MANUAL DE PREVENCIÓN DE RIESGOS LABORALES

Few studies have investigated whether ewe body condition score (Jefferies 1961) affects ewe and lamb post-partum behaviour and survival.

In late-pregnancy, the nutritional demand for the multiple-bearing ewe is significantly increased (Nicol & Brookes 2007). If the ewe cannot meet the increased nutritional demand via intake, she must utilise body reserves. Therefore, it may be expected that the impact of BCS on fetal growth and lamb birth weight would be greatest in late-pregnancy (Kenyon et al., 2014). In the majority of previous studies, ewe BCS has had little effect on lamb birth weight or survival, possibly due to the large variation in the timing of BCS measurement, the number of fetuses per ewe and maternal nutrition. For a full review see Kenyon et al. (2014).

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that lost a large amount of condition during pregnancy were lighter at birth than those born to ewes that did not lose body condition.

Several studies have reported that ewe BCS can affect lamb survival (Al-Sabbagh et al. 1995; Kenyon et al. 2011; Kenyon et al. 2012; Kenyon et al. 2013; Kenyon et al. 2014), although, studies are often inconsistent. It is possible that some of the effects of ewe BCS on lamb survival are driven by changes in ewe and lamb behaviour.

The effects of litter size on ewe and lamb behaviour

It has been suggested that litter size stimulates maternal ability. O’Connor et al. (1985) reported that there was a positive relationship between MBS and litter size. This relationship has also been found by others (Lambe et al. 2001; Corner et al. 2005; Everett-Hincks et al. 2005b; Ekiz et al. 2007), however, other authors have found no relationship (Dwyer and Lawrence 1998; Corner et al. 2010). The reason for these inconsistent results is not yet clear.

Ewe and lamb high-pitched bleats, i.e. ‘distress bleats’, have also been shown to be positively correlated with litter size. Ewes rearing twin- or triplet-born lambs emitted more high-pitched bleats in the neonatal period than ewes with singletons (Pollard 1992; Dwyer et al. 1998). Pollard (1992) argued that this greater number of bleats was associated with an increased likelihood for ewes with twins and triplets being separated from their offspring. Twin-born lambs have also been found to bleat more frequently in

the neonatal period than singletons, possibly due to the ewe having to divide her attention between her offspring (Hernandez et al. 1992).

The duration of intense grooming of individual lambs after birth for twin- and triplet-born lambs is less than for singletons (Alexander et al. 1990; Dwyer and Lawrence 1998). Alexander et al. (1990) reported that as a result of the dam spending less time grooming each multiple-born lamb the formation of the ewe-lamb bond was weaker. They hypothesised that the time the ewe spent grooming and in close contact with her lambs was directly related to her ability to discriminate her lambs.

Separation of the lamb from its dam is more common in multiple-born lambs than in singletons during the first days following birth (Alexander et al. 1983), thus resulting in fewer opportunities to nurse and to learn maternal features. Nowak and Lindsay (1992) suggested this may be a reason for a delayed ability of multiple-born lambs to discriminate their mother in a triangle test compared with singletons.

The effects of parity on ewe behaviour

Primiparous ewes may have a more difficult parturition (Wallace 1949), more birth injuries (Woolliams et al. 1983) and poorer maternal behaviour (Wallace 1949) than multiparous ewes. Poor maternal behaviour in primiparous ewes is well established

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behaviour is influenced by experience (Poindron 2005) with improvement shown between the first and second birthing event.

A study by Poindron (2005) reported that primiparous ewes showed nearly 50% more behavioural problems compared with multiparous ewes. Primiparous ewes have been found to display less and delayed physical contact (Poindron and Neindre 1980; Alexander et al. 1993; Otal et al. 2009) and grooming behaviours towards their young (Owens et al. 1985; O'Connor et al. 1992; Ekiz et al. 2007) than multiparous ewes. They are also more likely to move away from their lambs and circle to avoid sucking attempts by their lambs (O'Connor et al. 1992; Alexander et al. 1993; Dwyer and Lawrence 2000) resulting in increased rejection rates (Dwyer and Lawrence 2000; Otal et al. 2009) compared with mature ewes. Alexander (1993a) reported primiparous ewes were more likely than mature ewes not to groom or show any interest in their lambs. Further, Mulvaney et al. (2011) reported that MBS was lower in primiparous ewes compared with mature multiparous ewes. Mulvaney et al. (2011) also reported that one-year-old ewes emitted a greater number of high-pitched ‘distress’ bleats than mature ewes.

