Estimation of genetic and phenotypic parameters in a closed ...

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r^/ith the number of pigs born alive and the litter weíght at birth. The
genetic correlation betr¿een number of pigs born alive and 1ítter weight
at birth was also hígh1y positive.
Young eË al. (1978) anaryzeð. data from 2,095 girts and reporred
phenotypic correlations between litter size and total litter weight at
birth and at 42 days to be high and positive.
In genetic correlations,
pig birth weight was positively correlated with total number born (O .37),
number born alive (0.35) and nuuber rueaned (0,04).
The genetic correlations
between pig weaning weight and lítter
size at birth (total
number born and number born alive) were negligible, while a moderately
negative correlation Ítas found between pig weaning weight and number
weaned.
B. Carcass measurernents and age to ma¡]¡s¡ weight
I. HerÍtabílity estimates
The suntmary of heritability
estímates of carcass measurements and.
age to markeË weight reported frorn different researchers is presented in
Table 2. rt is clear that the majority of swine carcass traits are
moderately or highly heritable. HerítabilÍty of carcass length reported
in the lÍterature ranged froro 0.46 to 0.87 and averaged 0.63. Backfat
thickness including indivídual shoulder, rnÍd-back and loin fat thickness
measurement, and the mean frorn ,two or three fat thickness measurements,
ranged from a 1ow of 0.25 to a high of 0.74 and averaged 0.50. Loin eye
area ranged from 0.35 to 0.70 and averaged at 0.50. Dressing percentage
was moderately heritable and ranged from 0.26 to 0.40 with an average of
0.32. HeritabÍlity of age to market weight (approx. 90 kg) \^¡as reported