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The Bayes factor (BF) procedure was applied to examine the additive genetic component of several physiological and vitality variables for newborn pigs. Nine variables were studied: heart rate, arterial oxygen saturation, rectal temperature (all at birth and 60 mm later), birth weight, interval between birth and first teats contact, and interval between birth and first colostrum intake. The available numbers of data ranged from 288 (heart rate at 60 mm) to 839 records (birth weight) from F2 Iberian × Meishan newborn pigs. We compared a model with zero heritability (nonheritable) with the one where the additive genetic background was included. The BF was used to discriminate between both candidate models. Very strong evidence of genetic background was detected for heart rate 60 mm after birth (BF = 48.90), and strong evidence was detected for rectal temperature at birth (BF = 13.82). Posterior modes (means) of heritabilities were 0.29 (0.32) and 0.40 (0.39), respectively. In addition, substantial evidence of absence of genetic background was detected for arterial oxygen saturation at birth. [ABSTRACT FROM AUTHOR]

Iberian × Meishan F2 piglet's preweaning survivability was analyzed using categorical data regression procedures within the proportional hazards assumption. A frailty sire model was assumed with the litter effect treated as an additional random source of variation. Moreover, the relative birth weight within litter and the litter effect were considered time-dependent covariates that changed their values in the second day of life due to cross fostering carried out to standardize litters. Six variables had a significant effect on survivability: birth weight (P < 0.01), relative birth weight within litter (P < 0.001), rectal temperature 60 min after birth (P < 0.01), type of presentation at birth (P < 0.05), presence of stillbirths (P < 0.001), and presence of mummified fetuses (P < 0.001). Small piglets (<0.98 kg) suffered a high hazard ratio (6.57; P < 0.001), with this variable being clearly lower for the rest of birth weight categories. Piglets that were small in relation to their siblings (relative birth weight within litter) also suffered an increased death risk, with a hazard ratio of 1.81 (P < 0.05), which was similar to animals with posterior presentations at birth (hazard ratio = 1.80; P < 0.05). Piglets with a rectal temperature lower than 35.4°C 60 min after birth showed the highest hazard ratio (7.18; P < 0.01). Furthermore, the presence of mummified fetuses decreased the survivability of the remaining siblings, with a hazard ratio of 2.03 (P < 0.01), as did the presence of stillbirths (hazard ratio = 3.55; P < 0.001). The inclusion of the two random effects allowed us to estimate the mode of the joint posterior density of the sire variance (0.08) and the litter variance (1.98). The estimated heritability of preweaning survival reached a value of 0.03. We conclude that piglet survival involves several systematic influences related to birth weight, thermoregulatory ability, and injuries suffered during gestation and farrowing. The genetic variance was small compared with those generated by the common environment, for which the genetic improvement of piglet survival seems difficult. [ABSTRACT FROM AUTHOR]