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The aim of this study was to assess the effect of GnRH vaccination in boars (BO), barrows (BA), and gilts (GI) slaughtered at an average BW of 133 kg. Forty BO, 40 BA, and 40 GI were housed individually, fed ad libitum, and divided into 2 groups of 20 pigs per sex, a control group (CON) and a GnRH vaccinated group (IC). The IC group received 2 injections of GnRH vaccine (Improvac) at 70 and 105 kg. In BA, GnRH vaccination had minor effects on performance. Observed effects in BO and GI are therefore probably not caused by the GnRH vaccination itself but by the subsequent withdrawal of gonadal hormones. In BO, the increased feed intake after GnRH vaccination (P< 0.001), accompanied by a fall in estradiol and testosterone levels, led to faster growth (P= 0.014), increased back fat thickness (P= 0.021), and a tendency for a decreased meat percentage (P= 0.052). GnRH vaccination of BO decreased the boar taint–related sensory attribute scores similar to the levels of BA and GI (P< 0.001). In GI, the increased feed intake after GnRH vaccination (P< 0.001), accompanied by low progesterone levels, led to faster growth (P< 0.001), increased back fat thickness (P= 0.018), decreased meat percentage (P= 0.032), and a decreased shear force (P= 0.002) without significant differences in the sensory profile.

The Asp298Asn polymorphism of the melanocortin-4 receptor (MC4R) in pigs is known to affect economically important traits such as growth rate and backfat thickness. We have assessed the possible use of this polymorphism as a molecular marker to perform genetic selection toward lower boar taint levels without compromising growth performance and carcass and meat quality in commercial boars and gilts. Homozygous boars and gilts of the AA genotype and GG genotype were compared in an intervention study with a 2 × 2 design to assess main effects and possible interactions between sex and MC4Rgenotype. The concentrations of the 3 boar taint compounds androstenone (P= 0.044), skatole (P= 0.049), and indole (P= 0.006) were significantly higher in fat of AA boars compared to GG boars. However, no effect on the sensory analysis of the fat samples could be observed. Between 20 and 115 kg BW, AA pigs showed higher ADFI than GG pigs (P< 0.001). An interaction between genotype and sex was observed for ADG (P= 0.044): AA boars had a significantly higher ADG than GG boars but there was no significant difference between the gilts. Daily lean meat gain tended to be higher in boars compared to gilts (P= 0.051), independent of genotype. Similarly, boars showed higher G:F compared to gilts (P< 0.001), without effect of genotype. Genotype and sex affected several carcass quality parameters but there was no interaction. Pigs of the AA genotype displayed a lower dressing percentage (P= 0.005), lower ham width (P= 0.024), lower muscle thickness (P= 0.011), and higher fat thickness (P< 0.001), resulting in a lower lean meat percentage (P< 0.001) in comparison with GG pigs. Gilts had a significantly higher dressing percentage (P< 0.001), higher muscle thickness (P< 0.001), higher ham width (P< 0.001), and lower ham angle (P< 0.001) compared to boars. Other than the boar taint compounds, meat quality was not affected by genotype. Pork of gilts was darker (P= 0.014) and less exudative during cooking (P< 0.001) and contained more intramuscular fat (P= 0.013). These results indicate that genetic selection against boar taint is possible using this marker. This will also result in lower feed intake and ADG and, consequently, better carcass quality.

Lowering the crude protein (CP) level in the piglet diet reduces the risk of post-weaning diarrhea and nitrogen (N) excretion to the environment. The question remains at what point CP becomes limiting. Therefore 12 diets were formulated with 2 standardized ileal digestible (SID) lysine (LYS) levels (10 and 11 g SID LYS) and 6 CP levels (140, 150, 160, 170, 180, 190 g/kg) which were fed to piglets between 4 and 9 weeks of age in a 2 x 6 design with 6 pens of 6 animals per treatment. Serum urea levels were measured to assess N metabolism, with lower levels indicating a higher N efficiency. Linear plateau models could be fitted in function of the SID LYS:CP ratio. With 10 g SID LYS, serum urea decreased with decreasing CP levels down to a minimal level of 3.1 mg/dl at 63.9 g SID LYS/kg CP (156 g CP/kg). With 11 g SID LYS, serum urea decreased with decreasing CP levels to a minimum of 3.9 mg/dl at 63.3 g LYS/kg CP (174 g CP/kg). Over the 12 treatment groups, a breakpoint was calculated at 63.5 g SID LYS/kg CP, above which the protein breakdown was minimal and therefore N efficiency maximal. Both LYS and CP level affected daily gain and gain to feed (G:F). The breakpoint in G:F was at 60.6 and 62.5 g SID LYS/kg CP (165 and 175 g CP/kg) for pigs receiving 10 or 11 g SID LYS/kg, respectively. The results suggest that, apart from essential amino acids, the dietary profile of non-essential amino acids may be limiting performance. The ratio of 63.5 g SID LYS/kg CP may be a guideline/threshold value for maximizing the conversion of vegetal to animal protein in piglets.