As a result of these negative behavioural traits primiparous ewes tended to have weaker attachments to their lambs often resulting in rejection of the lamb (O'Connor et al. 1992; Dwyer et al. 1998; Dwyer and Lawrence 2000; Dwyer 2003; Otal et al. 2009). Kendrick et al. (1991) reported that primiparous ewes were less accurate in discriminating their lambs from alien lambs at four to six hours after birth. Primiparous ewes have also been shown to be separated more often from their lambs than multiparous ewes (Alexander et al.1984).

The effects of parity on lamb behaviour and survival

Alexander (1993) reported that parity had no effect on neonatal lamb behaviour. A number of studies, however, have reported conflicting evidence. In contrast, Dwyer (2003) reported a negative correlation between parity and the time taken for lambs to perform all neonatal righting and standing behaviours with the exception of time to raise and shake head. Lambs from primiparous ewes were especially slow to stand and suck. Dwyer (2003) also stated that lambs born to primiparous ewes exhibited less frequent play behaviour compared with those born to multiparous ewes. Primiparous ewes have been shown to display aggression towards their lambs and exhibit non- cooperative sucking behaviours more frequently than multiparous ewes (Alexander et al. 1993; Dwyer and Lawrence 2000). This may help explain the slow neonatal progress of these lambs as neonatal lamb behaviour is known to be affected by ewe behaviour (Dwyer et al. 2003).

Frequency of lamb vocalisation has also been found to be affected by ewe parity. Dwyer et al. (1998) reported that lambs born to primiparous ewes bleated more frequently than lambs born to multiparous ewes. They suggested that the greater bleating rates from lambs born to primiparous ewes may indicate a lack of sucking, since their time to suck successfully was prolonged (O'Connor et al. 1992). Mulvaney (2011) reported that singleton lambs born to primiparous one year old ewes emitted a greater

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A number of studies have suggested that lamb mortality is greater for primiparous compared with multiparous ewes (Muñoz et al. 2009; Morel et al. 2010; Mulvaney 2011). There is, however, conflicting evidence as neither Alexander et al. (1993), Ekiz et al. (2006) nor Mulvaney (2010) reported any effects of parity on lamb survival. Corner et al. (2013) compared the performance of primiparous versus multiparous ewes. In a study of singleton bearing ewes, lamb survival was lower in lambs born to primiparous ewes. In a second study, which included both singleton and twin bearing ewes, lamb survival was only lower in twin lambs born to primiparous ewes.

The effects of breed on ewe and lamb behaviour

Previous studies indicate that ewe breed and experience, rather than age, affect maternal care in ewes. Previous research has shown that there are differences between breeds in the ability of the lambs to identify their dam (Nowak and Lindsay 1990), lamb vigour (Stevens et al. 1984), time to stand and suck after birth (Cloete et al. 2002) and vocalisation (von Borstel et al. 2011). Breed differences in ewe behaviour has also been reported.

The New Zealand Romney breed, when compared with Merinos, had lower rates of twin-separation in primiparous ewes when lambed under similar conditions (Alexander et al. 1983). A study conducted by Dwyer and Lawrence (1998) found that Suffolk ewes showed poorer maternal behaviour compared with Blackface ewes. Suffolk ewes were more likely to abandon their lamb and to show aggression towards it,

whereas Blackface ewes were more cooperative to lamb sucking attempts and spent more time grooming their lambs. Blackface lambs were also more active in all aspects of neonatal behaviour and made more sucking attempts (Dwyer and Lawrence 1998; Dwyer 2003). Dwyer and Buenger (2012) stated that breeds selected narrowly for greater productivity were more likely to experience poor lamb vigour. The more selected breeds of sheep, such as the Merino, were thus believed to be inferior mothers to the more wild-type breeds, such as Bighorn (Dwyer and Lawrence 1998).

The effects of maternal stressors on the lamb

Stress has been defined as “the biological response elicited when an individual perceives a threat to its homeostasis” (Moberg, 2000). Prenatal stress has been defined by Braastad (1998) as “stress experienced by the pregnancy mother which affects the development of the offspring”. Prenatal stressors can alter fetal growth and birth weights (Mellado et al. 2000; Morris et al. 1999) and cause abnormal endocrine and behavioural responses to a stressor (Lay et al. 1997; Roussel et al. 2005). Sheep may be exposed to a variety of stressors including disease, injury, poor nutrition and hypo/hyperthermia (Dwyer and Bornett, 2004). The focus of this thesis is to examine the effects of ewe mid-pregnancy BCS and nutrition on ewe and lamb behaviours, therefore the potential outputs of the other stressors will not be reviewed.

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