Direct enzymeimmunoassay of progesterone in bovine milk

A sensitive enzymeimmunoassay has been developed for measuring progesterone in unextracted bovine milk. An N-hydroxysuccinimide ester of 11 alpha -hydroxyprogesterone 11-hemisuccinate has been synthesised and used to form conjugates with beta-galactosidase in buffer at pH 7.0. The degree of incorporation of progesterone into the enzyme was demonstrated using (14C)-labelled steroid and by radioimmunoassay binding inhibition. Standard curves of comparable range and sensitivity to radioimmunoassay were obtained in the presence of whole milk taken from a cow at oestrus. These advances have allowed the development of a simple micro-titre plate enzymeimmunoassay of progesterone in whole milk and will be of particular value in determination of pregnancy, prediction of the day of oestrus and diagnosis of reproductive disorders.     

Responses to selection for milk traits in dairy buffaloes

The aim of the present study was to estimate the index and individual responses to selection for milk (MY), fat (FY) and protein (PY) yields for different breeding goals for two commercial buffalo milk production systems in S?o Paulo State characterized by: 1) all milk produced is sold to the industry (MILK) and 2) all milk produced is used in the mozzarella cheese-making process at the farm (MOZZARELLA). The current payment policy is based exclusively on milk volume. The mozzarella price refers to the wholesale selling price. Index responses to selection (IR) were calculated for three different breeding goals (BG): 1) MY exclusively (BG(1)); 2) FY + PY (BG(2)) and 3) MY + FY + PY (BG(3)). IR for the MILK system were 41.79 US dollars (BG(1)), 5.91 US dollars (BG(2)) and 38.22 US dollars (BG(3)). For the MOZZARELLA system, IR were 179.50 US dollars (BG(1)), 262.85 US dollars (BG(2)) and 402.41 US dollars (BG(3)). The results suggest that for the present circumstances, selection for milk components is not advantageous when milk is produced for sale to the industry. However, when mozzarella making is added to the system, the selection for components and milk volume is the most economically beneficial.     

A specific enzymeimmunoassay for progesterone in human plasma.

An enzymeimmunoassay for plasma progesterone was established using progesterone covalently linked to the enzyme, horseradish peroxidase, as the 'label'. Separation of free and bound steroid was effected by Sepharose-coupled antiprogesterone-11alpha-hemisuccinyl bovine serum albumin antiserum (Sepharose-antisera). The enzymeimmunoassay satisfied the normal criteria of specificity, precision and accuracy. Comparison of assay results obtained by radioimmunoassay (with and without thin-layer chromatography) and enzyme-immunoassay (with and without thin-layer chromatography) showed excellent agreement of results in all cases (r greater than 0.98). This enzymeimmunoassay is particularly applicable to the routine determination of plasma progesterone in the smaller clinical laboratory.     

Milk progesterone profiles in various reproductive states in dairy buffaloes under field conditions

Fifty-one dairy buffaloes in the last two months of gestation were selected at seven private peri-urban farms in the Peshawar district. Observations were recorded in buffaloes during normal (NBS, August to January) and low breeding seasons (LBS, February to July). After parturition, rectal examination of reproductive organs was carried out. Estrus detection was made through visual observation and the use of intact bull. Postpartum ovulation was confirmed by ovarian palpation per rectum and milk progesterone levels (MPL), determined through radio-immunoassay. MPL was higher (p < 0.01) at various intervals in NBS calves (1.97 +/- 0.30 ng/ml) as compared to LBS calves (0.68 +/- 0.08 ng/ml). During LBS, MPL remained < 0.30 ng/ml up to the third fortnight and started rising later, reaching a peak of 1.27 ng/ml during the sixth fortnight. During NBS, there was a sharp rise in MPL during the second fortnight, reaching 3.64 ng/ml during the sixth fortnight. MPL was significantly different on different experimental farms (p < 0.01). MPL reached the lowest levels on the day of estrus (0.10 ng/ml), reached it's peak on day 7 and started declining on day 17 of estrus. MPL showed two postpartum elevations. In true anestrus buffaloes, MPL remained consistently low. However, in the anestrus period, silent ovulations were also noted, as reflected by increasing MPL without estrus signs. In pregnant buffaloes, MPL remained > 1 ng/ml. Results of the study showed that the low postpartum reproductive performance in dairy buffaloes during LBS was primarily due to inadequate functioning of the corpus luteum in secreting optimum concentrations of progesterone. The higher incidence of silent estrus during LBS indicated improved management for the detection of estrus.     

