Mammary Glucose Uptake in the Lactating Ewe and the Use of Methionine Arterio-Venous Difference for the Calculation of Mammary Blood Flow

The contribution of leg muscle, pregnant uterine tissue and lactating mammary gland to overall energy utilization was determined in Merino ewes. Ewes were offered one of three diets based on chaffed oaten hay (7 . 9 MJ metabolizable energy per kilogram dry matter); chaffed lucerne hay (8 . 6 MJ /kg); or a 50: 50 (w/w) mixture of chaffed oaten and lucerne hays (8·2 MJ/kg). Measurements were made during five different physiological states: dry (non-pregnant), at 94 and 125 days after mating, and at 20 and 50 days after lambing.Tissue energy use was calculated from oxygen uptake and carbon dioxide output obtained from measurement of blood flow and arteriovenous difference. Whole-body energy use was calculated from carbon dioxide energy rate. Energy use by leg muscle was 144 ± 8 (mean ± s.e.) kJ kg-I day-I, and unrelated to metabolizable energy intake, but leg energy use increased with ewe body weight. On the basis that leg muscle was representative of all muscle, total muscle energy use accounted for 26 ± 4% of whole-body energy expenditure in dry ewes. Uterine energy use per unit weight was respectively 348 ± 53 and 254 ± 23 kJ kg-I day-I at 94 and 125 days after mating.Milk production was highly correlated with weight of secretory tissue, and with blood flow to the mammary gland. The ratio of blood flow to milk produced was 473: 1 in ewes producing from 200 to 1000 ml of milk per day. The mammary gland used energy to produce milk with an efficiency of O· 90 ± 0 ·01, a value close .to the theoretical estimate ofO· 89. On the basis that metabolic rate does not increase during lactation, the efficiency of use of metabolizable energy for milk production was 0·51 ±0·05. Examination of energy use by different tissues indicated that energy use by muscle was related to weight, but energy use by remaining tissues (whole body less muscle, uterus and mammary gland) was related to metabolizable energy intake. The results reveal an increase in energy use by the remaining tissue in lactating ewes (8500 ± 569 kJ/day) compared with dry (5634 ± 216 kJ/day) and pregnant ewes (5815 ± 393 kJ/day).

Section: Lactationmentioning

confidence: 32%

Partitioning of Nutrients in Merino Ewes. I. Contribution of Skeletal Muscle, the Pregnant Uterus and the Lactating Mammary Gland to total Energy Expenditure

Oddy¹,

Gooden²,

Annison³

1984

“…Glucose would seem to be the most likely metabolite, since in addition to its role as a precursor of lactose, the oxidation of glucose provides much of the energy for the synthesis of the major constituents of milk (see Annison 1971). Davis and Bickerstaffe (1978) have shown in the lactating ewe that the ratio of glucose uptake by the mammary gland to lactose output in milk is about 2. If we use this ratio to calculate mammary uptakes of glucose during feed restriction, falls in lactose output from 36 to 12 g/day in group 1 ewes and from 33 to 16 g/day in group 2 ewes correspond to reductions in the mammary uptakes of glucose of 48 and 34 g/day respectively.…”

Section: Discussionmentioning

confidence: 99%

Control of Gluconeogenesis in the Lactating Sheep

Gow¹,

McDowell²,

Annison³

1981

Aust. J. Bioi. Sci. 1981, 34, 469-78 Ewes which had been lactating for 3-4 weeks and which had been milked by hand from the day of parturition were subjected to food restriction for 4 days. One group of three ewes was fed ad libitum and a second group of four ewes was fed to meet calculated requirements for maintenance and milk production. Over 4 days food intake was reduced by 80 % in both groups of ewes.In response to food restriction, milk yields and body weight decreased. Blood amino acids, plasma glucose, glucose pool size, glucose irreversible loss, insulin, thyroxine and the insulin: glucagon molar ratio decreased. In contrast, plasma glucagon remained relatively unaffected and plasma free fatty acids and growth hormone increased. These changes were similar for both groups of ewes and were reversed when food intake was restored.The results suggest that the hormonal control of gluconeogenesis in the ruminant is similar to that in the non-ruminant.

“…This represents a difference in daily irreversible loss of glucose of approximately 60 gjday which is more than sufficient to account for mammary uptake of glucose for lactose biosynthesis (see Davis and Bickerstaffe 1978). The difference in irreversible loss of glucose for the two groups of ewes (c. 40 mgjmin) is equivalent to the rate of infusion of glucose into group 2 ewes.…”

Section: Glucose Biokineticsmentioning

confidence: 99%

The Importance of Glucose Supply at the Initiation of Artificial Lactation in the Ewe

Leenanuruksa¹,

McDowell²

1982

Ewes induced to lactate artificially were given continuous intravenous infusions of either saline or glucose in saline during the first 5 days of lactation. Glucose-infused ewes secreted significantly greater (P < 0·05) amounts of milk than control ewes during the first 10 days of lactation. On the tenth day of lactation glucose-infused ewes secreted approximately twice as much milk as control ewes (c. 320 v. 160 g/day). Plasma concentrations of glucose and insulin were significantly higher (P < O· 05) on the first 2 days of lactation for glucose-infused than control ewes.The results suggest that glucose supply to the mammary gland at lactogenesis may be rate-limiting for milk production during early lactation.