Genetics of the interval from weaning to estrus in first-litter sows: distribution of data, direct response of selection, and heritability1

Abstract

A selection experiment with a selection and a control line maintained for eight generations was set up to study efficacy of selection for a short interval from weaning to estrus after weaning the first litter and to estimate genetic variation in the Dutch Landrace population. Intervals were recorded without truncation (i.e., intervals up to 234 d were observed). A mating scheme with 10 mating groups was used to avoid inbreeding. Distribution of intervals from weaning to estrus was described by a mixture of a normal and an exponential distribution. Between lines, both underlying distributions were similar, but the contribution to the total distribution was different. From generation 4 onward, intervals were significantly shorter in the selection line than in the control line. Variances within lines, generations, and mating groups varied to a large extent. Response per unit selection differential was calculated for original data and three sets of transformed data, both with and without correction for unequal subclass numbers. Standardized responses were more precise and linear, when data were log-transformed, and when corrected for unequal subclass numbers. The assumed best estimate of the realized heritability was .17. The heritability in the foundation population was estimated at .36 f .05, using an animal model including all genetic relationships in the data. It was concluded that genetic selection decreases the average interval from weaning to estrus by reducing the number of sows with a record in the exponential part of the distribution.

Genetics of the interval from weaning to estrus in first-litter sows: correlated responses.

“…Heritabilities of normal intervals, prolonged intervals, and incidence of prolonged intervals (Table 5 ) were all lower than the heritability of the interval from weaning to estrus (.36) reported by Ten Napel et al (1995a). The genetic correlation between normal intervals and prolonged intervals was estimated at −.04.…”

“…The experimental design involved a mating period of strictly 4 wk for gilts in each mating group (Ten Napel et al, 1995a). Gilts that were not seen in estrus after 3 wk in the mating period were treated with 400 IU of PMSG + 200 IU of hCG intramuscularly to obtain a sufficient number of gilts served in the mating period.…”

“…The experiment started with a foundation population of purchased animals (generation 0), followed by seven generations of intense selection (generation 1 to 7 ) and one generation of relaxed selection (generation 8). Selection and management procedures were described by Ten Napel et al (1995a).…”

“…Variation in the interval from weaning to estrus is determined by variation in the incidence of prolonged intervals, duration of normal intervals, and duration of prolonged intervals (Ten Napel et al, 1995a). Genetic selection was effective for reducing the intervals from weaning to estrus.…”

Genetic parameters for feed intake, litter weight, body condition and rebreeding success in primiparous Norwegian Landrace sows

“…BC was recorded specifically for this study, but most farmers had previously used the scale when deciding on feeding norms. Routinely collected data were used to determine weaning-to-service interval after 1st weaning, which was analysed as two traits; the 1-to 7-day interval (WSI7) where intervals larger than 7 days were regarded as missing and the 1-to 50-day interval (WSI50) where intervals larger than 50 days were regarded as missing and intervals larger than 5 days were transformed using the logarithmic transformation following ten Napel et al (1995) to adjust for the skewed distribution of the interval:…”