Environmental effects on progesterone profile measures of dairy cow fertility

Environmental effects on fertility measures early in lactation, such as the interval from calving to first luteal activity (CLA), proportion of samples with luteal activity during the first 60 days after calving (PLA) and interval to first ovulatory oestrus (OOE) were studied. In addition, traditional measurements of fertility, such as pregnancy to first insemination, number of inseminations per service period and interval from first to last insemination were studied as well as associations between the early and late measurements. Data were collected from an experimental herd during 15 years and included 1106 post-partum periods from 191 Swedish Holsteins and 325 Swedish Red and White dairy cows. Individual milk progesterone samples were taken twice a week until cyclicity and thereafter less frequently. First parity cows had 14.8 and 18.1 days longer CLA (LS-means difference) than second parity cows and older cows, respectively. Moreover, CLA was 10.5 days longer for cows that calved during the winter season compared with the summer season and 7.5 days longer for cows in tie-stalls than cows in loose-housing system. Cows treated for mastitis and lameness had 8.4 and 18.0 days longer CLA, respectively, compared with healthy cows. OOE was affected in the same way as CLA by the different environmental factors. PLA was a good indicator of CLA, and there was a high correlation (-0.69) between these two measurements. Treatment for lameness had a significant influence on all late fertility measurements, whereas housing was significant only for pregnancy to first insemination. All fertility traits were unfavourably associated with increased milk production. Regression of late fertility measurements on early fertility measurements had only a minor association with conception at first AI and interval from first to last AI for cows with conventional calving intervals, i.e. a 22 days later, CLA increased the interval from first to last insemination by 3.4 days. Early measurements had repeatabilities of 0.14-0.16, indicating a higher influence by the cow itself compared with late measurements, which had repeatabilities of 0.09-0.10. Our study shows that early fertility measurements have a possibility to be used in breeding for better fertility. To improve the early fertility of the cow, there are a number of important factors that have to be taken into account.     

Validation of a 13,14-dihydro-15-keto-PGF(2alpha) enzymeimmunoassay and its application for reproductive health monitoring in postpartum buffaloes

The objective of the present study was to validate a simple, sensitive and direct enzymeimmunoassay (EIA) procedure for 13,14-dihydro-15-keto-PGF(2alpha) (PGFM) for use in buffaloes with postpartum reproductive disorders and determine the practicalities of using plasma concentrations of 13,14-dihydro-15-keto-PGF(2alpha) for monitoring their reproductive health. The EIA was used for determination of the circulating levels of PGFM associated with the retention of fetal membranes, postpartum endometritis and variable postpartum intervals. The concentrations of PGFM with retention of fetal membranes in the periparturient period were lower as compared to buffaloes that had uneventful parturitions. Concentrations of PGFM associated with postpartum endometritis were elevated as compared to those in buffaloes free of reproductive tract infections. Buffaloes having higher plasma concentrations of PGFM in early postpartum period had shorter postpartum intervals, indicating the association between PGFM concentrations postpartum and uterine involution as well as the resumption of estrous cycle in this species. The study presents the possibility of using circulating PGFM concentrations for monitoring the postpartum reproductive health of buffaloes.     

Post-insemination milk progesterone concentration and embryo survival in dairy cows

Logistic regression analysis was used to evaluate the relationship between post-insemination milk progesterone concentration and embryo survival, and between milk yield and milk progesterone concentration. Milk samples were collected on Days 1, 4, 5, 6, and 7 (insemination=Day 0) following 871 inseminations in spring-calving dairy cows. Milk progesterone concentrations were measured by enzyme-immunoassay and pregnancy diagnosis was conducted with transrectal ultrasonography at approximately Day 30. There was a negative linear relationship (P<0.01) between milk progesterone concentration on Day 4 and embryo survival while, in contrast, there was a positive linear and quadratic relationship between milk progesterone concentration on Days 5, 6 and 7 (P<0.05) and also between the rate of change in progesterone concentrations between Days 4 and 7 inclusive and embryo survival (P<0.05). There was a weak negative linear relationship between average daily milk yield at the time of insemination and milk progesterone concentrations (P<0.001). There was no association between many production parameters, including liveweight and body condition score measured at various stages between calving and insemination, and milk progesterone concentration between Days 4 and 7 inclusive (P>0.05). In conclusion, low progesterone during Days 5-7 (after insemination) was associated with low fertility in dairy cows and there were indications of a range of progesterone concentrations within which embryo survival was maximal.     

