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[日记&资讯] 德牧母犬的母性

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发表于 2011-2-23 12:13:15 | 显示全部楼层 |阅读模式

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在繁殖者眼中,判断母犬的最佳方式之一就是观察她的母性。然而不幸的是,人们在选择繁殖母犬时,它的母性表现或是其亲代关系的母犬的母性行为(尤其是母亲与女儿间的亲代关系)通常并不是他们考虑的主要因素。母性能力有很强的遗传性,但是其他因素也对母性有同样的影响。 母性行为的激素情况 以下介绍诱发母性行为的四种激素,分别为:雌性激素,黄体酮,催乳激素以及后叶催产素(脑下垂体后叶荷尔蒙的一种)。 雌性激素是生育过程中最活跃的荷尔蒙素,在犬发情期间第一阶段的物理和行为变化(包括阴部肿大,**出血,以及分泌吸引雄性的性引激素)发挥了重要的作用。其次,对乳腺发育,哺乳期内,及母性行为也有着关键性的影响。为了让雌性激素分子能引起反应,目标组织就要在细胞膜上设雌性激素的感受器。大脑中感受器的位置和集中区域决定了反应的种类和强度。 第二种母性激素,即黄体酮,人们又称之为怀孕激素。卵巢囊泡细胞在排卵后开始发生改变,分泌黄体酮来维持机体正常受孕。怀孕激素能诱发母性行为,尤其是感受器内有雌性激素的时候。 在母犬分娩之前,黄体酮水平会突然急剧下降,但与此同时,伴随着第三种木性激素的迅速上升,这就是催乳激素。两种指标的相对变化可能负责母性行为的立即促成,例如筑巢,强烈的母性保护意识。催乳激素的主要作用是刺激母体产后的哺乳。如果目标组织内已有大量雌性激素,那么催乳激素的分泌会增加,母犬在哺乳期的母性表现也会增强。 最后第四种,就是由脑垂体对幼犬在母体子宫颈内产生的物理压力所引起的反应而分泌的后叶催产素。催产素的其中一个作用是在生产期间子宫收缩的同时,刺激奶水的分泌。它与其他激素一样,能刺激母体对幼犬产生认识及保护的行为。 母体行为因素 除了发情期和繁殖期的行为以外,母犬只有在临近生产和分娩时才会有怀孕的特殊表现。与此同时,她会有“筑巢”的表现,特别会去寻找一个有保护又私密的空间,这样才会觉得安全。 幼犬出生之后,如果适量的荷尔蒙激素开始运作,母犬就会表现出母性,舔舐幼犬。最初,母犬与幼犬间的联系就通过母体分娩时幼犬身上的羊水气味来辨别。母犬舔舐幼犬时为了刺激它们呼吸,并弄干它们身上的被毛。一段时间以后,由于幼犬还不会自主排泄,母犬开始舔每条幼犬的生殖器,包括排尿及排便处,以此来刺激它们排泄,直到三个星期之后,幼犬开始自主进行为止。母犬还会通过舔舐幼犬的头部来引导它们吸奶。 消极母性行为 母犬有一些产后的行为是无法让人接受的。它们可能攻击自己的幼犬,尤其是在幼犬发出声音,使母犬感到焦躁的时候。引起此类伤害的原因多种多样。我们首先要考虑的就是母犬自身是否有身体的伤痛。乳腺炎会引起母体强烈的疼痛,诱发对幼犬的攻击行为。如果母犬没有认出自己的幼犬,同样也会触发伤害。后叶催产素不足会影响母犬认知幼犬的行为,因为荷尔蒙能让大脑在分娩及信息素分泌后,通过羊水的气味立即分别出幼犬的味道。另一个母犬伤害幼犬的原因发生在幼犬在产后被移走或是立即清理身体,失去了羊水的味道的情况下,因为母犬无法通过气味来判断是不是自己的小孩。 在一些极端情况下,伤害或攻击可能上升到同类相食的惨状,即母犬可能会吃掉自己的幼犬。我们将这一行为称之为杀食后代(kronism)。再次强调,母体的疼痛是最主要原因,在这之前,也同时需要考虑是否有乳腺炎的因素存在。 另一个诱发因素是前期子痫症,即母犬的血钙太低,但还没有表现出应有的类似发热或虚弱的症状。其他的原因则还有可能是遗传因素的影响(缺少雌性激素感受器,对荷尔蒙的刺激产生消极作用),心理因素的影响(第一次做母亲,由于没有经验而非常紧张等),生理因素的影响(由于噪音或育婴室周围太多的脚步声或一些其他刺激而释放出升高的神经传递素)。 在一个相对较的伤害水平上,拒绝喂食幼犬也是一个问题。如果只发生在一条到两条幼犬的身上,那么可能是幼犬自身的原因;然而,如果情况发生在一窝幼犬中,那么问题很有可能出现在母犬上。在母犬生产第一胎幼犬时,这一情况会比较普遍。通常,如果只是一两条幼犬,可能是因为体温过低或是静止不动的缘故。 对不足月的幼犬最大的三大威胁是:体温过低,血糖过低,以及脱水。如果发现及时,幼犬可能缓慢恢复体温;如果脱水,可以通过人工喂养来缓解。警告:我们不能尝试喂养一个体温低的幼犬,因为它们没有能力咀嚼,牛奶还可能流入肺部引起窒息。一旦幼犬恢复正常体温,母犬自然就会接纳它。重要的是,我们要知道,母犬偶尔的拒绝,会逐渐扩大到吃掉幼犬的地步。 总结 总的来说,母性表现是激素分泌,生理学现象及基因因素共同作用的结果。 不理想的母性表现有多种原因引起,例如激素的影响(感受体缺乏,分泌不足,或是诱发不够),缺乏经验,过度紧张,压力过大,或是疼痛所造成。 我们在评估一条母犬的母性能力时,应当谨慎考虑以上这些因素。 原为摘自 Breeder's Handbook: Maternal Behavior By Bretaigne Jones, DVM Senior Veterinary Services Manager ?2010 ROYAL CANIN USA, Inc. One of the best traits a ***** can have in the eyes of a breeder is good mothering ability. Unfortunately, the mothering behavior of the ***** or the female relatives of the stud dog (especially mothers and daughters) is not often a primary consideration when choosing the dogs to be bred. Mothering ability has a strong hereditary aspect, but other factors exert influence as well. Hormonal aspects of maternal behavior There are four hormones that trigger aspects of mothering behavior: estrogen, progesterone, prolactin, and oxytocin. Estrogen is the most active hormone in reproduction from its primary actions in stimulating the physical and behavioral changes associated with estrus (swollen vulva, bloody vulvar discharge, and pheromones to attract male dogs), to its secondary role as a primer for mammary development, lactation, and maternal behavior. In order for the estrogen molecule to trigger a response, the target tissue must have estrogen receptors on the cell membranes. The location of the receptors within the brain and their concentration will determine the type and strength of the response. The second maternal hormone, progesterone, is recognized as the pregnancy hormone. The ovarian follicular cells start to change after ovulation and secrete progesterone to maintain pregnancy. It has some effect on inducing maternal behavior, particularly when its receptors are primed with estrogen. Just before birthing, progesterone levels drop abruptly, with a concurrent rise in prolactin, the third maternal hormone. This combination of level changes seems to be largely responsible for stimulating immediate mothering behavior such as nesting and protective maternal aggression. Prolactin’s function is largely stimulatory for lactation. Both actions of prolactin, maternal behavior and lactation, are enhanced if estrogen has “primed” the