Animal Behaviour and Welfare, Scottish Agricultural College, Edinburgh, United Kingdom.
PLoS One. 2012;7(1):e30318. doi: 10.1371/journal.pone.0030318. Epub 2012 Jan 17.
For the most part solutions to farm animal welfare issues, such as piglet mortality, are likely to lie within the scientific disciplines of environmental design and genetic selection, however understanding the ecological basis of some of the complex dynamics observed between parent and offspring could make a valuable contribution. One interesting, and often discussed, aspect of mortality is the propensity for it to be sex-biased. This study investigated whether known physiological and behavioural indicators of piglet survival differed between the sexes and whether life history strategies (often reported in wild or feral populations) relating to parental investment were being displayed in a domestic population of pigs. Sex ratio (proportion of males (males/males+females)) at birth was 0.54 and sex allocation (maternal investment measured as piglet birth weight/litter weight) was statistically significantly male-biased at 0.55 (t(35) = 2.51 P = 0.017), suggesting that sows invested more in sons than daughters during gestation. Despite this investment in birth weight, a known survival indicator, total pre-weaning male mortality was statistically significantly higher than female mortality (12% vs. 7% respectively z = 2.06 P = 0.040). Males tended to suffer from crushing by the sow more than females and statistically significantly more males died from disease-related causes. Although males were born on average heavier, with higher body mass index and ponderal index, these differences were not sustained. In addition male piglets showed impaired thermoregulation compared to females. These results suggest male-biased mortality exists despite greater initial maternal investment, and therefore reflects the greater susceptibility of this sex to causal mortality factors. Life history strategies are being displayed by a domestic population of pigs with sows in this study displaying a form of parental optimism by allocating greater resources at birth to males and providing an over-supply of this more vulnerable sex in expectation of sex-biased mortality.
在大多数情况下，解决农场动物福利问题的方法，例如仔猪死亡率，可能在于环境设计和遗传选择等科学学科，但了解父母与子女之间一些复杂动态的生态基础可能会做出有价值的贡献。死亡率的一个有趣且经常讨论的方面是其性别偏向性。本研究调查了仔猪存活率的已知生理和行为指标是否在性别之间存在差异，以及与父母投资有关的生活史策略（通常在野生或半野生种群中报道）是否在猪的家养种群中表现出来。出生时的性别比例（雄性比例（雄性/雄性+雌性））为 0.54，性别分配（作为仔猪出生体重/窝重衡量的母体投资）在统计学上显著偏向雄性，为 0.55（t(35) = 2.51 P = 0.017），这表明母猪在怀孕期间对儿子的投资多于女儿。尽管这种投资增加了出生体重，这是一个已知的生存指标，但总断奶前雄性死亡率在统计学上显著高于雌性死亡率（分别为 12%和 7%，z = 2.06 P = 0.040）。雄性比雌性更容易受到母猪的挤压，而且统计上更多的雄性死于与疾病相关的原因。尽管雄性平均出生体重较高，体质量指数和比容指数较高，但这些差异并未持续存在。此外，雄性仔猪的体温调节能力比雌性仔猪差。这些结果表明，尽管初始的母体投资更大，但仍存在雄性偏向性死亡率，这反映了这种性别对因果死亡率因素的更大敏感性。生活史策略正在被一个家养猪群所表现出来，本研究中的母猪通过在出生时向雄性分配更多的资源并提供这种更脆弱的性别过剩，表现出一种父母的乐观主义，以期望性别偏向性死亡率。