A review of the causes of poor fertility in high milk producing dairy cows

Fertility in dairy cows has declined over the past five decades as milk production per cow has increased. Many hypotheses have been proposed to explain this including issues of genetics, physiology, nutrition and management, and these factors have been investigated at the animal, organ and cellular level at critical time points of the productive life of dairy cows. This paper reviews the physiological events and their causes and consequences affecting fertility in dairy cows and summarises these in a downloadable poster. We consider the following points to have the greatest negative impact on fertility and that they need to be prioritised in efforts to ameliorate the problem (others have been included in the review). Firstly, minimise negative energy balance and resolve any infection of the post partum uterus. Secondly, expression and detection of oestrus followed by insemination with high quality semen (day 0). Thirdly, ovulation and fertilisation of a high quality oocyte (day 1). Fourthly, an early increase in progesterone secretion from the corpus luteum (days 3-7). Fifthly, the uterine endometrium must produce an early and appropriate environment to stimulate embryo development (days 6-13). This leads to sixthly, a large embryo producing adequate quantities of interferon tau (days 14-18) that alters uterine prostaglandin secretion and signals maternal recognition of pregnancy (days 16-18). Future strategies to improve dairy cow fertility are needed for the benefit of the dairy industry and for cow welfare and should be based upon an integrative approach of these events.     

Radioimmunoassay and enzymeimmunoassay of plasma progesterone as monitors of progesterone sponge treatment in ewes

The daily plasma progesterone (P) concentrations achieved during insertion of P (750 mg) sponges into two groups of ewes were examined. Group I received prostaglandin (PG) treatment, which was required to suppress the P production (to levels of < 0.3 ng hormone/ml plasma) from the corpora lutea (CL) of a previous superovulation treatment, following which these Group I ewes and the anestrous Group II ewes were sponge treated. Radioimmunoassay (RIA) and enzymeimmunoassay (EIA) were used to measure the P levels in both groups. Progesterone (750 mg) sponges with and without citric acid impregnation were inserted into all the ewes for 12 days (d). Citric acid lowered the P levels reaching the plasma from the sponges, but it did not mask the characteristic profile (during the treatments) determined by the states of the ewes (single PG and double PG injected, Group I or in the anestrous Group II). The plasma P levels in Group I and II ewes rose to at least 7.0 ng/ml at intervals during treatment. The duration and magnitude of the P concentrations in the plasma were higher in the single PG compared with the double PG ewes during sponge insertion in Group I. The anestrous Group II ewes showed two major peaks (Day 1, P<0.01 and Days 11 to 12, P<0.05) during sponge treatment. A P level > 2.0 ng/ml was maintained over the entire treatment in the single PG and in the anestrous hormone-treated ewes, and was of shorter duration (7 d) in the double PG-treated animals. These endogenous patterns in P profiles of the ewes indicate that the hormone level during sponge insertion varies in magnitude and duration, parameters determined by the physiological/endocrinological state of the ewes at the start of the treatment. The EIA correlated significantly (P<0.001) with the RIA for the measurement of P concentration, when analyzed daily on an individual animal basis.     

A comparison of alkaline phosphatase, beta-galactosidase, penicillinase and peroxidase used as labels for progesterone determination in milk by heterologous microtitre plate enzymeimmunoassay

Assays for alkaline phospatase, beta-galactosidase, penicillinase and peroxidase were optimised for quantitation in microtitre plate wells. Their value as labels in microtitre plate enzymeimmunoassay (EIA) for progesterone was assessed following coupling with 11 alpha-hydroxyprogesterone 11-glucuronide using an active ester procedure. Bridge-heterologous antiserum (11 alpha-hydroxyprogesterone 11-hemisuccinate-bovine serum albumin as immunogen) was used to minimize bridge recognition. The limits of detection of the enzymes were in the order penicillinase greater than peroxidase greater than alkaline phosphatase greater than beta-galactosidase. Under appropriate conditions it was possible to achieve greater than 50% displacement of label with 50 pg of progesterone for all four labels.     

