Maternal care plays an important role in the survival of offspring in mammals. In the ewe initial maternal care is expressed by nurturing the young and formation of an exclusive olfactory bond with the lamb. After the neonatal period, maternal care is associated with co-operation with sucking interactions, maintenance of a close ewe–lamb relationship, communication with lambs, vigilance and a tendency to seek absent lambs. Two breeds of ewe, Suffolk and Scottish Blackface, have previously been shown to differ in their expression of early maternal care, and in lamb survival. It was hypothesised that these differences in the expression of maternal behaviour would persist throughout the lactation period and continue to be expressed in other aspects of maternal care. The maternal behaviour of 32 primiparous ewes (18 Suffolk, 14 Blackface) was observed from birth until weaning at 12 weeks of age. As shown previously, Blackface ewes spent more time grooming their lambs than Suffolk ewes (P<0.001), and were more cooperative with the early sucking behaviour of their offspring (P<0.01). Blackface ewes were significantly closer to their lambs from birth and throughout the lactation period (P<0.05). There were no significant differences between breeds in maternal vocal communication with their lambs, however, Blackface ewes were significantly more vigilant (head alert) than Suffolk ewes from week 4 of lactation onwards (P<0.01). The lambs of Suffolk ewes had a significantly higher frequency of sucking bouts (P<0.05) than lambs of Blackface ewes in the first weeks of lactation. However, Blackface ewes accepted a greater proportion of lamb sucking attempts than Suffolk ewes (P<0.01), and these sucking bouts were longer than with Suffolk ewes (P<0.05). The results therefore show that differences in the expression of maternal care seen in the initial post partum period in sheep persist throughout lactation, and would be expected to contribute to lamb survival.

Lamb survival is impaired in low birth weight lambs, and those that are slow to stand and suck. Many of the factors that influence lamb vigour, such as parity, litter size, and breed, may exert their effects, at least partially, before birth by influencing placenta development. Our hypothesis was that retarded lamb behavioural development was due to differences in placentation in these animals. Data were collected from Blackface and Suffolk lambs in the first 2 h after birth and placentas were collected when delivered. Suffolk lambs, which were behaviourally slower and had lower rectal temperatures than Blackface lambs, were associated with larger but less efficient placentas (placental efficiency defined as foetal weight supported per g placenta) with fewer foetal cotyledons than Blackface placentas. Triplet lambs were significantly slower than twin or single lambs to suck and had lower rectal temperatures. Although placenta efficiency increased with litter size, placenta and cotyledon weight, and cotyledon number increased with twinning but not thereafter. It seemed likely that triplet lambs suffered some placental insufficiency in comparison to other litter sizes. Lambs born to first parity mothers were slower to stand and reach the udder than lambs of more experienced ewes, and first parity ewes also had smaller and less efficient placentas although cotyledon number was not affected. Male lambs tended to be slower than female lambs for most behaviours, although rectal temperatures were not affected. The sire of the lamb also influenced lamb behaviour and rectal temperature. Both lamb sex and lamb sire influenced the average weight of placental cotyledons, thus some of the sire effect on the behaviour and birth weight of his progeny might be mediated through placental development. Lamb neonatal vigour was correlated with placental efficiency suggesting that lamb behaviour immediately after birth is related to placental development and function.

Lamb vigour at birth (i.e. time to stand after delivery) is known to be affected by a number of maternal factors, such as parity and litter size (Dwyer, 2002), as well as lamb breed (Dwyer et al., 1996), and is related to subsequent lamb survival (Dwyer et al., 2001). It is likely that these factors act before birth to influence lamb development and may exert their effects through differences in placental development and function. The purpose of this experiment was to examine the effects of ewe parity, litter size and ewe breed on placental components, and relate these to lamb behavioural development at birth.