[Lactation Success 哺乳母猪成功饲养的关键]

11 September 2014

A review of recent research on mammary gland development in the sow and gilt was presented by Chantal Farmer of Agriculture and Agri-Food Canada's Dairy and Swine R&D Centre at the London Swine Conference 2014.

Abstract

摘要

Lactation success is key to the profitability of a farrowing unit and producers are now faced with an increased challenge because of the current use of hyperprolific sow lines.Numerous factors come into play to affect lactation success and one major aspect which has been overlooked in the past is mammary development.The current overview will succinctly cover various factors that can affect sow milk yield and will then focus on mammary development, namely, when it happens, how it happens and what can be done to stimulate it.Lastly, results from a project looking at the importance of teat use in first lactation for its milk yield in second lactation will be presented.

随着高产母猪饲养的普及，如今猪场面临越来越大的挑战，而哺乳母猪的成功饲养是提高胎产小猪效益的关键。影响哺乳母猪饲养的因素众多，过去一直被忽视的其中一个重要方面就是母猪乳腺的发育。项目测试结果显示，第一胎次哺乳期母猪乳腺的发育及产奶情况将对下一胎次哺乳造成相应的影响。下文将概述影响母猪乳腺发育和产奶量的因素及管理方案。

Sow Milk Yield

母猪的产奶量

Sow milk yield is the main determinant of piglet growth rate as it is the only source of energy for suckling piglets.Sows do not produce enough milk to sustain optimal growth of their litter and this problem was made worst with the current use of hyperprolific sow lines.Milk yield is influenced by numerous factors such as litter size, parity, nutrition, genetics, management, environment and endocrine status. Yet, one important factor that is often overlooked is mammary development. Indeed, sow milk yield is dependent on the number of milk-producing cells that are present in mammary glands at the onset of lactation.There is a positive correlation between the number of mammary cells and piglet growth rate. Periods with relatively high mammary growth are of particular interest since it is during those periods that mammary growth may be susceptible to being stimulated by nutritional or hormonal manipulations.

母乳是未断奶仔猪的唯一能量来源，母猪的产奶量决定了哺乳期仔猪的生长速度。目前，高产母猪普遍面临的一个严重问题是无法分泌足够的奶水来满足仔猪发挥最优生长潜力的需要。影响母猪产奶的因素众多，如产仔数（仔猪的大小）、胎次、营养、遗传、管理、环境和内分泌状态等。然而，母猪乳腺的发育情况却常常被忽视。事实上，母猪的产奶量取决于乳腺中泌乳细胞的数量。乳腺细胞和小猪生长速率之间呈正相关关系。乳腺快速增长的时期容易受到营养和激素刺激的影响。

Mammary Development in Swine: Hormonal Control

母猪的乳腺发育：激素控制

Mammary development in swine occurs at three developmental stages: from three months of age until puberty, during the last third of pregnancy, and during lactation.It is controlled by a complex interaction of various hormones. During gestation, oestrogens and prolactin are essential for mammary development and relaxin is also needed to stimulate total mammary gland growth.Few studies have looked at the effect of providing hormones on mammary development. Gilts receiving injections of porcine prolactin for a period of 28 days, as of 75kg bodyweight, increased their mammary development (based on visual appraisal) and also had lacteal secretions already present (McLaughlin et al., 1997).Interestingly, the degree of mammary gland development did not appear to be related to the dose of prolactin injected.A further study where gilts were slaughtered and mammary development actually measured, confirmed that injections of porcine prolactin to gilts for a period of 29 days, starting at 75kg bodyweight, stimulate mammary development at puberty (Farmer et al., 2005). Yet, the impact of such a treatment on subsequent milk yield is not known. Furthermore, porcine prolactin is not currently available commercially.