Spore germination based assay for monitoring antibiotic residues in milk at dairy farm

Spore germination based assay involves the transformation of dormant spores of Bacillus stearothermophilus 953 into active vegetative cells. The inhibition of germination process specifically in presence of antibiotic residues was used as a novel approach for monitoring target contaminants in milk. The indicator organism i.e., B. stearothermophilus 953 was initially allowed to sporulate by seeding in sporulation medium and incubating at 55 °C for 18 ± 2 h. The spores exhibited a typical chain behavior as revealed through phase contrast microscopy. The minimal medium inoculated with activated spores was incubated at 64 °C for 2-3 h for germination and outgrowth in presence of specific germinant mixture containing dextrose, whey powder and skimmed milk powder added in specific ratio along with reconstituted milk as negative control and test milk samples. The change in color of the medium from purple to yellow was used as criteria for detection of antibiotic residues in milk. The efficiency of the developed assay was evaluated through a surveillance study on 228 samples of raw, pasteurized and dried milks and results were compared with AOAC approved microbial receptor assay. The presence of antibiotic level was 10.08 % at Codex maximum residual limit having false positive result only in 0.43 % of the samples. The results of the present investigation suggest that developed spore based assay can be a practical solution to dairy industry for its application at farm level, milk processing units, independent testing and R & D centres in order to comply with the legal requirements set by Codex.     

Relationships between fertility, peak milk yields and lactational persistency in dairy cows

Peak milk yield, lactational persistency and conception rates were studied using 5928 lactation records of high milk-producing cows at three California dairies. Log-linear analysis was used to study relationships between peak milk yield, lactational persistency, dairy of origin, lactation number and conception rates in 3850 completed lactations. Cows with peak milk yields greater than the median (38.2 kg milk per day) were less likely to have conceived in one or two breedings than cows with peak milk yields lower than or equal to the median. Cows with a higher than median (0.755) lactational persistency were less likely to have conceived in one or two breedings than cows with a lactational persistency lower than or equal to the median. Dairy of origin had a significant effect on the probability of conceiving in one or two breedings. Cows in the first lactation were more likely than those in subsequent lactations to conceive in one or two breedings. This retrospective study demonstrated that subfertility is associated with high peak lactational yields in high milk-producing California cows.     

Excretion rate of progesterone in milk and faeces in lactating dairy cows with two levels of milk yield.

This study was conducted to measure the effect of the level of daily milk yield on the excretion rate of progesterone (P4) in milk and faeces in high-producing (HP) and low-producing (LP) lactating dairy cows. A GnRH-agonist was implanted to block endogenous production of P4. A CIDR device was inserted into the vagina and left in place for 11 days. The average and peak milk yields were greater in HP cows (P < 0.0001). Mean plasma concentrations of P4 were also similar in both groups (P = 0.44), even though the average mass of P4 delivered from a CIDR device was higher with HP cows (P = 0.02). Average milk P4 concentration was similar in both groups (P = 0.81), so that average daily excretion of P4 in the milk was greater with HP cows (P = 0.05). The concentrations (P = 0.83) and daily yields (P = 0.4) of total faecal progesterone metabolites were not affected by level of milk yield. These data show that the concentrations of plasma and milk P4, and the concentration and yield of P4 metabolites are not affected by the levels of daily milk yield.     

Effects of postinsemination progesterone supplementation on fertility and subsequent estrous responses of dairy heifers

