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Union Nationale des Coopératives d'Elevage et d'Insémination Artificielle, and Institut National Agronomique de Paris-Grignon, 78850 Thiverval-Grignon, France
(Received 11th July 1974)
It is now well established that dairy bulls attain their mature rate of spermatogenesis by 1 year of age (Attal & Courot, 1963; Macmillan & Hafs, 1968) and that gonadotrophins and steroid hormones are involved in the process of initiation and maintenance of spermatogenesis (Steinberger & Steinberger, 1969). Already by this age, testosterone is the most important androgen secreted by the interstitial tissue (Lindner, 1969). Rawlings, Hafs & Swanson (1972) observed an increase in the plasma levels of testosterone in five bulls up to 11 months of age and then a drop the following month. Since the levels found were highly variable, it was apparent that data from quite a large number of animals would be required to establish whether there is a significant increase or decrease in the
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Summary. Peripheral plasma samples were collected from 37 young bulls every other month from 2 to 12 months of age. Androstenedione and testosterone were measured by radioimmunoassays. Androstenedione values increased from 2 to 4 months of age (525 ± 296 (s.d.) pg/ml) and then decreased. Testosterone concentrations increased regularly from 2 months (0·17 ± 0·14 ng/ml) to 6 months (2·79 ± 1·29 ng/ml) and then remained at levels around 3 ng/ml. Coefficients of correlation between the hormone concentrations were significant only at 6 months and thereafter.
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Summary. Blood samples collected from 54 Montbéliarde young post-pubertal bulls were assayed for FSH. In the first trial, 0·25 mg GnRH was given to each of 25 bulls at 12 months of age. In a second group of 29 bulls, each received 20 mg dexamethasone followed by 0·25 mg GnRH 5 h later. Based on measurements of semen output, the bulls were classified into three categories: good, medium and poor semen producers. The total FSH response was significantly different among individuals (P < 0·05) and repeatable (r = 0·45) only after the combined treatment. The mean total responses did not differ significantly between the 3 categories of semen producers, but individual FSH responses were significantly and negatively correlated to quantitative and qualitative semen production characteristics (r = 0·4–0·7).
It was concluded that measurement of FSH after a combined dexamethasone-GnRH challenge permits the demonstration of a significant relationship between FSH release and semen production in individual bulls.
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Summary. The sperm output of each of 54 dairy bulls of the Montbéliarde breed was carefully investigated from 15 weekly semen collections at 51–65 weeks of age. Assessment of classical characteristics of semen output led to classification of bulls as good, medium and poor semen producers.
At 12 and 13 months of age, bulls were injected i.m. with 0·25 mg GnRH (N = 25) or with 20 mg dexamethasone + 0·25 mg GnRH (N = 29). Peripheral plasma LH and testosterone responses to these injections were evaluated from frequent sampling. In the two groups, the mean areas under the curve of LH (μg/ml × 150 min) were significantly different between bulls (P < 0·05). Intra-class correlation was 0·35 after the single GnRH administration (P < 0·05) and 0·57 after dexamethasone–GnRH (P < 0·05). This latter value indicates a predominant individual influence over the LH response to such a combined treatment. No significant individual differences were seen from the testosterone responses to either of these challenges. Correlations between individual LH responses and any of the semen output criteria were not significant (P > 0·05) and there were no significant differences in terms of mean LH responses between bulls in the 3 categories of semen production.
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Summary.
The binding of testosterone, corticosterone and 17α-hydroxyprogesterone by bull plasma protein was studied by equilibrium dialysis. Testosterone in bovine plasma was bound by a CBG-like protein and by a specific protein (testosterone-binding protein or TBP) of limited capacity and high affinity. The TBP was specific for C18 and C19 steroids with a 17β-hydroxy group. Precision of the steroid-protein binding measurements was tested and was satisfactory. The testosterone-binding capacity in bull plasma samples did not seem to be related to testosterone levels in peripheral plasma. Significant differences between bulls and cows with regard to the binding capacity were observed.
