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Pregnancy-specific protein B (PSPB) and progesterone concentrations were determined by RIAs in venous plasma during early pregnancy after 177 artificial inseminations (AI) performed in 76 cows and 71 heifers. The females were bled at 24, 26, 30\p=n-\35 days and \m=~\70 days (for non-returns to oestrus) after AI. In non-pregnant females without extended CL maintenance (progesterone < 1\m=.\5 ng/ml on Day 24) and or showing a normal time of return to oestrus (Group 1, N = 63), PSPB concentrations were undetectable whatever the stage after AI except in 2 cows. In pregnant animals (N = 83; Group 2) progesterone concentrations were > 10 ng/ml from Day 24 to the time of rectal palpation and PSPB concentrations rose continuously from 0\m=.\42\m=+-\0\m=.\07 (s.e.m.) ng/ml (Day 24) to 4\m=.\06 \ m=+-\ 0\m=.\3 ng/ml (time of rectal palpation). No coefficient of correlation between PSPB and progesterone concentrations was significant whatever the day of gestation studied. In cows with extended luteal function and subsequently found to be non-pregnant (late embryonic mortality) PSPB was undetectable (N = 21; Group 3) or detectable (N = 10; Group 4) at Days 24, 26 and/or 30\p=n-\35of pregnancy. At 24 and 26 days after AI progesterone concentrations were intermediate between those of Groups 1 and 2. At Day 24 females of Group 4 had higher progesterone concentrations than those of Group 3 (P < 0\m=.\05), but no differences between these two groups existed at subsequent stages after AI. Animals of Group 4 had lower PSBP concentrations than those of Group 2 between Days 24 and 30\p=n-\35 (P < 0\m=.\025) but at the time of rectal palpation PSPB values fell to undetectable levels in all but 1 cow of Group 4. We conclude that (1) most pregnancy failures in cows are due to nonfertilization or early embryonic death and if AI is performed after 70 days post partum >95% of these females have no detectable PSPB concentrations; (2) peripheral progesterone concentrations are lower at Days 24\p=n-\26after AI in cows with late embryonic mortality than in pregnant cows; (3) only 30% of non-pregnant females with extended luteal function (late embryonic mortality) have detectable PSPB levels which are lower than in pregnant cows; and (4) in pregnant animals there is no correlation between PSPB and progesterone concentrations. This suggests that under physiological conditions PSPB has no major effect on progesterone production or vice versa.

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Effects of postpartum energy restriction, parity and time after parturition on energy status (measured by glucose, insulin, non-esterified fatty acids (NEFAs) and beta-hydroxybutyrate), LH secretion and follicular growth were investigated in ten primiparous and nine multiparous suckled cows. Females were allocated by parity, body mass and body condition score at calving to diets supplying either 100% (CE, n = 10) or 70% (LE, n = 9) of energy requirements until day 70 postpartum. Metabolic parameters were measured every week from calving to day 70 postpartum. Blood samples were collected at intervals of 15 min for 10 h on day 30 and day 50 after parturition for LH measurement. Ovaries were examined between days 20 and 30 and days 40 and 50 postpartum by ultrasonography. Energy supply affected mean plasma concentrations of glucose (CE: 0.64 +/- 0.01 g l-1 versus LE: 0.61 +/- 0.01 g l-1; P < 0.05) and NEFA (CE: 168 +/- 17 mu eq l-1 versus LE: 309 +/- 18 mu eq l-1; P < 0.01) but by day 70 postpartum, glucose and NEFA concentrations were not significantly different between the two groups. LH pulse amplitude and frequency were not affected by energy supply (P > 0.10). However, at day 30 postpartum, LH pulse frequency was negatively correlated with plasma concentration of NEFA (r = -0.61; P < 0.01). Cows fed diets supplying 100% of energy requirements had more large follicles than did cows fed low energy diets (CE: 0.82 +/- 0.05 versus LE: 0.31 +/- 0.05; P < 0.05). The size of the largest follicle was greater in CE cows than in LE cows (CE: 10.2 +/- 0.1 mm versus LE: 8.7 +/- 0.2 mm; P < 0.05). Between 40 and 50 days postpartum, the size of the largest follicle was negatively correlated with NEFA concentration (r = -0.5; P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)