The objective of Experiment I, replicated twice, was to evaluate whether fertility of estrus-synchronized dairy heifers could be improved by postinsemination progesterone supplementation. Estrous cycles were synchronized using two injections of prostaglandin (PG) F(2alpha) adiministered 11 days apart. Heifers displaying estrus were inseminated and assigned to control (n = 155) and treated (n = 159) groups. Treatment consisted of intravaginal insertion of controlled internal drug release (CIDR) devices for Days 7 to 13 (Day 0 = day of estrus). The conception rate for CIDR-treated heifers (57.9%) did not differ significantly from that of the controls (53.6%). The return-to-estrus rate and pattern of return estruses were not affected by treatment, but indicated that early embryonic mortality may have occurred in some of the heifers diagnosed nonpregnant. The objective of Experiment II was to evaluate if used CIDR devices were effective in resynchronizing returns to estrus in previously synchronized inseminated but nonpregnant and noninseminated heifers. Estrous cycles of dairy heifers of breeding age were synchronized with PGF(2alpha). Heifers displaying estrus were assigned to be inseminated (n = 117) or not inseminated (n = 35). All heifers were treated with 9-day used CIDR devices for Days 17 to 22 after synchronized estrus in order to resynchronize returns to estrus. Of the inseminated but nonpregnant heifers (n = 41), 78.1% were detected in estrus after CIDR removal (versus 94.3% of noninseminated heifers [n = 35]; P < 0.05) and 61.0% of the estruses occurred within 4 days of CIDR removal (versus 91.4% of noninseminated; P < 0.05). Estruses of synchronized inseminated nonpregnant heifers occurred over a longer period compared with those of noninseminated heifers (P < 0.025). The results indicate that response to the resynchronization protocol was altered by the outcome (early embryo death or failed fertilization) of the previous unsuccessful insemination, and support the hypothesis that delayed returns to estrus can be attributable to a pregnancy which was initiated but failed to establish itself. Such factors should be considered when evaluating responses of cattle to treatments designed to enhance fertility.     

Interaction of calf suckling, use of oxytocin and milk yield with reproductive performance of dairy buffaloes

Calf suckling and oxytocin injections are commonly used for pre-milking stimulus in dairy buffaloes under field conditions. A study was conducted to investigate effect of these treatments on reproductive performance. Fifty one Nili-Ravi buffaloes were monitored from parturition up to 150 days postpartum through rectal examination. Data on milk yield, body condition score (BCS) and reproductive parameters were recorded weekly. Postpartum ovulation interval (POI) was determined by presence of an ovulation depression or a very soft corpus luteum haemorrhagicum and was confirmed through milk progesterone levels (MPL). Suckling was used to stimulate milk let down, and where the calf had died, injection of oxytocin was resorted to. Milk samples were analyzed for MPL using radioimmunoassay (RIA) and fat; and milk yield was converted to 4% fat corrected milk (FCM). The mean postpartum uterine involution length (PUI) was 34.30 ± 1.33 days. Mean POI was 59.37 ± 4.76 days and mean postpartum estrus interval (PEI) was 69.03 ± 6.03 days. Suckling period averaged 26.40 ± 5.57 days and correlated with POI (r = 0.19, P < 0.01) and PEI (r = 0.23, P < 0.01). POI was shortest in buffaloes suckled for one month (P < 0.05). Oxytocin was used with a mean dosage of 7.50 IU, delaying placental expulsion time (PET) and POI but shortening PEI. BCS shortened PET, POI and PEI (P < 0.01). Mean FCM was 14.50 ± 0.20, ranging from 2 to 35 kg/d; and was higher in estrus group; correlating positively with POI (r = 0.31, P < 0.01). MPL were 1.37 ± 0.17 ng/ml and increased after ovulation, remaining greater than 1.5 ng/ml from Day 4 to 14 of the estrus cycle, followed by a rapid decline up to next estrus. BCS in buffaloes resuming oestrus was constantly higher than those failing to resume ovarian cyclicity. Live weight, prepartum was 510.0 ± 5.9 kg with a loss of 3.7 ± 2.12 kg, 30 days postpartum. The present study suggests a lower reproductive efficiency of dairy buffaloes under the peri-urban farming system reflected by ovarian cyclicity in 68.63% buffaloes within 150 days postpartum and silent estrus in 51.5% of the cases. Increasing suckling duration and use of oxytocin delayed POI, however, POI was shortest in buffaloes suckled for one month. The high yielding buffaloes also manifested better reproductive cyclicity; while moderate yielder showed shorter ovulation intervals and higher conception rate.     