母猪的乳腺发育主要发生在三个时期：从三月龄到配种前期、妊娠期的后三分一阶段和哺乳期间。这是复杂的由各种激素相互作用产生的结果。在妊娠期分泌的雌激素、催乳素和耻骨松弛激素等可有效刺激乳腺的增长。关于激素对乳房发育影响的相关研究很少。

McLaughlin等，在1997研究发现，给75公斤体重的母猪连续28天注射催乳素，能促进母猪乳腺的发育（基于视觉评价），并且（在母猪乳房中）已经存在乳状分泌物(McLaughlin et al., 1997)。有意思的是，乳腺的发育程度似乎并未与催乳素的剂量有关。

Farmer 等，于2005做了进一步的研究，将试验母猪屠宰并进行乳腺发育的实质测量，证实从75公斤体重开始给母猪连续29天注射催乳素，能刺激青春期乳腺的发育。然而，这种操作方案对后续母猪泌乳可能造成的影响尚不明确。此外，猪用催乳素目前并没有开始商业化。

Can Pre-pubertal Nutrition Affect Mammary Development?

青春期前的营养会影响乳腺的发育吗？

Nutrition does influence mammary development in growing gilts, yet, data on thesubject is sparse (see review by Farmer, 2013).

Either a 20 per cent or a 26 per cent feed restriction from 90 days of age until puberty drastically reduces mammary tissue mass (Table 1).

营养会影响生长期母猪的乳腺发育，但是相关研究数据却很少。(see review by Farmer, 2013)

从90日龄开始至青春期，对小母猪进行20%或26%的限饲，将大大降低乳腺组织的质量（表1）。

On the other hand, earlier feed restriction, from 28 to 90 days of age, did not affect mammary development at puberty (Table 1).

Furthermore, lowering protein intake (14.4 versus 18.7 per cent crude protein) during the period from 90 days of age until puberty does not hinder mammary development of gilts (Table 1).

Composition of diets fed to prepubertal gilts influences their mammary development.Phytoestrogens are naturally-occurring plant compounds that can have oestrogenic properties. They are present in large amounts in soya and one class of these phytoestrogens comprises the molecule genistein. Gilts fed 2.3g per day of genistein from three months of age until puberty had a 44 per cent increase in the number of mammary cells at 183 days.

On the other hand, dietary supplementation with flax as seed, meal or oil during prepuberty brought about the expected changes in circulating fatty acids without any alteration in mammary development. Yet, when 10 per cent flaxseed was supplemented from day 63 of gestation until weaning, beneficial effects (30.9 per cent increase in parenchymal mass and 11.6 per cent increase in number of parenchymal cells) were noted in the mammary tissue of the female offspring of these sows at puberty.This was the first demonstration of such an in-utero effect and it opens new avenues in terms of potential management schemes to stimulate mammary development of gilts.

一方面，在28-90日龄间控料，对母猪乳腺发育影响不明显。（表1）

此外，在90-202日龄降低粗蛋白摄入量(14.4 vs. 18.7%)，对母猪乳房发育的影响也不明显。

日粮的组成成分对青春前期母猪乳腺发育有一定的影响。植物雌激素是自然产生的化合物，具有雌激素的特性。他们大量存在于大豆和由植物激素类组成的染料木黄桐中。小母猪从三月龄开始至青春期每天饲喂2.3g染料木黄桐，在183天中母猪乳腺细胞数量增加了44%。

另一方面，在母猪青春前期阶段日粮中添加亚麻种子、油等，带来可预见的脂肪酸循环变化，而对乳腺的发育没有影响。但是，在母猪妊娠63天直至断奶每天补充10%的亚麻籽，能给这些母猪所产的小母猪乳腺发育带来有利的影响（乳腺实质质量增长30.9%和实质细胞数量增加11.6%）。这是第一个关于在子宫内影响（乳腺发育）的示例，将为刺激小母猪乳腺发育打开新的管理途径。

Nutrition in Late Gestation and Lactation: Effects on Mammary Development

妊娠后期和哺乳期营养对乳腺发育的影响

Effects of late gestation and lactation feeding on mammary development in swine were recently reviewed by Farmer (2013).During gestation, feeding very high energy levels (44 versus. 24MJ ME per day) may have detrimental effects on mammary development and subsequent milk production whereas increasing the amount of dietary protein (16 versus 4g lysine per day) did not affect mammary development but may increase subsequent milk production.

When manipulating body composition of gilts by changing their protein and energy intakes during pregnancy, overly fat gilts (36mm backfat at the end of gestation) on a high-energy–low-protein diet had reduced mammary development (Head et al., 1991) and produced less milk than leaner gilts (25mm backfat) at the same bodyweight (Head and Williams, 1991). However, backfat of gilts in that study was much thicker than what is normally seen and the ideal body condition required to ensure maximal mammary development in late gestation should be investigated further.

