Effect of herbage allowance during pregnancy and lactation on feed intake, milk production, body composition and energy utilization of ewes at pasture

Abstract

In two experiments Dorset ewes were offered low (LP) or high (HP) herbage allowances during pregnancy to induce light (45-50 kg) or heavy (60-65 kg) post-partum body weights, respectively. During the first 6 weeks of lactation three herbage allowances were offered in a 2 x 3 factorial design: 2 (LL), 5 (ML) and 8 (HL) kg D.M./eweperday. In the first experiment (Expt 1) lambs were removed and ewes machine-milked twice daily. In the second (Expt 2) they were suckled by two lambs; a further group on the ML allowance (MML) was machine-milked. Ewes were slaughtered during early pregnancy, post-partum and after 6 weeks of lactation for determination of body composition. Diet selection and faecal output were measured during lactation.Absolute level of milk production was not affected by pregnancy nutrition when rearing two lambs and producing 2-0-2-7 kg milk/day or at 30-50% lower milk production when machine-milked. When expressed as g/kg W 0 '' 6 per day milk production was 14 % greater in LP than in HP ewes. Milk fat content was higher at low allowances and was positively related to rate of body fat mobilization. Milk protein concentration was lower in suckled than in machine-milked ewes (40 v. 47 g/kg) though total milk protein secreted (g/day) was similar. Milk production was 11-13% greater in ewes bearing twin lambs compared with those bearing singles whether machine-milked or suckling two lambs.Mean intakes during the 6 weeks of lactation were 58, 69 and 73 g DOM/kg W 0 " 76 per day, respectively, for LL, ML and HL groups when machine-milked and 51, 75 and 83 g DOM/kg W°' 76 /day, respectively, for ewes rearing two lambs. LP ewes consumed 13 % (Expt 1) and 17 % (Expt 2) more feed (g DOM/kg W 0-' 6 /day)duringlactationthan HP ewes, though in absolute terms (kg D.M./day) there was no difference. The difference in OMD between herbage offered (OMD = 0-77) and consumed ranged from 0 when sheep grazed to a residual herbage mass of 910kgD.M./ha to +0-04 when residual herbage was < 1600 kg D.M./ha.All sheep, irrespective of pregnancy nutrition, milk production or herbage allowance, were in negative body energy balance during lactation. Mobilization of body fat during lactation averaged 40 g/day for machine-milked and 150 g/day for suckled ewes and was greatest in HPLL groups (92 and 219 g/day in Expts 1 and 2, respectively). In LP groups body protein loss during pregnancy was 10 and 16 g/day in Expts 1 and 2, respectively, and little further net protein loss occurred during lactation. The maximum rate of body protein loss in HP groups was 30 g/day in ewes rearing two lambs on the low herbage allowance.Maintenance energy requirement during lactation averaged 0-238 MJ ME/kg W per day for ewes in both experiments; efficiency of use (K, (t)) of total energy available above maintenance for milk synthesis (namely, milk energy/ME intake -estimated energy requirement for maintenance (MEJ + mobilized tissue energy) decreased from 0-84 to 0-51 with increasing rate of tissue energy mobilization. There was a positive relationship be...

The effect of constant dietary energy supply during late gestation and early lactation on performances of prolific D’man ewes

“…According to Chilliard [16], Geenty and Sykes [20] and Khaldi [25], the energy resulting from mobilisation of body reserves is used to compensate for the increased demand for foetal development. For nonprolific breeds facing an energy deficit, the ability to deplete their body reserves is well documented in dry [4] and lactating ewes [8,15,28].…”

Production by ewes rearing single or twin lambs: effects of dietary crude protein percentage and supplemental zinc methionine1

“…Milkfat content may be increased on low feed allowances and positively related to fat mobilization (Geenty and Sykes, 1986 milk from ewes fed the 11.3% CP diet. The zinc methionine supplement had no effect ( P > .17) on milk composition.…”

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).…”

“…Le niveau de production laitière n'est toutefois pas réduit lorsque des brebis maigres à la mise bas sont correctement alimentées pendant la lactation (Peart, 1967(Peart, , 1970Cowan et al, 1980 ;Geenty et Sykes, 1986 (Reid et Hinks, 1962a ;Forbes, 1970Forbes, a, b, 1977Arnold, 1975). L'augmentation du niveau d'ingestion reste toutefois plus faible que chez la ratte, peut-être en raison d'une moindre réponse à la progesté-rone chez les ruminants (Forbes, 19711.…”