Studies on reproduction in prolific ewes. 4. Sequential changes in the maternal body during pregnancy

Abstract

Seventy-eight Finnish Landrace x Dorset Horn ewes in lamb to Suffolk rams were slaughtered serially between 50 and 145 days of gestation. The mean litter size was 2-7. The daily feeding regime aimed to provide each ewe with 15 MJ of metabolizable energy (ME) in the first month of gestation and 9-4 MJ in the second and third. Thereafter the ewes were provided with a basal intake of either 9-6 MJ (low plane, LP) or 13-4 MJ (high plane, HP) plus 1-3 MJ for each foetus.For ewes with 2, 3 and 4 foetuses the mean percentage changes in maternal body weight over pregnancy were respectively -5, -10 and -14 (LP) or + 3, -2 and -6 (HP). Changes in weights of blood, liver and the empty gastro-intestinal tract through gestation varied with the plane of nutrition but not with number of foetuses. In contrast, udder weight at parturition was dependent on number of foetuses but not on plane of nutrition.Increased hydration of the maternal tissues in late pregnancy tended to mask concurrent losses of body fat. For example, over the last 2 months, HP ewes carrying quadruplets lost on average 1-0 kg in body weight but 5-5 kg of (chemically determined) fat. The latter was lost at a rate which increased up to an average of 170 g/day over the last 2 weeks of pregnancy. Net changes in body protein were estimated to be relatively small, but there was some redistribution, including loss from muscle and gain by the udder. There was no evidence of any demineralization of the maternal skeleton.The practical significance of the changes in body composition is discussed, in particular that of the increasing rates of loss of body fat with increasing litter size. It is suggested that the dangers implicit in these rates of fat loss must be taken into consideration when deciding on dietary regimes and the timing of breeding cycles for highly prolific ewes, or indeed when embarking on a programme of increased prolificacy. emulate the changes that normally occur under hill conditions has been made indoors with a view to Experiments on the effects of pregnancy on body relating these changes to the intake of dietary composition of ewes can be broadly divided into nutrients (Sykes & Field, 1972). The second catetwo categories. First, there are studies concerned gory of study involves ewes kept under a more with ewes in hill and upland environments for which favourable nutritional regime and mostly bearing both nutrient intake and reproductive performance twins. Not surprisingly, the extent to which are low. Russel, Gunn & Doney (1968) killed and maternal body tissue is mobilized to provide analysed six Scottish Blackface ewes at mating nutrients for normal foetal growth and developand 11 mainly single-bearing ewes at parturition and ment under these conditions is much less than in the showed that about 50 % of the fat and 20 % of the hill and upland environment (Rattray et al. 1974a

Leptin secretion and hypothalamic neuropeptide and receptor gene expression in sheep

“…The empty carcass weight decreases during late pregnancy, mostly because of loss of adipose tissue lipid (58,59); hence, the decreased body weight of the ewes at day 2 postpartum was not unexpected. Food intake increases after birth, reaching a plateau between 2 and 3 wk postpartum (24,60).…”

Revue bibliographique : Variations quantitatives et métabolisme des lipides dans les tissus adipeux et le foie au cours du cycle gestation-lactation 2e partie : chez la brebis et la vache

“…Cette caractéristique a été reliée à l'antagonisme existant entre néoglucogenèse et lipogenèse. Il faut toutefois remarquer que la lipogenèse de novo hépatique est également faible chez certaines espèces monogastriques telles que le porc (O'Hea et Leveillé, 1969 ;Mersmann et al, 1973) Heaney, 1973a ;Rattray et al, 1974a ;Heaney et Lodge, 1975) mais l'inverse a pu être observé (Foot, 1969) ; les brebis portant 3 ou 4 fcetus perdent plus de lipides (ou en déposent moins) que celles qui n'en portent qu'un ou deux (Robinson et a/., 1978 ;Purroy Unanua et al, 1978) ; celles qui reçoivent une alimentation libé-rale peuvent soit mobiliser, soit déposer des lipides pendant le dernier tiers de la gestation (Wallace, 1948c ;Foot, 1969 ; Tissier et al, 1980a, b) ; les quelques résultats concernant la première moitié de la gestation sont contradictoires ; des brebis sous-alimentées peuvent mobiliser plus de 50 % de leurs réserves lipidiques pendant la gestation IField et al, 1968 ;Russel et al, 1968 ; Field, 1972 ;Robinson et al, 1978b ;Rattray et al, 1980 ;Geenty et Sykes, 1986).…”

“…A partir d'études calorimétriques mesurant la rétention globale d'énergie chez 4 brebis de race Mérinos portant un seul foetus (Graham, 19641, et (Robinson et al, 1978 Wallace (1948c).…”

Changes in body composition during pregnancy and lactation

“…Using the beginning of pregnancy as a baseline, Anderson (1975) brought together information for a number of species on the relative amounts of mammary tissue growth during pregnancy and lactation. In sheep, whose relatively long gestation period of 5 months provides time to grow the lobule-alveolar epithelial cell system that is needed for maximal milk yield, 98% of mammary growth occurs in pregnancy (Anderson, 1975) and the quantity of mammary tissue at birth is directly proportional to litter size (Robinson et al 1978). The value of 98% for sheep contrasts with 60, 67 and 78% for the rat, rabbit and mouse respectively, three species in which the intensity of the sucking stimulus would appear to play a significant role in mammary growth.…”