Search

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 MC4R genotype. 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. [ABSTRACT FROM AUTHOR]

Lowering the CP level in piglet diets reduces the risk of postweaning diarrhea and N excretion to the environment. The question remains at what point CP becomes limiting. An experiment was designed with 2 standardized ileal digestible (SID) Lys levels (10 and 11 g) and 6 CP levels (140, 150, 160, 170, 180, 190 g/kg) in a 2 × 6 factorial design (with 6 pens of 6 animals each per treatment). Linear and quadratic (QP) mixed models of performance in function of CP were fitted to study the effect of SID Lys and CP and their interaction. To determine optima, QP models and broken line models with linear (BLL) or quadratic (BLQ) ascending portions were fitted through the data. It was hypothesized 1) that the response to a decreasing digestible CP level could be described with broken line models and 2) that the break point of these models is dependent on the dietary SID Lys level. Decreasing the CP level decreased ADG (P < 0.001). For G:F, the effect of decreasing CP level depended on the SID Lys level (P of the interaction = 0.028 in the linear model and P = 0.002 in the QP model). According to the BLL model, with 11 g SID Lys in the diet, G:F started to decline with CP levels < 176 g CP [SID Lys:CP = 0.062, SID Lys:apparent total tract digestible (ATTD) CP = 0.077], and with 10 g SID Lys, CP levels < 165 g/kg (SID Lys:CP = 0.061, SID Lys:ATTD CP = 0.075) depressed performance. Serum creatinine levels showed a linear decrease with increasing SID Lys:CP levels (P < 0.001). Across both SID Lys levels, when fitting a BLL model, minimal serum urea levels were reached at an SID Lys:CP ratio of 0.064. This seems to be the point where CP and not Lys limits muscle deposition. The small difference in break point between serum urea level and performance suggests that the composition of nonessential AA may also be at stake. The effect of decreasing CP level depends on SID Lys, and using a maximal SID Lys:CP ratio may be useful for optimizing the AA profile of dietary CP. When the SID Lys:CP ratio exceeds 0.064 (SID Lys:ATTD CP > 0.079), protein and not individual AA limits growth in most piglets between 4 and 9 wk of age., (© The Author(s) 2018. Published by Oxford University Press on behalf of American Society of Animal Science. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)