Feeding in lactation also affects mammary development; an increase in weight of functional mammary glands is seen when sows are fed either more protein (65 versus 32g of lysine per day) or more energy (17.5 versus 12Mcal ME per day; Kim et al., 1999).It is, therefore, imperative to maximise sow feed intake during lactation.

Farmer (2013)对关于妊娠后期和哺乳期母猪采食对乳腺发育的影响进行了综述。妊娠期间，饲喂高能饲料（44与24MJ ME/天）将会对乳腺的发育及哺乳期的产奶量产生不利的影响。而增加蛋白质的量（16与4g赖氨酸/天）对乳腺的发育不产生影响，但可能会增加哺乳期的产奶量。

当通过改变妊娠期蛋白及能量的摄入来调控母猪的体况，饲喂高能量低蛋白日粮的母猪过肥（妊娠后期背膘厚达36毫米）及乳腺发育水平降低(Head 等, 1991) ，而且产奶量也低于同样体重但较瘦（背膘厚25毫米）的母猪。然而，在这项研究试验中的母猪背膘比实际生产中常见的要厚很多，需要做进一步的试验来确定促进母猪乳腺发育所需的最佳体况。

哺乳期的饲养管理也会影响乳房的发育，当哺乳母猪饲喂更高蛋白（65与32g赖氨酸/天）或更高能量（17.5与12Mcal ME/天；Kim 等, 1999）日粮时，可见功能性乳腺的重量增加。因此，必须让哺乳母猪的采食量最大化。

Involution of Mammary Glands

乳腺的退化

Mammary involution at weaning is an essential process of the mammary gland and much remains to be learned about it in swine.It is associated with dramatic changes occurring rapidly in the seven to 10 days following weaning, with a loss of more than two-thirds of the weight of mammary glands (Ford et al., 2003).

Mammary gland involution also takes place in early lactation when a gland is not being suckled. It occurs rapidly during the first seven to 10 days after farrowing and was irreversible after three days of non-suckling.

On the other hand, involution is reversible after 24 hours of non-suckling but the 'rescued' gland will never produce as much milk as if used right from the onset of lactation (see review by Farmer 2013).

乳腺退化是断奶过程中不可避免的一个现象，在猪方面的相关研究仍比较缺乏。这是发生在断奶后7到10天的一个急剧变化，乳腺重量下降超过三分之二（Ford 等, 2003）。

乳腺退化也发生在哺乳早期母猪不喂奶，在分娩7-10天后停止哺乳3天则不可逆转地发生乳腺退化。另一方面，停止哺乳24小时后发生的乳腺退化是可逆的，但是“获救”的乳腺产奶量将会打折扣。

Does Teat Use in First Lactation Affect Its Milk Yield in Second Lactation?

第一胎次哺乳母猪的乳房使用程度对第二胎次的产奶量有影响吗？

With today's hyperprolific sow lines, swine producers are faced with a problem in their farrowing rooms: should they “load” the primiparous sows with as many piglets as possible or should they leave some teats unused to give these sows a “respite”. This is particularly important in first parity sows with poor body condition, to avoid the “lean sow syndrome” that potentially leads to reproductive problems.

New findings demonstrate for the first time that teats that are used in first lactation will produce more milk in the second lactation (Farmer et al., 2012). Indeed, piglets suckling teats which were previously used weighed 1.12 kg more on day 56 than piglets suckling a previously unused teat.Furthermore, development of a teat that was previously used is improved in the second lactation and piglets suckling teats which were not used previously show a greater level of hunger in second lactation.Interestingly, piglets seem to be able to differentiate between previously-used and -unused teats.

