Effect of halothane genotype (NN, Nn, nn) on growth, carcass and meat quality traits of pigs slaughtered at 95 kg or 125 kg live weight By C. LARZUL', P. LE ROY', R. GUEBLEZ', A. TALMANT3, J. GOGUE4, P. SELLIER' and G. MONIN3three halothane genotypes (NN, Nn, and nn). In recent studies using DNA-based genotyping, but involving only N N and Nn pigs, GARC~A-MAC~AS et al. (1996) andLEACH et al. (1996) found no significant halothane genotype by slaughter weight interaction.This work aimed to compare the NN, Nn, and nn halothane genotypes, as determined by a DNA-based test, among pigs sharing the same polygenic background (Pietrain x Large White F2 cross) and slaughtered at either of two live weights (around 95 kg or 125 kg), thus bracketing the current average slaughter weight of French market pigs (105-110 kg), to study slaughter weight x HAL genotype interaction.
Materials and methods
An i m a 1 sThis study involved a total of 446 F2 Pietrain x Large White pigs from two contemporary experiments. Though these experiments were not carried out at the same place, important similarities in their designs (genetic type, slaughtering conditions, traits measured) enabled the data, after separate analyses gave similar results for common traits (GU~BLEZ et al. 1995;LARZUL et al. 1996), to be pooled for a global analysis.
Experiment 1In this experiment, carried out on the INRA Farm in Bourges (Cher), 22 Large White sows were inseminated by seven Pietrain boars. The expected N n halothane genotype of the resulting F1 pigs was verified, using a DNA-based test (DALENS and RUNAVOT 1993).
U.S.Eight F1 boars were mated to F1 gilts to produce 57 F2 litters, in which the same DNAbased test was used to determine the halothane genotype of the piglets. In four fattening batches, females and castrated males were reared in pens homogeneous for sex and halothane genotype (around nine animals per pen), and they were given ad libitum access to feed (crude protein: 17.0 %; ME 3091 kcal/kg) until their live weight reached 100 kg ('light') or 125 kg ('heavy'). The experiment was designed so that about two-thirds and one-third of the pigs were allocated to the 'light' and 'heavy' slaughter weight treatments, respectively.During fattening, the mortality rates were 1.1%, 0.6%, and 15% for the NN, Nn, and nn genotypes, respectively, and, within one slaughtering series, the three nn pigs died during transport to the abattoir.
Experiment 2This experiment was carried out on three commercial farms, where Pietrain x Large White sows were inseminated by 18 Pietrain x Large White boars, in order to obtain F2 piglets from the three halothane genotypes, as determined by the same DNA-based test described in experiment 1. Castrated males from 42 F2 litters were reared in two fattening batches on a single commercial farm. They were penned by halothane genotype (around 11 animals per pen) and fed ad libitum, with a commercial diet of similar energy and crude protein content to that used in experiment 1, until their live weight reached 90 kg ('light') or 125 kg ...
