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A farming systems study of abortion in dairy cattle on the Atherton Tableland: 4. Pasture composition and plasma progesterone concentrations of pregnant cows in affected herds
Author(s) -
NORTON JH,
TRANTER WP,
CAMPBELL RSF,
IVERS N.,
MARTIN P.
Publication year - 1989
Publication title -
australian veterinary journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.382
H-Index - 59
eISSN - 1751-0813
pISSN - 0005-0423
DOI - 10.1111/j.1751-0813.1989.tb09794.x
Subject(s) - pasture , zoology , ruminant , herd , biology , pregnancy , lactation , dry matter , agronomy , genetics
SUMMARY To provide more evidence for an apparent association between immature, high protein pasture diets and abortion in dairy cows on the Atherton Tableland in tropical north Queensland, pastures and cows on 4 farms were sampled on 5 occasions during a 7‐month period. Pasture samples were analysed for dry matter (DM), protein, nitrate and fibre content. Plasma progesterone concentrations were determined in 18 to 20 pregnant cows. Fifty‐four pasture samples (38 grass and 16 legume) were analysed and the distribution for 3 DM ranges was: 10% to 14.9%—20 samples, 15% to 19.9%—27 samples and 20% to 24.9%—7 samples, while the distribution for 4 protein ranges was: 15% to 19%—5 samples, 20% to 24%—20 samples, 25% to 29%—21 samples and 30% to 34%—8 samples. Both pasture protein and DM content fluctuated with time. Pasture nitrate was low and insignificant while fibre (cell wall) levels appeared to be satisfactory for ruminant nutrition. Significant differences occurred between the mean plasma progesterone levels on 3 of the 4 farms. Raised levels in pregnant cows suggested the possibility of increased progesterone production in response to a previous low progesterone crisis or, alternatively, a decreased metabolic clearance rate of progesterone in pregnant cows on a declining plane of nutrition towards the end of the summer wet season. Progesterone data were not available from cows which previously aborted. It is suggested that high protein and low DM in the pasture were related to the abortions through reduced plasma progesterone caused either by a reduced availability of precursors for progesterone formation or by an increased metabolic clearance rate of plasma progesterone. These options require further experimental confirmation.