Concentrations of progesterone in milk as a monitor of early pregnancy diagnosis in dairy cows

The objectives of the experiment were to evaluate the efficacy of using progesterone concentrations in milk and palpation per rectum on days 21 or 22 postbreeding to estimate pregnancy and evaluate management practices; and to investigate physiological occurrences leading to incorrect diagnosis of pregnancy when serial samples of milk were collected. Of particular interest were indications of early embyronic death and insemination of cows not in estrus. Milk samples were collected at the afternoon milking of days 0 or 1 (day 0 = day of estrus), 9 or 10, 21 or 22 and 27 or 28 following breeding in 200 lactating dairy cows. Tentative diagnosis of pregnancy was made based on concentrations of progesterone in milk on days 21 and 22 alone and on days 21 or 22 and 27 or 28. In addition all cows were palpated per rectum on days 21 or 22 postbreeding and a tentative pregnancy diagnosis was made. Pregnancy was confirmed by examination of the genital tract per rectum between 35 and 50 days after breeding. Values of 4 ng/ml or greater and/or the presence of a mature corpus luteum were considered positive signs of pregnancy. Progesterone in milk ranged from 0.1 to 18 ng/ml. On days 0 or 1, 9 or 10, 21 or 22 and 27 or 28 concentrations of progesterone in milk averaged 1.5 +/- 0.3, 11.1 +/- 0.5, 12.0 +/- 0.4 12.5 +/- 0.5 ng/ml for pregnant cows. Corresponding samples from nonpregnant cows averaged 1.2 +/- 0.2, 10.3 +/- 0.4, 3.0 +/- 0.4, 6.8 +/- 0.6 ng/ml, respectively. Ninety-six and 104 cows were classified as pregnant and nonpregnant on days 21 or 22 as compared to 78 and 118 cows diagnosed as pregnant and nonpregnant on days 21 or 22 and 27 or 28 combined. Pregnancy detection by progesterone in milk on days 21 or 22 with pregnancy determined via rectal palpation 35 to 50 days postbreeding was 77 and 100% accurate for positive and negative diagnosis, respectively. The percent agreement using progesterone in milk on days 21 or 22 and 27 or 28 combined was 95 and 100%, respectively, for positive and negative diagnosis. Diagnosis based on rectal palpation 21 or 22 days postbreeding was 63 92 (69%) and 76 88 (87%) for pregnant and nonpregnant cows, respectively. Ten of the 200 cows had progesterone concentratins in milk of > 4 ng/ml at the time of breeding. Six of these cows were pregnant from a previous insemination. The other four cows were nonpregnant and were inseminated during the luteal phase of the cycle. In conclusion, measurement of progesterone in milk is a useful tool in early detection of pregnant and nonpregnant cows and may be useful in detecting reproductive problems in a dairy herd. It will probably be most useful when used in combination with later pregnancy diagnosis per rectum .     

Relationship between progesterone concentrations in milk and blood and time of ovulation in dairy cattle

The objective of this study was to investigate whether monitoring progesterone concentrations in milk and blood plasma can be used to predict time of ovulation in dairy cattle. Whole milk was sampled twice daily and blood samples were collected once a day before the morning milking. Ovulation was assessed by trans-rectal ultrasonography at 4h intervals beginning from the end of estrus. For a parameter to be useful as predictor for time of ovulation, it should be precise (i.e. variation between animals should not exceed 12h). In milk, progesterone concentration dropped <15 ng/ml at 97.7+/-17.8h (range: 54-126 h) before ovulation, to <5 ng/ml at 79.7+/-11.2h (range: 54-98) before ovulation to decline further to <2n g/ml at 70.7+/-16.8h (range: 38-90 h) before ovulation (n=20). In plasma, progesterone concentration dropped to <4ng/ml 90.5+/-19.6h (range: 66-138 h) before ovulation and to <2 ng/ml at 75.0+/-12.2 h (range: 50-98) before ovulation. These intervals were not influenced by parity, milk production or days in milk. In conclusion, monitoring of progesterone alone is not sufficient to predict ovulation because of the large variation in timing of decrease of progesterone concentrations relative to ovulation between animals. At best the range is about 2 days.     

