected. From the harvest group, 1 loin was collected from 120 randomly selected carcasses (20 loins/treatment) to evaluate pork quality traits. Overall, ADG was reduced in CaCl2, Corn, and 20% NDF pigs compared with CON pigs (P < 0.001). However, ADFI was only reduced in CaCl2 and 20% NDF pigs compared with CON (P < 0.001). Feed efficiency was reduced in CaCl2 and Corn pigs compared with CON (P < 0.001). Hot carcass weights were reduced in CaCl2 pigs at all harvest dates (P < 0.001) and were reduced in Corn and 20% NDF pigs at days 28 and 42 compared with CON pigs (P < 0.001). In general, CaCl2 and 20% NDF diets resulted in leaner carcasses, whereas the Corn diet increased backfat by 42 d on test (P < 0.05). Loin pH was reduced and star probe increased in CaCl2 pigs compared with CON pigs (P < 0.05); no treatments differed from CON pigs regarding drip loss, cook loss, color, firmness, or marbling (P ≥ 0.117). Overall, these data indicate that several dietary strategies can slow finishing pig growth without evidence of behavioral vices. However, changes to carcass composition and quality were also observed, indicating quality should be taken into consideration when choosing diets to slow growth.

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

“…Similarly, overall 28 day ADFI and G:F did not differ; however there was a tendency for reduced ADG as dietary NDF increased (linear P = 0.054). This is in contrast with previous work wherein both 20% ( Helm et al, 2021 ) and 25% ( Mauch et al, 2018 ) NDF have proven sufficient to slow growth rates. The minimal responses observed herein may be partially attributed to the smaller sample size in the current study (11–12 pigs per treatment) and greater variability.…”

“…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).…”

“…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 ).…”

“…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 ). However, as this work only evaluated a single level of each experimental approach, better precision is needed to understand which levels of various approaches are successful at slowing growth rates.…”