现今的高产母猪在产房正面临着一个问题：初产母猪应该尽可能多带仔还是少带仔以便让母猪的部分乳房得到休息？为了避免因哺乳掉膘严重而影响下一胎次的繁殖，这对于体况较差的初产母猪来说是特别重要的一个问题。

新的研究发现，让初产母猪在首个哺乳期所有乳头都得到仔猪的充分吸允，会使下一胎次的产奶量得到提高(Farmer 等, 2012)。事实上，吸允以前经过哺乳的乳房的小猪与吸允（前一胎次）未经哺乳的乳房的小猪相比，在56日龄时的体重多1.12㎏。此外，第一胎次得到充分使用的乳房在第二胎次产奶量会更高，而且第二胎次的小猪吸允第一胎次未经哺乳的乳房时饥饿感会比较强（吃不饱）。有趣的是，小猪似乎能够区分以前曾哺乳和未曾哺乳的乳房。

Conclusions

总结

A combination of factors are involved in the control of sow milk yield and with the current use of hyperprolific sow lines it has become imperative to provide the best-adapted management and feeding strategies to improve upon it.

Nutrition of replacement gilts and of late-pregnant sows requires special attention to ensure maximal mammary development and future milk yield potential.

Management of first-litter sows can also impact subsequent lactation performances.

We now know that teats which were suckled in first lactation produce more milk and have a greater development in second lactation than teats which were not suckled in first lactation.

Such knowledge is critical for producers to make the best decision in terms of management strategies for their first-parity sows.

影响母猪产奶的因素众多，当务之急是寻找适用的饲养管理方案来改善高产母猪的哺乳问题。

后备母猪和妊娠后期母猪的营养设定特别要注意以确保母猪乳腺的发育和促进产奶潜力的发挥为前提。

初产母猪的饲养管理会对下一胎次的产奶造成影响。

我们现在知道，在第一胎次得到充分使用的乳房产奶量会更高，而且在第二胎次哺乳期时会比第一胎次未经哺乳的乳房发育得更好。

这些知识可以为生产者做好母猪的饲养管理决策方案提供重要的参考。

Literature Cited文献引用

· Farmer, C. 2013. Review: Mammary development in swine: effects of hormonal status, nutrition and management. Can. J. Anim. Sci. 93:1-7.

· Farmer, C. and M.F. Palin. 2005 Exogenous prolactin stimulates mammary development and alters expression of prolactin-related genes in prepubertal gilts. J. Anim. Sci. 83:825-832.

· Farmer, C., M.F. Palin, P.K. Theil, M.T. Sorensen and N. Devillers, N. 2012 Milk production in sows from a teat in second parity is influenced by whether it was suckled in first parity. J. Anim. Sci. 90:3743-3751.

· Farmer, C., D. Petitclerc, M.T. Sorensen, M. Vignola and J.Y. Dourmad. 2004. Impacts of dietary protein level and feed restriction during prepuberty on mammogenesis in gilts. J. Anim. Sci. 82:2343-2351.

· Ford, J.A. Jr., S.W. Kim, S.L. Rodriguez-Zas and W.L. Hurley. 2003 Quantification of mammary gland tissue size and composition changes after weaning in sows. J. Anim. Sci. 81:2583-2589.

· Head, R.H. and I.H. Williams. 1991. Mammogenesis is influenced by pregnancy nutrition. p. 33. Manipulating Pig Production III. Australasian Pig Science Association, Werribee, Australia.

· Head, R.H., N.W. Bruce and I.H. Williams. 1991. More cells lead to more milk. p. 76. Manipulating Pig Production III. Australasian Pig Science Association, Werribee, Australia.

· Kim, S.W., W.L. Hurley, I.K. Han, H.H. Stein and R.A. Easter. 1999. Effect of nutrient intake on mammary gland growth in lactating sows. J. Anim. Sci. 77:3304-3315.

· McLaughlin, C.L., J.C. Byatt, D.F. Curran, J.J. Veenhuizen, M.F. McGrath, F.C. Buonomo, R.L. Hintz and C.A. Baile. 1997 Growth performance, endocrine, and metabolite responses of finishing hogs to porcine prolactin. J. Anim. Sci. 75:959-967.

· Sorensen, M.T., C. Farmer, M. Vestergaard, S, Purup and K. Sejrsen. 2006. Mammary development in prepubertal gilts fed restrictively or ad libitum in two sub-periods between weaning and puberty. Livest. Sci. 99:249-255.

Reference

Farmer C. 2014. Lactation success. Proceedings of the London Swine Conference. London, Ontario, Canada. 26 to 27 March 2014. p23-26.

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