Endocrine control of nutrient partition in lactating ruminants

Abstract

Berks RG2 p l TThe subjects of nutrient partition during lactation in ruminants and the hormonal control of the relevant aspects of metabolism, particularly in relation to blood hormone concentrations, have been extensively reviewed (Convey, 1974;Bassett, 1978;Trenkle, 1978Trenkle, , 1981Bauman & Currie, 1980; Bell, 1980;Cowie et al. 1980;McDowell, 1983). The purpose of this paper is to describe the metabolic situation in lactating cows; to briefly emphasize the more important aspects of the hormonal control of nutrient partition and to describe two of our recent experiments on the manipulation of hormone secretion. Metabolic status of the high-yielding dairy cowThe capacity of the cow to produce milk is determined by a combination of the growth and development of the mammary gland before and during pregnancy and the animal's ability to supply the substrates for milk synthesis once lactation is established. It is still not clear which of these factors is more important for maximum milk production. There is no doubt that, despite decades of intensive breeding, considerable variation remains in the ability of individual cows to produce what is currently regarded as a good milk yield in the UK (6000-8000 kg milk in a 305 d lactation). Some of the reasons for this variation are obviously genetic in origin and this is easily demonstrated by comparing the changes in milk yield and body-weight that occur during lactation in beef and dairy breeds of cattle offered the same ration (Hart et al. 1975, 1978, 1979). The former produce low yields of milk, in accordance with the smaller mammary gland, and preferentially partition dietary energy to milk production and supplement this by mobilizing considerable amounts of body tissue. This is an important economic consideration because improved milk yield in early lactation is associated with a proportionately greater partitioning of nutrients towards milk at the expense of body reserves at mid-lactation (Broster, 1976).Bauman & Currie (1980) have used the data of others to examine the relationship between energy intake and requirements for lactation in high-yielding cows (average 9534 kg milk containing 332 kg fat in a 305 d lactation). As expected, they found that the peak in milk yield preceded maximum dietary intake by several weeks and that during the first one-third of lactation the cows were in negative energy balance and mobilizing body tissue. In fact the cows did not consume sufficient energy to meet their requirements until approximately 16 weeks of lactation when milk yield had fallen to less than 80% of peak production. They emphasized this situation by calculating that during the first month of lactation the available at https://www.cambridge.org/core/terms. https://doi

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

“…est encore débattue (Williams et al, 1963 ;Palmquist, 1972 ;Baird et al, 1977 ;Snoswell et al, 1978 ;Bell, 1980 ; Waghorn (1983), ce qui est difficile à concilier avec l'absence de lipogenèse de novo hépatique (Ballard et al, , 1969 (Forbes, 1970a(Forbes, , 1971Burlacu et al, 1978 ;lwasaki et al, 1980 ;Doreau et Rémond, 1982 ;Koong et al, 1982 (Flatlandsmo, 1971 ;Luthman et Jonson, 1972b ;Johnson et al, 1976 ;Miller et al, 1978 ;Thilsted, 1983), mais pas dans des expériences où l'alimentation était généralement plus libérale Koprowski et Tucker, 1973 ;Schwalm et Schultz, 1976 ;Walsh et al, 1980 ;Blum et al, 1983 ;Davey et al, 1983 ;Hart, 1983 Phillips, 1978 ;Miller et al, 1978 ;Bauman et al, 1979 ;Mc Dowell, 1983 ;De Boer et al, 1985. Inversement, l'insulinémie diminue dans ces situations nutritionnelles, où la disponibilité en glucose est plus faible (lbid.…”

“…et al, 1973 ;Emery, 1973 ;Rao et al, 1973 ;Yang et Baldwin, 1973a, b ;Etherton et Evock, 1986), directement ou en augmentant l'utilisation du glucose (Prior et Vernon et al, 1985b (Bernal-Santos, 1982 (Salaman, 1972 ;Lee et al, 1974 ;Assa et Laron, 1977 ;Frigeri, 1980 ;Bauman et al, 1982 ;Hart, 1983 ;Hart et al, 1984a1, et (Murase et al, 1981 ;Schoenle et al, 1982 ;Bornstein et al, 1983 ;Frigeri et al, 1982 ;Goodman et Grichting, 1983). Selon Goodman et Schwartz (1974) Hancock, 1955 ;Bourne et al, 1977 ;Bines et al, 1980).…”

Responses of North American and New Zealand strains of Holstein–Friesian dairy cattle to homeostatic challenges during early and mid-lactation

“…-E-mail: stephen.butler@teagasc.ie ratio of somatotropin to insulin (Bonczek et al, 1988), though relative differences are reduced when high-producing cows are placed on a higher plane of nutrition (Hart, 1983). Previous investigations have shown an association between genetic merit and changes in insulin secretion in response to a glucose challenge in juvenile dairy bulls (Mackenzie et al, 1988), while Kolver et al (2001) reported a greater lipolytic response to an epinephrine challenge for cows of greater milk yield potential.…”

Orientations et coordination hormonale du métabolisme protéique chez les ruminants

“…Il y a sans doute une diminution de la réponse du tissu à l'insuline au cours du développement puisque la baisse des acides aminés libres du sang, provoquée par une injection de l'hormone, est moindre chez l'adulte que pendant la période de croissance (Prior et Christenson, 1978 ;Grizard et al, 1987b1. Toutefois, par (Hart, 1983 ;McDowell, 1983 ;Moe et Tyrrell, 1986 ;Chilliard, 1987) de Chilliard, 1988 ;Tucker et Merkel, 1987).…”