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产羔时,单胎或双胎美利奴母羊的群体大小在饲料供应充足时可能不会影响羔羊的存活率。

Mob size of single-bearing or twin-bearing Merino ewes at lambing may not influence lamb survival when feed-on-offer is high.

机构信息

1School of Veterinary and Life Sciences,Murdoch University,Murdoch,WA 6150,Australia.

2Department of Primary Industries and Regional Development,South Perth,WA 6151,Australia.

出版信息

Animal. 2019 Jun;13(6):1311-1318. doi: 10.1017/S175173111800280X. Epub 2018 Oct 29.

Abstract

Limited research has suggested that higher lambing densities increase interference from foreign ewes at lambing which disrupts the ewe-lamb bond and compromises lamb survival. This may be particularly evident in mobs of twin-bearing ewes compared to single-bearing ewes because a greater number of lambs are born per day. Therefore, we hypothesised that; (i) decreasing the mob size of ewes at lambing has a greater impact on the survival of twin-born lambs than single-born lambs; (ii) the relationship between mob size and lamb survival can be explained by differences in the rate of interaction with foreign ewes and lambs at lambing; and (iii) ewes will utilise a limited area of the paddock at lambing and thus lambing density will be defined by the distribution of ewes in the paddock rather than the paddock area. Merino ewes were allocated into a 2×2 factorial combination of ewe pregnancy status (single- or twin-bearing) and mob size (high (n=130 ewes) or low (n=50 ewes)) on day 140 from the start of joining. Each treatment had two replicates excepting the low mob size for twins which had a third replicate. Ewes lambed at a stocking rate of 11 ewes/ha. Feed-on-offer during lambing exceeded 2400 kg dry matter (DM)/ha. Ewe-lamb behaviour was observed and dead lambs were autopsied over 11 days during the peak of lambing. The distribution of ewes in each paddock was recorded every 2 h during daylight hours by counting the number of ewes occupying 2500 m2 grids. The proportion of ewes and their newborn progeny which interacted with foreign ewes at lambing did not differ between the high and low mob sizes for single- (24.9% v. 20.8%) or twin-bearing ewes (14.3% v. 19.6%; P=0.74). Similarly, interaction with foreign lambs did not differ between the high and low mob sizes for single- (14.5% v. 25.2%) and twin-bearing ewes (34.5% v. 26.4%; P=0.44). The distribution of ewes within the paddock did not differ between treatments (P=0.95). On average, single-bearing ewes which lambed at the high and low mob sizes occupied 34% and 36% of the paddock during daylight hours, and the corresponding values for twin-bearing ewes were 40% and 43%. Survival of twin-born lambs was lower than single-born lambs (75.3% v. 87.9%; P<0.01), however, lamb survival was not influenced by mob size regardless of birth type. These results suggest that higher mob sizes may not compromise lamb survival when feed-on-offer during lambing exceeds 2400 kg DM/ha.

摘要

有限的研究表明,较高的产羔密度会增加分娩时外来母羊的干扰,从而破坏母羊与羔羊的联系,并降低羔羊的存活率。这在多胎产羔的母羊群中可能更为明显,因为每天会有更多的羔羊出生。因此,我们假设:(i)降低分娩时母羊群的规模对双胎羔羊的存活率的影响大于对单胎羔羊的影响;(ii)母羊群规模与羔羊存活率之间的关系可以通过分娩时与外来母羊和羔羊的互动率的差异来解释;(iii)母羊在分娩时只会利用围场的有限区域,因此产羔密度将由围场内母羊的分布而不是围场的面积来定义。在开始合群后的第 140 天,将美利奴母羊分配到母羊怀孕状态(单胎或多胎)和母羊群规模(高(n=130 只母羊)或低(n=50 只母羊))的 2×2 析因组合中。除了三重复的低群规模的双胞胎外,每个处理都有两个重复。母羊的存栏密度为 11 只/公顷。分娩期间的供料量超过了 2400 公斤干物质(DM)/公顷。在产羔高峰期的 11 天内,观察母羊-羔羊行为并对死亡羔羊进行剖检。在白天,每隔 2 小时记录每个围场内母羊的分布情况,方法是统计占用 2500 平方米网格的母羊数量。在高群规模和低群规模下,与外来母羊互动的单胎(24.9%比 20.8%)或多胎(14.3%比 19.6%;P=0.74)母羊的比例没有差异。同样,与外来羔羊的互动在高群规模和低群规模下的单胎(14.5%比 25.2%)和多胎(34.5%比 26.4%;P=0.44)母羊之间也没有差异。处理之间围场内母羊的分布没有差异(P=0.95)。平均而言,在高群规模和低群规模下产羔的单胎母羊在白天占据了围场的 34%和 36%,多胎母羊的相应值为 40%和 43%。双胎羔羊的存活率低于单胎羔羊(75.3%比 87.9%;P<0.01),但无论产羔类型如何,产羔密度都不会影响羔羊的存活率。这些结果表明,当产羔期间的供料量超过 2400 公斤 DM/公顷时,较高的群规模可能不会降低羔羊的存活率。

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