In order to fine-tune standardised ileal digestible (SID) lysine (Lys) requirement of modern piglets (RA-SE genetics hybrid sow x Pietrain boar), two dose-response studies to Lys were conducted in 4 to 9 weeks piglets (8–24 kg). In trial 1, only commercially available feed-grade amino acids (AA) were used, without maintaining dietary crude protein (CP; 201–210 g/kg). Net energy was fixed at 9.8 MJ/kg. In trial 2, all the range of feed-grade AA needed were used while dietary crude protein was kept constant at 180 g/kg by adding L-Glutamic acid with decreasing Lys levels. Net energy level decreased slightly from the lowest to the highest Lys level (from 10.1 to 9.8 MJ/kg), because of the high energy content assigned to glutamic acid. All feeds were pelleted. On both trials, SID Lys ranged from 8.5 to 13.5 g/kg, divided over 5 levels. Six (trial 1) or nine (trial 2) pens of 6 piglets were tested per level. ADG, ADFI and G:F showed clear dose-responses to supplementation of Lys in both trials. In trial 1, it was not possible to reach an optimum for any of the growth parameters using a non-linear regression model, suggesting an optimum above 13.5 g/kg SID Lys. In contrast, in trial 2, best performance was observed at 11.4 and 13.2 g/kg SID Lys for ADG and G:F, respectively using a curvilinear-plateau model. While maximal performance was similar in the two trials (G:F=0.744-0.737, ADG=450-446 g/d), the effect of Lys shortage was higher in trial 1, probably due to an imbalanced AA:Lys ratio. To the contrary in trial 2, the SID Lys:CP ratio was 0.075 at the highest Lys level, suggesting that nitrogen or non-essential AA may have become limiting.

A dose-response study was performed to estimate the valine (Val) requirement in piglets between 4 and 9 weeks of age. For this end, 432 piglets (weaned at 4 weeks of age, 8.0 ± 0.9 kg) were distributed among eight diets differing in their Val to lysine (Lys) ratio expressed on a standardized ileal digestible (SID) basis. Two low crude protein diets (168 g/kg) only differing in SID Val:Lys level, one deficient in SID Val:Lys (0.58 SID Val:Lys) and the second one with a SID Val:Lys ratio expected to be above requirements (0.825 SID Val:Lys), were mixed in different proportions to obtain eight SID Val:Lys levels. The diets were formulated to be isocaloric (9.8 MJ net energy/kg) and with a sub-limiting SID Lys level (10.5 g/kg), allowing to estimate the Val requirement relative to Lys. The average daily gain (ADG) and feed intake (ADFI) were improved with increasing SID Val:Lys level; the best performance being obtained with 0.72 SID Val:Lys. Feed intake increased from 402 ± 45 g/day at 0.58 to 556 ± 42 at 0.72 Sid Val:Lys. Daily gain improved from 276 ± 37 g/day at 0.58 Sid Val:Lys to 391 ± 38 at 0.72 Sid Val:Lys. Using ADG and ADFI as response criteria, the requirement was estimated to be 0.675 and 0.742 SID Val:Lys with curvilinear-plateau and quadratic models, respectively. These results are in line with the literature and confirm that piglets react to a Val deficiency by lowering their ADFI which reduces their ADG without affecting feed efficiency. The results of the present experiment highlights that the Val level has to be controlled in piglet diets to avoid losing growth rate.