Seasonal changes in plasma concentrations of proteins, urea, glucose, calcium and phosphorus in sheep grazing a hill pasture and their relationship to changes in body composition

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Abstract
SUMMARY The seasonal changes in plasma concentrations of albumin, globulin, transferrin, urea, Ca, P and glucose were measured in 59 Scottish Blackface sheep grazing a hill pasture. The sheep were classified according to age and state of permanent incisor dentition into four groups. Sheep were slaughtered at mating (November), mid-lactation (June) and in the late dry period (November), and the changes in plasma constituents related to changes in body composition. A protein-free supplement was offered during late pregnancy. Another group of sheep was used in the subsequent year to investigate the significance of helminth infections on such pastures. Plasma albumin concentration fell from 32·0 g/1 in all sheep in early pregnancy to 17·5–19·5 g/1 in late pregnancy and early lactation in 5½- to 6½-year-old animals. Younger animals (2½ year old) maintained higher (23·0 g/1) levels at these latter times. The extent of the decrease in plasma albumin concentration of the groups was related to the loss of N from their soft tissues during the same period. Plasma volume increased from 2·10 to 2·491 between early pregnancy and midlactation (45 and 66 ml/kg body weight respectively). The increase in volume was considered to account for the reduction in the concentration of plasma globulin which took place during this period. Plasma urea-N concentrations were extremely low (50—60mg/l) between February and April and had fallen from their highest values (240 mg/1) in August to 150 mg/1 by the following November. It is argued that the fall in albumin concentration which occurred in early pregnancy, coupled with the extremely low urea-N concentration, reflects a very low digestible crude protein intake during most of pregnancy. Transferrin concentration followed a similar seasonal pattern to urea. The concentration was extremely low in February (2·2–2·4 g/1), highest in August (3·45 g/1) and had fallen by November (3·0 g/1). The value of transferrin as a nutritional index is discussed. Regular dosing with anthelminthic of sheep on these pastures had a beneficial effect on plasma albumin concentrations, particularly during critical nutritional periods, namely late pregnancy and lactation. Plasma glucose, Ca and P concentrations were of no value in monitoring the nutritional status of the animal with respect to these nutrients.

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