Effects of restricted feeding and sex on the feed to muscle gain ratio of growing pigs

Visuels d'intervention (EAAP 2022) à Porto, Portugal, le 5-9 septembre 2022.

Abstract. The aim of the study was to determine tissular growth performance by using computed tomography and to test the effects of feeding level and sex. Two feeding levels, ad libitum vs restricted (85% of ad libitum), and two sexes, female vs castrated male, were compared on a sample of 134 pigs. Two batches, one in winter and the other in summer, were used with four pens of six gilts or castrates per treatment each. The pigs were crossbred between Pietrain boars and Large White × Landrace sows and were heterozygous for the halothane gene. Half carcases were scanned with computed tomography to measure the muscle volume, calculate the lean meat content (LMC), and to assess the average daily muscle gain (ADGm) and the feed to muscle gain ratio (F:Gm). Least squares means of growth and feed efficiency criteria were assessed by a general linear model by pen, while least squares means of LMC were assessed by pig. The overall means of initial and final body weight were 26 and 120 kg respectively. The effect of feeding level was significant on the final body weight (BW), the daily feed intake (DFI), the average daily gain (ADG), ADGm, the feed to gain ratio (F:G), and LMC. Feed restriction decreased BW by 6.7 kg (116.8 vs 123.5; P<0.001), DFI by 0.40 kg/d (2.00 vs 2.40; P<0.001), ADG by 189 g/d (757 vs 946; P<0.001) and ADGm by 87 g/d (465 vs 552; P<0.001). It increased LMC by 2.3 percent points (61.7 vs 59.4; P<0.01) and F:G by 0.11 kg/kg (2.70 vs 2.59; P<0.01), but not F:Gm (4.39 vs 4.45). The effect of sex was significant on DFI, ADG, F:G, F:Gm, and LMC. Compared to females, castrates had a higher DFI (2.28 vs 2.12; P<0.01) and ADG (872 vs 831; P<0.05), but not ADGm (508 vs 509), a higher F:Gm (4.57 vs 4.27; P<0.01), but not F:G (2.67 vs 2.62), and a lower LMC (59.0 vs 62.2; P<0.001). This study showed that a severe feed restriction, meeting the amino acid requirements, improved carcase leanness without negative effect on the feed to muscle gain ratio. The use of computed tomography is to be recommended in feeding trials and more generally in animal production trials to determine tissue deposition, and associated feeding efficiency and final tissular body composition.