Impact of selection for birth weight variability on reproductive longevity: A mice model

Abstract

Uniformity, understood as a similar performance in relevant livestock traits, such as birth weight within the litter, is being included as one of the selection objectives in breeding programmes, especially for polytocous livestock species. A divergent selection experiment for birth weight within‐litter variability in mice during 23 generations showed that homogeneous animals were better for litter size, survival and feed efficiency but less heavy than heterogeneous animals. The aim of this study was to compare the reproductive longevity in both divergent lines as time to the end of the reproductive period. Two generations from both lines with an initial number of 43 females and 43 males were mated one to one and stayed together to have consecutive parturitions until the end of the reproductive life. Females were discarded when the time elapsed from the last parturition was longer than 63 days. The time to the end of the reproductive period between both lines was compared by fitting a Cox proportional hazard regression model adjusting for line, generation and its interaction. The rate of parturitions in both lines was also compared using a Prentice–Williams–Peterson model adjusted for the same effects. The low variability line was associated with a higher parturition rate, e.g., adjusted hazard ratio was 2.93 (95% CI 2.17–3.94). The Cox model showed that the low variability females also presented benefits of time to the end of the reproductive period, with an adjusted hazard ratio of 0.26 (95% CI 0.16–0.41). The median of reproductive days was 55.50 in the high variability line whilst the median was 252.50 days for the low variability females. The homogeneous line presented important reproductive advantages suggesting higher robustness and animal welfare. Further research should confirm whether the findings presented here of a better performance in the low variability line could be properly applied to some livestock species.

Embryo survival and fertility differ in lines divergently selected for birth weight homogeneity in mice

“…According to the results of the present study, the line selected for low variability presented important reproductive advantages. Higher longevity was previously demonstrated in homogeneous animals suggesting higher robustness and better animal welfare (Formoso‐Rafferty et al, 2022). The results of our study suggest that selection for homogeneity may provide a valuable tool for optimizing litter size in commercially important prolific breeds.…”

“…These differences between divergent mice lines in the litter size at birth were already shown to be maintained throughout lactation resulting in bigger litter size at weaning (Formoso‐Rafferty et al, 2017). Also, important was higher reproductive longevity reported with a threefold probability of performing a new parturition in the homogeneous line relative to the heterogeneous line (Formoso‐Rafferty et al, 2022). The advantage of the L‐line is added to the ones already found, such as litter size, weaning weight, and survival, presenting benefits in production (Formoso‐Rafferty et al, 2016b), animal welfare (Formoso‐Rafferty et al, 2016a), heritability (Formoso‐Rafferty et al, 2016b), and robustness traits (Formoso‐Rafferty et al, 2018, 2019).…”

Genetic and Phenotypic Parameters of Rabbit Individual Body Weight in the Preweaning Period

“…However, the success of selection is directly related to its genetic determination [ 4 , 22 ]. In the last decade, new strategies have been proposed to improve the survival of the offspring during the lactation period, i.e., selection for within-litter birth weight variability [ 7 , 23 ] and selection for litter size variability [ 6 ].…”

“…Therefore, to guarantee good viability and growth, it is essential to have newborn kits with a birth weight that is adequately proportionate to that of their littermates. Recently, the practice of selecting rabbits for variability in birth weight within the litter has been reported as an effective method to improve survival [ 7 ].…”

Differential patterns in runs of homozygosity in two mice lines under divergent selection for environmental variability for birth weight

“…As a result of the divergent experiment, two divergent lines were created: a high variability line (H‐Line) and a low variability line (L‐Line). The L‐Line presented benefits in production, animal welfare, heritability and traits related with robustness traits such as feed efficiency or longevity (Formoso‐Rafferty et al., 2016b, 2017, 2019, 2022; 2023). Moreover, a higher response to selection was observed in the L‐Line than in the H‐Line (Formoso‐Rafferty et al., 2020).…”