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Summary. The lignan identified in human and bovine semen was trans 2,3-bis(3′-hydroxybenzyl)-γ-butyrolactone. It was present in unconjugated and conjugated forms. Mean seminal plasma concentrations were always higher than the corresponding blood plasma levels (between 2·5 and 25 times higher), indicating an efficient clearance capacity of the male reproductive system.
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The effects of Trypanosoma congolense infection were investigated at the pituitary level on trypanosome resistant Baoulé bulls (aged 3–6 years), using immunohistochemistry of LH-and FSH-secreting cells and a combined dexamethasone and GnRH challenge. The pituitaries of two control and five naturally infected Baoulé bulls were removed after slaughter and the LH- and FSH-secreting cells were examined immunohistochemically, using specific polyclonal antibodies against βLH and βFSH. No significant impairment of the labelling and distribution of LH- and FSH-secreting cells was seen in infected bulls when compared with control animals. No parasites were found in the pituitary glands. Plasma LH and testosterone concentrations were determined in eight control and eight infected bulls by enzymeimmunoassay and radioimmunoassay techniques, respectively. Blood samples were collected at intervals of 30 min two times before and nine times after dexamethasone treatment (20 mg i.m.). GnRH (Busereline: 20 μg, i.m.) was injected 4.5 h later and samples were collected every 15 min for 180 min. After dexamethasone treatment, LH and testosterone concentrations declined dramatically in both groups. Four hours after treatment, the mean testosterone concentration for both groups was 0.44 ng ml−1. After GnRH injection, LH concentrations in the infected group increased rapidly to a mean maximum value of 30 ng ml−1 by 165 min. In contrast, the increase in LH concentration in non-infected bulls was more gradual and the mean maximum value, reached at the same time, was only 20 ng ml−1. Testosterone concentration increased rapidly and in a similar manner in both groups for the first 90 min (0.08 ± 0.04 ng ml−1). There was almost no further increase in testosterone concentration in the infected group (different from controls; P < 0.05) although LH concentrations continued to rise. The testosterone concentration of the non-infected group increased steadily, up to the end of the sampling period. It is concluded from the immunohistochemical study and from the pituitary response to GnRH that the parasites do not alter pituitary function but that they do affect testicular function.
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Summary. Fluorogestone acetate (vaginal sponge for 4 days) and PMSG (i.m. injection at the time of sponge insertion) treatment was administered to seven 3-month-old calves to induce superovulation. Samples of peripheral plasma were taken every 4 h during treatment (4 days) and then every 2 h for 7 days. FSH, LH, oestradiol and progesterone were measured by radioimmunoassays. In all calves oestradiol concentrations increased 24 h after PMSG injection and reached the highest levels (41–502 pg/ml) during the preovulatory surge of both gonadotrophins. The surge of LH and FSH occurred from 12 to 22 h after cessation of treatment. The maximum levels of LH and FSH were 11–72 ng/ml and 23–40 ng/ml respectively and occurred within 4 h of each other. Between 40 and 68 h after the LH peak the concentrations of progesterone began to increase from basal values, reaching 24·0–101·7 ng/ml when the animals were killed. A quantitative relationship was found between plasma oestradiol concentration and the numbers of ovulating follicles. Progesterone levels seemed to be related to the numbers of corpora lutea and also to the numbers of unovulated follicles. Gonadotrophin output was not quantitatively related to ovarian activity or to steroid secretion.
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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 β-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 μeq l−1 versus LE: 309 ± 18 μeq 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). These results suggest that LH pulse frequency might be affected by energy supply when energy balance was strongly negative, whereas follicular growth was affected at a later stage, after parturition.
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Summary. 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, 30–35 days and ∼ 70 days (for non-returns to oestrus) after AI. In non-pregnant females without extended CL maintenance (progesterone < 1·5 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 0·42 ± 0·07 (s.e.m.) ng/ml (Day 24) to 4·06 ± 0·3 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 30–35 of 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 < 0·05), 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 30–35 (P < 0·025) 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 24–26 after 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.
Keywords: PSPB; progesterone; pregnancy; embryonic death; cow