A simplified fertility test in the dairy bull utilizing superovulated dairy cows

Dairy bull fertility level has received less attention than production transmitting ability. A simplified fertility test may be beneficial. A study was designed to test the use of tris-(1-aziridinyl)-phosphine oxide (TEPA) treated sperm, which arrests early cell division of the fertilized egg, in heterospermic insemination of superovulated cows. Semen samples were collected and pooled from University of Illinois dairy bulls. Semen samples were washed once, suspended in Illini Variable Temperature diluent (IVT) and incubated with or without TEPA (1.0 to 5.0 mg/ml) for 15 min. Samples were then washed again to remove excess TEPA. Additions of 1.0 to 5.0 mg/ml TEPA to sperm concentrations of 8 x 10(8) sperm/ml had no adverse effect on motility or morphology. The first part of the study utilized superovulated cows inseminated with treated (six cows) or untreated (six cows) sperm in different samples from the same bulls. Secondly, superovulated cows (eight cows) were artificially inseminated with treated and untreated split ejaculates from the same bulls. Lastly, superovulated cows (five cows) were heterospermically inseminated with treated (bull No. 1) and untreated (bull No. 2) spermatozoa. Out of 54 and 39 ova recovered in control and test cows, 40 blastocysts and 31 embryos arrested at the one- to five-cell stage resulted, respectively. Out of a predicted 123 ovulations, 78 fertilized ova were recovered; 40 of these were fertilized by control spermatozoa and 36 by TEPA-treated spermatozoa for parts one and two of the study respectively. These results indicated no significant difference in fertilizability of ova between control and TEPA-treated spermatozoa. Of 41 fertilized ova recovered (part 3), bull No. 1 fertilized significantly more ova (mean +/- standard deviation 5.0 +/- 2.3) than bull No. 2 (2.6 +/- 1.8). Results indicate a difference in fertility between bulls.     

Screening for high fertility in high-producing dairy cows

A retrospective study involving 2756 pregnancies from two commercial dairy herds in northeastern Spain determined relationships between management, production and reproductive data, and high fertility (conception before 90 days in milk) in high-producing dairy cows. High fertility was registered in 989 (35.9%) cows. The following data were recorded for each animal: herd, repeated animal (cows included two or more times within the study in which data were obtained from different lactational periods), parity (primiparous versus multiparous), previous twinning, reproductive disorders following calving (retained placenta, primary metritis) and at postpartum gynecological examination (incomplete uterine involution, pyometra and ovarian cysts), days in milk at conception, previous estrous synchronization and season of calving and conception. In order to evaluate the possible effect of high production during the peak milk yield on subsequent fertility, daily milk production at Day 50 postpartum was also recorded and cows were classified as high (> or = 50 kg) and low (< 50 kg) producers. Logistic regression analysis indicated no significant effects of herd, repeated animal, previous twinning, reproductive disorders such as primary metritis, incomplete uterine involution, pyometra and ovarian cysts, previous estrous synchronization and season of calving and insemination. Based on the odds ratio, the likelihood of high fertility increased in high-producer cows by a factor of 6.8. High fertility was less likely for multiparous cows (by a factor of 0.35) and for cows suffering placenta retention (by a factor of 0.65). High fertile cows produced a mean of 49.5 kg milk at Day 50 postpartum, in contrast to that 43.2 kg milk of the remainder cows. These findings question the negative effect of high production on fertility. Our results indicated that high individual cow milk production can be positively related to high fertility.     

Metabolic variables and plasma leptin concentrations in dairy cows exhibiting reproductive cycle abnormalities identified through milk progesterone monitoring during the post partum period

We have used milk progesterone analysis to monitor reproductive function in lactating dairy cows and have then related this reproductive function to a variety of metabolic variables. Monitoring of cows (n = 41) during the period of onset of luteal function (first milk progesterone reading>5 ng/ml) revealed that delayed onset was associated with increased milk yield and greater loss of body weight and body condition but was not related to plasma metabolite or leptin concentrations. Further monitoring of reproductive function in these 41 cows and an additional 33 cows (total n = 74) during the mating period (from weeks 6 to 14 post partum) identified reproductive cycle abnormalities in 29 (39.2% of animals). The occurrence of cycle abnormalities was associated with increased milk yield (P < 0.05), elevated plasma beta hydroxybutyrate (P < 0.05) and reduced plasma leptin (P < 0.01) concentrations as well as a lower (P < 0.05) rate of gain of body weight and condition score but was not associated with plasma urea or glucose concentrations. Furthermore, cows exhibiting cycle abnormalities had a longer (P < 0.01) interval to first service and a smaller percentage had conceived by 100 days post partum (34.5% versus 66.7%; P < 0.01). These results provide further evidence that impaired reproductive function during the post partum period in dairy cows is caused by a poor energy status and not elevated urea concentrations. Reduced plasma leptin concentrations in animals suffering reproductive dysfunction further supports this view.