tissues. Lastly, oxytocin is released from the pituitary gland in response to the physical pressure of a puppy against the cervix during labor. One of the actions of oxytocin is to synchronize contractions of the uterus in birthing and to stimulate the let-down of milk. In conjunction with the other hormones, it stimulates maternal recognition of her pups and care behavior. Behavioral elements of mothering Other than the behavior exhibited in the estrus cycle and breeding, there are not behaviors specifically associated with pregnancy until the dam nears labor and delivery. At that time, she will exhibit nesting behavior, typically searching out a protected, private place where she can feel safe. Once the puppies are born, if appropriate hormonal activity has occurred, the dam will begin her mothering by licking them. Initially it is the scent of her amniotic fluid that communicates that the puppies are hers. The dam performs the licking in order to stimulate breathing and to dry the pups’ coats. Later she will lick the genitalia of each pup to stimulate urination and defecation since the pups won’t eliminate on their own until about three weeks of age. The ***** will also use licking on the heads of the pups to guide them to nurse. Negative maternal behaviors Some postpartum behaviors, however, are undesirable. Dams may be aggressive to their pups, especially when the pups are making noise. Causes of this aggression can be varied. The first consideration is if the ***** is in pain. Mastitis is a condition that can cause pain and can trigger aggressive behavior toward the pups. Aggression can also be triggered if the ***** does not recognize the pups as her own. Inadequate levels of oxytocin can influence this recognition, as the hormone makes the brain receptive to the amniotic fluid smell immediately after birth and pheromone secretion. Another factor is if the pups are removed and cleaned up so thoroughly immediately after being born that when returned to the ***** they no longer have the amniotic fluid scent to identify them as hers. In extreme cases, aggression can escalate to cannibalism of one or more of the pups. This type of cannibalism is called kronism. Again, pain can be the cause, and as before, mastitis needs to be considered. Another trigger is pre-eclampsia, a condition where the *****’s blood calcium (unbound) is too low, but she isn’t yet exhibiting the classic signs of seizures, fever and weakness. Other causes can be hereditary (a lack of estrogen receptors, which negatively impacts the action of other hormones), psychological (first-time mom, very nervous, and so on), and physiological (elevated neurotransmitter release due to too much noise, too much foot traffic in the nursery, overcrowding in the nursery area, and other stimuli.). On a less aggressive level, rejection of the pups can also be a problem. If it is just one or two pups, it may indicate something is wrong with those particular pups; whereas if it is the entire litter, the problem usually lies with the dam. It can be more common in first-litter *****es. Usually if it involves just one or two pups, they may be cold or too still. The three big threats to the survival of neonates are hypothermia, hypoglycemia, and dehydration. If caught soon enough, the pup can be slowly warmed, or if dehydrated, it can be bottle fed to stimulate activity. Warning: One should never attempt to feed a cold puppy, as they are not capable of swallowing and may aspirate the milk into their lungs instead. Once the puppy has reestablished a normal body temperature, the dam will accept it. It is important to note that occasionally rejection will escalate to cannibalism. Summing up In summary, maternal behavior is a composite of hormonal, physiological, and genetic factors. Undesirable maternal behavior can be triggered by a variety of factors, such as hormonal (lack of receptors, inadequate production, or lack of stimulation), inexperience, nervous disposition, stress, or in reaction to pain. It is important to consider all of these factors when assessing a *****’s mothering ability.
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